UNIVERSITY OF MEDICINE AND PHARMACY OF CRAIOVA

THE DOCTORAL SCHOOL

PHD THESIS Abstract

Synthesis, physico-chemical characterization and investigation of

some compounds with

nematic and smectic liquid crystal properties

PhD Supervisor,

Prof. univ. PhD. Neamţu Johny

PhD Student,

Petrescu (Golescu) Manuela Ileana

Craiova

2015

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Table of contents

Introduction…………………………...........…..………………..……………………….............……. 4 State of knowledge………………….....................……………………………………............……….. 7 Chapter 1. Synthesis of liquid crystals………………………………………………………….............. 7 Chapter 2. General aspects about liquid crystals……..........……………………………………............. 14 2.1. Liquid crystals characteristics………………….......……………………………………............….. 14 2.2. Types of liquid crystals…………………………..……………………………………….............… 15 2.2.1. Calamitic thermotropic liquid crystals………………………………………………….............… 15 2.2.2. Discotic liquid crystals……………………....………………………………………............……. 17 2.2.3. Polymeric liquid crystals……………………...………………………………………............….. 18 2.2.4. Lyotropic liquid crystals………………...……………………………………………............…... 21 2.3. Phase transitions for liquid crystals……….........…………………………………………............... 22 2.4. External influences on liquid crystals……........……………………………………….............…… 23 2.5. Chemical properties of liquid crystals…….....………………………………………….............….. 23 2.6. Liquid crystals with biological functions…………………………………………………............... 24 2.7. Areas that use liquid crystals.............……………………………………………….............…..….. 25 Chapter 3. Applications of liquid crystals in medicine and pharmacy..……………………............….... 27 3.1. Applications of liquid crystals in medicine………………………………………………................ 28 3.2. Applications of liquid crystals in pharmacy...…………………………………………..............….. 30 3.2.1. Drugs with liquid crystals properties................…………………………………………............... 31 3.2.2. Liquid crystals for improving the pharmaceutical products solubility.........……………............... 36 3.2.3. Colloidal dispersions with pharmaceutical role...……………………………………….............… 36 3.2.4. Smectic nanoparticles with pharmaceutical role…………………………………………............. 36 3.2.5. Dermal applications of liquid crystals..…………………………………………………............... 36 3.2.6. Systems for releasing drug that use liquid crystals structures...............................………......…… 37 Personal contributions............................................................................................................................. 40 Chapter 4. Synthesis and physico-chemical characterization of some new azomonoetheramides with liquid crystals properties............................................................................................................................ 40

4.1. Synthesis of azomonoetheramides...................................................................................................... 40 4.1.1. Working procedure.......................................................................................................................... 41 4.1.1.1. Synthesis of 4-chloro-4'-hydroxyazobenzene............................................................................... 41 4.1.1.2. Synthesis of 4-ethyl-N-chloroacetylaniline.................................................................................. 42 4.1.1.3. Synthesis of 4'-cyano-4-(p-ethyl-N-phenylacetamidoxy) azobenzene......................................... 43 4.2. Results and discussions...................................................................................................................... 44 4.2.1. UV-VIS spectra............................................................................................................................... 51 4.2.2. FTIR spectra.................................................................................................................................... 55 4.2.3. Mass spectra.................................................................................................................................... 63 4.2.4. 1H-NMR spectra.............................................................................................................................. 85 4.2.5. 13C-NMR spectra............................................................................................................................. 89 4.3. Research for liquid crystals properties................................................................................................ 92 4.4. Raw materials and equipment............................................................................................................. 1034.5. Structure-property correlation (QSAR).............................................................................................. 1054.6. Uses of liquid crystals......................................................................................................................... 107Conclusions............................................................................................................................................... 109References................................................................................................................................................. 113

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INTRODUCTION A liquid crystal represents an unique organic material, which exists between the solid

phase and the liquid isotropic phase. Between certain limits of temperature, the liquid crystal shows a specific molecular structure that can be compared with the crystalline state. The incident light is splitted selectively and it forms the base for measuring the temperature. The material with liquid crystal properties is represented in a solid amorphous state, under a certain value of temperature, and in a liquid phase, over a superior limit of temperature.

Figure 1. Representation of liquid crystal phase, between the solid and the liquid phases.

The liquid crystals used in nanomedicine are very useful tools for drugs transportation. Those with pharmaceutical purposes have already proven their efficiency for treating some viral diseases, like herpes, and also in the “fight” against tumours, like cancer of the bladder or that of prostate. For this reason, they have given strong hopes regarding the transdermal applications, due to their high capacity to go straight to the target, thus to the inflamed tissue. Generally, it has been demonstrated that those liquid crystals with pharmaceutical properties are relatively secure to be used as drugs. In this sense, the specialty research studies realized until the present moment have indicated their very low toxicity.

