NMR Basic Principles and Progress Grundlagen und F ortschritte

Volume 9

Editors: P. Diehl E. Fluck R. Kosfeld

With 18 Figures

Springer-Verlag

Berlin . Heidelberg . New York 1975

Professor Dr. P. DIEHL

Physikalisches Institut der Universitat Basel

Professor Dr. E. FLUCK

Institut fUr Anorganische Chemie

der Universitat Stuttgart

Professor Dr. R. KOSFELD

Institut fUr Physikalische Chemie

der Rhein.-Westf. Technischen Hochschule Aachen

ISBN-13: 978-3-642-45475-2 001: 10.1007/978-3-642-45473-8

e-ISBN-13: 978-3-642-45473-8

Library of Congress Cataloging in Publication Data. Nuclear magnetic resonance studies in lyotropic liquid crystals. (NMR, basic principles and progress; v.9) Cover title. Includes bibliographical references and index. 1. Liquid crystals-Spectra. 2. Nuclear magnetic resonance spectroscopy. I. Khetrapal, Chunni Lal, 1937-. II. Series. QC490.N2 vol. 9 [QD923] 538'.3s [548'.9] 75-16370

This work is subject to copyright. All rights are reserved, whether the whole or part of the materials is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, repro­duction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher.

© by Springer-Verlag Berlin' Heidelberg 1975 Softcover reprint of the hardcover 1 st edition 1975

The use of general descriptive names, trade marks, etc. in this publication, even if the former are not especially identified, is not be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act. may accordingly be used freely by anyone.

Nuclear Magnetic Resonance Studies in Lyotropic Liquid Crystals

C. L. KHE'QlAPAL

Raman Research Institute Bangalore, India

A.C.KuNWAR Raman Research Institute Bangalore, India

A. S. TRACEY

Department of Physics University of Basel KlingelbergstraBe 82 4056 Basel, Switzerland

P. DIEHL

Department of Physics University of Basel Klinge1bergstraBe 82 4056 Basel, Switzerland

Contents

Part I. Introduction . . . . 3 1. Lyotropic Liquid Crystals 3 2. Basic Principles. . . . . 9

2.1. Spectra of Lyotropic Phases 9 2.1.1. Nuclei with Spin I =t 9 2.1.2. Nuclei with Spin I> t 10

2.2. Spectra of Molecules Dissolved in Nematic Lyotropic Phases 11 2.2.1. The Hamiltonian . . . . . . . . . . . . . . . . 11 2.2.2. Direct Coupling and Degree of Order . . . . . . . 12 2.2.3. Interpretation of the Dipolar Couplings and Obtainable

Structural Information. . . . . . . . . . . . . . . .. 13 2.2.4. Chemical-shift Anisotropy . . . . . . . . . . . . . .. 14 2.2.5. Anisotropic Contribution of the Indirect Spin-spin Couplings 14 2.2.6. The Quadrupole Interaction . . . . . . . . . . . . .. 14

2 Contents

3. Experimental ...... . 15 15 16 16 17

3.1. Preparation of Samples 3.2. NMR Measurements .

3.2.1. Phases without Additional Solutes. 3.2.2. Solutes Dissolved in Nematic Phases.

Part II. Studies of Lyotropic Liquid Crystals. 19 4. Introduction . . . . ... . . . . 19 5. Applications . . . . . . . . . . . . . 21

5.1. Critical Micelle Concentration . . . 21 5.1.1. Chemical-shift Measurements. 21 5.1.2. Spin-lattice Relaxation Time Measurements. 23

5.2. Spectral Changes and Phase Transitions . . . . . 24 5.3. Proton and Deuteron Magnetic Resonance in Hydrated Fibrous

Materials . . . . . . . . . . '. . . . 28 5.4. Self-diffusion in Lyotropic Liquid Crystals . . . . 29 5.5. Interactions ofIons in Anisotropic Media . . . . 31

5.5.1. Ordering of Spherical and Tetrahedral Ions. 31 5.5.2. Ion Binding and Ion Competition 32 5.5.3. Halide Ions. . . . . . . . . . . . . . . 33 5.5.4. Alkali Ions. . . . . . . . . . . . . . . 33 5.5.5. Proton, Deuteron and Alkali Resonance Studies 34 5.5.6. PMR of Nonionic Surfactants in the Presence of Anionic

Surfactants. . . . . . . . . . . . . . . .. 35 5.5.7. 14N Quadrupole Interactions . . . . . . . . . . . . . . 35

5.6. Alkyl Chain Motion in Lyotropic Liquid Crystals. . . . . . . . 36 5.6.1. The Concept ofthe Order Parameter as Applied to the Hydro-

carbon Chain. . . . . . . . . . . . . . . . . . 36 5.6.2. Structure and Dynamics of the Hydrocarbon Region. 36

5.6.2.1. Micellar Solutions . 36 5.6.2.2. Anisotropic Phases. 37

5.7. Sonicated Lamellar Systems . . 41 Appendix to Part II: Systems Reported. . 42

Part m. Studies of Molecular and Ionic Species Dissolved in the Nematic Phase of Lyotropic Liquid Crystals . 47

6. Introduction. . . . . . . . . . 47 7. Applications. . . . . . . . . . . . . 48 8. Order in Nematic Lyotropic Phases . . . 54

8.1. Some General Comments Concerning the Order Parameter 54 8.2. Molecular and Ionic Species in Aqueous Phases 55

8.2.1. Benzenes and Related Compounds . . . . . . . . 55 8.2.2. Ionic Species as Solutes. . . . . . . . . . . . . 58

Appendix to Part III. Compounds Studied and Information Derived 59 Acknowledgements 74

References . . . . 74

Part I. Introduction

1. Lyotropic Liquid Crystals

The class of compounds known as thermotropic liquid crystals has been widely utilized in basic research and industry during recent years. The properties of these materials are such that on heating from the solid to the isotropic liquid state, phase transitions occur with the formation of one or more intermediate anisotropic liquids. The unique and sometimes startling properties of these liquid crystals are the properties of pure compounds. However, there exists a second class of substances known as lyotropic liquid crystals which obtain their anisotropic properties from the mixing of two or more components. One of the components is amphiphilic, containing a polar head group (generally ionic or zwitterionic) attached to one or more long-chain hydrocarbons; the second component is usually water. Lyotropic liquid crystals occur abundantly in nature, particularly in all living systems. As a consequence, a bright future seems assured for studies on such systems. Even now, many of the properties of these systems are poorly understood. It is the purpose of this review to consolidate the results obtained from nuclear magnetic resonance studies of such systems and to provide a coherent picture of the field.

Probably the most familiar example of a lyotropic liquid crystal is soap in water. A common soap is sodium dodecylsulphate where an ionic group (sulphate) is attached to a hydrocarbon chain containing twelve carbons. The sulphate head group is sufficiently soluble in water to allow complete dispersion of the soap in dilute solutions. As the concentration of soap increases, the hydro­phobic paraffin chains tend to associate preferentially with one another since they are quite insoluble in water. At a concentration known as the critical micelle con­centration, aggregates of the alkylsulphate ions form stable entities known as 'micelles'. The nonpolar hydrocarbon chains occupy the interior of the micelles with the ionic head groups on the surface (Fig. 1) where they can interact efficiently with the solvent. This type of behaviour is typical not only for soaps but also for such naturally occurring materials as phospholipids. The critical micelle concentration and the aggregation number depend on many factors­the nature of the polar head group and of the hydrocarbon chain, and the presence or absence of electrolytes, to mention a few.

As the concentration of the soap increases, an anisotropic liquid crystalline material may be formed. There are many articles describing the formation,

4 Introduction

Fig. 1. A representation of the isotropic micellar phase. The polar groups are on the surface of the micelle, the hydrocarbon chains occupy the interior. [Reprinted from the J. Soc. Cosmetic Chern. 19, 581 (1968) with permission from the copyright owners and the author]

properties and uses of such systems [1- 7]. Several types of anisotropic liquids exist and a systematic classification has been made from X-ray studies [8-10].

The most common lyotropic meso phase (neat soap) has a lamellar structure. The hydrocarbon chains form the superstructure with the polar groups lying along the interface with water. The arrangement is such that the hydrocarbon chains are perpendicular to the interface and each layer is approximately two hydrocarbon chain lengths thick (Fig. 2).

If a lamellar phase is irradiated with high-frequency sound, an isotropic solution may be formed. Sonication does not destroy the lamellar structure, but causes the formation of closed bilayer structures called vesicles (Fig. 3). They are spheroidal in shape and enclose a volume of water dependent on the diameter of the vesicle and separated from the interstitial water.

With changing composition, the lamellar structure often becomes unstable and cylindrically shaped aggregates may form in a hexagonal packed structure (Fig. 4). The polar head groups in this case lie on the surface of the cylinder with the hydrocarbon chains in the interior (middle soap). The hexagonal and the lamellar anisotropic liquids are by far the most common lyotropic phases.

Lyotropic Liquid Crystals 5

Water NEAT

Fig. 2. A representation of the anisotropic lamellar phase. The hydrocarbon superstructure layers are of indefinite extent and are separated by the interstitial water. [Reprinted from the J. Soc. Cosmetic Chern. 19, 581 (1968) with permission from the copyright owners and the author]

Fig. 3. A representation of the isotropic vesicular phase. Each vesicle contains a volume of water which is separated from the interstitial water

6 Introduction

MIDDLE

Water

Fig. 4. A representation of the anisotropic hexagonally packed cylindrical phase. Cylinders are of indefinite length and separated from one another by the interstitial water. [Reprinted from the 1. Soc. Cosmetic Chern. 19, 581 (1968) with permission from the copyright owners and the author]

However, for some soaps, nematic liquid crystals capable of being ordered by a magnetic field also exist. Although it is generally assumed that such phases have a cylindrical superstructure resembling the hexagonal phase, this certainly is not clearly established. An optically isotropic phase with cubic symmetry may also form at times.

In the presence of relatively small amounts of water an inverted hexagonal phase may occur, particularly in the presence of an organic solvent. In this case, the cylinders are formed in a hexagonal packing such that the polar groups still occupy the cylindrical surface but the inner part consists of water and the hydrophobic groups occupy the space between the cylinders. Similarly, inverted micelles may be formed in hydrocarbon solvents [11,12].

For a fuller description of these and other intermediate phases, the reader is referred to the literature [13-18].

It is interesting to note that on a micro scale, the structure of the various phases in lyotropic liquid crystals is similar and that three regions of the system

Lyotropic Liquid Crystals 7

Fig. 5. A representation of the interface region. This region is similar for the isotropic and anisotropic phases

are clearly defined, as illustrated in Fig. 5. Region 1 in Fig. 5 consists essentially of hydrocarbon chains, throughout which only small amounts of water and ions may be. dispersed. Region 2 is an interface region where the relatively immobile polar head groups are located. They interact strongly with the solvent and the counterions and keep the system in solution. Region 3 is formed by interstitial water and some counterions. For zwitterionic species such as phospholipids, of course, no unattached counterions are present.

All three regions of the lyotropic liquid crystals are of interest and subject to investigation by NMR techniques. Effects of concentration, of addition of ionic and molecular species and of protein dispersions have been and are being in­vestigated by NMR. Ion binding and ion competition for binding sites in region 2 are of interest, as is transport of ions and molecules across region 1. Structures of the various regions have also been investigated by NMR.

This monograph is divided into the introduction and two sections: the first describing studies of the type mentioned above, the other concerning itself strictly with studies in the nematic mesophase. Nematic phases are of particular interest since they may be ordered by a magnetic field and thus provide a homogeneous, highly ordered anisotropic matrix. The structure of the dissolved molecules or ions may then be determined from intramolecular dipolar interactions [19-35] which do not average to zero in anisotropic liquids. This method was proposed by SAUPE and ENGLERT [36] in 1963 when they observed that the IH-NMR spectrum of benzene in a thermotropic liquid crystalline nematic phase had a relatively complex appearance compared to a single-line spectrum in an isotropic phase. The interpretation of this spectrum led to the discovery of a new method for the determination of molecular geometries. It provides the only available technique for the precise determination of the relative arrangement of nuclei in the liquid

8 Introduction

phase and is the most recent addition to the earlier existing list of methods for the determination of molecular structure, e.g. X-ray, neutron and electron diffraction and microwave spectroscopy.

During the span of about a decade since its discovery, the method has been extensively used. Initially, investigators were mainly concerned with under­standing the scope and limitations of the method and hence only simple mole­cu1es, whose structures were already known, were studied and the results compared with those obtained by other methods. During the last few years, considerable progress has been made towards understanding the experimental and theoretical aspects of the method. As a consequence, a broader applicability has been developed. Attempts have been made to discover different types of liquid crystalline materials, to simplify the spectra with the help of selective isotopic substitution followed by heteronuc1ear spin decoupling, to apply vibrational corrections to the observed dipolar couplings and to understand the anisotropic contributions of the indirect couplings [25,37-46]. The greater part of the work has been done on thermotropic liquid crystals. The results are sum­marized in the literature [19-45].

The first nematic lyotropic solvent used in NMR experiments was the one suggested by LAWSON and FLAUTT [47] in 1967. It is formed by a mixture of sodium Cg or C lO alkylsulphate, the corresponding alcohol, sodium sulphate and water (or deuterated water) in approximate ratios of 8: 1: 1 : 10. The addition of sodium sulphate to the nematic pure ternary phase causes separation of the phase into a smectic and a nematic state [48,49]. Addition of more sodium sulphate or of some solutes recombines the two into a single nematic phase. Such solutes can be conveniently studied by NMR [47]. Other nematic lyotropic phases have also been used [50-52].

Synthetic polypeptides (NH-CHR-CO)n in the oc-helical conformation may form a lyotropic liquid crystal when the polypeptide concentration exceeds a certain critical value. A sufficiently strong magnetic field then arranges them with the polypeptide helix axes aligned parallel to the field [53-55]. The use of such materials in NMR experiments [56-63] is discussed in more detail in part III of this review.

The use oflyotropic nematic mesophases for the determination ofthe geometry of molecular or ionic species has certain advantages over thermotropic phases. For instance, polar molecules, which are quite insoluble in a thermotrepic solvent, often readily dissolve in a lyotropic one. Ions may be readily investigated in lyotropic but not in thermotropic systems. Generally, nematic lyotropic meso­phases may be spun about an axis perpendicular to the direction of the magnetic field (the arrangement in conventional spectrometers) without destroying the molecular order. This results in highly resolved NMR spectra for the dissolved molecules. However, there is a type of nematic lyotropic phase which cannot be spun in conventional spectrometers without destroying the orientation [46]. The spinning of both types of these phases without destruction of the molecular order is permissible in spectrometers with cryogenic magnets. Lyotropic nematic phases are more sensitive than thermotropic phases to solvent-solute interactions. This is a disadvantage for studying dissolved molecules. On the other hand, much sharper transitions allow the use of considerably lower concentrations than are

N uc1ei with Spin 1= t 9

normally employed in thermotropic systems. Modem Fourier-transform spectro­meters make this even less of a problem since quite low solute concentrations may be used.

2. Basic Principles

2.1. Spectra of Lyotropic Phases

For the pure lyotropic phases, the appearance of the NMR spectra is quite simple. The protons of the hydrocarbon chain give rise to a broad peak, the shape and width of which have been used to investigate intermolecular interactions and mobilities in a variety of biological and other ordered systems [64-75].

2.1.1. Nuclei with Spin 1 =t Lineshapes of the proton magnetic resonance spectra from lyotropic liquid crystals have been the subject of considerable discussion [76-103]. 'Normal' high­resolution NMR spectra are observed only in 'micellar' solutions, cubic phases and aqueous dispersions of membrane fragments [104-107]; the peak assign­ments and the derivation ofthe parameters in these cases can be achieved with the help of textbook knowledge on NMR [108], without going into the detailed analysis described in Section 2.2. However the lineshape observed in the hexagonal and the lamellar phases is such that the lines are narrow at the centre but have more intensity at the bottom than would be predicted from a Lorentzian function [77] (Fig. 6).

This lineshape is generally referred to as 'super-Lorentzian' [76,77]. Of the various explanations advanced to interpret such a lineshape, the one

given recently [91] in terms of nonvanishing intramolecular dipolar interactions between the protons in the alkyl chain in the lamellar phase seems the most plausible and is briefly described below.

Under some simplifying assumptions, the lineshape L(v - vo), which is a symmetric function centred at the resonance frequency (vo), is given by Equation (1) [109]:

1

L(v - vo) = J 13cos2 0 - 11- 1 f[(v - vo)fl3cos2 0 - 11] d cosO (1) o

where f(x) is a normalized one-parameter function and 0 is the angle between the lamellae director and the magnetic field.

Equation (1) shows that, if f(OH= 0, L(O) diverges towards infinity as -logx. This singularity is removed if other interactions are taken into account; the line has a sharp maximum at Vo. The lineshape L(v - vo) for an assumed Gaussian

10 Introduction

~.=.......-~ I I

Gauss-1.6 -1.2 -0.4 o 0.4 0.8 1.2 1.6Gauss

Fig. 6. PMR spectrum of sodium stearate at 1260 C. The smooth curve is the calculated Lorentzian lineshape. [Reprinted from Advan. Chern. Ser. 63, 26 (1967) with permission of the copyright owners and the authors. Copyright by the American Chemical Society]

Fig. 7. Lineshape calculated from Eq. (1) with f(x) = exp( - nx2 ). The observed lineshape is shown in Fig. 6. [Reprinted from Chern. Phys. Letters 18,41 (1973) with permission of the copyright owners and the author. Copyright by the North Holland Pub!. Co.]

shape of f(x) is shown in Fig. 7. A comparison of observed and calculated line shapes (Figs. 6 and 7) shows that the agreement between the two is satisfactory.

A direct application of these results has been made for dimyristoyl and dipalmitoyllecithin-cholesterol-water systems [103].

2.1.2. Nuclei with Spin I>!

A quadrupolar nucleus (the one with spin 1>!) interacts with the electric-field gradients of its environment through the quadrupole moment. If such a nucleus tumbles anisotropically, quadrupole splittings are observed in the NMR spectrum of that nucleus. For such a case, the first-order perturbation term corresponds to the splitting of the NMR signal into 21 symmetrical components. If, however, the quadrupole interaction is large enough, a second-order perturb-

The Hamiltonian 11

ation and the corresponding spectral asymmetry are noticeable [109]. Quadrupole splittings have been and are being used for the precise determination of quadrupole coupling constants [110-113], ion-binding studies [114-133], and investigations involving segmental motion of the fatty acid chains [134-140], and may help in the analysis of the complicated proton magnetic resonance spectra of molecules dissolved in liquid crystals.

2.2. Spectra of Molecules Dissolved in Nematic Lyotropic Phases

Solute molecules in a nematic phase are sufficiently mobile to allow the inter­molecular dipolar couplings to be averaged to zero. However, the motion of the solute molecules is anisotropic such that the intramolecular dipolar interactions still have nonzero average value. The NMR spectrum of such a solution, therefore, consists of relatively sharp lines (widths may be around one Hertz) derived from the solute; it may be superimposed over a broad background if the structure­building component contains the same type of nuclei as those being investigated.

The spectra are theoretically well understood in terms of chemical shift, direct and indirect spin-spin and quadrupole coupling tensors, and also the degree of order which may be described by the order matrix S [141], the motional constants [142], or the averaged second-order Wigner rotation matrices [29,32]. Details of these treatments are reported in the literature. The present section discusses some important points related to the theoretical interpretation of the spectra, and the order matrix S which is used to describe molecular orientation. The standard nomenclature of the spectra [23] has been followed throughout this article.

2.2.1. The Hamiltonian

The Hamiltonian for 'oriented' molecules is defined as follows [21]:

.it' = - I (1- CTi - CTia) VOizi + II [(Jij + 2Di) iz;izj i i<J

+!(Jij-Di ) (it ~- +k ~+)] + IB;ij (2)

i

where CTi and Jij represent one third of the traces of the relevant tensors and are identical to the chemical shifts and indirect spin-spin couplings in the normal high-resolution NMR spectra; CTia is the anisotropic contribution of the chemical ~hift..s; Dj,j is the direct dipole-dipole coupling; Bi is the quadrupole interaction; and Izi , It, I i- are spin operators. _~ince the anisotropic contributions to the indirect dipolar couplings have the same angular dependence as the direct couplings, Dij

may contain a certain amount of the former. Fortunately, this contribution has been shown to be negligible for HH couplings and hence, whatever 'direct dipolar

12 Introduction

coupling' one obtains from the analysis of such spectra are the 'true dipolar couplings', which are directly related to the molecular geometry. On the other hand, significant contributions of the anisotropy of the indirect F-F couplings have been observed [23,29,45,143,144].

Equation (2) transforms to the Hamiltonian for the 'isotropic' case if D jj ,

(Jia' and Bj are set at zero. Obviously, existing computer programs for the iterative analysis of NMR spectra of isotropic liquids can easily be modified for ordered liquids. One such modification, LAOCOONOR [145], is being widely used. Expressions for the frequencies and the intensities of the allowed transitions in systems where they are analytical functions of the parameters have been reported [23].

It should also be mentioned that the values of the dipolar couplings derived by means of the definition given in Ref. [142] have been halved throughout this article for the sake of uniformity.

2.2.2. Direct Coupling and Degree of Order

The direct coupling (Dij) between nuclei i and j is defined by:

(3)

where Ojj is the angle between the magnetic field direction and the axis con­necting nuclei i andj which are separated by the distance rjj. y is the magnetogyric ratio. The angular brackets, ( ), imply the average over inter- and intramolecular motion. If i and j belong to the same rigid part of the molecule and if rij is independent of Ojj' rij can be taken out of the angular brackets since it is then a constant. In such a case Eq. (3) reduces to:

(4)

where Sjj defines the degree of order of the axis ij. It may be emphasized that Eq. (4) neglects the influences of all types of molecular vibrations and intra­molecular motions and takes into account only the 'average' molecular order. This may sometimes lead to complications [146] but in most of the cases presented in this article it provides reasonably satisfactory results.

The S values of the various axes in the molecule are interdependent and the average order of a rigid molecule is given by a symmetric and traceless matrix S with five independent elements. If x, y, and z are the axes of a Cartesian co­ordinate system fixed within the molecule, and Ox, 0y, and Oz are the angles between these axes and the magnetic field direction, the elements (Spq) of the S matrix are given by .

