BG Summer Research Poster Final
1
Introduction Liquid crystals (LCs) are a state of matter that is an intermediate between the solid and liquid phases. They have anisotropic optical properties and the molecules can be oriented in the presence of external forces. Typically, molecules that can form liquid crystal phases –or mesophases– are rod-like and characterized by a rigid core and a flexible chain. All mesophases have a high orientational order, which allows the molecules to be anisotropic, and have a low positional order. There are several types of thermotropic LC phases (Figure 1). The self-assembly and temperature ranges of LC phase transitions are determined by molecular shape and intermolecular forces such as hydrogen bonding, ionic bonding and Van der Waals forces. 1,2 Amphiphilic mesogens, which are typically molecules that are capable of forming hydrogen-bonding networks, tend to form smectic LCs. Cyclodextrins (CDs) are cyclic molecules consisting of 6-8 glucose units and are structurally shaped like a truncated cone with a varying diameter, depending on the number of glucose units. A cavity is present within the molecule, which allows it to form inclusion complexes with hydrophobic guests in aqueous solutions. 3,4 The β-CD’s have seven glucose units with 7 primary hydroxyl groups that occupy the narrow end of the cone, and 14 secondary hydroxyl groups located at the wider end of the cone. Synthesis with CDs can be difficult because of the multiple reactive sites which can lead to low yields and difficult purification. Previous Work In a previous study, it was found that CD amphiphiles needed to establish a sufficiently strong hydrogen-bonding network in order for the molecules to drive themselves to self-assemble to form an LC phase. Various derivatives were modified based on a baseline derivative of n-octadecylthio β-CD ( 1) (Figure 2) which contains 2 hydroxyl groups per glucose unit, for a total of 14 in the whole molecule. Recent studies have discovered the molecule exists in the smectic phase from 57 to 280 °C on heating. Ultimately, upon modifying the secondary face and interfering in the hydrogen-bonding network, the clearing temperature was greatly affected while the melting temperature was not as greatly affected. 5 Acknowledgements This project was funded by the University of Puget Sound Chemistry Department and the University Enrichment Committee Special thanks to Eric Scharrer for allowing us the use of his DSC/TGA and POM Synthesis of cyclodextrin derivatives and the investigation of their liquid crystalline properties Isabella Graves and Sandra Ward Department of Chemistry, University of Puget Sound, Tacoma WA References: (1) Jeffrey, G. A. Accounts Chem Res 1986, 19, 168 (2) Singh, M. K.; Jayaraman, N.; Rao, D. S. S.; Prasad, S. K. Chem Phys Lipids 2010, 163, 580 (3) J.L. Atwood, J.-M. L. Comprehensive Supramolecular Chemistry; Pergamon Oxford, U.K, 1996; Vol. 3 (4) Duchene, D. 1991 (5) Ward, S.; Calderon, O; Zhang, P.; Sobchuk, M.; Keller, S. N.; Williams, V. E.; Ling, C. C. J. Mater. Chem. C. 2014, 2.4928 Figure 2: Derivatives Synthesized in Previous Work Figure 3: Target Product: Compound (11) Results Initially, a synthesis was carried out to produce a brominated β-cyclodextrin (7). The bromine was used as a leaving group, which was displaced by the azide in order to protect the C6 position during the acylation of the C2 and C3 positions. Both bromine and NBS were successful reagents in producing the brominated CD. The bromine was successfully displaced by the azide to produce a pure azido compound. The acylation was carried out with a hexanoic anhydride as well as a lauroyl chloride (C12). The hexanoic anhydride successfully acylated the CD and formed a semi pure product, however, the lauroyl chloride was not successful. The optimization of the reduction reaction with a palladium catalyst is still underway. Scheme 3: Overall Synthesis O O O O O H 2 N O O O O NH 2 O O O O NH 2 O O O O NH 2 O O O O NH 2 O O O O H 2 N O O O H 2 N O O O O O O O O O O O O O O Project Goals The initial goal of this project is to successfully synthesize a 6 carbon derivative of β-cyclodextrin with an amine in the primary hydroxyl group position. This can be accomplished by introducing a good leaving group (halogen) in order for a good nucleophile to be installed (azide). The secondary hydroxyl groups are more hindered due to steric crowding and twice as many reactive sites. Therefore, the azide on the primary face will serve as a protecting group while acylating the secondary hydroxyl groups before reducing the azide to an amine. The amine will serve as the hydrophilic group at the primary face and the hydrophobic group will be kept at the secondary face. I am interested in how this will affect the physical properties, such as the phase change temperatures and liquid crystalline characteristics. Future Work In addition to compound 11 we are also interested in synthesizing and characterizing derivatives with longer hydrophobic chains such as C-12 and possibly a C-14 derivative. The LC properties of our final compounds will be characterized by the temperature and enthalpy of the phase changes by differential scanning calorimetry (DSC) as well as using polarized optical microscopy (POM). Once the LC properties are characterized we are interested in inclusion complexes with guest molecules in order to observe any possible changes to the physical properties of the CDs by non-covalently making new compounds, without a lengthy synthesis. 