Keywords: azomonoetheramides, nematic, smectic, spectral analysis, QSAR (Quantitative Structure Activity Relationship)

STATE OF KNOWLEDGE

Chapter 1. Synthesis of liquid crystals This chapter presents synthesis of compounds with liquid crystal properties, for example

compounds with pyridine structure, benzoic 4-(4-alkyloxyphenylazo) acids, several copolymers, compounds from terphenyls series and quaterphenyls non-collinear.

Thus, it was observed that from the terphenyls series those non-collinear materials do not have liquid crystalline activity, excepting the 4-dodecyloxy-3”-methoxy-p-terphenyl, which has a smectic B monotropic phase, while the SmA phase was reported at only one quaterphenyl non-collinear compound, fact that have conducted to further researches on this interesting class of materials.

Figure 1.4. Optical textures of benzoic 4-(4-decyloxyphenylazo) acid (3e) at cooling: a) nematic drops

of isotropic liquid at 245oC; b) Schlieren texture at 244oC and c) smectic texture at 176oC.

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Chapter 2. General aspects about liquid crystals The liquid crystal state combines the properties of liquid phase with those of the solid

phase. The liquid state is associated with the compound capacity of flowing, while the solid state is characterized by an ordered and crystalline structure. The crystalline solids have distributions on short or long distances in function on the molecules position and orientation. In general, liquids are amorphous, but they can have distributions on short distances regarding position and/or orientation. The liquid crystals give at least distributions on long distances from the orientational point of view, but they can also present distributions on short distances, while the positional distributions on long distances disappear. As consequence, the liquid crystal phases represent intermediary states and they are also called mesophases. Formation of liquid crystals mesophases depends on the therapeutic objective and on the molecular size, and also on the analytical significance for their identification.

Chapter 3. Applications of liquid crystals in medicine and pharmacy

Materials based on liquid crystals are unique in properties and uses. Researches in this domain are into a continuous development and new applications for liquid crystals are found permanently. Thus, liquid crystals present an essential role in the modern technology.

The physical and clinical properties of cholesteric liquid crystals are numerous and they were discovered few years ago. Recently, there have been highlighted only those properties that are beneficial in medical applications for liquid crystals thermography. Therefore, these utilizations of liquid crystals in medicine involve applications on the skin level for determining the relative temperatures, which are modified by subjacent disorders.

Figure 3.1. Thermographic liquid crystals.

For symptomatic cases but clinically undefined, liquid crystals help for determining the place of inflammatory injuries. A real example is the case of a patient diagnosed with juvenile rheumatoid arthritis with severe involvement of all joints, especially the small joints of the hand.

Figure 3.2. Thermogram of rheumatoid arthritis in hands (a) before and (b) after the treatment.

Thermography of liquid crystals is also used for determining the presence and spreading of different tumours.

Figure 3.3. Thermogram of some vascular

disorders at inferior limbs.

Figure 3.4. Thermogram of a tumour

at knee.

Compounds with liquid crystal properties from the pharmaceutical domain are used as: drugs with liquid crystals properties, liquid crystals for improving the pharmaceutical products solubility, colloidal dispersions with pharmaceutical role, smectic nanoparticles with pharmaceutical role, dermal applications of liquid crystals, systems for releasing the drug.

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PERSONAL CONTRIBUTIONS Chapter 4. Synthesis and physico-chemical characterization of some new

azomonoetheramides with liquid crystals properties

4.1. Synthesis of azomonoetheramides Synthesis of azomonoetheramides was realized by condensation in an alkaline medium of

some 4-(phenylazo) phenols, namely: 4-(phenylazo) phenol, 4-(4'-methyl-phenylazo) phenol, 4-(4'-trifluoromethyl-phenylazo) phenol, 4-(4'-chloro-phenylazo) phenol, 4-(4'-nitro-phenylazo) phenol, 4-(4'-cyano-phenylazo) phenol with 4-ethyl-N-chloroacetylaniline, according to a bimolecular nucleophilic substitution mechanism (SN

2) [199,200]:

N NR O-Na+ + ClCH2 C NH

O

CH2 CH3

+ NaCl N NR CH2 C NHO

O

CH2 CH3

R = H, CH3, CF3, Cl, NO2, CN.

4.2. Results and discussions The high reaction yields are dependent on the reaction products solubility into the used

solvent. The elevated melting points are due to the presence of different substituents in the para

position.