Spq =!(3cosOp cosOq - bpq ) (5)

Interpretation of the Dipolar Couplings and Obtainable Structural Information 13

where p, q = x, y, z and tJ pq = 1 for p = q and 0 otherwise. The S value, Sjj' of an axis forming angles rx~ (p = x, y, z) with the molecule fixed-coordinate system is related to the tensor elements S pq according to

Sjj = L cosrx~' cosrx~' S~q. (6) p,q

By a suitable choice of molecular axes, the number of independent S values necessary for the description of the orientation can be reduced from five to one, depending upon the molecular symmetry. If the molecule has a 3-fold or greater axis of symmetry, its selection as the z axis leaves Szz as the only independent orientation parameter. When there are two perpendicular planes of symmetry in the molecule with the x and y axes in the intersecting planes, only two inde­pendent S values (Sxx and Syy) are needed for a complete description of molecular orientation. If the molecule possesses only one plane of symmetry, a selection of the z axis perpendicular to this plane leaves Sxx, Syy, and SXy as the only inde­pendent elements of the S matrix.

2.2.3. Interpretation of the Dipolar Couplings and Obtainable Structural Information

If the number of independent dipolar couplings equals the sum of the in­dependent geometric and order parameters required, one can solve the simul­taneous equations connecting the various parameters. If, however, the number of the independent dipolar couplings is less than the 'sum' as defined above, one has to make assumptions regarding molecular geometry; the number of such assumptions equals the number by which the direct couplings fall short of the 'sum'. It should be kept in mind that in just determined or slightly overdetermined systems the results obtained cannot confirm the correctness of an assumed model but only produce data in agreement with both the assumed non unique model and the observed spectrum. If the number of dipolar couplings exceeds the sum of the geometric and orientational parameters, one must use an iterative procedure which computes the geometry and the order parameters by a 'weighted least-squares fit' method. The iterative program SHAPE [147] has been widely applied for such a purpose.

It follows from the above that a system of less than four interacting nuclei does not provide any new geometric information. On the other hand, the spectrum becomes more and more complex with the increase in the number of interacting nuclei. Systems containing 7 to 8 interacting nuclei can be handled but this drastically increases the time of computation, imposing a serious limitation on the range of applicability of the method. However, recently a technique (which effectively reduces the number of interacting nuclei) involving selective deuteration of the molecule followed by heteronuclear decoupling has been suggested and used [25, 37-39]. The development of such a technique is expected to make this method of determination of molecular geometries

14 Introduction

applicable to larger molecules also. Equation (4) shows that if Sij and rlj are changed by a constant factor, Dij remains unchanged. Since no method is yet available for the precise determination of Sij without the knowledge of an inter­nuclear distance, NMR studies of oriented molecules do not allow the measure­ment of absolute distances; only relative distances and molecular shapes can be determined.

2.2.4. Chemical-shift Anisotropy

The anisotropic contribution to the chemical shift (UiJ may be expressed in terms of the tensor components:

Uia=! L SpiUpqi+ Uqpi) , (7) P.q

where p, q = x, y, z. Molecular symmetry reduces the number of independent elements of the

chemical-shift tensor as has been reported in the literature [23].

2.2.5. Anisotropic Contribution of the Indirect Spin-spin Couplings (D:jd)

A substitution of J for U in Eq. (7) provides relations for the anisotropic contribution to the indirect couplings. Jia obtained in this way corresponds to 2Dljd.

2.2.6. The Quadrupole Interaction

The quadrupole interaction of a nucleus with I>! may be defined as follows:

(8)

where p, q = x, y, z. eQ is the nuclear quadrupole moment and Vpq are the elements of the electric-field gradient tensor at the position of the nucleus studied. Equation (8) is valid for any molecular coordinate system. In particular, if the coordinate axes coincides with the principal axes of V and I v"zl ~ I Y,yl ~ I Yxxl [108], then

\9)

where 17 = (Yxx - Y,y)/v"z is the asymmetry of the tensor V.

Preparation of Samples 15

The quantity Qc = eQ ~z/h is the quadrupole coupling constant so that

(10)

and the observed multiplet quadrupole splitting is Ll v = 2B.

3. Experimental

3.1. Preparation of Samples

Samples are usually prepared by weighing out the various components, placing them in a test tube, then alternately mixing and centrifuging the sample. Heating to 50° or 60° often facilitates the process of dissolution. For sensitive samples or critical measurements, the components can be weighed into a glass tube which is sealed at one end and constricted in the centre. The open end finally is sealed so that the material may be centrifuged forward and backward through the constriction until dissolution is complete [148, 149].

With a synthetic polypeptide, approximately 12 mole per cent of the peptide is dissolved in a low-molecular-weight solvent like dichloromethane or chloro­form and the solute of interest is dissolved in it. If the material under investigation is a liquid capable of dissolving the polypeptide, the solution may be prepared directly without an additional solvent.

For relaxation time and linewidth studies, sample purity is important since these parameters are influenced by impurities. Oxygen may be removed by repeated freeze-pump-thaw cycles. Chelex-100 resin has sometimes been used to remove paramagnetic impurities such as Cu + + [150]. Finally, the tubes are sealed under vacuum or dry nitrogen. For linewidth studies, the samples are left for a few days (about a week) at constant temperature, before recording the spectra. On the other hand when relaxation-time studies are performed, experi­ments are completed as soon as possible after the preparation of the sample so as to avoid effects associated with leaching of paramagnetic ions from the sample tubes [151].

For the preparation of macroscopically oriented non-nematic samples [152 -154], the following procedure is usually adopted. Samples are first prepared as mentioned earlier by mixing appropriate amounts of components until dis­solution is complete. A small amount of this material is placed on a microscope cover glass and a second cover slip is pressed gently on the liquid crystal layer which finally has a thickness of between 10 to 20 microns. This is done under conditions of controlled humidity. The macroscopic orientation is thus achieved through the surface effect of the cover glasses, which should be scrupulously clean. Each of the 'sandwiches' is examined under a polarizing microscope and

16 Introduction

only the homogeneously oriented ones are selected. A stack of several such 'sandwiches' (about 15, prepared on 8 x 16 mm cover glasses can be fitted tightly into a 10-mm NMR sample tube so as to ensure that the slides are parallel to each other and to the axis of the tube [99]) is kept for a few days at uniform temperature and humidity before measurements are made.

To obtain 'oriented' samples of fibrous materials, the fibres may be wound parallel to each other on a thin Teflon disc. For example, for collagen fibres [155], the dimensions of the disc used were (7 x 8 x 0.6) mm3 for studies at room temperature, (5 x 4 x 0.6) mm3 and (5 x 6 x 0.6) mm3 for PMR and DMR studies at variable temperatures. Water contents are adjusted by equilibrating the samples in atmospheres with constant relative humidities, obtained in desiccators with saturated solutions of suitable salts.

F or studies involving the temperature dependence of NMR parameters, samples ate equilibrated in the probe for about 30 min at the desired temperature before spectra are recorded. If the samples decompose when subjected for extended periods to temperatures' of around 110 'to 120° C, new samples should be prepared from the initial bulk material [76].

3.2. NMR Measurements

Commonly available high-resolution, wide-line, spin-echo, pulsed and Fourier­transform spectrometers are used.

3.2.1. Phases without Additional Solutes

In such cases the conventional 'rapid passage' or 'pulse' techniques are used for relaxation-time studies. Self-diffusion coefficients are measured by the variable field-gradient proton spin-echo method [156,157]. The stimulated spin-echo method has been used to eliminate static dipolar couplings [158]. Sometimes line-sharpening in liquid crystalline solutions may be obtained by spinning the samples about an axis inclined at the 'magic' angle (54.7°) [159,160].

Linewidths are obtained in the absorption mode by measuring the peak widths at half-height if they are not very large, otherwise they are determined, by recording the 'derivative signals' where the widths correspond to the separation between points of maximum slope. In the latter case, a modulation frequency of a few Hz is used. The radiofrequency power is maintained well below the saturation limit. In some cases, a slight overmodulation is essential for improving the signal-to­noise ratio; though it causes some line-broadening, it does not produce signifi­cant effects on the splittings [124,161].

For measurements of chemical shifts, particularly in micellar solutions, 'internal references' are usually preferred to 'external' ones so as to avoid 'bulk susceptibility' corrections. For micellar solutions, signals due to long-chain 'methylene protons' are considered ideal internal references [151,162] since the chemical-shift change of the methyl and the methylene protons is found to be negligible on going from water to a micellar environment. Sometimes external

Solutes Dissolved in Nematic Phases 17

references like cyc1ohexane, chloroform etc. have been used [163,164]. For 19F chemical-shift studies, trifluoroacetic acid has been used as an external reference in a capillary centred in the sample tube by means of a nylon plug, so as to ensure reproducible geometry [165].

3.2.2. Solutes Dissolved in Nematic Phases

These solutions in general are fairly viscous and must usually be kept spinning in the magnetic field for several hours before spectra with sharp lines (widths around 1 Hz) are obtained. It should be mentioned again that in certain cases it is not possible to spin the sample without destroying the orientation in spectro­meters which have the magnetic field orthogonal to the axis of spinning. Such a situation arises in general in the pure ternary phase formed from sodium or lithium decylsulphate, decanol and water [46]. The degree of order in lyotropic phases does not depend upon the rate of spinning except in polypeptide solutions, where spinning reduces it to one fourth of the value without spinning [56].

Spectral spread is usually much smaller in nematic lyotropic phases than in thermotropic systems. Spectra can generally be conveniently recorded on the conventionally available sweep widths with either the deuterium 'lock' on 0 20 or the proton 'lock' on the residual HOO ofthe 0 20 used for preparing the phase. The small spectral spread in lyotropics may lead to problems in spectral analysis, when the chemical· shifts are of the same magnitude as the dipole couplings. Relatively small changes in the chemical shift resulting from different solvent conditions or perhaps anisotropy may change the spectrum considerably from that expected using the isotropic chemical shifts. Occasionally, the dipole couplings are small enough for the spectrum to become almost first-order and analysis is then straightforward [50,63].

Part II. Studies of Lyotropic Liquid Crystals

4. Introduction

NMR studies of liquid crystalline substances have been extensively used to derive information on the mesophase structure, molecular arrangements, mo­bilities and mechanism of binding of small ions or molecules. Such studies of lyotropics are particularly important since these systems have fairly well-defined physical and chemical properties and can serve as models for the more complicated biological systems [166,167]. The smectic liquid crystalline lipid­water phase serves as a particularly good model for the study of some properties of biological membranes since both biomembranes and lecithin-water mixtures have a bilayer structure [168-175]. The mechanism of binding of ions and molecules in lyotropic liquid crystals provides a deeper insight into these aspects of passive membrane functions.

In the sonicated dispersed state, phospholipids in water produce well-defined high-resolution spectra due in part to the fact that the magnetic field inhomo­geneity effects that are present with coarse aggregates are averaged out when the phase consists of the finer particles [104, 106, 176, 177]. This principle has been used for studying molecular interactions in biomembranes [178-181]. Non­sonicated lipid-water systems sometimes give only slightly broadened spectra, particularly at higher operating frequencies (e.g. 220 MHz) [107], because of the considerable mobility of various groups. The nature and the origin of the spectra in the sonicated and the unsonicated dispersions have been discussed [106, 107,182-184]. 1 H, 13C, and 31 P magnetic resonance spectra of phospholipid membranes in the presence of paramagnetic ions permit one to distinguish between signals arising from nuclei in the inner and the outer surfaces [185-191].

As previously mentioned, lyotropic liquid crystals give rise to a variety of phases depending upon the relative concentrations of the components and the temperature. Investigations of the state of water molecules, their motion and diffusion, mobility of the alkyl chains and binding of small ions in the various phases have been undertaken with the help of NMR. Lineshape, relaxation time and quadrupolar interaction data have been used in attempts to understand these systems. Interpreting such data unfortunately often presents special difficulties arising out of the fact that the medium is anisotropic.

A large amount of literature is available which describes NMR investigations into various anisotropic systems. It is extremely difficult to include each and

20 Studies of Lyotropic Liquid Crystals

every article on this subject in the present monograph, particularly for biological systems and micellar solutions. An attempt has, however, been made to present most of the results, even though some of the systems actually studied may have been omitted.

Although in this review we have presented the conclusions of the various authors much as they were given, the assumptions implicit in many papers are difficult to substantiate. It is consequently useful to make a few general comments about the interpretation of NMR data obtained from anisotropic systems.

a) Linewidths. Except perhaps in the case of solutes in exceptionally highly ordered single-crystal liquid crystals (Le. nematic phases), it will be virtually impossible to observe transitions with a natural linewidth.

The hydrogen component of, say, a detergent bilayer structure will give rise to more than 2" allowed transitions where n is the number of protons (i.e. more than 221 transitions for the case of sodium decylsulphate). To talk of proton linewidths is rather meaningless since one never observes a single line even when quite freely moving groups are present.

Quadrupolar ions might possibly give rise to transitions of naturallinewidth: in nematic solution but in lamellar systems magnetic-field inhomogeneity will contribute substantially to the linewidth even in the best macroscopically ordered samples.

Clearly, except in rare cases, the use of observed linewidths to obtain spectral parameters is a particularly dangerous procedure.

b) Lineshapes. Lineshapes will be affected by parameters similar to those which affect linewidths.

c) Chemical shifts. If resonances corresponding to specific groups are observed because of motional narrowing, difficulties are still encountered. The problem of bulk magnetic susceptibility may be reduced if an internal reference is used but the anisotropy of chemical shift will usually be a significantly large and unknown quantity affecting either the reference or the resonance of interest or most probably both. Working with ordered samples may alleviate this problem somewhat.

d) Relaxation times. Relaxation times in isotropic systems are very difficult to interpret quantitatively. The quantitative characterization of molecules by relaxation times from anisotropic solutions is an even more difficult task.

e) Dipole couplings. Dipole couplings within the structure-building com­ponent of the liquid crystal are usually not observable because of the extremely large number of transitions. Specific substitution of deuterium for hydrogen may allow observation of dipole couplings between deuterons if the protons are decoupled. In principle, such dipole couplings can be very useful; in practice, deuterium-deuterium couplings may be too small to be of practical value. The use of other nuclei may prove to be more rewarding.

f) Quadrupole splittings. Quadrupole splittings, like dipole couplings, provide a good method for the investigation of anisotropic systems. Many nuclei of interest give rise to quadrupolar splittings, D, Li, Na, K, Cs and 170, to mention a few.

Three points should be considered when quadrupole splittings are used to describe orientation of nuclei. The first two are 1'/, the asymmetry parameter, and Qc' the quadrupole coupling constant. For the description of motion in hydro-

Chemical-shift Measurements 21

carbon chains, the deuteron is the most important nucleus. Fortunately, rt is usually negligibly small for deuterium and Qc is approximately 170 kHz for methylene groups. Both these quantities are molecular parameters and conse­quently depend on the individual molecules. Finally, the usual assumption that the bond axis coincides with the principal axis of the field-gradient tensor is not necessarily fulfilled.

5. Applications

5.1. Critical Micelle Concentration

5.1.1. Chemical-shift Measurements

Many studies involving NMR chemical shifts, particularly of hydrogen and fluorine [151, 162-164, 192-219], have been undertaken in micellar solutions. 13C chemical-shift studies in aqueous sodium or ammonium octanoate systems have been reported [121, 220]. The observation that NMR spectra are not broadened by micelle formation has been used as evidence for a 'liquid-like' state of micelles [221-223].

The term critical micelle concentration describes the minimum concentration of the surfactant molecules above which micelles are formed. At the critical micelle concentration the hydrocarbon chains undergo a substantial change in their environment since below this concentration they are interacting mainly with the solvent and above it primarily with each other. This difference may be reflected in the nuclear magnetic shielding as revealed by changes in the chemical shift of the nucleus of interest. If the chemical shift is plotted against con­centration a break in the curve, as shown in Fig. 8, usually appears at the critical micelle concentration.

Critical micelle concentrations have been determined for octanoic, decanoic, dodecanoic and tetradecanoic acids in 95.5 % sulphuric acid [194] and are found to be consistent with those determined from surface-tension measurements [224]. Aqueous solutions of sodium alkylsulphates [162] and D 20 solutions of phenothiazine tranquillizers [204] have been investigated. Dodecylammonium salts of butanoic, octanoic and dodecanoic acids have been studied in carbon tetrachloride [194]. Results have been obtained for octylammonium salts of propanoic, butanoic, hexanoic, nonanoic, decanoic and tetradecanoic acids in both carbon tetrachloride and benzene [207]. PMR investigations on alkyl­ammonium carboxylate micelles in several other nonaqueous solvents have also been undertaken [225, 226]. A typical critical micelle concentration for long­chain hydrocarbons is that of hexadecylpyridinium chloride, which has been found from proton NMR studies to be 0.706 x 10-3 molar in water; this surfactant does not form micelles in methanol [193].

PMR studies of butyl-, hexyl-, octyl- and dodecylammonium propionates in deuterochloroform, dichloromethane, chlorobenzene and N,N-dimethyl-

22

--594 If u

:g -596 .s [ ,,-59B 'g u 'g -600 cJ

~ '0 -602

1-0

-604

Studies of Lyotropic Liquid Crystals

Wt. percent of decanoic acid 3 5 7 9

-610 !C u III

-620 B e a.

-640 ~

u '0

-660 c .s u o

-680 ~ '-Q

Fig. 8. Acid proton chemical shift-concentration curves for octanoic acid (0) and decanoic acid (e) in 95.5% sulphuric acid. The long-chain methyl signal is the reference. [Reprinted from the J. Colloid Interface Sci. 30, 177 (1969) with permission of the copyright owners and the authors. Copyright by Academic Press, Inc.]

acetamide as a function of concentration, established the formation of micelles with aggregation numbers in the range 3 to 8 [211]. The aggregation numbers are evaluated from chemical-shift data assuming a simple mass-action model [150,198,199,202,203,207,211,227]. Values of critical micelle concentrations decrease with increasing number of carbon atoms in the alkyl chain and for each surfactant they increase with increasing solvent polarity. The aggregation number of the micelles formed by ionic detergents increases with increasing ionic strength.

Changes in the chemical shift of the phenyl protons in aromatic alcohols and phenols solubilized in aqueous solutions of surfactants like sodium dodecyl­sulphate have been examined on going from the water environment to the micellar. The solubilization of these materials causes a high-field shift of the phenyl proton resonances [228].

Critical micelle concentrations have been determined from 19F chemical shifts in sodium 12,12,12-trifluorododecylsulphate in aqueous solution and in mixed solvents such as aqueous urea, glycerol, glycine, acetamide, methanol, acetone, ethanol, dioxane, and tetrahydrofuran [203]. iO,10,10-trifluorodecyl­trimethylammonium and 12,12,12-trifluorododecyltrimethylammonium halides and hydroxides [150J have critical micelle concentrations about twice those of their nonfluorinated analogues. The 19F chemical-shift studies in 12,12,12-tri­fluorododecyltrimethylammonium fluoride in the presence of potassium fluoride reveal a second critical micelle concentration. Similar behaviour has been

Spin-lattice Relaxation Time Measurements 23

observed for other systePls [229]. The explanation appears to lie in the fact that micelles of two aggregation numbers are formed such that, with increasing concentration, micelles of the higher aggregation number become stable.

Critical micelle concentration data from 19F chemical shifts in 8,8,8-trifluorooctylhexaoxyethylene glycol monoether and 8,8,8-trifluorooctyl­methylsulphoxide in aqueous and aqueous urea solutions have substantiated that the presence of a trifluoromethyl group increases the critical micelle concentration compared to the nonfluorinated analogue and there has been estimated to be about an 8 % decrease in the free energy of micellization [202].

19F chemical-shift studies in perfluorobutanoic acid in water have indicated that the critical micelle concentration falls on raising the temperature from 0° to 26° C [165]; thus, micelle formation is endothermic over this temperature range. Similar results have been obtained for aqueous solutions of the sodium salts of 9,9,9-trifluorononanoic acid and 11,11,11-trifluoroundecanoic acid, where micelle formation is slightly endothermic at lower temperatures and exothermic at higher temperatures [199]. Nonfluorinated systems show a similar behaviour [230, 231]. Thermodynamic results thus indicate that, except for a small decrease in the enthalpy of micellization fluorinated systems are not significantly different from the nonfluorinated ones. .

The effects of temperature, electrolytes and varying counterions on per­fluoromethylalkylates have been investigated. The critical micelle concentration was found to depend strongly upon electrolyte concentration but not signifi­cantly on the various counterions, Li+, Na+, K+ and (CH3)4N+ [199, 232]. Surface-tension [233] and light~scattering [234] studies on the sodium, lithium and tetramethylammonium salts of dodecylsulphate, however, indicated that the counterions do have a substantial effect on micellization.

The addition of nonionic detergent Triton X -100 to aqueous phosphatidyl­choline dispersion has been found to convert the bilayer structure to the mixed micellar [235].

5.1.2. Spin-lattice Relaxation Time Measurements

Critical micelle concentration determinations from spin-lattice relaxation times (T1) are very sparse. This is a result, no doubt, of the relative inaccuracy of the method compared to chemical-shift measurements and other more traditional ways of determining it. Particularly for protons, the method is of limited value since information from specific nuclei of interest is generally difficult or im­possible to obtain. In such cases, an 'average' proton Tl of many CH2 groups is obtained since the various methylene proton resonances are not resolved. For protons, the information on Tl leading to critical micelle concentration is some­times derived from other resonances like the solvent peak. On the other hand, spin-lattice relaxation times from 13C-NMR studies are of more value since the large chemical shifts allow a more detailed investigation of specific nuclei of interest [236, 237].

. Spin-lattice relaxation time studies of water protons in solutions with alcohols and sodium alkylsulphates as a function of concentration provide

24 Studies of Lyotropic Liquid Crystals

critical micelle concentrations. For alcohols and solutions of the C2 and C4

alkylsulphates, the relaxation rates (1/T1) for water protons vary linearly with concentration. The higher alkylsulphates cause a change in slope near the critical micelle concentration [151].

19F spin-lattice relaxation time studies in heptafluorobutyric acid-water and sodium pentadecafluorooctanoate-water have provided critical micelle con­centrations [238]. A replacement of H2 0 by 0 20 has no effect on the spin-lattice relaxation time in the micellar solution.

l3C spin-lattice relaxation times of the various carbons in aqueous solutions of several n-alkyltrimethylammonium bromides [236] and n-alkylammonium trifluoroacetates [237] show a sharp decrease in Tl above the critical micelle concentration.

5.2. Spectral Changes and Phase Transitions

Abrupt changes in apparent NMR linewidths are usually observed at phase transitions and may in part be caused by variations in relaxation times resulting from differential freedom of motion. Anisotropic phases provide NMR spectra influenced by several contributions, including the anisotropic properties of the media, and hence only qualitative conclusions may be drawn from them. Typical results obtained when proton NMR linewidths are plotted as a function of concentration are shown in Fig. 9. The system represented in Fig. 9 is dimethyl­dodecylamine oxide (OC12AO) at various concentrations in 0 20; the phase transitions are clearly revealed [76]. The low concentration region marked FI is isotropic micellar. At a concentration of around 33 wt.- % of the surfactant, a transition to the hexagonal phase occurs. In this phase dipolar interactions domi­nate the spectrum and lines due to individual transitions are no longer resolved, so that only the spectral width is obtained. At about 62 wt.- % ofthe surfactant concen­tration, the system undergoes a transition to the isotropic cubic phase. In this case, lines due to individual groups are obtainable and, as indicated by Fig. 9, the widths differ only slightly from those of the normal micellar solution. At about 71 wt.- %, a second anisotropic phase, in this case lamellar, is obtained. The spectral width here is similar to that of the hexagonal phase. A transition to the crystalline material causes a further increment in the spectral width. The sodium dodecylsulphate-octanol system has also been similarly examined [239]. NMR spectroscopy in conjunction with results from other techniques, such as X-ray diffraction, optical microscopy and differential thermal analysis, has revealed the presence of two cubic phases in the dodecyltrimethylammonium chloride-water system [240]. Spectral changes due to phase transitions in the N,N,N-trimethylaminododecylimide-water system have been examined and a phase diagram has been constructed [241]. The same authors have also investi­gated the sodium di-(2-ethylhexyl)sulfosuccinate (aerosol OT)-water system. Addition of water to the aerosol OT-octane system introduces transitions of the type clear-turbid-clear-turbid [242, 243]. The PMR spectrum of the first turbid region shows two peaks attributed to water protons of the separated aqueous phase and of the micellar solubilized form. The coexistence of the two signals

Spectral Changes and Phase Transitions

o 10.0

1.0

3 0.1 .r. -~

CI> c: 0.01 ::i

0.001

o

. Volume fraction OC12AO 0.39 0680.75 0.87 1.0

00 HOO •• NCH3 •• CH2 r

FI M , VI N: C

h I I I I I I I

40 60 %OC12 AO (w/w)

I I I

80 100

25

Fig. 9. Proton NMR linewidths [in Gauss (G)] in dimethyldodecylamine oxide-D20 as a function of the relative concentrations of the components at room temperature. FI = micellar, M = hexagonal, VI = cubic, N = lamellar, C = crystalline [Reprinted from the J. Phys. Chern. 72, 2066 (1968) with the permission of the copyright owners and the authors. Copyright by the Americal Chemical Society]

shows that the proton exchange rates between the 'solubilized' and the 'separated' water is slow. Th~ influence of addition of salts of mono-, di- and trivalent metals on the state of water in the aerosol OT-octanol-water system has also been examined [244].

Tl measurements in the quaternary micellar system of sodium decylsulphate, n-decanol, water. and sodium sulphate have been made as a function of frequency and temperature [245]. It was found that, whereas the linewidths showed abrupt changes at the phase-transition temperatures, Tl values did not. PMR linewidth studies in solutions of hexadecyltrimethylammonium bromide­butanol-water (buffered at pH = 11.5) systems as a function of water concentration show correspondence with light-scattering results [246].

Tl and T2 measurements in ternary systems of sodium dodecylsulphate­octyltrimethylammonium bromide with approximately 95 % D20 provided Tl varying from 0.5 to 1.0 sec and T2 from 0.5 to 0.025 sec [247]. Widths of the lines due to various groups (which were used to estimate T2) showed a large change around 77 mole-% concentration of sodium dodecylsulphate. The discontinuous change in motion around 77 mole- % of sodium dodecylsulphate has been attributed to either the presence of two types of micelles or a change in the

26 Studies of Lyotropic Liquid Crystals

micellar type. Similar results were obtained for the micellar systems of hexa­decyldirnethylammonio propanesulphonate-sodium dodecylsulphate-water [248, 249].

NMR spectra from anhydrous sodium dodecanoate, tetradecanoate, hexa­decanoate, and octadecanoate have been studied as a function of temperature [77,250-256]. It is apparent from the linewidth studies that sodium dodecanoate in the mesomorphic state is structurally different from the longer-chain aliphatic acid salts. It was also observed that in the crystalline phase at constant temperature the linewidth decreases with increasing chain length. This result indicates that the longer chains have more freedom of movement.

Proton and phosphorus linewidths in the NMR spectra of aqueous dispersions of egg-yolk lecithin have been found to be field-dependent, although only the widths of the proton lines are concentration-dependent [106,257-260]. The temperature dependence of relaxation times revealed a phase change in egg-yolk lecithin. Such results indicate that relaxation-time studies may be useful for the determination of phase changes in lipids. The field dependence of the 31 P resonance has been interpreted in terms of a chemical-shift anisotropy from the phosphate group, and that of the proton lines at least partially, to insufficient motional narrowing [106]. Correlation time.s and diffusion constants have been derived from the frequency dependence of the linewidths.

In steady-state absorption NMR, T2 is given by the inverse of the linewidth and the values thus determined reflect molecular mobility when determined for isotropic solutions, for example, of micelles and serum lipoproteins [73, 162, 261, 262]. The extension of this concept to anisotropic systems is not justified [82,83,91] as indicated by the considerable amount of work involving 12 measure­ments from free-induction decay and spin-echo methods [263-265]. At most only qualitative information is provided by such measurements, since single transitions are seldom if ever observed, particularly for protons. The real or apparent broadening of the transitions results from interactions due to anisotropy of the medium, if not simply from field inhomogeneity. Thus large errors may arise from such studies in anisotropic soaps, phospholipids and other similar systems [83-85, 92, 93, 106, 266-270]. In liquid crystals, T1 is always larger than T2 probably because of the presence of slow movements like translational diffusion, chain mobility etc., which contribute more effectively to T2 than to T1•

Interactions of phospholipids and synthetic phospholipid stt;uctures with water have been investigated from line shape studies. It was found that, with added water, the trimethylammonium group moves more freely [71,271-273]. The stability oflecithin micelles in benzene has also been examined [274]. Binding of bovine serum albumin to various fluorinated surfactants has been investigated from 19F chemical-shift and linewidth studies [275, 276] and also from proton linewidth and electron-spin resonance studies [277, 278].

Studies on the interaction of valinomycin with unsonicated lecithin bilayers indicate that, whereas valinomycin interacts with dipalmitoyl lecithin bilayers

. predominantly in the region of polar heads, with dimyristoyl lecithin the valinomycin molecules penetrate into the hydrophobic core of the bilayer [279]. This difference in behaviour is attributed to the variation of the bilayer stability with fatty-acid chain length.

Spectral Changes and Phase Transitions 27

A large number of sttldies involving measurements of spin-lattice and spin-spin relaxation times (Tl and T2) have been undertaken in lyotropic liquid crystals in an attempt to investigate the problem of molecular association in biomembranes, in aqueous dispersions of phospholipids and in aqueous soap systems [78--83,89-91,97,280-284].

Tl and chemical-shift measurements of water in the polyoxyethyleneglycol monoethers-water system revealed no discontinuity in chemical-shift or Tl on going from anisotropic to isotropic micellar solution [285]. This result implies that the mobility and the hydrogen bonding of water molecules do not depend on the phase structure in these systems but that they do depend upon temperature and concentration. Similar results have been obtained from deuterium Tl studies of deuterochloroform and dideuterodichloromethane in isotropic and anisotropic solutions with poly-y-benzyl-L-glutamate [286]. Proton spin-lattice relaxation times from poly-y-benzyl-L-glutamate itself show little dependence on concen­tration or temperature. However, it has a strong frequency dependence [286,287], showing a minimum at the highest frequency. On the other hand, the deuteron T1's are strongly dependent on concentration and temperature but practically independent of frequency (within the range 4.5 to 10.5 MHz). Poly-y-benzyl-L­glutamate shows considerable differences in its relaxation behaviour, depending upon whether it is in a helix or a random-coil form.

Data on deuteron relaxation times in the lamellar phase of the potassium dodecanoate-D20 system have been interpreted in terms .of two different types of motion of water molecules with characteristic correlation times of 10- II

and 10~ 6 sec [90]. The activation energy calculated for the fast motion (4.1 kcaljmole at 85° C) is not far from the corresponding value in D 20 [288] (3.9 kcal/mole at 90° C). However, the results have been reinterpreted as re­sulting from double quantum transitions [289], as for the DMR spectrum of the lamellar phases from sodium octanoate, octanoic acid and D20. The spin-spin relaxation time was found to increase abruptly [82, 89, 90] on going from the lamellar to the cubic phase because of a long-range diffusion of water molecules.

Proton relaxation time measurements in potassium dodecanoate-24 % H20 provide Tl = 1.8 sec and T2 = 20 msec at 20° C [90, 290]. It was shown from the proton Tl measurements in the potassium dodecanoate-D20 system that trans­lational diffusion exists with similar rates in the lamellar, cubic and hexagonal phases [89].

For the system, potassium dodecanoate-D20, T2 was found to be essentially frequency-independent in the range 10 to 40 MHz [291]. Similar results were obtained for ghost lipids, dipalmitoyl lecithin and egg lecithin [86, 291]. At higher fields, however, dependence of the PMR linewidth on the magnetic field strength has been observed [84, 101, 106] and was attributed to the chemical­shift anisotropy effects [292].

NMR relaxation rate studies have been made in the lamellar phases from ammonium perfluorooctanoate-water, sodium octanoate-decanol-water, and ammonium perfluorooctanoate-hydrocarbon additive-water [97, 281, 282]. Fluorine Tl and 12 measurements in the first system showed that the relaxation rates are qualitatively similar to those for alkyl chain protons in similar systems. The TI values indicated that at 25° C the rotation of the CF 2 group about the

28 Studies of Lyotropic Liquid Crystals

long axis of the chain is slower than in the hydrocarbon system; the activation energy of the process is of the same order as or smaller than that found for the hydrocarbon system.

Proton Tl studies on ammonium perfluorooctanoate-hydrocarbon chain additives (e.g. n-alkyl primary alcohols, sodium octanoate, octanoic acid, octyl­trimethylammonium bromide and 1, iO-n-decane-diol)-H20 systems indicated that the CH2 rotational motion becomes more restricted with the increase in chain length, in contrast to ESR spin-label results [293-295].

Temperature and frequency dependence of Tl have been investigated for the various protons in sonicated dipalmitoyl lecithin vesicles. Difficulties in inter­preting such data in terms of specific motions in the phospholipid molecule were pointed out [296].

5.3. Proton and Deuteron Magnetic Resonance in Hydrated Fibrous Materials

As we have seen in the previous sections, molecular mobilities influence the NMR linewidths as well as the dipolar and the quadrupolar splittings. Using such properties, the PMR and DMR spectra provide information on the state of water (or 0 20) adsorbed on fibrous materials. The water of hydration in some fibrous proteins was shown to retain its 'liquid-like' mobility even at temperatures well below the freezing point of water [297-300]. In hydrated collagen [68, 69, 155,299-314], keratin [304,315-318], rayon [74], nerve tissues [67,319-323] and some forms of DNA [324-326], the water protons have revealed orientation­dependent one- to three-line spectra, separate from most of the macromolecular protons. For the 'single-line' spectra, linewidths have an angular dependence.

The PMR spectrum of hydrated collagen consists of an orientation­dependent dipolar doublet due to anisotropically rotating water molecules and a nearly isotropic central line [155, 299-308]. The DMR spectrum of 0 20-hydrated collagen gives a quadrupolar doublet and a central line which is sometimes absent [68, 155, 315]. The doublet separations decrease with in­creasing water content. The appearance of the doublet was initially interpreted in terms of one of the following models: (1)- a definite structural state of water where such molecules form chains parallel to the fibre axis with anisotropic motion in each chain [299, 302-306], or (2)- a random diffusion of water molecules between the collagen fibres [68] such that their motion is anisotropic because of the fact that some of the hydrogen bonding states of water in the pores between the strands are more likely than the others. However, these models do not explain the dependence of the dipolar and the quadrupolar splittings on the water contents. In a more recent approach, it was assumed that only some of the adsorbed water molecules bind with the collagen triple helix [327] and are oriented; the rest are rapidly reorienting [155, 308]. The two types of water molecules were assumed to exchange rapidly, so that the dipolar and quadrupolar splittings observed' are the time-averaged values of bound and unbound water molecules. Under various assumptions [328,329], the preferential orientation of

Self-diffusion in Lyotropic Liquid Crystals 29

water molecules was shown to be the one where the HH direction is perpen­dicular to the fibre axis [155]. The PMR and the DMR results agree [330] with the specific-water-binding model [327].

The central line in the PMR spectrum of collagen was earlier attributed to a separate phase of adsorbed water [307]. Later it was pointed out that it may come from the mobile side-chain protons [68, 155]; however, the presence of small molecules giving rise to this line cannot be entir~ly excluded. Self­diffusion and relaxation time studies have recently been undertaken in collagen and gelatin containing different quantities of water [331], the result being inter­preted in terms of a model based on a distribution of correlation times.

The dipolar doublet in the PMR spectrum collapses into a singlet with in­creasing temperature [155,299] whereas the quadrupolar splitting in the DMR spectrum remains invariant with temperature [68, 155, 326]. This is due to proton exchange between water molecules or between water molecules and proton-accepting or -donating groups. Such an exchange reduces the lifetime of protons of water molecules at one site and thus influences the intramolecular dipolar interaction. However, in the DMR spectrum, a jump of d~uterium to a neighbouring water molecule results in the rotation of the electric-field gradient through 180°, leaving the quadrupolar splitting unchanged.

From the temperature dependence of the linewidths, correlation times of molecular rotation of water, proton-exchange times and activation energies have been obtained using Arrhenius' equations and relaxation theory [332-334]. For a water content of 45 g/100 g collagen, the rotational correlation time is 3 x 10- 8 sec at 25° C with an activation energy of 4.8 kcalfmole, and the proton exchange time is 1.3 x 10-4 sec with an activation energy of 10 kcalfmole [155]. It should be emphasized that the correlation time as determined by NMR is the weighted average from the various species of water molecules.

Addition of ions has been found to have an effect on the NMR spectra from several biological tissues and fibres. The dipolar and the quadrupolar splittings are smaller in the presence of salts [155,301,308,310]. The central peak in the DMR spectrum grows in intensity in the presence of salts because ofthe coordina­tion of water molecules with the ions, which increases the exchange rate. The physical state of water and ions, particularly sodium, in a variety of tissues as revealed by changes in the NMR spectra has been widely investigated [335-340].

5.4. Self-diffusion in Lyotropic Liquid Crystals

The apparent linewidth in macroscopically oriented samples [152] varies as (3 cos2 () - 1) where () is the angle between the optical axis and the magnetic field such that at the 'magic' angle (54.7°) the dipolar broadening vanishes and the lines are very narrow. Such effects have been observed in several soap, synthetic polypeptide and lecithin systems [159, 160, 341-343]. This minimization of the dipolar interaction permits the observation of a pulsed NMR Carr-Purcell [263] spin echo from the surfactant protons in the lamellar phases. The echo can only be seen at the 'magic angle' and its observation provides a method'to measure diffusion coefficients using the well-knowtl pulsed-gradient technique [344]. True

30

4.2

u 3! 3.8 .....

N

5 3.6 III

~ ~ 3.4

~ 3.2 c 8 3.0 6 ·iii 28 :E . 15 2.6

2.4

o

Studies of Lyotropic Liquid Crystals

Lecithin in n-hexane

Fig. 10. Diffusion coefficients as a function of the concentration of lecithin in n-hexane. [Reprinted from the Mol. Cryst. Liquid Cryst.17, 281 (1972) with permission of the copyright owners and the author. Copyright by Gordon and Breach, Science Publishers]

translational diffusion coefficients (i.e., parallel to the bilayers) can be measured from the spin-echo measurements [156]. Diffusion coefficient studies have been made in anhydrous sodium hexadecanoate and sodium hexadecanoate-water mixtures [156, 157].

The diffusion coefficient of water in the lamellar and the hexagonal phases increases with temperature before it drops at the transition to the isotropic point. The diffusion coefficient in such cases is quite large, i.e. in the hexagonal 30 % sodium hexadecanoate-70% H 20 system at 77° C, it is lower than in pure water by only a factor of 3 and is an order of magnitude larger than in zeolites. The coefficient was found to decrease with the decrease in water content. The corre­sponding coefficients for sodium hexadecanoate were too small to be measured by the technique used [157]. The diffusion coefficient in the cubic phase of potassium dodecanoate-D20 was found to be 2 x 10- 6 cm2/sec at 90° C with an activation ener:gy of 5.8 kcallmole r81, 891

Diffusion coefficient studies have been made of lecithin in various solvents like n-hexane, n-decane and methanol and the potassium octadecanoate-water system [345]. Although the diffusion coefficients of lecithin itself could not be obtained, the effect of lecithin on the coefficients of the various solvents was readily detected. Results on the lecithin-n-hexane system are shown in Fig. to. Figure 10 shows that the diffusion coefficient for the pure solvent (4.2 x to- 5 cm2/

sec) initially starts to fall rapidly on addition of lecithin. However, around 6 % concentration of the lecithin, the diffusion coefficient starts to increase, reaching a maximum around 10% concentration of the lecithin; with further solute, the diffusion coefficient decreases, reaching a plateau around 14 to 20 % concentration. Near the last mentioned concentration, the solution appears as a gel.

Ordering of Spherical and Tetrahedral Ions 31

It has been concluded from such studies that the micelles are spherical below 5 %, pass through a transition region from 5 to 10%, and above 10% appear as cylinders increasing in length with increasing lecithin concentration.

Proton and deuteron magnetic resonance spectra from a I-mono-octanoin­water (H20 or D 20) system have been reported for 'macroscopically' and 'randomly' oriented samples. Proton second moments and the dipolar and quadrupolar splittings have been examined at different temperatures and compositions [96, 99] and the results interpreted in terms of the anisotropy in the motion of the water molecules.

5.5. Interactions of Ions in Anisotropic Media

5.5.1. Ordering of Spherical and Tetrahedral Ions

A priori there is no reason why ions like Li+, Na +, Cl-, NDt, BF;, etc. should give quadrupole splittings, even in an anisotropic medium. Let us consider, for example, the terms that contribute to the quadrupolar splitting (Ll v) of the deuteron in the ND t ion, assuming the ion can order.

Ll v is given by

(11)

where SC3 is the degree of order along the C3-axis, QD is the deuteron quadrupole coupling constant and y is the tetrahedral angle (109°28'). The multiplier of the common factor in Eq. (11), i.e. (0.25 + 0.375 (3 cos2 y - 1)), is identically zero for a tetrahedral geometry. The quadrupolar splittings in such cases can arise only if distortions from tetrahedral geometry occur. If the quadrupolar nucleus is in the centre of tetrahedral or higher symmetry, like 14N in 14NHt, still no splitting will be observed unless distortions from the tetrahedral or spherical symmetry occur. Since spherical ions are strongly hydrated, the quadrupolar splittings most probably arise from distortions in the hydration shell, just as quadrupole splittings in the ammonium ion arise from distortions from tetrahedral geometry. The mechanism of such distortions is of considerable interest.

It is generally accepted that distortions of tetrahedral molecules in thermo­tropic phases arise from van der Waals interactions with the solvent. The distortions in these tetrahedral species are not fixed within the molecule so actually Eq. (4), and consequently Eq. (11), does not properly describe them. Eq. (3) is required. One interpretation advanced is that because of the uniaxial nature of the system, one should regard the direction of distortion as constant, being determined by the overall order of the liquid crystal. The tetrahedral molecules then tumble inside this distortion sheath which remains directed in space; this would give rise to the usual dipolar or quadrupolar spectrum [346].

A similar mechanism could operate in lyotropic systems [346]. The distortions in this case might arise from interactions with the charged surface, which polarizes

32 Studies of Lyotropic Liquid Crystals

the tetrahedral ion or the hydration shell of the spherical ion, so giving rise to the quadrupolar splitting.

Such an interpretation of quadrupolar splittings is conceptually quite different from the alternative mechanisms proposed, which involve specific bind­ing sites [123,347]. It is implicitly assumed in such proposals that electric field gradients arise only when the nucleus is bound to specific regions of the phase and this binding is what provides the field gradients, either by direct contact or by distorting the hydration sheath.

In actual practice, a Combination of the two above-stated mechanisms may provide a more realistic description of these systems.

5.5.2. Ion Binding and Ion Competition

Studies of ion interactions in nematic liquid crystals indicate that one must be careful in interpreting spectra from ions in terms of binding sites. For instance, it has been found that the tetradeuteroammonium ion in the nematic phase of decylammonium chloride-ammonium chloride-020 is ordered [348]. Moreover, if, in the above phase, the chloride ion is replaced by a tetrafluoroborate ion, the deuteron quadrupole splitting in the NOtion increases by an order of magnitude [349]. No such increase occurs in the deuterium splitting of either 0 20 or'the head group (- NOt). It is emphasized that no binding sites occur in this phase as both the decylammonium and the ammonium ions have the same charge. Interestingly enough, the deuterium quadrupole splitting of the tetradeuteroammonium ion in a sodium decylsulphate phase, which has potential binding sites, is not as large as for the decylammonium tetra­fluoroborate phase which has none [350]. It is therefore clear that the mechanism whereby quadrupolar splittings occur in spherically or tetrahedrally arranged quadrupole nuclei is not simply one of ion binding.

Ion-water and ion-ion competition reactions have been followed in nematic liquid crystalline phases [350,351]. The basic assumption in this work is that if ion competition does occur, then a difference in the ratios of quadrupolar splittings should be observed as components of the system are changed. It has been found that, as cesium decylsulphate replaces sodium decylsuiphate in the sodium decylsulphate-decanol-020 phase, the ratio L1 vNa/L1 Vo (where L1 v refers to the quadrupolar splitting) increases significantly. This has been interpreted to mean thatthe alkali ions replace 0 2 0 in the more ordered regions of the phase. However, when lithium decylsulphate replaces sodium decylsulphate in the above system, a slight decrease in the ratio L1 vN JL1 Vo is found, indicating a pre­ferential displacement of the alkali ions from highly ordered regions. The ratio L1 vNJL1 VLi was found to remain practically constant as the concentration oflithium decylsulphate is increased from 12 to 24 mole- % of the surfactant.