Table 4.1. Synthesis data for the six azomonoetheramides

No. Structural formula Name

Molecular formula

M g/mol

M.p. oC

η %

1. N NN N CH2 CH3CH2 C NHO

O

CH2 C NHO

O 4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C22H21N3O2 359 197–198 75.26

2. CH3 N NN N CH2 CH3CH2 C NHO

O

CH2 C NHO

O 4'-methyl-4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C23H23N3O2 373 191–192 70.72

3. F3C N NN N CH2 CH3CH2 C NHO

O

CH2 C NHO

O 4'-trifluoromethyl-4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C23H20N3O2F3 427 185–186 80.18

4. Cl N NN N CH2 CH3CH2 C NHO

O

CH2 C NHO

O 4'-chloro-4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C22H20N3O2Cl 393.5 210–211 82.65

5. CH2 CH3N NO2N CH2 C NHO

O

N NO2N CH2 C NHO

O 4'-nitro-4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C22H20N4O4 404 220–221 71.23

6. NC N NN N CH2 CH3CH2 C NHO

O

CH2 C NHO

O 4'-cyano-4-(p-ethyl-N-phenylacetamidoxy) azobenzene

C23H20N4O2 384 181–182 76.14

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It is observed that the six new azomonoetheramides present a temperature range on which they melt, fact necessary for substances that have nematic and smectic liquid crystals properties.

According to chromatograms obtained from the HPGC-MS 5890 MD 5971 spectrometer at 70 eV, the carrier gas being He at 2 ml/min, it is noticed that these compounds are pure, fact demonstrated from the appearance of a single peak.

The elemental and spectral analysis (UV-Vis, FTIR, 1H-NMR, 13C-NMR and mass spectra) have confirmed the structures of the new synthesized compounds.

4.3. Research for liquid crystals properties [199, 200, 209]

4-(p-ethyl-N-phenylacetamidoxy) azobenzene (1) presents a narrow area of temperatures for existence of nematic phase at cooling.

Fig. 4.38. DSC diagram Fig. 4.39. Nematic phase appearance from isotropic liquid at cooling

4'-methyl-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (2) presents at heating a polymorphism of solid phase, while at cooling a nematic phase, followed by a smectic A phase.

Fig. 4.40. DSC diagram of 4'-methyl-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (2)

(a) (b) (c)

Fig. 4.41. Textures of (a) solid, (b) smectic and (c) nematic phases

(a) (b) Fig. 4.42. Nematic mesophase, characterized by the so-called

droplets texture (a), Schlieren texture (b).

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(a) (b)

Fig. 4.43. Nematic-smectic phase transition (a), phase characterized by the fan texture (b)

4'-trifluoromethyl-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (3) presents at heating a smectic A phase on a very narrow domain and a paramorphic nematic phase.

Fig. 4.44. DSC diagram Fig. 4.45. Paramorphic smectic phase

4'-chloro-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (4) presents nematic and smectic textures.

Fig. 4.46. DSC diagram Fig. 4.47. Texture of N-SA transition 4'-nitro-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (5) presents an exothermal effect

at heating from solid phase and a succession of nematic-smectic A phases at cooling.

Fig. 4.48. DSC diagram Fig. 4.49. Polygonal smectic phase

4'-cyano-4-(p-ethyl-N-phenylacetamidoxy) azobenzene (6) presents a smectic A phase more stable than the compound 2 with a methyl substituent.

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Fig. 4.50. DSC diagram Fig. 4.51. Smectic A phase

4.5. Structure-property correlation (QSAR)

I have correlated the melting points of the six new synthesized azomonoetheramides to the chemical structures represented by different structural properties, generically called descriptors. These structural descriptors (electrostatic, topological, thermodynamic or quanto-molecular), which represent the chemical structures, are in fact an interface between the proper chemical structures and the studied physico-chemical property. The procedure of statistical correlation between these molecular descriptors and property (activity) is realized by multiple linear regressions that is called QSAR (Quantitative Structure Activity Relationship) or QSPR (Quantitative Structure Property Relationship) [210].

4.6. Uses of liquid crystals The liquid crystals phase is probably the most interesting state of the matter, which has

attracted researchers from different areas of science like, chemistry, physics, materials science, engineering, medicine and pharmacy [211,212].

CONCLUSIONS

1. Synthesis of azomoetheramides consisted in the condensation in an alkaline medium of some 4-(phenylazo) phenols, namely: 4-(phenylazo) phenol, 4-(4'-methyl-phenylazo) phenol, 4-(4'-trifluoromethyl-phenylazo) phenol, 4-(4'-chloro-phenylazo) phenol, 4-(4'-nitro-phenylazo) phenol, 4-(4'-cyano-phenylazo) phenol with 4-ethyl-N-chloroacetylaniline, according to a bimolecular nucleophilic substitution mechanism (SN

2). The synthesis of the six new compounds took place in an anhydrous medium. This was

realized with an azeotropic distillation in which an azeotropic mixture water-ethanol-benzene is removed because the azophenoxide synthesis occurred into a benzene-ethanol mixture (1:1 in volume). The synthesis took 5–6 hours, depending on the reagents nature. The reaction products were very nice crystallized, having a colour from yellow to brown, with elevated melting points.