Addition oflithium sulphate to the sodium decylsulphate-decanol-02 0 phase reveals a small increase in sodium splittings with respect to the lithium as the lithium sulphate concentration is increased. However, a preference of water for more highly ordered regions is indicated.

Alkali Ions 33

The results seem to indicate that for the above system little ion competition fot the charged, highly ordered surface is present. On the other hand, ion-water competition seems quite marked.

5.5.3. Halide Ions

The influence of phase composition on the 81Br- magnetic resonance linewidth in lamellar, hexagonal, and micellar solutions has been investigated [352-354].

The linewidth in the lamellar phase of the hexadecyltrimethylammonium bromide-hexanol-water system increases with decreasing water and/or hexanol concentration, the change being more marked at higher water contents [123J. It increases immensely with increasing hexadecyltrimethylammonium bromide content. Since an increase in linewidth is presumed to indicate enhanced binding, a decrease of water or hexanol concentration indicates a firmer binding of the bromide ions in the lamellar phase. This is due to the reinforced hydration of the bromide ions or a release by hexanol of counterions from the charged surface.

In the hexagonal phase, the 81 Br- linewidth is nearly independent of the concentration of the components, though minor changes in linewidth are noticeable on increasing hexadecyltrimethylammonium bromide content. Thus, the counterion binding is similar in different parts of this phase. Similar studies in the above mixture have been conducted in the 'reversed' micellar region [354]. Attempts have been made to rationalize the results in terms of electric-field gradients and correlation times.

81Br- magnetic resonance studies in the aqueous micellar solution of hexadecylpyridinium bromide and octylammonium bromide show that the line­widths are much larger (about 2 orders of magnitude larger) near and above the critical micelle concentration [352, 353J, probably due to larger correlation times of the molecular motion. Linewidth decreases with increasing temperature in the hexadecylpyridinium bromide solution.

79Br- NMR linewidths in aqueous solutions of mono-, di-, tri-, and tetra-n­alkylammonium bromide increase strongly with carbon chain length, number of alkyl groups in the cation, and electrolyte concentration [355J.

In the octylammonium chloride-decanol-water [125J system, the 35CI­quadrupole splitting is independent of temperature. This may indicate that ,the factors determining the quadrupole splittings are invariant to temperature changes. However, such a situation may also arise from cancellation of opposite effects. Studies of the concentration dependence of the 35C1- splittings in the above lamellar mesophase suggest that the interaction increases with decreasing water content and the splittings are greatest at the highest concentration of octyl­ammonium chloride.

5.5.4. Alkali Ions

For the alkali ions, generally first-order splittings are observed in the lamellar mesophase (for 85Rb, however, second-order quadrupole effects have been observed [131J).

34 Studies of Lyotropic Liquid Crystals

The influence of temperature, concentration and phase composition on the magnitude ofthe splittings has also been investigated [46,124,356]. A decrease in the splitting of the 23Na + resonance lines with an increase of temperature occurs in the sodium octanoate-decanol-water system. The temperature variation of the splitting for 'macroscopically oriented' samples is much weaker than for the 'powdered' (randomly oriented) ones.

23Na quadrupole splittings of 'powdered' lamellar mesophase samples of egg yolk lecithin-cholesterol-aqueous alkali chloride solutions and of egg yolk lecithin-alkali chloride-water have also been studied [124]':, For the cholesterol­containing sample, an increase in the 23Na quadrupole interaction has been observed with increasing cholesterol content and is attributed to a decrease of the distance between lecithin head groups.

A substitution of heavy water for ordinary water leads to a marked increase in the 23Na 'powder' splitting [124J in the lamellar phase. This has been attributed to a considerable reduction in the exchange rate of 23Na between the micro crystallites, analogous to the retardation of the translational motion of sodium ions in aqueous solution on substitution of D20 for H20 [357].

Tl measurements for the 23Na + ions in the lamellar phase of the lecithin­sodium cholate-water system show that the value of Tl is about 2 orders of magnitude smaller than in an aqueous NaCI solution [126].

Comparative studies of the ion-binding effects for various alkali ions have also been made [124, 358]. DMR spectra in the lamellar mesophase of alkali octanoate-decanol-water consist of two quadrupolar doublets [l61J, one due to water deuterons (with large intensity and small splitting) and the other to decanol deuterons (smaller intensity and an order of magnitude larger splitting). The splittings of the intense peaks initially increase with temperature and then de­crease with increasing temperature. At high temperatures only one doublet could be observed, due to faster exchange of deuterons between water and decanol. The coalescence temperature of the two separate resonances depends upon the alkali ion. The water orientation is the largest for Li+ counterions; for Na +, K +, and Rb +, it increases with the atomic number of the counterion. The degree of the amphiphile orientation on the other hand depends very little on the counterion.

In experiments involving competitive binding of Ca + + and Na + in lamellar liquid crystalline systems prepared from dipalmityl lecithin, dimyristyl lecithin, and egg yolk phosphatidylethanolamines dispersed in D20 solutions of sodium chloride, it was found that the Ca + + ions have a strong preferential binding to egg yolk phosphatidylethanolamine but not to lecithin [358].

5.5.5. Proton, Deuteron, and Alkali Resonance Studies

The water proton spin-lattice relaxation rate (1ITl) in aqueous micellar solution of sodium dodecylsulphate containing 10- 3 molar manganese sulphate is larger by about 30 % when Mn + + ions bind to the micellar surface. This is due to a decrease in the rotational mobility of the aquated Mn + + ions resulting in a

14N Quadrupole Interactions 35

chaJ;lge in the correlation time [359]. However, the change in the spin-spin relaxation rate (1/7;) is much less.

Deuteron and sodium resonance studies have been carried out in ternary lamellar systems like sodium octanoate-octanoic acid-water (D20), sodium octylsulphate-decanol-water (D20), sodium octylsulphonate-decanol-water (D20) and hexadecyltrimethylammonium bromide-hexanol-water (D20) [358, 360, 361]. In systems with aliphatic alcohols at low temperatures, separate quadrupolar doublets in the deuteron magnetic resonance spectra have been observed for the water and the OD deuterons of alcohol. However, they coalesce at high temperatures due to rapid exchange between the hydroxyl and the water deuterons and the splittings increase with temperature.

In the lamellar phase oflecithin in D20 with varying concentrations of sodium chloride, at various temperatures, both the sodium and the deuteron quadrupole splittings increase with concentration of sodium chloride as well as temperature [358, 362]. The increased binding of sodium ions and water is related to a con­formational change in lecithin. The cholesterol containing samples undergo a re­arrangement of the molecular organization of the bilayer near a molar ratio of lecithin to cholesterol of 4 : 1.

In samples consisting of lecithin, cholesterol, alkali chloride, and heavy water, or of lecithin, alkali cholate, and heavy water, the degree of water orientation is lower with K + ions than with other alkali ions [362]. K + ions were shown to interact more strongly with the amphiphilic molecules than did other alkali ions.

5.5.6. PMR of Nonionic Surfactants in the Presence of Anionic Surfactants

A study of aqueous solutions of dodecylpolyoxyethylene ethers with dif­ferent numbers of oxyethylene units in the presence of sodium dodecyl­sulphate and sodium p-octylbenzenesulphonate at different relative concentra­tions of the anionic and nonionic surfactants has been reported [363]. The resonance due to the protons of the polyoxyethylene chain shifts to higher fields when sodium p-octylbenzenesulphonate is added to dodecylpolyoxyethylene, but its position remains unchanged on addition of sodium dodecylsulphate. The shift to the high field in the former is attributed to an interaction of the 1t electrons of the benzene ring of sodium p-octylbenzenesulphonate in the mixed molecules. The extent of the high-field shift depends upon the chain length of dodecyl­polyoxyethylene and the relative concentrations of sodium p-octylbenzene­sulphonate and dodecylpolyoxyethylene.

5.5.7. 14N Quadrupole Interactions

Such interactions have been studied in the ternary mixture of the ammonium octanoate-decanol-heavy water system and are found to be nearly independent of the sample composition [356].

36 Studies of Lyotropic Liquid Crystals

5.6. Alkyl Chain Motion in Lyotropic Liquid Crystals

5.6.1. The Concept of the Order Parameter as Applied to the Hydrocarbon Chain

The order parameter (S) provides the most simple and straightforward means of describing the anisotropic motion of the hydrocarbon chains. Since the chains are not rigid, the order parameter of each methylene group within the chain must be described separately. In general, five independent elements of the order matrix are needed for the description of the motion of each segment, as for phospholipids, which have no symmetry. This number may be reduced to three because of 'effective' Crsymmetry, e.g. in cases like n-alkyl ammoniums or n-alkyl sulphates.

Proton-proton dipolar or deuterium quadrupolar splittings provide a single piece of information about the order matrix of the segment. The direct dipolar interaction describes the order of the internuclear vector and is given by Eq. (4). The order parameter along the C-D bond axis (SCD) may be determined with the help of Eq. (12) by neglecting the asymmetry parameter and assuming a known value for the deuteron quadrupole coupling constant (e.g. ~ 170 KHz in aliphatic hydrocarbons) [364].

S ~ 2L1v CD 3QD (12)

In actual practice a single independent order parameter may describe the entire orientational state of a particular segment because of "effective" axial symmetry. "Effective" axial symmetry means that if the order parameter is deter­mined for any direction perpendicular to the molecular axis it must be constant. One way to determine this is to label the methylene group with deuterium and obtain a deuterium spectrum from the ordered sample while simultaneously decoupling the protons. The deuterium spectrum will then provide a deuterium quadrupole splitting and simultaneously a deuterium-deuterium dipole coupling, both for the same methylene group. Assumption of reasonable structural param­eters for Eq. (4) and of QD for Eq. (12) permits the derivation of the two S values SDD and SCD' Since these values are for different directions then if they are the same, the assumption of axial symmetry is reasonable. The technique has previously been described [113].

5.6.2. Structure and Dynamics of the Hydrocarbon Region

5.6.2.1. Micellar Solutions

Spin-lattice relaxation times of individual carbons have been used to investigate segmental motions in simple molecules and in biopolymers [237, 365-372].

Proton-decoupled natural-abundance l3C partially relaxed Fourier transform NMR spectroscopy [373] has been used to obtain information on segmental motion in n-alkyltrimethylammonium ions [236] and in n-alkylammonium ions

Anisotropic Phases 37

8 6,7 5 9

'l • :p .* , ..... ........... f .. -'" ."

t. 2 3

A

10

B ......... "tJ1~t ~ .. ~; ............... _ ......... "" ... ~ Fig. II. 13C-Fourier transform NMR spectra of the n-decylammonium ion (CF3 COO- salt in D2 0). The peak assignments correspond to the numbering of the carbons starting from the head group. The lower spectrum (B) was obtained from an anisotropic phase at 36°. The upper spectrum (A) was from the same solution at 39°, at which temperature the isotropic micellar phase is stable. [Reprinted from the 1. Am. Chern. Soc. 96, 5456 (1974) with permission of the copyright owner and the authors. Copyright by the American Chemical Society]

[237]. l3e Tl values for most of the individual carbons of the alkyl chains in aqueous micellar solutions have been determined. A typical spectrum is shown in Fig. 11 which also depicts the drastic change which occurs in a spectrum at the phase transition to an anisotropic liquid. Table 1 gives the spin lattice relaxation times for some systems. It is particularly interesting to note that TJ's remain practically constant until near the terminal position and then increase quite rapidly. Such a result indicates that the motional freedom along the chain is not significantly different from carbon to carbon until near the end of the chain. As discussed in the next section, similar results are obtained from deuterium label studies in lamellar systems. Thus, the motion of the alkyl chain in micelles is not significantly different from that in lamellar phases.

The influence of an electrolyte (sodium chloride) on the motion of alkyl chains in aqueous micellar solution of sodium dodecylsulphate has also been in­vestigated from J3e relaxation-time studies. It has been found that the motion of the methylene group adjacent to the head group becomes increasingly free with the increase in sodium chloride concentration, but inside the micelles the motion remains unchanged [371].

Sodium dodecylsulphate micelles containing nitroxide spin probes have been investigated by means of a combination ofESR and NMR experiments [374,375]. The rotational correlation times of the probes determined from the ESRex­periments have been utilized to compute PMR linewidths, which are in reasonable agreement with the observed linewidths, particularly at lower con­centrations of the nitroxide spin probes. An association of the micelles with the nitroxide radical was postulated [374] but it was concluded from a later study that the spin probes are located near the surface of the micelles [375].

5.6.2.2. Anisotropic Phases

The properties of the alkyl chains in such phases have been investigated by proton, deuterium and carbon-13 NMR spectroscopy and by fluorine magnetic resonance in partially or completely fluorinated derivatives [71, 94, 134- 136, 180'-291,376- 389]. The NMR method (except possibly when fluorine is used

Tab

le 1

. 13

C r

elax

atio

n tim

es in

aqu

eous

sol

utio

n [2

36, 2

37J

Com

poun

d C

once

ntra

tion

T

empe

ratu

re

Typ

e of

T

j (s

ec.)

(± 1

0-15

%)

(M)

°C

solu

tion

C

H3

CH

2 C

H2

n-he

xyla

mm

oniu

m

0.35

38

m

olec

ular

6.

3 5.

0 4.

1 tr

iflu

oroa

ceta

te

n-he

xyla

mm

oniu

m

2.0

38

mic

ella

r 4.

3 2.

3 1.

7 tr

iflu

oroa

ceta

te

n-oc

tyltr

imet

hyl-

0.2

34

mol

ecul

ar

4.3

3.9

amm

omum

bro

mid

e n-

octy

ltri

met

hyl-

2.0

34

mic

ella

r 3.

4 1.

4 1.

2 am

mon

ium

bro

mid

e n-

octy

lam

mon

ium

0.

3 38

m

icel

lar

3.5

1.5

1.1

trif

luor

oace

tate

n-

decy

lam

mon

ium

0.

3 38

m

icel

lar

3.8

2.0

1.2

trif

luor

oace

tate

n-

decv

lam

mon

ium

1.

2 38

in

vert

ed

4.1

3.2

2.3

trif

lu~r

oace

tate

(in

ben

zene

) m

icel

lar

a A

vera

ge o

f tw

o ca

rbon

s.

b A

ssig

nmen

t of

freq

uenc

ies

ambi

guou

s.

C

R is

~N(CH3); o

r ~NH;.

CH

2 C

H2

CH

2 C

H2

CH

2

3.8

1.3

2.3

a 2.

3a

0.8

a 0.

8a

0.5

0.78

0.

70

0.61

0.70

O

.64

b O

.64

b 0.

52b

0.56

0.86

0.

82b

0.62

b O

.64

b 0.

42

CH

2 C

H2

3.6

3.0

1.2

0.95

2.3

2.3

0.5

0.45

0.62

0.

60

0.55

0.

44

0.48

0.

21

RC

w

00

IZl

......

~

0-

(;j'

en

0 -.

l'

'< ~

.... 0 '0 n' ~

.0 5: (J

.... '<

en

...... r::. en

Anisotropic Phases 39

as the label) has the distinct advantage over more traditional techniques of in­vestigation (for example those using spin probes) in that the uncertainty re­garding environmental perturbations caused by the probes is eliminated.

It may be mentioned that the electron spin resonance and the nuclear magnetic resonance methods are complementary to each other in that the motions that may be revealed by ESR may be averaged on the NMR time scale. The question still remains as to whether the difference in the observed motion is a result of the perturbation due to the spin label or not.

Proton magnetic resonance has been used to study lamellar systems [99,106,154,343,374]. It was found that in the octylammonium chloride-water and potassium cis-9-octadecenoate-water systems most of the dipolar broadening could be removed by macroscopic orientation of the sample at the 'magic' angle. The residuallinewidths were used to set upper limits to the rates of rotational and translational motion [154]. From observations at 0° and 90° angles of rotation, it was found that there were at least two major contributions to the wide line spectrum. This was interpreted in terms of a region of constant high orientation (S ~ 0.6) for the first five methylene fragments, giving rise to a dipolar doublet structure and a sudden decrease to a low value of the order parameter (S ~ 0.2) to give the central transition. Since the degree of order of the superstructure is near unity, the authors interpreted the difference as arising from a collective tilt of about 30° in the hydrocarbon chains [i.e. ! (3 cos2 30-1) ~ 0.6].

Due to the inherent complexity of the proton spectra, considerable work has been done on the specific replacement of protons by deuterons. This procedure completely eliminates the necessity of interpreting proton spectra where a large number of interacting nuclei with relatively small chemical shifts have to be considered and allows a very simple interpretation in terms of deuterium quadru­pole splittings.

The lamellar system of 1,1-dideuterodecanol with sodium decanoate or 10,10,10-trideuterodecanoate and water or with sodium octanoate and water has been investigated [134]. A more complete study of the sodium decanoate system has also been reported in which all different positions along the alkyl chain were specifically but separately deuterated [138] to exclude ambiguity concerning line assignments. A similar study for the potassium dodecanoate-D2 0 system has been reported [135] for the perdeuterated compound. The spectrum of this system is shown in Fig. 12. The spectrum exhibits discrete quadrupole split doublets; the innermost, designated as .I.XH), arises from the\3 ~et~x! ~~ut~r()n~;J P( 1), y( 1), <5(1), cp(1) are from consecutIve methylene deuterons; and e(6Jcomes from the next 6 methylene groups.

The results for both the systems are very similar. The order parameter is relatively constant from the head group to near the terminal position, where it falls off rapidly. The spin label results indicate a near constant decrease in the order along the chain. The discrepancy between the deuterium and the spin label results has been attributed to the perturbing effect of the spin label [139].

Phospholipid bilayers have also been investigated by deuterium labelling [137-140]. Perdeuter~ted dimyristoyl lecithin was studied but detailed inter­pretation of the broad-line powder spectrum was not possible because of over­lapping transitions [375].

40

o

-a-10=90°

Studies of Lyotropic Liquid Crystals

7(1) 6(1) e(6) 9'(1)

-b-10=55°

Fig. 12. DMR spectrum of a "macroscopically oriented" perdeutero potassium laurate-21 % H20 phase at two different orientations of the optic axis in the magnetic field. (a) 4>=90°, (b) 4>=55°, where 4> is the angle between the normal to the glass plates and the external magnetic field. (One half of the symmetrical spectrum is shown except for the innermost doublet). [Reprinted from Chern. Phys. Letters 23, 345 (1973) with the permission of the copyright owner and the authors. Copyright by North-Holland Pub!. Co.]

The deuteron magnetic resonance spectrum of a N,N,N-trimethyl-d3-

phosphatidylcholine probe in aqueous dispersion has been examined [140]. The order parameter and the relaxation times have been derived from the observed quadrupolar splitting and the line shape, respectively.

Specifically deuterated dipalmitoyllecithin has been examined by deuterium magnetic resonance [137, 138]. The deuterium quadrupole splittings of the fatty acid chain were found to collapse at the 'magic' angle, as for the simpler soap solutions establishing the uniaxial nature of the liquid crystal. Quadrupolar splittings were mostly obtained from the 'powder' spectra. The spectra often showed two quadrupolar doublets establishing the nonequivalence of the chains in dipalmitoyl lecithins. The results of the deuterium resonance were explained in terms of rotational isomerization, where the gauche conformations occur in complementary pairs [138, 139]. Average dimensions of the hydrocarbon chain were estimated and an approximate description of the chain packing was provided. The results agreed well with the X-ray data [138J.

Molecular field calculations on the ordering of the hydrocarbon chain within bilayer membranes have also been made [390, 391J and they strongly support the above work. Support for the above description of motion has also been provided from studies on specifically deuterated decylammonium chloride [392J, decanol [348, 393J and sodium decylsulphate [393J in nematic phases.

Sonicated Lamellar Systems 41

In these studies,adjacent positions were simultaneously investigated and dif­ferences in the order parameter were interpreted in terms of specific gauche rotations. The effect of various substituted ammonium ions on the parameters in the deuterium spectrum were also studied and described in terms of their interaction with the hydrocarbon region of the liquid crystal [393].

5.7. Sonicated Lamellar Systems

As previously mentioned, ultrasonic mixing of lamellar systems gives an isotropic solution in which the bilayers are rearranged into a spheroidal shape [394]. NMR measurements show that the spheroids are completely closed [106, 186, 191]. When paramagnetic ions are added to the sonicated dispersions, only a part of the spectrum is affected by the added ions. In the case of phosphatidyl­choline [106], it was found that 72% ofthe intensity of the methyl resonance from the trimethylamino group was lost on adding Mn + + ions to the solution. The remaining 28 % of the methyl group intensity and the methylene resonances re­mained unchanged. The results are consistent with closed spheres with a radius of about 230 A and a bilayer thickness of about 46 A. 31 P-NMR studies from some other sonicated lipids [187, 189,395,396] often showed two types of resonances, only one of which is affected by addition of paramagnetic ions.

These studies indicate that the movement of ionic species across the hydro­carbon region is highly restricted. The movement of ions across the lipophilic region of bilayers is a particularly interesting subject. Usually techniques other than NMR are used for the study of this phenomenon and hence it is not within the scope of this review. For a brief introduction, however, the reader is re­ferred to the literature [397].

The observation that aqueous dispersions of phospholipids provide NMR spectra with sharp lines after sonication [140, 378, 398] has been explained in terms of the rapid isotropic tumbling of the vesicles [106]. For instance, for the N,N,N-trimethyl-d3-phosphatidylcholine probe in sonicated aqueous dispersion, the deuteron quadrupole splittings vanish and the intensity becomes centered round a single frequency with a linewidth of 8 Hz [140]. The rotational correla­tion time for spherical body tumbing has been estimated as 10- 6 sec for the vesicles as compared to 10- 2 sec for the lamellae. That all the line-sharpening arises from the rapid tumbling has, however, been questioned since the tumbling is not fast enough [177]. It has been suggested from proton relaxation time studies that the motion of the hydrocarbon chains in sonicated bilayers is much faster than in normal bilayers [94]. Carbon-13 spin lattice relaxation time studies, however, dispute this conclusion since T1's are not significantly different whether determined from multilayers or vesicles [399]. It has peen shown [400] that the sharpening of the spectra arises from the symmetry of the bilayer structure and the explanation does not require the motional freedom within the vesicular structure to be different from that in the unsonicated bilayer.

Several 13C-NMR studies of lipid bilayers have been reported [370,374,378, 382, 401, 402] and are in qualitative agreement with the results obtained from proton magnetic resonance studies [375, 403] of similarly sonicated systems.

42 Studies of Lyotropic Liquid Crystals

The results generally indicate that a mobility gradient exists as one goes from the head group to the terminal positions of the hydrocarbon chain.

Both proton and phosphorus magnetic resonance studies have been under­taken to investigate the effect of pH on the mobility of the head groups in phosphatidylethanolamine (-NH; in the head group) and phosphatidylcholine (-N(CH3); in the head group). It was found that the phosphatidylethanolamine head group is more mobile at high pH (i.e. negatively charged species) than at low pH (i.e. zwitterionic species) [404]. 31 P magnetic resonance has also shown that, when mixtures of several phospholipids are sonicated, a separation of com­ponents may occur so that the ratio of the species contained in the outer surface of the bilayer vesicle is different from that in the inner layer. The presence of hydrogen bonding in organic solutions of phospholipid vesicles [405] has also been indicated from 31 P magnetic resonance studies. 31 P chemical-shift aniso­tropy as a function of magnetic field strength, and 31 P relaxation times have been investigated in sonicated lecithin [259]. Methyl-12-dimethylsilastearate, in­corporated into lecithin vesicles by sonication, has been used as a label for the bilayer structure [406].

Appendix to Part II: Systems Reported Note: Throughout this table 'water' is used for both 'H20' and 'D20'.

System Phase Nucleus

sodium alkylsulphates + water sodium or ammonium octanoate or

sodium hexadecanoate + water

n-alkylmethylsulphoxide + water (dimethylalkylammonio) propane­

i-sulphonate + water alkylammonium bromide + water alkyltrimethylammonium bromide

+ water decyll'yridinium bromide + water octylammonium chloride + water octyltrimethylammonium chloride + water n-alkylammonium trifluoroacetate + water

(or benzene) potassium cis-9-octadecenoate + water

12, 12, 12-trifluorododecyltrimethylammonium bromide (fluoride, chloride or hydroxide) + water

10,10,1 O-trifluorodecyltrimeth ylammoni urn bromide (fluoride, chloride or hydroxide) + water

1-mono-octanoin + water dimethyldodecylamine oxide + water

type studied

micellar lH hexagonal, lH,2H, lamellar, 13C micellar micellar lH micellar lH

lamellar, lH, 13C, micellar 35Cl,

slBr

lamellar lH,2H

micellar 19F

micellar 19F

lamellar lH,2H phase IH,2H transitions

References

151,162,214 121,156,157, 220

232 232

120, 131,154, 236,237

152,154,341, 342 150

150

96,99 76,82

Appendix to Part II: Systems Reported 43

System Phase Nucleus References type studied

anhydrous soaps or esters of fatty acids phase lH 250-256 + temperature transitions

sodium pentadecafluorooctanoate micellar 19p 238 + water

p-tert-octylphenoxy(polyethoxy) ethanols micellar lH 164 + water

sodium dodecylsulphate + octanol phase IH 239 transitions

dodecyltrimethylammonium chloride phase lH 240 + water transitions

N,N,N-trimethylaminododecano-imide phase lH 241 + water transitions

aerosol OT + water phase lH 241,356 transitions

potassium dodecanoate + water lamellar, 2H 78~81, 89, cubic, 90,135,291 hexagonal

sodium cis, cis 9, 12-octadecadienoate lamellar 23Na 128 + water

binary and ternary systems containing lamellar lH, 88,352,353 octylamine, octylammonium chloride micellar 81Br (or bromide) + water

12,12,13,13,14,14,14-heptafluoro- lamellar lH,l9p 98 tetradecanoate + water

hexadecylpyridinium chloride or bromide micellar lH,8lBr 193,352 + water

octanoic, decanoic, dodecanoic micellar IH 194 and tetradecanoic acids in 95.5 % sulphuric acid

dodecylammonium salts of butyric, micellar lH 194 caprylic or dodecyl acids in carbon tetrachloride

trifluoromethyl alkali or tetramethyl- micellar 19p 198, 199 ammonium alkylate + water (with or without an electrolyte)

heptafluorobutyric acid + water micellar 19p 165,238 copper dodecylsulphate + water micellar lH 216 phenothiazine derivatives + water micellar lH 204,213 sodium, potassium or tetramethyl- micellar 19p 205,227

ammonium perfluorooctanoate, caprylate or propionate + water (or aqueous urea)

w-phenylalkyltrimethylammonium bromide micellar lH 212 + water

alkylpolyoxyethylene glycol monoethers lamellar, lH 215,285 + water micellar

mono-, di-, tri-, tetraalkylammonium bromide micellar 79Br 355 + water

alkylammonium carboxylates micellar lH 207,209,211, + nonaqueous solvents 225, 226

monofluorostearic acid + lecithin vesicle lamellar 19p 181 sodium 8,8,8-trifluorooctylbenzene- micellar 19p 275

p-sulphonate + water + with and without serum albumin

44 Studies of Lyotropic Liquid Crystals

System Phase Nucleus References type studied

sodium 12,12,12-trifluorododecylsulphate micellar 19p 276 + water + serum albumin

sodium 13,13, 13-trifluorotridecylsulphate micellar 19p 276 + water + with and without serum albumin

rubidium caprylate or rubidium caproate micellar 85Rb 119 + water

dodecylpolyoxyethylene ether + sodium micellar lH 363 dodecylsulphate or sodium p-octylbenzene-sulphonate + water

8,8,8-trifluorooctylmethylsulphoxide micellar 19p 202 + water, aqueous urea, dioxane or tetrahydrofuran

8,8,8-trifluorooctylhexaoxyethylene glycol micellar 19p 202 monoether + water or aqueous urea

ammonium perfluorooctanoate (with or lamellar lH,2H, 97,282 without hydrocarbon chain additive) 19p + water

binary and ternary systems containing lamellar, lH,2H 129, 197 octylamine, the corresponding micellar hydrochloride or hydrobromide, nonylphenol polyethylene glycol ethers, octanoic acid, decanol, p-xylene, hexanol, hexadecyltrimethylammonium bromide, hexadecane and water

sodium dodecylsulphate + water micellar lH 374,375 + nitroxide probes

sodium methyl- (or dodecyl) sulphate molecular + water + with or without dodecanol lamellar, lH 359 + with or without MnS04 micellar

sodium dodecylsulphate micellar lH 122 + Gd2(S04h, MnCl2 (or MnS04) + water

hexadecyltrimethylammonium bromide micellar iH 122 + Gd2(S04h + water

sodium octanoate + octanoic acid + water lamellar 23Na,2H 131, 132,289, 356

alkali or ammonium octanoate lamellar lH,2H, 124,131,161, + decanol + water 14N, 281,356,360

alkali ion hexadecyltrimethylammonium bromide, micellar lH 163

sodium decanoate with or without sodium chloride, polyoxyethylene, lauryl ether, tetramethylammonium bromide with or without sodium chloride, tetra-n-butyl-ammonium bromide with or without sodium chloride or sulphate + water + benzene

sodium 12,12,12-trifluorododecylsulphate micellar 19p 203 in water and in mixed solvents including aqueous urea, glycine, glycerol, acetamide, methanol, acetone, ethanol, dioxane, tetra-hydrofuran

sodium dodecylsulphate + octyltrimethyl- phase lH 247 ammonium bromide + water transitions

Appendix to Part II: Systems Reported 45

System Physe Nucleus References type studied

sodium decanoate or a specifically deuterated analogue + decanol or 1, 1-di-deuterodecanol + water

sodium 10,10,1 O-trideuterodecanoate + decanol + water

sodium octanoate+ 1,1-dideuterobutanol lamellar 2H, 23Na 134, 138,139 + water

octanoic acid + 1, 1-dideuterohexanol + water

sodium octanoate + 1, 1-dideuterooctanol + water

sodium octanoate + 1,1-dideuterodecanol + water

sodium octanoate + octanoic acid + water sodium octanoate + decanol + water sodium octylsulphate + decanol + water lamellar, 1H,2H, 48,118, 123, sodium octylsulphonate + decanol + water hexagonal, 170, 124,125,217, sodium decylsulphate + decanol + water reversed 23Na, 218, 246,280, hexadecyltrimethylammonium bromide hexagonal, 35CI, 281,348,354,

+ hexanol + water micellar, 37CI, 361 hexadecyltrimethylammonium bromide reversed 79Br,

+ butanol + water buffered at micellar, 81Br, pH 11.5 with phosphate buffer nematic

octylammonium chloride + decanol + water

decylammonium chloride + ammonium chloride + water (0.1 N HCl)

sodium dodeyclsulphate + aromatic alcohol micellar IH 228 or phenol + water

sodium dodecylsulphate + water + NaCl micellar 13C 371

hexadecyldimethylammonio-propane- micellar 1H 248,249 sulphonate + sodium dodecylsulphate + water

w-phenylpentyltrimethylammonium micellar 1H 196 bromide + w-phenyloctyltrimethyl-ammonium bromide + water

hexadecyltrimethylammonium bromide micellar 1H 197,200 + (benzene, N :N-dimethylaniline, nitro-benzene, cyclohexane or isopropylbenzene) + water

lithium dodecylsulphate + water + with or without urea

sodium decylsulphate + water + with or without urea

sodium dodecylsulphate + water micellar 1H 233 + with or without urea

sodium hexadecylsulphate + water + with or without urea

tetramethylammonium dodecylsulphate + water + with or without urea

polyoxyethylene alkanol + urea + water micellar 1H 233

46 Studies of Lyotropic Liquid Crystals

System Physe Nucleus References type studied

sodium dodecyl ether alcohol sulphate micellar lH 233 + urea + water

polyoxyethylene alkanol + dodecanol micellar lH 233 + (water or electrolytic solution of NaCl, NaCNS, Na2S04' LiCI or tetramethyl-ammonium chloride)

sodium dodecylsulphate or trimethyldo- micellar lH 195 decylammonium chloride + benzene + water

aerosol OT + water + octane + with or micellar lH 242,244 without an electrolyte like NaCI, CaCI2, AICl3

alkali decylsulphate(s) + decanol + water nematic 2H, 46,350 + with or without lithium sulphate alkali ion

sodium decylsulphate + decanol or di- micellar, 2H 48, 100,245, deuterodecanol + sodium sulphate + water nematic 348,393

1, 1, 1,2,2-pentadeuterodecylammonium nematic 2H 392 acetate-d3 + decanol + ammonium chloride + decylammonium chloride + water (acidified with H2SO4)

poly-y-benzyl-L-glutamate + deutero- nematic lH 286 chloroform

hydrated fibrous materials state of lH,2H, 66,68,69,74, water 23Na 127,155,

297-326

phospholipids and biomembranes lamellar, lH,2H, a large micellar, 13C, 23Na, number of sonicated 31p references

Part III. Studies of Molecular and Ionic Species Dissolved in the Nematic Phase of Lyotropic Liquid Crystals

6. Introduction

Nuclear magnetic resonance spectra from molecules oriented in the nematic phase of liquid crystals are interpretable in terms of chemical shift tensor, (1,

indirect, J, and direct, D, coupling tensors, as well as, for nuclei of spin greater than 1/2, quadrupole tensors Q.

The magnitudes of the dipolar couplings from solutes in lyotropic solvents are usually smaller than in thermotropic ones. This at times aids in the analysis of the spectra [50,63,407]. The highly resolved transitions usually obtained from species dissolved in lyotropic phases allow a very precise analysis of the spectra. As a consequence the precision of final parameters may be affected by the accuracy of the indirect couplings. In cases where the uncertainties of such couplings can have an effect on structural parameters, they should either be redetermined from isotropic solution or, if the spectrum is sensitive enough, adjusted when fitting the spectrum from the anisotropic solution.

Structures obtained from lyotropic systems may differ from those obtained from thermotropic solvents. Such deviations reflect the very large intrinsic differences in the two types of solvents [50, 408, 409]. Since the orientation parameters for the solute molecules in a lyotropic or a thermotropic phase are quite different, simultaneous studies in both these phases may provide the necessary relations for the determination of the components of for example the chemical shift tensor if the system has C 2v or lower symmetry. The relatively small order in lyotropic systems may also make it possible to observe 14N and 35CI quadrupole splittings which cannot usually be observed in thermotropic solvents.

In this section we report the results from NMR studies of species in lyo­tropic liquid crystals. The literature to the middle of 1975 was covered as completely as possible (see Appendix to part III).

Various solvents which have so far been used for these studies are given below, where water refers either to H 20 or D 20. (I) An 8:1:1:10 mixture (by weight) of sodium Cs or C10 alkylsulphate, the

corresponding alcohol, sodium sulphate and water [47]. (II) A 14: 1: 1 :20 mixture (by weight) of sodium dodecylsulphate, decanol, sodium

SUlphate and water [50]. (III) A 7.5 :1.5:1 :15 mixture (by weight) of potassium laurate, decanol, potassium

chloride and water [51].

48 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

(IV) Lyotropic phases in which the ions from the phase itself provide high­resolution NMR spectra have also been used [52,410-412].

(V) A 10: 1 :20: 1 mixture (by weight) of decylammonium chloride, decanol, water and ammonium chloride. Ammonium chloride in this phase may be replaced by other salts [52]. Unlike the four phases described above, this phase has a superstructure carrying a positive charge.

(VI) A few mole per cent ( ~ 12) solution of a synthetic polypeptide in some low­molecular-weight solvent. The synthetic polypeptides used are: (a) Poly-y-benzyl-L-glutamate [56, 413J, (b) PolY-L-glutamic acid [63, 414J, (c) Poly-y-ethyl-L-glutamate [415J, (d) Equal proportions of poly-y-ethyl-L-glutamate and poly-y-ethyl-D­

glutamate [415J, (e) Poly-e-carbobenzoxY-L-lysine [414].

7. Applications

Lyotropic liquid crystals are usually quite viscous and they orient relatively slowly in the magnetic field. In cases where the spinning of the samples in the magnetic fields does not destroy the order, NMR spectra with reasonable line­widths are obtained after a few minutes of spinning. However, spectra with lines having widths around one Hz or so are normally obtained only after spinning the sample for several hours in the magnetic field. This is particularly true for the sodium decyl- or dodecylsulphate phases.

The mechanics of the orientation mechanism are best demonstrated by observing the deuterium spectrum from D 20 in a typical nematic phase [47,416]. Immediately after the sample is placed in the spectrometer, a "powder pattern" from microcrystallites in random orientation is observed. After some time in the magnetic field (ranging from several minutes to several hours, depending on the particular phase) a 1:1 quadrupolar doublet is observed where all micro crystallites are now arranged perpendicular to the magnetic field. Upon rotation of the sample tube through 90°, a two-dimensional powder pattern is generated which then decays to the doublet structure. Successive repetitions of this procedure produce a doublet structure which is independent of the rotation angle, a result obtained much more quickly by continuous spinning. This will be referred to as the nematic Type II phase.

Figure 13 shows a spectrum obtained from a nematic lyotropic phase which cannot undergo spinning in a conventional spectrometer without destruction of the order. For convenience we will refer to this as the nematic Type I phase. The deuterium doublet from D 20 in a Type I phase gives a (3 cos2 e -1) angular dependence of the splitting upon rotating the sample. The maximum splitting of the doublet is at 0° of rotation. This should be contrasted with the previous nematic Type II phase which gives a powder pattern on the initial rotation.

Applications

-0.3 o kHz

0.3

b

-0.3 o kHz

49

Q3

Fig. 13. Deuteron magnetic resonance spectrum of D20 in the lyotropic Type I phase: (a) soon after placing the sample in the magnetic field, (b) after several hours. [Reprinted from Mol. Cryst. Liquid Cryst. 7, 201 '(1969) with permission of the copyright owner and the authors. Copyright by Gordon and Breach, Science Publishers.]

The two phases are readily distinguished without rotation experiments since the doublet structure of the Type I phase grows from the wings of the powder spectrum (Fig. 13) while that of the Type II phase grows from the two maxima of the powder spectrum. The latter behaviour is shown in the diagram of reference [47].

The results indicate that the optic axis is parallel to the magnetic field (Ho) in a Type I phase and perpendicular in the Type II system.

Spinning of both systems is allowed in cryogenic magnets but only of Type IT in conventional spectrometers. Considerable confusion has arisen in the literature [47,148,350] because it was not recognized that there are two, and perhaps more nematic phases. This confusion has no doubt been compounded by the fact that small changes in concentration or the addition of ionic or even molecular species may serve to convert from one phase to the other [46]. Results similar to those from deuterium NMR have been obtained from proton NMR studies of methanol in the nematic phases. Here again, the maximum splitting in the Type I phase arises at the zero angle of rotation, confirming that the preferred orientation of the optic axis is parallel with Ho [46L.:

The D20 doublet separation in solvent (III) is roughly constant with tem­perature to 63° C, at which point a central D20 transition from the isotropic phase appears [417]. In 30% sodium hexadecanoate-70% D20, the deuteron splitting first increases with temperature, stays constant and finally disappears at the transition to an isotropic liquid [156, 157].

The proton magnetic resonance spectra usually consist of sharp lines arising from the solute molecules. A spectrum of benzene dissolved in solvent (III) is shown in Fig. 14. A comparison of this spectrum with that of benzene in a thermotropic solvent [141] shows that the molecular order of benzene in the lyo-

50

I -688.84 Hz

Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

I o

Fig. 14. Observed and calculated PMR spectra of benzene oriented in the lyotropic mesophase (III). [Reprinted from the Proc. Am. Chem. Soc. Meeting, Plenum Press (1974) with permission of the copyright owner and the authors. Copyright by the American Chemical Society]

tropic phase is about 40 % of the value in the thermotropic solvent. Many other solutes are, however, comparatively much less highly ordered in the lyotropic phase.

Descriptions of the various systems studied have been collected together in the Appendix to part III. The remainder of this section is devoted to discussions of various problems of particular interest.

a) Spectra from Lyotropic Phases. As was previously mentioned, the analysis of spectra from molecules oriented in a lyotropic mesophase is sometimes simpli­fied because the magnitudes of the dipolar couplings can be smaller than the chemical-shift differences (15) such that the condition for "weak" coupling [(J + 2D)2 /15 ~ linewidth] may be satisfied. For such cases, the spectral parameters can be guessed quite accurately from "first-order" considerations. A good illustra­tion is the spectrum of pyrimidine (Fig. 15) where the doublet of quartets at the highest field is due to the proton which is at the f3 position from nitrogen.

A comparison of geometric data for pyrazine, pyrimidine and pyridazine obtained from studies in lyotropic and thermotropic phases (Appendix to part III) indicates that the structure of pyrimidine and pyrazine is unaffected by the change of solvent. However, significant deviations observed in the data for pyridazine have been attributed to the specific solvent-solute interactions which it undergoes in the lyotropic phase. Similar deviations have also been observed for ethylene carbonate [408], ethylene monothiocarbonate [408], thiophene [445] and pyri­dine [409].

Spectra of the type ANBB' with C2v symmetry, for which two dipolar couplings between the protons along an axis perpendicular to the C2 axis are

Applications 51

"--50Hz~

Fig. 15. Observed and calculated PMR spectra of pyrimidine oriented in the lyotropic mesophase (II)

nearly equal, do not provide all the spectral parameters to a reasonable precision in the thermotropic liquid crystals if some of the dipolar couplings are very large compared to the cheinical-shift differences [23, 455]. This insensitivity is com­plicated by the relatively large linewidths in thermotropic solvents. This situation is quite often encountered in unsymmetrical p-disubstituted benzenes. On the other hand, in lyotropics where the transitions are relatively sharp and usually none of the dipolar couplings dominate, the spectra may provide all the parameters with normal accuracy [143, 407] as in the spectrum of y-hydroxy pyridine oriented in phase (II).

b) Nonplanarity in Rapidly Equilibrating Systems. The question of planarity about nitrogen is of interest, particularly in the amide structure which forms the basis of the peptide unit of biological systems [434,436,437].

If a molecule is planar, then with the proper choice of coordinate system (2 axes in plane, 1 perpendicular) a maximum of three independent S values is sufficient to describe the orientation. If there is no plane of symmetry, five S values are required to describe the orientation.

When enough geometric information is known, an attempt may be made to fit such geometry to the known D values. If the agreement between the geo­metry and dipole couplings is not good when three S values are used, then it should be concluded that the system being investigated requires five S values and is nonplanar. Unfortunately, the inverse argument that, if three S values are sufficient to describe the NMR spectrum then the system is planar, is not necessarily valid. There may exist an insensitivity to some of the S values or the spectrum may sometimes be interpreted equally well with a larger number of order parameters.

52 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

lIv~~ ii)

IlIVA)( rt (8)

(A)(~O)

-II- LlV8X (8)

PGA: ~O: OMF: OMF -07 1 : 3 : I. : I.

(A) 100Hz Va

.. t'

IA) (A)

...J1L--_.L.1 _--L1_--l1'--_.L.1 _--I.' __ 1L--_.L.1--,---I.1 __ l..1 _--LO'_-L' b Ipp.m) -10 -9 -8 -7 -6 -5 -I. -3 IS) -2 -1 +\

Fig. 16. PMR spectrum of dimethylformamide (DMF) oriented in poly-L-glutarnic acid (PGA) with ratio of water and DMFshown in the figure. [Reprinted from the J. Chern. Phys. 56, 3920 (1972) with permission of the copyright owner and the authors. Copyright by the American Institute of Physics]

The planarity-nonplanarity problem has been investigated in the15N-enriched formamide molecule [433]. In this system six dipole couplings were fitted to a microwave structure. It was found that the microwave structural parameters could not be reproduced with an assumption of three S values but only with five, thus establishing the nonplanarity of formamide in lyotropic solution. Un­fortunately, the system is only slightly overdetermined with six dipole couplings. The use of the 13C, 15N di-enriched compound could give some information about the degree of nonplanarity in the CNH2 moeity.

c) Quadrupole Tensors. A typical PMR spectrum of dimethylformamide dis­solved in the glutamic acid phase (VIb) is shown in Fig. 16. The spectrum is amenable to first-order analysis with assignment of the various lines to specific nuclei as shown. As the spectrum is first-order, the relative signs of the couplings cannot be determined, particularly since the scalar HH coupling~ are less then 0.8 Hz.