2. The obtaining yields were as high as the solubility at cold of azomonoetheramides in the solvent chosen for recrystallization was lower.

3. The melting points were dependent on the substituents present in the para position from the compounds structure, generally being elevated.

The melting points were determined both in the capillary (sulphuric acid bath) and with the Boetius and Sanyo Gallenkamp devices.

4. Purification of compounds was realized by recrystallization from toluene. In addition, their purity was verified with the gas chromatography (HPGC-MS). Chromatograms showed the presence of a single peak for each compound purified.

5. The elemental analysis occurred with the CHNOS Vario El analyser. 6. All these compounds were physico-chemical characterized (UV-VIS, FTIR, mass,

1H-NMR and 13C-NMR spectra). 7. UV-VIS spectra The absorption bands of medium intensity were recorded at 240–271 nm, they being the

consequence of the presence of some bands of E or B benzene type. Furthermore, intense

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absorption bands were observed. They were given by the K type bands at 347–369 nm. At 408–457 nm were recorded some R type bands of low intensity.

The low intensity bands of R type from VIS were the consequence of the presence of the chromophoric –N=N– group in these compounds.

The π electrons conjugation from the benzene rings led to the appearance of bands of medium intensity, of E or B type, while the K type intense bands were due to the conjugated Ar–N=N–Ar system.

The electronic spectra were recorded with a Jasco V-530 spectrophotometer in the range 200–700 nm. The dioxane solutions (4 . 10-5) were prepared with 24 hours before the spectra recording and kept in a dark place.

8. FTIR spectra The recorded FTIR spectra put into evidence those bands due to vibrations of valence

corresponding to νN=N, 2CHOCAr −−ν unsymmetrical and symmetrical, and νCO-NH amide I and amide II,

but also some bands due to benzene rings, which were characteristic to all new compounds. The FTIR spectra were recorded in potassium bromide tablet (KBr - Merck) with a

Bio-Rad FTS 135 spectrometer in the 3500–400 cm-1 range. 9. Mass spectra Molecular masses were established with accuracy by the help of mass spectra. The fragments that characterize the six compounds were obtained from the molecular ion

by splitting some bonds like O–CH2, CO–NH. Mass spectra were obtained with the HPGC-MS 5890 MD 5971 spectrometer at 70 eV, the

carrier gas being He at 2 ml/min. 10. 1H-NMR and 13C-NMR spectra The proton magnetic resonance spectra have confirmed the structural formula deduced

from the equations of synthesis chemical reactions. The 1H-NMR spectra were recorded with a Varian EM-360 spectrometer at 300 MHz in

CDCl3 and DMSO-d6. The chemical shifts were recorded in function of an internal reference standard, namely tetramethylsilane (TMS).

The 13C-NMR spectra were recorded with a Varian NMR-System 300 spectrometer at 125.7 MHz in CDCl3 and DMSO-d6.

11. Mesomorphic character of the synthesized azomonoetheramides was studied through the following methods: polarizing optical microscopy – POM and differential scanning calorimetry – DSC).

The first method was realized with a microscope with polarized light of IOR MC-5A type, equipped with a heated table at rates of 10oC/min, both for heating and cooling.

The second method consisted in the analysis process of the compounds with a Perkin Elmer DSC-2 type device, having the same heating-cooling rate (10oC/min). Sometimes, for separating the transition peaks, the study took place also at lower rates (5oC/min, 2oC/min). The device was fixed at a sensitivity of 5 mcal/s in an inert atmosphere of argon.

12. Majority of compounds that present liquid crystal properties were found to be smectogen with monotropic behaviour, presenting mostly a solid phase polymorphism. In addition, the presence of nematic phase, generally paramorphic with marmorated texture, was highlighted for some compounds. The so-called droplets texture was noticed in the case of nematic mesophase. It was converted into the Schlieren texture with the temperature decreasing, in the same time with the nematic-smectic phase transition, phase characterized by the fan texture.

13. Moreover, it was realized a correlation between the melting points and the chemical structures represented by different structural properties, generically called descriptors. These structural descriptors (electrostatic, topological, thermodynamic or quanto-molecular), which represent in fact the chemical structures, were an interface between the proper chemical structures and the studied physico-chemical property. The procedure of statistical correlation between these molecular descriptors and property (activity) is realized by multiple linear regressions. It is called QSAR – Quantitative Structure Activity Relationship or QSPR – Quantitative Structure Property

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Relationship. 14. Thermotropic or lyotropic liquid crystals are used as drugs (in the treatment of viral

disorders, like herpes, and also in combating tumours, like different types of cancer), creams, ointments, gels, colloidal dispersions and transdermal patches in the pharmaceutical industry and the cosmetics, due to their very low toxicity.

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