With assumptions of a planar configuration about the N atom and the known molecular structure from other techniques, it is possible to obtain the three independent elements of the S matrix [63]. From the internal consistency of such calculations, the relative signs of the various S values and hence of the dipolar couplings could be determined. The HCN bond angle, X, of 107 ± 10 of the amide was also obtained from the PMR spectrum.

Order matrices from the proton spectra and quadrupolar splittings from the deuteron and 14N-NMR spectra were used to obtain the complete quadrupole coupling tensors for the 2H and 14N nuclei in dimethylformamide with the assumption that the quadrupole-coupling tensors are unaffected by a change in orientation. Three different orientations were achieved by the addition of

Applications 53

-600 o +600Hz

Fig. 17. The PMR spectrum of the methylammonium ion (CH3 15NHt) in a lyotropic phase. The strong peak exceeding the recorder limit is the water signal in the phase. [Reprinted from the J. Am. Chern. Soc. 96, 1198 (1974) with permission of the copyright owners and the authors. Copyright by the American Chemical Society

variable amounts of water to the polypeptide solution, thus yielding several sets of S values and quadrupole splittings. Three simultaneous equations involving different S values were solved to yield the complete quadrupole coupling tensor in the molecular axis system. The results were then checked from a fourth orienta­tion.

d) Structure of Ions. Nuclear magnetic resonance spectra from ions in lyotropic liquid crystals provide the only means of determining structures of ions in other than the solid state. The ions are usually introduced into the nematic phase by adding them in the form of a salt, either a decyl salt or a simpler sodium, chloride, nitrate, etc. A PMR spectrum of the 15N-enriched methylammonium ion is shown in Fig. 17. The pH of the solution was adjusted to slow down the exchange of the NH protons. The ion was introduced into the phase as methylammonium decylsulphate. The results from several other ions are reported in the appendix.

23Na-NMR studies of system (I) have been undertaken [48,350]. The spectrum from the pure ternary phase (without sodium sulphate) shows a triplet with an intensity ratio of' 3:4 :3 (Fig. 18) and with a splitting corresponding to a degree of order of the major quadrupolar axis of ~O.02. Addition of a small amount of sodium sulphate caused the formation of a two-phase system which separated after standing. One phase then gave a spectrum similar to that of Fig. 18. The other gave a sharp central component with the same chemical shift

54 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

~- ........................................ -_ .. -- lS.8±O.1 KHz- .. ------- ......... _-

Fig. 18. 23Na-NMR spectrum in a ternary lyotropic phase. [Reprinted from the 1. Am. Chern. Soc. 94, 4384 (1972) with permission of the copyright owner and the authors. Copyright by the American Chemical Society]

as the corresponding component of the first layer. The outer transitions in this case were not observed. The situation has been considered analogous to the "hidden sodium" results in biological systems [335,456-458]. Similar studies in sodium linoleate-water [128], lecithin-sodium cholate­water [126] and oriented DNA [127] systems show that the 23Na signal is split into a relatively narrow central component and broad components symmetrically displaced about it.

8. Order in Nematic Lyotropic Phases

8.1. . Some General Comments Concerning the Order Parameter As previously discussed in Section 2.2.2 the degree of order of the axis connecting two interacting nuclei, i and j, is given by the expression

4n2 r? Sij = - hYiy~J Dij (13)

where Sij provides the degree of order with respect to the magnetic field. For lyotropic systems this is usually the order parameter which is reported in

the literature (Appendix to part III). The order parameter as originally defined by Saupe [21] should include a term which relates the value Sij to the optic axis ofthe liquid crystal, that is Sij=i(3 cos2 IX - 1) S?j where IX is the angle that the optic axis

Benzenes and Related Compounds 55

forms with the magnetic field axis and SPj is the degree of order with respect to the optic axis. For thermo tropics and Type I lyotropics Sij = SPj since IX = 0°. For Type II phases in a conventional spectrometer the optic axis is at 90° to the magnetic field and consequently Sij= -ts~. Ifwe have the same phase in a cryogenic magnet the optic axis is parallel to Ho and Sij = S~. The dipole splitting Du' however, is not changed whether obtained from a cryogenic or conventional spectrometer. This results because the individual units of superstructure are perpendicular to Ho in either spectrometer but are arranged radially around Ho in the cryogenic magnet but along the spinning axis in a conventional spectrometer, that is to say that the mechanical process of spinning at right angles to the magnetic field direction imposes a preference for orientation parallel to the spinning axis and perpendicular to Ho. This results in a rotation of the optic axis by 90° but does not affect the spectrum or the degree of order with respect to the field but clearly does so with respect to the optic axis. The order with respect to the superstructure must be unaffected by such a rotation of the optic axis. We can resolve this problem in S values by introducing a second orientation term so that Eq. (14) is obtained.

Sij = t(3 cos2 IX - 1) t(3 cos2 P - 1) Srj (14)

where p refers to the angles that the individual units of nematogen form with the optic axis, a cone angle so to speak. Sri is the degree of order with respect to the superstructure or in thermotropics with respect to the individual nematogen molecules. For a thermotropic or Type I lyotropic IX is small and P = 0°. For a Type II lyotropic in a conventional spectrometer IX = 90° and P = 0° (or small) while in a cryogenic spectrometer IX = 0° and P = 90°. Sji is therefore the same for Type II phases whether in a conventional or cryogenic spectrometer as it should be.

Equation (14) points out difficulties that are encountered when attempting to relate order to the liquid crystal superstructure since although IX should always be known, P will seldom be, at least accurately, neither for lyotropic nor thermotropic phases.

As a consequence a true degree of order with respect to the superstructure will in general not be obtainable. It seems logical, therefore, that a convention of reporting all order parameters with respect to the magnetic field as Sij be adopted, particularly as these values are identical to those usually reported in the literature. Order parameters referring specifically to some other axis could be then suitably superscripted as for instance S~ for the optic axis and Sri for the superstructure. Sij and S~ are known values provided directly from the spectrum and a knowledge of the optic axis. Sri will be based on assumptions concerning the properties of the nematic phase.

8.2. Molecular and Ionic Species in Aqueous Pbases 8.2.1. Benzenes and Related Compounds

Examination of Tables 2 and 3 provides some interesting data concerning the preferred orientations of aromatic molecules. The most obvious conclusion is, the less soluble (in water) the molecule is the more highly it is ordered. Table 2 gives the orientation parameters for the less soluble aromatics.

56 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

Table 2 S values for aromatic compounds which are relatively water insoluble.

Compound Structure Sxx· S • yy Sua Reference

benzene 0 -0.0229 -0.0229 0.0458 51

F F 1,3-difluorobenzene V -0.0159 -0.0414 0.0573 144

F

1,4-difluorobenzene ¢ -0.0436 -0.0179 0.0615 143

F

furan 0 0 -0.0154 -0.0084 0.0238 424

thiophene 0 S -0.0194 -0.0087 0.0281 424

selenophene n -0.0168 'Se/ -0.0104 0.0272 449

a The coordinate system is such that the y axis is directed along the major C2 symmetry axis, the x axis in the plane of the ring and the z axis perpendicular to this plane.

The reason for their higher order lies in the fact that the molecules studied are all very soluble in hydrocarbon solvents. Being comparatively insoluble in water they reside in the most highly ordered region of the phase, the hydrocarbon superstructure. For instance benzene has a degree of order Szz, where Szz refers to the C6 symmetry axis, of 0.046. This is the order with respect to the magnetic field. If we assume that the optic axis and the superstructure axis coincide, probably a good assumption, then S~z = -2Szz , that is the order with respect to the super­structure is - 0.092. Even this does not tell the full story since if the benzene is located within the cylindrical superstructure then we can proceed further and relate the values S~ to the individual hydrocarbon chains which are assumed to lie perpendicular to the axis of the superstructure. Consequently S:z, where n refers to the nematogen chains, is 0.184. Clearly the benzene molecule is very highly ordered. Such a high degree of order is only a factor of about three less than the hydrocarbon chains themselves [393]. Similar conclusions can be drawn for the other molecules of Table 2.

A further characteristic of these compounds is the fact that all Szz parameters are positive and all Sxx and Syy parameters are negative. (Sxx and Syy are, respective-

Benzenes and Related Compounds 57

Table 3 8 values for aromatic compounds which are relatively water soluble.

Compound Structure 8 8 xx 8yy8 8zz8 Reference

pyridine 0 0.0047 -0.0241 0.0194 409 N~

OH

y-hydroxypyridine 0 0.0112 0.0049 -0.0161 407 N"

pyridine-N -oxide 0 0.0054 -0.0037 -0.0017 409 ~ 0

pyrazine [:) 0.0059 -0.0092 0.0033 442

pyrimidine N"""N U -0.0045 0.0069 -0.0024 442

N-N pyridazine U 0.0088 0.0007 -0.0095 442

8 The coordinate system is such that the y axis is directed along the major C2 symmetry axis, the x axis in the plane of the ring and the z axis perpendicular to this plane.

ly, directed perpendicular to and parallel to the C2 axis, S zz is directed perpendicular to the plane of the ring.) These results are readily interpreted if it is assumed that the planes of the aromatic compounds are arranged preferentially parallel to the symmetry axis (optic axis) of the superstructure and simultaneously parallel to the hydrocarbon chain axis. That is, the molecules insert themselves edgewise intq the superstructure with the plane of the ring parallel to the superstructure axis. It is difficult to see why the planes of the molecules are not equally well ordered perpendicular to the symmetry axis. The explanation could lie in the packing of the surfactant chains. With a cylindrical superstructure, the hydrocarbon chains extend radially from the centre of the cylinder. The result would be to have less tight packing in one direction than in the other and thus a preferred location for the solute. It may of course be that the curvature of the surface imposes this preferred orientation. Investigations of these compounds in a Type I phase might resolve this problem.

One further point of interest is that for these molecules, Syy, the order along the symmetry (major dipole) axis is considerably smaller than Sxx, generally about one-half as large. This shows that the dipole axis is directed preferentially

58 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

perpendicular to the superstructure axis rather than along it. Thus the solutes are positioned in such a way that the polar' substituent interacts efficiently with the interface region while simultaneously leaving the more hydrophobic residue buried in the superstructure. Interestingly the 1,3-difluorobenzene with no substituent on the C2 axis orders with this axis (Syy) preferentially parallel to the superstructure axis.

The more water soluble aromatic compounds (Table 3) show a completely different behaviour with respect to their orientation. In general the various S values are considerably smaller than for the previous species. All except pyridine and perhaps pyrazine (for which the signs of the S values depend on the assumed sign of a long range indirect J coupling [442]) have values of Szz which are negative. This indicates that these aromatic compounds sit with the normal to the plane of the ring perpendicular to the magnetic field direction. Unfortunately relatively little data for other such compounds are availal?le and it is difficult to draw more meaningful conclusions about these systems.

8.2.2. Ionic Species as Solutes

Very few ions with other than a C3 or higher symmetry axis have been studied in detail. To date all ions which have a C3 axis and for which the signs of the dipole couplings are known have an SC3 which is negative. These include acetate [392], methylammonium [412], methylphosphonate [424], dimethyltin [411] and dimethylthallium [425]. Methanol, although nonionic has also been found to have SC3 negative [46]. These results mean that all these species have their symmetry axis directed preferentially perpendicular to the magnetic field. It is difficult to understand why ions as different from acetate and methylsulphonate as dimethyltin or dimethylthallium should have similar preferred orientations. Di­methylthallium was investigated in two phases, one with the superstructure carrying a negative charge (cesium decylsulphate) and one with the superstructure carrying a positive charge (decylammonium chloride) [425]. In the latter phase dimethyl­thallium was ordered about 1-2 % of that in the former phase but in both cases SC3 was negative.

Anilinium and 2,3,4,5,6-pentadeuteroanilinium ions were investigated in a Type I phase [461]. This ion had an extremely large order along the C2 axis, up to +0.19. Pentadeuteroanilinium and specifically deuterated decylsulphate were studied simultaneously by deuterium magnetic resonance. The degree of order of the hydrocarbon chain axis and the C2 axis of the anilinium ion were found to be virtually identical and directed in equivalent directions. This ion appears to be an extremely good example of the type of behaviour exhibited by the compounds of Table 2. Unfortunately it has not been investigated in a Type II phase.

App

endi

x to

Par

t II

I:

Com

poun

ds S

tudi

ed a

nd I

nfor

mat

ion

Der

ived

(Unl

ess

othe

rwis

e in

dica

ted,

thr

ough

out

this

tab

le t

he S

val

ues

refe

r to

a C

arte

sian

coo

rdin

ate

syst

em i

n w

hich

the

xy p

lane

con

tain

s th

e nu

clei

un

der

inve

stig

atio

n an

d th

e x

axis

con

nect

s nu

clei

1 a

nd 2

. The

ord

er p

aram

eter

of a

thr

eefo

ld s

ymm

etry

axi

s is

desi

gnat

ed b

y SC

3.)

Com

poun

d P

hase

R

esul

ts a

nd R

emar

ks

Ref

eren

ce

and

Str

uctu

re

Solu

te c

once

ntra

tion

T

empe

ratu

re ("

C)

Nuc

leus

stu

died

F

requ

ency

(MH

z)

Spec

tral

type

Chl

orof

orm

C

HC

l 3 a

nd C

DC

l 3

Dic

hlor

omet

hane

C

H2C

I 2, C

D2C

l 2

(VIa

)

lH,2

H

60,

15.4

A

(VIa

, V

Ic, V

Id)

lH,

2H,

35C

l

A2

The

deu

tero

n qu

adru

pole

spl

itti

ng v

arie

s lin

earl

y w

ith t

he r

eci­

proc

al t

empe

ratu

re,

slop

es b

eing

ind

epen

dent

of c

once

ntra

tion

.

1. T

he d

ipol

ar s

plit

ting

in t

he p

roto

n sp

ectr

um in

crea

ses

with

the

m

olec

ular

wei

ght

of th

e po

lype

ptid

e an

d it

redu

ces

to 1

/4 o

n sp

inni

ng.

Dou

blet

sep

arat

ions

hav

e be

en s

tudi

ed a

s a

func

tion

of

tim

e in

the

mag

neti

c fie

ld,

conc

entr

atio

n an

d te

mpe

ratu

re

[56,

418,

419,

460]

. 2.

The

PM

R s

pect

rum

in a

sam

ple

cont

aini

ng a

1 m

m t

hick

film

of

pol

y-y-

benz

yl-L

-glu

tam

ate

expo

sed

to t

he v

apou

rs o

f di

chlo

rom

etha

ne h

as b

een

inve

stig

ated

as

a fu

nctio

n of

film

or

ient

atio

n [5

9,41

4].

3.

Pro

ton

spin

-lat

tice

rel

axat

ion

times

of

CH

2Cl 2

in (

VIa

) ha

ve

been

stu

died

as

a fu

ncti

on o

f the

pol

ypep

tide

con

cent

rati

on f

or

two

diff

eren

t m

olec

ular

wei

ght

poly

pept

ides

[42

0].

4.

Spin

-ech

o ex

peri

men

ts u

sing

the

Car

r-P

urce

ll m

etho

d ha

ve

been

per

form

ed [

421]

.

56,2

86

56,5

9,62

, 28

6,

413-

415,

41

8-42

3,

460

~ ~ .... o ~ ......

......

...... n ~ o [ '" tzl 8- [ 8- d S' 8 g. t:l

tj

~ [ Vl

\0

Com

poun

d Ph

ase

Res

ults

and

Rem

arks

R

efer

ence

an

d S

truc

ture

So

lute

con

cent

rati

on

~

Tem

pera

ture

(0C

) N

ucle

us s

tudi

ed

Fre

quen

cy (

MH

z)

Spec

tral

type

5.

The

rol

e of

the

side

-cha

in o

f th

e po

lype

ptid

e m

olec

ule

on t

he

liqui

d cr

ysta

lline

beh

avio

ur i

n so

luti

ons

of d

ichl

orom

etha

ne

in (V

Ic) h

as b

een

exam

ined

. The

inf

luen

ce o

f the

ele

ctri

c an

d V

)

mag

netic

fie

ld s

tren

gth

on o

rien

tati

on h

as a

lso

been

....

exam

ined

[41

3,41

5].

~ 6.

In

a s

olut

ion

of p

oly-

y-be

nzyl

-L-g

luta

mat

e in

a m

ixtu

re o

f '" 0

dich

loro

met

hane

and

the

deu

tero

ana

logu

e, t

he d

eute

ron

....,

quad

rupo

le-c

oupl

ing

cons

tant

has

bee

n de

term

ined

as

160

KH

z s;::

0

with

an

assu

med

val

ue o

f th

e 35

Cl

nucl

ear

quad

rupo

le-

0-co

upli

ng c

onst

ant

of 7

2.4

MH

z [4

22,4

23].

("

) E.

I>l

Dib

rom

omet

hane

(V

Ia, V

Ic,

Vld

) 1.

The

dip

olar

spl

itti

ng i

n th

e pr

oton

spe

ctru

m h

as b

een

56,4

13,

....

CH

2B

r 2

stud

ied

as a

fun

ctio

n of

tim

e in

the

mag

netic

fie

ld a

nd o

f 41

5.

8-27

° co

ncen

trat

ion

[56]

. .....

0

lH

2.

Stud

ies

sim

ilar

to t

hose

rep

orte

d in

ite

m (

5) f

or d

ichl

oro-

::s 60

m

etha

ne s

olut

ions

hav

e al

so b

een

unde

rtak

en [

413,

415]

. o· V

)

A2

'0

0

Met

hyl

alco

hol

(I, I

II a

nd V

) T

he H

CH

bon

d an

gle

has

been

det

erm

ined

as

108.

81±

0.06

° 46

,47,

51,

o.

0 '" C

H30

H

from

the

pro

ton

spec

trum

of

13C

H30

H [

46].

(10

9.33

° [4

35])

" 52

,417

, 0

and

13C

H3O

H

rHC

H/r

CH

= 1

.626

4 ±

0.00

06

424

17;.

fI)

lH

SC3

= -0

.006

97

0 ~

A3

and

A3X

0.

. S· ....

Met

hyl h

alid

e (I)

T

he p

roto

n ch

emic

al s

hift

ani

sotr

opy

(Lla

) in

the

se c

ompo

unds

42

6 go

CH

3X

(w

here

ha

s be

en d

eter

min

ed u

sing

the

gra

dien

t m

etho

d [4

27,

428]

. Z

X

=F

, C

I, B

r, I)

LI IT

val

ues

usin

g m

etha

ne a

s th

e in

tern

al r

efer

ence

are

-2.

0 ±

0.6,

8 I>

l lH

2.

2 ±

0.4,

4.1

± 0

.3 a

nd 5

.4 ±

0.5

ppm

for

the

fluo

ro, c

hlor

o, b

rom

o g.

100

and

iodo

com

poun

ds,

resp

ectiv

ely.

Sig

nifi

cant

dev

iatio

ns i

n th

e ~

A3,

A3

X

valu

es o

f LI

lT ob

tain

ed f

rom

stu

dies

in t

herm

otro

pic

solv

ents

hav

e I>

l be

en o

bser

ved

(LIlT

val

ues

deri

ved

from

suc

h st

udie

s ar

e -

0.5

± 0.

5,

'" 0 1.

3 ±

0.2,

2.5

± 0

.5 a

nd 3

.4 ±

0.2

ppm

for

the

fluo

ro,

chlo

ro, b

rom

o an

d io

do c

ompo

unds

, res

pect

ivel

y).

:>

1,3,

5-T

riha

lo

(I)

The

pro

ton

chem

ical

shi

ft a

niso

trop

y ha

s be

en d

eter

min

ed u

sing

42

8 '" '"

benz

ene

10-4

mol

e/gm

(in

c\. t

he

the

sam

e m

etho

d as

men

tion

ed f

or m

ethy

l ha

lides

. T

he .d

O"

(J) ::s

H

inte

rnal

ref

.) va

lues

det

erm

ined

with

met

hane

as

the

inte

rnal

ref

eren

ce a

re

Co

~.

x*x

-6.

3 ±

0.4

and

-7.

4 ±

0.4

ppm

, re

spec

tivel

y, f

or t

he c

hlor

o an

d ....

IH

brom

o co

mpo

unds

. T

he v

alue

s ag

ree

witl

L th

ose

obta

ined

0 '"t

l 10

0 ( -

5.7 ±

0.4

and

-7.

7 ±

0.6

ppm

) fr

om s

tudi

es in

a t

herm

o-I>

' H

.--:

; H

..,

A3

trop

ic s

olve

nt.

.... >-<

>-<

X

......

(X=

Cl

or B

r)

(1 ~

Ace

toni

trile

(I

and

VIa

+ di

chlo

ro-

IH_

and

14N

-NM

R s

pect

ra o

f ac

eton

itri

le s

olut

ions

of

(VIa

) in

42

4,43

0 0

CH

3CN

m

etha

ne-d

2)

dich

loro

met

hane

-d2

prov

ide

the

14N

qua

drup

ole-

coup

ling

con

stan

t, §

8 :3

1 :6

1 m

olar

rat

ios

of V

Ia,

3.60

± 0.

10 M

Hz

[430

J. T

he v

alue

is

foun

d to

be

in r

easo

nabl

e C

o en

acet

onitr

ile

and

dich

loro

-ag

reem

ent

with

tha

t (3

.738

MH

z) o

btai

ned

from

stu

dies

in

the

IZl ....

met

hane

-d2

solid

pha

se [

431]

. 5- o·

IH,

14N

C

o I>

' ::s Co ......

::s

IH_

and

14N

-NM

R s

pect

ra p

rovi

de a

val

ue o

f 1.

45 ±

0.05

MH

z 6'

N

itro

met

hane

(V

Ia +

dich

loro

met

hane

-d2)

43

0 8

CH

3N0

2 10

:23:

67 m

olar

rat

io o

f VIa

, fo

r th

e 14

N q

uadr

upol

e-co

upli

ng c

onst

ant

unde

r th

e as

sum

pt.io

ns

~.

nitr

omet

hane

and

dic

hlor

o-th

at t

here

is a

fre

e ro

tati

on a

bout

the

C-N

bon

d on

the

NM

R

0

met

hane

-d2

time

scal

e an

d th

at t

he q

uadr

upol

ar n

ucle

us r

eori

ents

::s tl

ra

pidl

y al

ong

the

C-N

axi

s.

(J)

IH,1

4N

~.

(J) Co

IX-L

-ala

nine

(I)

T

he c

arbo

xyl

and

the

amin

o pr

oton

s ex

chan

ge r

eadi

ly w

ith

416

H

3 %

(by

wei

ght)

th

e w

ater

pro

tons

in

the

phas

e an

d ar

e no

t se

en a

s se

para

te

I si

gnal

s. T

he o

bser

ved

spec

trum

is

from

the

alk

yl p

roto

ns a

nd o

f H

3C-C

-CO

OH

IH

th

e A

3X

type

. I NH

2 A

3X

0'1 ,...

0\

Com

poun

d Ph

ase

Res

ults

and

Rem

arks

R

efer

ence

IV

and

Str

uctu

re

Solu

te c

once

ntra

tion

T

empe

ratu

re (0

C)

Nuc

leus

stu

died

Fr

eque

ncy

(MH

z)

Spec

tral

type

fj-a

lani

ne

(I)

Due

to

rapi

d ex

chan

ge o

f th

e C

OzH

and

NH

z pr

oton

s w

ith t

he

416

IZl

.....

H

H

3 %

(by

wei

ght)

wat

er o

f th

e ph

ase

the

spec

trum

is

of th

e A

A' B

B'

type

. S.

I I

co· til

HzN

-C-C

-CO

OH

IH

0

I I

.... ~

H

H

AA

'BB

' 0 G

' ("

)

1,2-

dich

loro

etha

ne a

nd

(VIa

) 1.

B

ecau

se

of r

apid

in

tern

al

rota

tion

, th

e P

MR

spe

ctru

m

is 41

8 E- el

1,2-

dich

loro

etha

ne-d

4 in

terp

reta

ble

in t

erm

s of

two

diff

eren

t dir

ect d

ipol

ar c

oupl

ings

. \>:>

::: 0..

......

2. T

he q

uadr

upol

ar s

plitt

ing

in t

he z

H-N

MR

spe

ctru

m in

crea

ses

X

X

0 ::: I

I IH

, zH

, 35

Cl

with

the

pol

ypep

tide

con

cent

rati

on.

o·

Cl-

C-C

-Cl

IZl

'0

I I

AA

'A"A

'"

Cb ~.

X

X

til

(X=

lH

or

zH)

t:1

s;.

til

Tet

rafl

uoro

-(I)

with

slig

htly

T

he e

xist

ence

of

thre

e F

F d

irec

t di

pola

r co

uplin

gs i

n th

is c

ase

424,

432

1 1,

3-di

thie

tane

di

ffer

ent c

once

ntra

tion

s.

esta

blis

hes

the

DZ

h s

ymm

etry

. The

y pr

ovid

e th

e tw

o or

der

para

m-

S·

(Z)

(3)

3 %

(by

wei

ght)

et

ers

and

the

only

inde

pend

ent

dist

ance

rat

io if

the

anis

otro

py

.....

:;,""

F S

F of

the

indi

rect

FF

cou

plin

gs i

s ne

glig

ible

. F

rom

stu

dies

per

-Cb

"-..

../"

-..

../

19F

form

ed a

t va

riou

s te

mpe

ratu

res,

an

aver

age

valu

e of

the

rati

o Z

C

C

84

.66

of th

e di

stan

ce b

etw

een

the

gern

inal

and

the

cis

-lik

e vi

cina

l 8

./

"-.

.../

"-

... A

A'A

"A'"

fl

uori

nes

has

been

fou

nd a

s 0.

549 ±

0.00

2. T

his

is i

n sa

tisfa

ctor

y a

F S

F o·

(I)

(4)

agre

emen

t w

ith t

hat

expe

cted

for

a m

odel

with

rea

sona

ble

CF

'"C

an

d C

C d

ista

nces

and

the

FC

F b

ond

angl

e. T

his

indi

cate

s th

at

:;,""

\>:>

th

e an

isot

ropy

of

the

indi

rect

FF

cou

plin

gs i

s ne

glig

ible

. ti

l Cb

For

mam

ide-

15N

(I

) w

ith 0

.03

M s

ulph

uric

W

ith

0.03

M s

ulph

uric

aci

d, t

he e

xcha

nge

of th

e N

H p

roto

n w

as

433

;g ac

id i

nste

ad o

f pu

re w

ater

sl

owed

so

that

all

six

dire

ct d

ipol

ar c

oupl

ings

cou

ld b

e ob

serv

ed.

C\l ::s

H

H

9 %

(by

wei

ght)

T

he m

icro

wav

e st

ruct

ure

was

use

d to

che

ck t

he s

elf-

cons

iste

ncy

Q..

~.

"" /

33.3

° of

the

six

dipo

lar

coup

lings

and

the

ord

er p

aram

eter

s. T

he

0-C

-15N

IH

re

sults

indi

cate

that

ther

e is

no p

lane

of s

ymm

etry

in th

e m

olec

ule.

;,c

/ ""

60

.., 0

H

AB

CX

.... .....

.....

.....

(T

rans

)-1,

2-(I

) T

he H

H a

nd t

he t

wo

HF

dir

ect

dipo

lar

coup

lings

tog

ethe

r w

ith

438

('1

0 di

fluo

roet

hyle

ne

the

know

n ge

omet

ry p

rovi

de t

he t

hree

ord

er p

aram

eter

s. T

he

,§ H

F

FF

dip

olar

cou

plin

g in

dica

ted

that

the

anis

otro

pic

cont

ribu

tion

of

0

"" /

IH,

19F

the

indi

rect

FF

cou

plin

g is

app

reci

able

. §

100,

56

Q..

C

=C

en

/ ""

AA

'XX

' en

... F

H

8. ('b'

Q..

p-D

ithi

in

(I)

r I4/r

12 =

1.8

25 ±

0.008

(1.

775

± 0.

020

[459

])"

439

!>' 5-

(4)

(I)

2% (

blw

eigh

t)

Sxx=

-0

.01

16

9

.....

::s H

S

H

25°

Syy

= -

0.02

488

0'

........

/ .....

... /

IH

S tr

tr 90

g.

C

C

AA

'A"A

'"

::s /

........

/ .....

... 0

H

S H

C

\l (3

) (2

) ~.

C\l

Eth

ylen

eim

ine

(III

) O

nly

the

met

hyle

ne p

roto

ns w

ere

obse

rved

. T

he d

ista

nce

rati

o 41

7,44

0 Q

..

IL

}I

1 % (b

y w

eigh

t)

rcis/

rgem

der

ived

on

the

assu

mpt

ion

that

the

fou

r pr

oton

s lie

at

the

36°

corn

ers

of a

rec

tang

le w

as f

ound

to

be 1

.363

± 0.0

01,

a va

lue

" IH

w

hich

is

inte

rmed

iate

bet

wee

n th

e va

lues

(1.

3572

and

1.3

847)

C

-C

/\/~

90

for

the

syn

and

anti

case

s. A

sim

ilar

stu

dy in

the

lyot

ropi

c ph

ase

H

~ H

A

A'A

"A'"

(I

) pr

ovid

es a

val

ue o

f 1.

364 ±

0.00

5 fo

r th

is r

atio

[44

0].

H

'" ....

Com

poun

d P

hase

R

esul

ts a

nd R

emar

ks

Ref

eren

ce ~

and

Str

uctu

re

Sol

ute

conc

entr

atio

n T

empe

ratu

re (0

C)

N u

c1eu

s st

udie

d F

requ

ency

(MH

z)

Spe

ctra

l typ

e

Eth

ylen

e (I

) r 1

4/r1

2=

1.38

9 (1

.358

[40

8])8

44

1 IZ

I -ca

rbon

ate

5 %

(by

wei

ght)

. 8"

,,,,=

0.00

913

~ (2

) (3

) 31

° 8 y

y =

-0.

0124

4 CD

H"

", /H

1H

'" 0

C--C

10

0 .....

H

/I

I""'H

s::

AA

'A"A

'"

0 (1

) 0

o (4

) ~

""'/

E. C

e:

II 8-

0 .... 0

Eth

ylen

e m

onot

hio-

(I)

r1Jr

12=

1.43

3(1.

362

[408

])8

441

~.

carb

onat

e 5

% (b

y w

eigh

t)

r 3Jr

12 =

0.8

80 (0

.938

)"

IZI

(2)

(3)

31°

8"""

= 0

.008

40

1i H"

", /H

1H

8 y

y =

-0.

0079

4 Q.

C--C

10

0 '"

H/I

I"

"'H

AA

'BB

' d /;

j' (1)

0

S (4

) '"

"'" /

[ C

II Er

0

- ff P

yraz

ine

(II)

r 1

4/r 1

2 =

0.6

07 ±

0.002

34

,50,

f (4

) N

(3

) 2 %

(by

wei

ght)

(0

.602

± 0.0

08 [

23])

8 41

7,44

2

H):

; J(

H

45°

8",,,,

= 0

.007

38

1H

8 yl'

= -

0.01

509

l H

N

H

60

P

yraz

me

has

also

bee

n st

udie

d in

pha

ses

(n a

nd (

lIn

[50

,41

7,4

42

].

(1)

(2)

AA

'A"A

'"

~

Pyr

imid

ine

(II)

r 1

4/r 1

2 =

0.9

49 ±

O.o

t8 (

0.95

0 ±

O.o

t [4

43])

" 34

,50,

~

(4)

2 %

(by

wei

ght)

r 3

4/r 1

2 =

1.

118

± 0.

017

(1.1

14 ±

0.0

2)"

417,

442

(1)

NIN

45°

Sxx=

-0.

0042

5 ::s Q

. 1H

Sy

y =

0.0

0428

;;<

.

~

60

Pyr

imid

ine

has

also

bee

n st

udie

d in

pha

ses

(I)

and

(III

) [5

0, 4

17,

8"

H

.P

H

AB

2e

442]

. '"d

e; (2

) (1

) ....

H

......

......

(3)

......

(J

0

Pyr

idaz

ine

(II)

r2

3/r 1

2 =

0.9

43 ±

0.0

14 (

0.98

8 ±

0.01

[44

4])"

34

,50,

~

(4)

2 %

(by

wei

ght)

r3

4/r1

2 =

1.

908

± 0.

006

(1.8

90±

0.0

04)"

41

7,44

2 0

H

35°

S xx

= 0

.005

64

§ Q.

>~

1H

Syy

= 0

.000

59

'" H

"N

C

I:l

60

It h

as a

lso

been

stu

died

in

phas

es (

I) a

nd (

III)

[41

7, 4

42].

....

I I

~ H

-"

'N

AA

'BB

' (2

) Q

.

H

~ (3

) Q

. .....

. ::s

Thi

ophe

ne

(I)

rdr3

4=

1.7

14±

0.00

1 (1

.745

±0.

OiO

[44

6])"

41

7,44

5,

0' S

(4)

(3)

1.2

% (b

y w

eigh

t)

r 14/

r 34

= 0

.985

± 0

.005

(0.

995

± 0.

005)

" 44

7 ~.

H

):(H

38

° Sx

x= -

0.01

94

0 1H

Sy

y= -

0.00

87

::s

H

S H

60

It

has

als

o be

en s

tudi

ed i

n ph

ase

(III

) [4

17]

as w

ell a

s in

pha

se (I

) t:

) (1

)

(1)

(2)

AA

'BB

' [4

47].

.... ~.

Q

.

Fu

ran

(I

) r d

r 34

=

1.48

7 ±

0.00

4 (1

.47

± 0.

02 [

448]

)"

417,

445

(4)

(3)

1.2

% (b

y w

eigh

t)

r14/

r34

= 0.

985

± 0.

006

(0.9

8 ±

0.02

)"

H):(H

38

° Sx

x= -

0.01

54

1H

Syy

=

-0.

0084

H

0

H

60

Als

o st

udie

d in

pha

se (

III)

[41

7].

(1)

(2)

AA

'BB

'

" V

alue

obt

aine

d fr

om a

stu

dy i

n a

ther

mot

ropi

c ph

ase.

0

\ V

l

0\

Com

poun

d Ph

ase

Res

ults

and

Rem

arks

R

efer

ence

0

\

and

Str

uctu

re

Solu

te c

once

ntra

tion

T

empe

ratu

re eC

) N

ucle

us s

tudi

ed

Fre

quen

cy (M

Hz)

Sp

ectr

al t

ype

en

Sele

noph

ene

(I)

r 12/

r 34

=

1.78

8 ±

0.00

5 44

9 .....

5. (4

) (3

) 1.

93 %

(by

wei

ght)

r 1

4/r 3

4 =

0.9

99 ±

0.00

2 (i

i'

HU

H

42°

Sxx=

-0.

0168

4 '" 0

1H

Syy

=

-0.

0103

9 ....,

H

H

60

T

he d

ista

nce

rati

o r 1

2/r 3

4 in

crea

ses

in th

e or

der 0

, S,

Se

for

fura

n,

~

(1)

Se

(Z)

0 A

A'B

B'

thio

phen

e an

d se

leno

phen

e.

0'

(') e. I>' ....

y-H

ydro

xypy

ridi

ne

(II)

T

he h

ydro

xyl

prot

on i

s no

t ob

serv

ed b

ecau

se o

f ra

pid

exch

ange

40

7 1'0

:::

t

2.5

% (b

y w

eigh

t)

with

wat

er.

0..

OH

.....

32

° r 1

4/r 1

2 =

0.5

49 ±

0.012

0

(l)xX(Z

) :::

t

H

""

H

1H

r34/

r 1Z

= 0

.950

± 0.0

02

(S.

I '"

100

Sxx

= o

m 11

5 en

"0

C1

> H

N

H

A

A'B

B'

Syy=

0.00

49

~.

(4)

(3)

'" 9- '" tr

ans-

{pyr

-ds)

(V

Ia in

met

hyle

ne

A v

alue

of 0

.745

has

bee

n es

tim

ated

for

rge

m/rc

is.

'" 45

0 0

ethy

lene

plat

inum

ch

lori

de-d

z)

i 0..

dich

lori

de

10 m

ole-

% (V

Ia),

S·

Cl

1/

20 m

ole-

% so

lute

, S-

I~

70 m

ole-

%, C

DzC

l z

C1>

(Py

--d

s}-P

t 1

28°

Z

1 "'--

c"

1H

a 22

0 e

Cl

1 A

A'A

"A"'

,AA

'A"A

'''X

(S

.

(X =

19

Spt w

ith s

pin

=

1/2

~

I>'

and

natu

ral

abun

danc

e 33

%)

'" C1>

Eth

anol

(I)

T

he O

H p

roto

n ra

pidl

y ex

chan

ges

with

the

wat

er o

f th

e ph

ase

148,

416

.6" C

H3C

H2O

H

3 %

(by

wei

ght)

and

coup

lings

to

it ar

e no

t obs

erva

ble.

't

l CD

Sxx=

-0.

0021

0 ::s

1H

Q..

Syy=

-0.

0157

3 ~.

100

SXy=

-0.

0231

6 .....

. 0

A3B

2 T

he C

arte

sian

coo

rdin

ate

syst

em is

suc

h th

at th

e x

axis

lie

s al

ong

'i:l

P>

the

C-C

bon

d an

d th

e z

axis

is

perp

endi

cula

r to

the

pla

ne o

f ~

sym

met

ry.

- -T

he m

ost

prob

able

ori

enta

tion

is w

ith t

he a

pplie

d fie

ld d

irec

tion

- ()

perp

endi

cula

r to

the

C-C

-O p

lane

. 0 S

Pyri

dine

(I

I)

rn/r

35 =

0.9

43 ±

0.0

05 (

0.96

2± 0

.003

[42

9])"

40

9 't

l 0 (4

) 2.

5 %

(by

wei

ght)

r1

5/r3

5 =

0.57

3 ±

0.00

2 (0

.579

± 0

.003

)"

8-

"'XX'"

30

° r 4

5/r3

5 =

0.58

3 ±

0.00

2 (0

.587

± 0

.004

)"

en

H

r-H

1H

Sx

x =

0.00

466

± 0.

0000

3 CI

.l .....

.

" 1

100

Syy

= -

0.02

412

± 0.

0005

6 §.

A

A'B

B'C

o·

H

N

H

Q

.. (1

) (2

) §

Pyri

dine

-N -o

xide

(I

I)

r 12/

r35

= 0.

957

± 0.

002

409

Q.. -

(4)

2.5

% (b

y w

eigh

t) r1

5/r3

5 =

0.58

3 ±

0.00

6 ::s 0'

H

30

° r 4

5/r 3

5 =

0.5

84 ±

0.0

03

3 (5

)X

x(3

)

1H

Sxx

= 0.

0053

7 ±

0.00

002

H

r-H

g.

~ 1

100

Syy

= -

0.00

373

± 0.

0005

5

H

N

H

AA

'BB

'C

::s 0 (1

) 1

(2)

CD '"'

0 ::r CD

Nit

robe

nzen

e-(V

Ia)

1 H-

and

14N

-NM

R s

pect

ra p

rovi

de a

val

ue o

f 1.

76 ±

0.0

7 M

Hz

430

Q..

(1 ,3

,5-d

3)

43 m

ole-

% n

itro

benz

ene

for

the

14N

qua

drup

ole-

coup

ling

con

stan

t. Fr

ee r

otat

ion

abou

t th

e

~D

C-N

bon

d al

ong

whi

ch l

ies

the

axis

of

the

larg

est

field

gra

dien

t 1H

,14

N

is a

ssum

ed.

H

""I

H

D

" V

alue

obt

aine

d fr

om a

stu

dy i

n a

ther

mot

ropi

c ph

ase.

0

\ -.

..j

0'1

Com

poun

d P

hase

R

esul

ts a

nd R

emar

ks

Ref

eren

ce

00

and

Str

uctu

re

Solu

te c

once

ntra

tion

T

empe

ratu

re (0

C)

Nuc

leus

stu

died

F

requ

ency

(MH

z)

Spec

tral

type

Ace

tone

(I

) J A

A, =

0.67

± 0.1

0 H

z 45

1 c;n

-C

H3

· CO

· CH

3 1.

7% (

by w

eigh

t)

The

axi

s of

larg

est

elec

tric

al p

olar

izab

ilit

y in

ace

tone

ori

ents

~

pref

eren

tially

alo

ng t

he o

ptic

axi

s of

the

nem

atic

liq

uid

crys

tal.

'" lH

0 ....,

10

0 ~

A3A 3

~ t"

)

Dim

ethy

l-(I

) J A

A, =

0.47

± 0.0

9 H

z 45

1 E.

. '" su

lpho

xide

2

% (b

y w

eigh

t)

The

axi

s of

larg

est

elec

tric

al p

olar

izab

ilit

y in

dim

ethy

l su

lpho

xide

... '"

CH

3· S

O·C

H3

orie

nts

pref

eren

tially

alo

ng t

he o

ptic

axi

s of

the

nem

atic

liq

uid

t:!

0..

lH

crys

tal.

.....

0 10

0 ~.

A3A 3

c;n

'C

Dim

ethy

lsul

phon

e (I

) O

nly

the

spec

trum

see

ms

to h

ave

been

rep

orte

d.

416

~. 3

% (b

y w

eigh

t)

'" H

3 C",

.;p

9. '" lH

'"

S S2.

/'

\-&

H

3C

0 A3

A 3

0.. S· -

Ben

zene

(I

II)

rmet

a/ro

rtho

= 1

.726

8 (1

.733

5[43

])'

51,1

49,

t:r'

(J)

H

0.5

% (b

y w

eigh

t)

r pa

rJr o

rtho

= 1

.992

1 (1

.999

7)"

416,

417

Z

25°

Szz

= 0.

0458

4 ~

H*H

lH

Ben

zene

has

als

o be

en s

tudi

ed in

pha

se (

I) [1

49,

416]

. T

he g

eo-

::to

90

met

ric

info

rmat

ion

deri

ved

in t

he tw

o ca

ses

is e

ssen

tially

the

sam

e.

t")

H

~

H

~

AA

'AIIA

'''A

II''A

'IIN

D

evia

tion

s fr

om t

he r

egul

ar h

exag

onal

geo

met

ry o

utsi

de t

he e

x-e;

H

peri

men

tal e

rror

are

fou

nd.

(J)

m-D

iflu

orob

enze

ne

(I)

The

H-H

and

the

H-F

cou

plin

gs h

ave

been

use

d to

det

erm

ine

144

(1)

2 %

(by

wei

ght)

th

e re

lati

ve n

ucle

ar p

osit

ions

and

the

tw

o in

depe

nden

t or

der

H

42°

para

met

ers:

'>7'"

1H,1

9F

r 13/

r 12

= 0.

522 ±

0.00

3 (0

.524

[45

2])

a

t F

""

F I

60,5

6 r 2

4/r 1

2 =

0.50

5 ±

0.00

2 (0

.504

)a

H

h H

A

BB

'CX

X'

r36/

r12

= 0.

942 ±

0.00

5 (0

.943

)a

(5)

\H

(4)

r 45/

r 12

= 0.

876 ±

0.00

4 (0

. 874

) a

~. -

Sxx=

:=-0

.041

4 0

(2)

Syy=

-0.

0159

~

.... F

rom

the

exp

erim

enta

l va

lue

of

the

dire

ct F

-F c

oupl

ing,

the

-....

anis

otro

pic

cont

ribu

tion

in

the

indi

rect

F-F

cou

plin

g ha

s be

en

.... ~ es

tim

ated

as

smal

l b

ut

sign

ific

ant.

Q

p-D

iflu

oror

o be

nzen

e (I

) 1f

if:D/r"

io =

1.71

7 ±

0.00

6 (1

.698

[45

2])a

14

3 ~

(5)

rFF/~ 0

= 2

.155

± 0.

002

(2.1

41)a

0

F Sx

x =

-0.

0436

§

":*'"

1H,1

9F

Syy =

:....

0.0

179

Q..

H

""

H

'" 60

,56

A s

mal

l bu

t si

gnif

ican

t an

isot

ropi

c co

ntri

buti

on i

n th

e in

dire

ct

til

I -

H

h H

A

A'A

"A"'

XX

' F

-F c

oupl

ing

cons

tant

was

det

ecte

d.

5. o· (4

) (3

) Q

.. F

8. (6

)

Dim

ethy

lfor

mam

ide

(VIb

) T

he b

on

d a

ngle

HC

N h

as b

een

obta

ined

as

107 ±

1°. T

he

62,6

3,

.... an

d th

e he

ptad

eute

rate

d qu

adru

pole

-cou

plin

g co

nsta

nts

and

the

asym

met

ry p

aram

eter

s 41

4 ~

anal

ogue

25

° ar

e de

term

ined

. ~

, /C

X3

1H, 2

H,

14N

T

he c

ompo

und

has

also

bee

n st

udie

d in

(V

Ia)

and

(VIe

) [6

2, 4

14].

g.

60

,8,4

::I

/C-N

",

0 (11 ::I.

0 C

X3

2-(X

=H

orD

)

N,N

-Dim

ethy

l-(I

) N

o w

orth

whi

le in

form

atio

n.

453

acet

amid

e-d 3

3

% (b

y w

eigh

t)

CD

3 C

H3

28°

1H

'" /

100

C-N

A3

B3X

3 /

'" 0

CH

3 (w

here

1=

1 fo

r th

e X

$

nucl

eus)

a V

alue

obt

aine

d fr

om a

stu

dy i

n a

ther

mot

ropi

c ph

ase.

Co

mp

ou

nd

an

d

Pha

se

Res

ults

an

d R

emar

ks

Ref

eren

ce

-..J

Str

uctu

re

Sol

ute

conc

entr

atio

n 0

Tem

pera

ture

(0C

) N

ucle

us s

tudi

ed

Fre

quen

cy (

MH

z)

Spe

ctra

l typ

e

p-X

ylen

e (V

Ia in

dic

hlor

omet

hane

) O

nly

the

spec

trum

is r

epor

ted.

62

~

0.05

ml

solu

te i

n CI

.l 0.

3 g/

0.95

ml

VIa

in

.... s:: di

chlo

rom

etha

ne

e: 0

23°

'" 0 IH

.....

.

220

~

CH

3 AA'A"A'''X3X~

~ (")

p-D

ioxa

ne

(VIa

) O

nly

the

spec

trum

is

repo

rted

. 56

,59,

~

419

...

sr012

1'0

::s Q..

IH

......

0

°

60

e. A

A'A

"AfIf

A""

Affl

"A""

UA

""'"

("

) CI.l

Ace

tate

and

per

deut

ero-

(IV

) r n

Jr 13

= 1

.636

3 ±

0.00

02

52

,39

2

'g

~.

acet

ate

ions

an

d t

he 1

3C

r 12/

r 14

= 0.

8329

± 0.

0002

'"

enri

ched

spe

cies

31

.1°

'1:H

IC3

C4

= 1

09

.W ±

0.05

° 9

IH,2

H

1: H

I C3H

2 =

109.

80° ±

0.05

° el

l

[(2)~~-COOr

'" 1:

C3C

4H

= 28

.74°

± 0.

07°

0 ~

H/(

3)

(4)

A3,

A3

X

SC3=

-0.

0071

6 Q

..

(1)

Th

e de

uter

on q

uadr

upol

e-co

upli

ng c

onst

ant

was

fou

nd t

o be

S·

17

0.4 ±

0.8

KH

z, a

ssum

ing

the

asym

met

ry p

aram

eter

'1 =

0 a

nd

.... t:

r th

e pr

inci

pal

qu

adru

po

lar

axis

alo

ng t

he C

-D b

ond.

0 Z

A

mm

oniu

m i

on

(IV

) T

he

dist

orti

on f

rom

the

reg

ular

tet

rahe

dral

geo

met

ry w

as

346,

349,

0

(NH

t, N

Dt,

ND

3H

+)

orig

inal

ly e

stim

ated

to

be a

ppro

xim

atel

y 1°

. Th

e d

ata

have

bee

n 35

1 ~

30.3

° re

inte

rpre

ted

and

a m

ore

reas

onab

le v

alue

of

0.02

° to

0.0

4°

g.

IH,2

H

obta

ined

[34

6].

~

100,

7.95

1'0

'" 0 A

4X

Tet

rafl

uoro

bora

te

(IV

) T

he d

isto

rtio

n fr

om t

he t

etra

hedr

al s

ymm

etry

has

bee

n fo

und

346,

349

:g io

n B

F4

to b

e 0.

013°

to 0

.020

°.

29.7

° (l

) ::s 19

F,11

B

Q.. S;;. 0-

A4

X (w

here

spi

n (I

) fo

r ~

nucl

eus

X =

3/2

) .., .....

.....

.....

C

acod

ylat

e io

n (I

V)

Thi

s io

n ha

s C

2v-s

ymm

etry

and

the

re a

re o

nly

two

dire

ct H

-H

410

.....

(J

[(C

H3)

zAs0

2] -

coup

ling

s; n

o st

ruct

ural

inf

orm

atio

n co

uld,

the

refo

re,

be d

eriv

ed.

0

lH

~ 0 ~ ::s

A3A

3 Q

.. '" CI.l .....

The

cou

plin

gs b

etw

een

prot

ons

and

117S

n as

weI

I as

119

Sn w

ere

410,

411

§.

Dim

ethy

ltin

ion

(IV

) cD

" [(

CH

3)zS

n]+z

ob

serv

ed.

Q.. ~

33°

rH3C

CH

,/rH

CH

= 2

.667

± 0

.020

Q

.. lH

rS

nC

H,/

rHC

H

= 1.

454

± 0.

015

-::s 60

1:

HS

nC

= 23

.4°

± 0.

2°

S A

3A

3,A

3A

3X

SC

3 =

-0.0

13

9

S g. M

ethy

lam

mon

ium

(I

V)

with

adj

uste

d T

he i

on h

as C

3v-s

ymm

etry

. 35

1,41

2 ::s t:l

io

n pH

so

as t

o sl

ow

rHN

Hir

HC

H =

0.9

334

± 0.

0002

(l

)

(CH

3l4N

H3)

+

the

prot

on e

xcha

nge)

r C

N/r

HC

H

= 0.

829

± 0.

005

~.

(l)

(13C

H N

H3)

+ rC

Hir

HC

H

=0.

6102

±0.

0006

Q

..

(CH/

~NH3

)+

rNH

/rH

CH

=

0.57

57 ±

0.0

006

(CH

3ND

3t

lH,2

H

1: +

NC

H =

108

.82±

0.1

1 °

60

1: C

+N

H =

110

.63

± 0.

02°

A3B

3,A

3B

3X

SC

3 =

-0.0

16

5

The

res

ults

are

in

bett

er a

gree

men

t w

ith t

he "

free

-rot

atio

n"

abou

t th

e C

-N b

ond

than

with

a "

hind

ered

-rot

atio

n". T

he

deut

eron

qua

drup

ole-

coup

ling

con

stan

t al

ong

the

N-D

bon

d is

foun

d as

176

.7 K

Hz

assu

min

g th

e as

ymm

etry

par

amet

er

11=

0.

-..l

-

-...l

Com

poun

d an

d Ph

ase

Res

ults

and

Rem

arks

R

efer

ence

tv

Str

uctu

re

Solu

te c

once

ntra

tion

T

empe

ratu

re (D

C)

Nuc

leus

stu

died

F

requ

ence

(M

Hz)

Sp

ectr

al ty

pe

Dim

ethy

lam

mon

ium

(I

V)

The

spe

ctra

wer

e st

udie

d w

ith a

djus

ted

pH s

o as

to

slow

dow

n th

e 45

4 C

Il .... IO

n ex

chan

ge o

f th

e N

H2

prot

ons.

The

rat

io o

f th

e di

stan

ce b

etw

een

5. [(

CH

3h 14

NH

2] +

th

e m

ethy

l pr

oton

s th

emse

lves

and

tha

t be

twee

n on

e of

thes

e til"

'" [(

CH

3h 1 S

NH

2] +

lH

pr

oton

s an

d ni

trog

en i

s fo

und

as 0

.847

1 ±

0.00

27. T

he C

NC

0 .....

, 10

0 an

gle

is 1

14.3

± 0.4

0•

s:::

A3A

;B2,

A3

A;B

2X

0 (1

) ("

) e. T

rim

ethy

l-(I

V)

In t

he n

eutr

al s

olut

ion,

the

spe

ctru

m i

s of

the A3A~A3

454

J:l am

mon

ium

ion

type

due

to

the

rapi

d ex

chan

ge o

f th

e N

-H p

roto

n. O

n ac

idif

ica-

Pl

[(C

H3h

NH

]+

tion,

the

spe

ctru

m b

ecom

es o

f th

e A

3A;A

3B ty

pe.

In t

his

case

5- -

lH

only

a f

ew n

on-o

verl

appi

ng tr

ansi

tion

s w

ere

obse

rved

and

0 i:

l 10

0 he

nce

a co

mpl

ete

anal

ysis

was

not

pos

sibl

e.

o· A3

A~A

3' A3A~A3B

CIl

'd

<1l ~.

Tet

ram

ethy

l-(I

V)

Onl

y so

me

line

broa

deni

ng w

as o

bser

ved;

due

to t

he o

verl

ap o

f an

454

'" am

mon

ium

ion

enor

mou

s nu

mbe

r of

tran

siti

ons,

no

fine

stru

ctur

e co

uld

be

9. '" [(

CH

3)4 N

]+

reso

lved

. '" 0

lH

<'

<1l

100

Q...

A3A~A3A3'

S·

.... t:r'

<1l

Met

hylp

hosp

hona

te

(I)

rCp/

r CH

= 1.

576 ±

0.00

9 (f

rom

the

pro

ton

spec

trum

) 42

4 Z

<1

l

Ion

1.84

% (b

y w

eigh

t)

r cp/r

CH =

1.6

8 ±

0.03

(fr

om t

he 1

3C-s

pect

rum

). 8

(13 C

H3P

03)

--

The

dif

fere

nce

betw

een

thes

e va

lues

has

bee

n at

trib

uted

to

the

Pl ~.

lH,1

3C

anis

otro

py o

f th

e in

dire

ct c

oupl

ings

and

/or

the

negl

ect

of th

e 'i:

I in

flue

nce

of m

olec

ular

vib

rati

ons.

t:r

' P

l

A3M

X

1: H

eH =

108

.23

± 0.

3°

r6

Dim

ethy

ltha

lliu

m i

on

(CH

3TIC

H 3)

+

Zei

se's

Sal

t H

1 H

2 ""

-/

C ! .. ·P

tCI 3

C

/""-

H3

H4

Stud

ied

both

in

syst

em (

IV)

and

in a

pha

se s

imila

r to

(I)

but p

repa

red

with

ces

ium

de

cyls

ulph

ate

inst

ead

of

sodi

um d

ecyl

sulp

hate

3-

4.5

% (b

y w

eigh

t)

30.6

1H

10

0 A3A~X

Stu

died

in a

sys

tem

sim

ilar

to

(I).

5.6

% (b

y w

eigh

t)

270

1H

90

AA

' A" A

"', A

A' A

" A'"

X

a V

alue

obt

aine

d fr

om a

stu

dy in

a t

herm

otro

pic

phas

e.

rH3

CC

H/r

HC

H =

2.6

63 ±

0.0

03

rT1C

H,/

rHC

H =

1.4

52 ±

0.0

07

-tH

ICT

= 2

3,4

± 0.

20

SC3

=

-0.

0670

in c

esiu

m p

hase

SC

3 fr

om -

1.13

x 1

0-3

to -

7.21

X 1

0-4

in s

yste

m (I

V).

The

lar

ge d

iffe

renc

e in

the

ord

er w

as a

ttri

bute

d to

the

fac

t th

at

the

supe

rstr

uctu

res

of th

e ab

ove

syst

ems

have

opp

osit

e ch

arge

s.

r13/

r12

= 1

.340

±0.0

02

r14/

r12

=

1.67

1 ±

0.00

2 Sx

x=0.

0359

S"

= 0

.007

1 12

D +

JIPtH

was

fou

nd t

o b

e ne

ar z

ero

for

seve

ral o

rien

tati

ons.

O

verl

ap o

f tra

nsit

ions

occ

ured

and

DPt

H co

uld

not b

e ob

tain

ed

accu

rate

ly.IJ

PtH

I =

66.

22±

0.0

6 H

z in

isot

ropi

c m

icel

lar

soap

so

lutio

n.

425

46

f ~ s ~ - - - f ~ I [ ~ ~ g. ~ [ ~

74 Studies of Molecular and Ionic Species Dissolved in the Nematic Phase

Acknowledgements

We are grateful to Drs. H. J. C. BERENDSEN, S. FORSEN, G. LINDBLOM, G. N. RAMACHANDRAN and I. C. P. SMITH for helpful discussions and to Dr. J. VOGT

for his moral support during the preparation of this manuscript.

References

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Am. Chern. Soc. 7. LA WRENCE,A. S. C., McDONALD,M. P. : a) Mol. Cryst. 1, 205 (1966) ; b) In: BROWN, G. H.,

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Resonance in Biological Systerns, Kandersteg, Switzerland (1974). 438. DENOTTER,G.J., MACLEAN,C.: Chern. Phys. 3, 119 (1974). 439. LONG,R.C.,Jr., GoLDSTEIN,J.H.: J. Mol. Spectr. 40, 632 (1971). 440. GAZZARD,I. J. : Mol. Phys. 25,469 (1973). 441. BARTON,S. A., RAZA,M.A., REEVES,L.W.: J. Mag. Res. 9, 45 (1973). 442. LONG,R.C.,Jr., Long,K.R., GoLDSTEIN,J.H.: Mol. Cryst. Liquid Cryst. 21, 299 (1973). 443. KHETRAPAL,C.L., PATANKAR,A. Y., DIEHL,P.: Org. Mag. Res. 2,405 (1970). 444. BURNELL,E.E., DELANGE,C.A.: Mol. Phys.16, 95 (1969). 445. LONG,R.C.,Jr., BAUGHCUM,S.L., GoLDSTEIN,J.H.: J. Mag. Res. 7, 253 (1972). 446. DIEHL,P., KHETRAPAL,C.L., LIENHARD,V.: Can. J. Chern. 46, 2645 (1968). 447. DEREPPE,J.M., MORISSE,J.P., MEERSSCHE,M.Y.: Org. Mag. Res. 3,583 (1971). 448. DIEHL,P., KHETRAPAL,C.L., KELLERHALS,H.P.: Helv. Chim. Acta 51,529 (1968). 449. DAHLQVlST, K.I., HORNFELDT,A.B.: Chernica Scripta 1, 125 (1971). 450. McMILLIN,D.R., DRAGO,R.S.: Inorg. Chern. 13, 546 (1974). 451. LINDON,J., DAll..EY,B.P.: Mol. Phys. 20, 937 (1971). 452. YIM,C.T., Gll..sON,D.F.R.: Can. J. Chern. 47, 1057 (1969). 453. ANDERSON,J.M., LEE,A.C.F.: J. Mag. Res. 4,160 (1971). 454. REEVES,L.W., TRACEY,A.S.: J. Am. Chern. Soc. 96, 7176 (1974)." 455. DIEHL,P., KHETRAPAL,C.L., LIENHARD,V.: Org. Mag. Res. 1, 93 (1969). 456. CoPE,F. W.: a) J. Gen. Physiol. 50, 1353 (1967); b) Biophys. J. 10,843 (1970); c) Proc.

Nat. Acad. Sci. U.S. 54, 225 (1965); d) Bull. Math. Biophys. 29, 691 (1967). 457. CZIESLER,J.L., FRITz,O.G.,Jr., SWIFT,T.J.: Biophys. J. 10,260 (1970). 458. ROTUNNO, c.A., KOWALEWSKI, Y., CERmnoo,M.: Biochirn. Biophys. Acta 135, 170 (1967). 459. RUSSEL,J.: Org. Mag. Res. 4, 433 (1972). 460. FILAS,R.W., HAIDo,L.E., ERINGEN,A.C.: J. Chern. Phys. 61, 3037 (1974). 461. DIEHL,P., TRACEY,A.S.: Can. J. Chern. (1975) (in press).

The following literature appeared after the prepation of the manuscript.

a) Belonging to Section 5.1. BUNTON,C.A., MINCH,M.J.: J. Phys. Chern. 78,1490 (1974) .. CoLEN,A.H.: J. Phys. Chern. 78,1676 (1974). FENDLER,J.H., FENDLER,E.J., INFANTE,G.A., SmH,P., PATTERSON,L.K.: J. Amer. Chern.

Soc. 97, 89 (1975).

References 85

GUTZEL,M., KALYANASUNDARAM,K., THoMAS,J.K.: J. Amer. Chern. Soc. %, 7869 (1974). McKINNEY,J.D.: Chern. Phys. Lipids 13, 249 (1974). MULLER,N.: J. Phys. Chern. 79, 287 (1975).

b) Belonging to Section 5.2. CATER,B.R., CHAPMAN,D.,HAWES,S.M., SAVILLE,J.: Biochim. Biophys.Acta363, 54(1974). CoRNELL,B.A., POPE,J.M., TRoup,G.J.F.: Chern. Phys. Lipids 13,183 (1974). FINER,E.G., DARKE,A.: Chern. Phys. Lipids 12,1 (1974). KLosE,G., STELZNER,F.: Biochirn. Biophys. Acta 363,1 (1974). NICOLAU,C., DREESKAMP,H., SCHULTE-FROHLINDE,D.: FEBS Lett. 43,148 (1974). OAKES,J.: J. Chern. Soc. Faraday Trans. I, 70, 2200 (1974). PREsTEGARD,J.H., WILKINSON,A.: Biochim. Biophys. Acta 345,439 (1974). RlBElRo,A.A., DENNIS,E.A.: Biochim. Biophys. Acta 332, 26 (1974). RlBElRo,A.A., DENNIs,E.A.: Chern. Phys. Lipids 12, 31 (1974). STOFFEL,W., ZIERENBERG,O., TUNGGAL,B., SCHREIBER,E.: Proc. Nat. Acad. Sci. (USA)

, 71, 3696 (1974).

c) Belonging to Section 5.3. FUNG,B.M., WITSCHEL,J. (Jr.), McAMIs,L.L.: Biopolymers 13, 1767 (1974). WESTOVER,C.J., DRESDEN,M.H.: Biochim. Biophys. Acta 365,389 (1974). WOESSNER,D.E.: J. Mag. Res. 16,483 (1974).

d) Belonging to Section 5.4. BULL, T., LINDMAN,B.: Mol. Cryst. Liq. Cryst. 28, 155 (1974). TIDDY,G.J.T., HAYTER,J.B., HECHT,A.M., WHITE,J.W.: Ber. Bunsenges. Physik. Chern.

78, 961 (1974).

e) Belonging to Section 5.5. LINDBLOM,G., PERssoN,N., LINDMAN,B., ARVIDSON,G.: Ber. Bunsenges. Physik. Chern. 78,

955 (1974).

f) Belonging to Section 5.6. AssMANN,G., HIGHET,R.J., SoKOLOSKI,E.A., BREWER,H.B.Or.): Proc. Nat. Acad. Sci.

(USA) 71, 3701 (1974). NIEDERBERGER,W., SEELIG,J.: Ber. Bunsenges. Physik. Chern. 78, 947 (1974). SEELIG,J.: Pathol. Microbiol. 41, 151 (1974).

g) Belonging to Section 5.7. BARSUKOV,L.I., SHAPIRo,Y.E., VIKTOROV,A.V., VOLKOVA,V.I., BYSTROV,V.F., BERGEL-

soN,L.D.: Biochern. Biophys. Res. Commun. 60, 196 (1974). CHANG, C., CHAN, S.I.: Biochemistry 13, 4381 (1974). FRISCHLEDER,H., FRENZEL,J.: Stud. Biophys. 43, 217 (1974). GENT,M.P.N., PREsTEGARD,J.H.: Biochemistry 13, 4027 (1974). HELFRICH, W.: Phys. Lett. SOA, 115 (1974). LICHTENBERG,D., PETERsEN,N.O., GIRARDET,J.L., KAINOSHO,M., KRooN,P.A., SEITER,

C.H.A., FIEGENSON,G. W., CHAN,S.I.: Biochim. Biophys. Acta 382, 10 (1975). SEARS,B., HUTTON,W.e., THOMPSON,T.E.: Biochern. Biophys. Res. Commun. 60, 1141

(1974).

G. Meier, E. Sackmann, J. G. Grabmeier

Liquid Crystals Research and Applications. 88 figures. 160 pages. 1975 DM 56,-; US $24.10 ISBN 3-540-07302-7

Contents: G. Meier, Physical Properties of Liquid Crystals. -E. Sackmann, Scientific Applications of Liquid Crystals. - J .G. Grabmeier, Medical and Technical Applications of Liquid Crystals.

This book surveys the range of possible applications of liquid crystals. It opens with a short introduction on the physical background (G. Meier). The first main section of the book (E. Sackmann) deals with the sicentific applications, particularly the use of liquid crystals as anisotropic solvents in spectroscopic studies to determine the anisotropic properties of molecules, also in analytical chemistry and gas chromato­graphy. The other main section (T. Grabmeier) is concerned with appli­cations in medicine and technology, mainly in thermography and for electrooptic displays. In view of the rapid advances that have been made in the field of liquid crystals, this volume should be much appredated for orientation purposes. It will appeal not only to physicists, chemists, physicians, and develop­ment engineers but also to advanced students seeking to expand their knowledge of liquid crystals.

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K. Schemer, H. B. Stegmann

Elektronenspinresonanz Grundlagen und Anwendungen in der organischen Chernie

145 Abbildungen. VIII, 506 Seiten. 1970 (Organische Chernie in Einzeldarstellungen, Band 12) Gebunden DM 148,-; US $63.70 ISBN 3-540-04984-3

Inhaltsiibersicht: Grundlagen der Elektronen-Paramagnetischen­Resonanz. - Elektronenverteilung und isotrope Hyperfeinstruktur von Tt'-Radikalen. - Anisotrope Hyperfeinstruktur undg Faktor. - Zwei­spinsysteme. - Weitere Hochfrequenzmethoden zur Untersuchung freier Radikale. - Radikale in Losung.

Die Elektronenspinresonanz kann Aufschltisse tiber paramagnetische organische Verbindungen liefern. Die ersten Abschnitte behandeln die theoretischen Grundlagen und die physikalischen Probleme, die als Voraussetzungen zum Verstandnis der Me~ergebnisse uner1ii~lich sind. Der zweite Teil bietet aus der Fiille der Resultate eine kritische Aus­wahl. Sie soil zur praktischen Ergiinzung der vorstehenden Kapitel und als experimentelles Vergleichsmaterial dienen. Dergestalt verrnittelt das Buch jene Kenntnisse, die zum Studium stabiler organischer Radikale und paramagnetischer Reaktions-Zwischenstufen notwendig sind.

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