5-amino-1-naphthol (Figure 5) has been chosen as a guest molecule due to its hydrogen bonding abilities. We predict the guest may disrupt the hydrogen bonding between the smectic layers of the host, similar to how the methyl groups decreased the hydrogen bonding network and a lower melting temperature was observed. No CD inclusion complexes have been reported to be LC in literature and we want to explore the results of these inclusion complexes to determine if guest molecules can allow LC properties. OH NH 2 Figure 5: 5-amino-1-napthol Figure 1: Liquid Crystalline Phases O SC 18 H 37 HO O MeO 7 O SC 18 H 37 HO O AllylO 7 O SC 18 H 37 HO O BnO 7 O SC 18 H 37 OH O OH 7 O SC 18 H 37 MeO O MeO 7 2 3 4 5 n-octadecylthio β-CD per-2,3-di-O-methylated β-CD per-2-O-methylated β-CD per-2-O-benzylated β-CD per-2-O-allylated β-CD Sm 57-280 °C No LC properties Sm 68-110 °C No LC properties No LC properties 1 O OH HO O OH 7 6 O Br HO O OH 7 NBS, PPh 3 DMF O N 3 HO O OH 7 NaN 3 DMF O N 3 O O O 7 O O Hexanoic Anhydride O NH 2 O O O 7 11 O O Pd/C H 2 7 (100%) 8 (70%) 10 (74%) Figure 4: H-NMR of product 10
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Transcript of BG Summer Research Poster Final
Introduction Liquid crystals (LCs) are a state of matter that is an intermediate between the solid and liquid phases. They have anisotropic optical properties and the molecules can be oriented in the presence of external forces. Typically, molecules that can form liquid crystal phases –or mesophases– are rod-like and characterized by a rigid core and a flexible chain. All mesophases have a high orientational order, which allows the molecules to be anisotropic, and have a low positional order. There are several types of thermotropic LC phases (Figure 1). The self-assembly and temperature ranges of LC phase transitions are determined by molecular shape and intermolecular forces such as hydrogen bonding, ionic bonding and Van der Waals forces.1,2 Amphiphilic mesogens, which are typically molecules that are capable of forming hydrogen-bonding networks, tend to form smectic LCs. Cyclodextrins (CDs) are cyclic molecules consisting of 6-8 glucose units and are structurally shaped like a truncated cone with a varying diameter, depending on the number of glucose units. A cavity is present within the molecule, which allows it to form inclusion complexes with hydrophobic guests in aqueous solutions.3,4 The β-CD’s have seven glucose units with 7 primary hydroxyl groups that occupy the narrow end of the cone, and 14 secondary hydroxyl groups located at the wider end of the cone. Synthesis with CDs can be difficult because of the multiple reactive sites which can lead to low yields and difficult purification. Previous Work In a previous study, it was found that CD amphiphiles needed to establish a sufficiently strong hydrogen-bonding network in order for the molecules to drive themselves to self-assemble to form an LC phase. Various derivatives were modified based on a baseline derivative of n-octadecylthio β-CD (1) (Figure 2) which contains 2 hydroxyl groups per glucose unit, for a total of 14 in the whole molecule. Recent studies have discovered the molecule exists in the smectic phase from 57 to 280 °C on heating. Ultimately, upon modifying the secondary face and interfering in the hydrogen-bonding network, the clearing temperature was greatly affected while the melting temperature was not as greatly affected.5
Acknowledgements This project was funded by the University of Puget Sound Chemistry Department and the University Enrichment Committee Special thanks to Eric Scharrer for allowing us the use of his DSC/TGA and POM
Synthesis of cyclodextrin derivatives and the investigation of their liquid crystalline properties
Isabella Graves and Sandra Ward
Department of Chemistry, University of Puget Sound, Tacoma WA
References: (1) Jeffrey, G. A. Accounts Chem Res 1986, 19, 168 (2) Singh, M. K.; Jayaraman, N.; Rao, D. S. S.; Prasad, S. K. Chem Phys Lipids 2010, 163, 580 (3) J.L. Atwood, J.-M. L. Comprehensive Supramolecular Chemistry; Pergamon Oxford, U.K, 1996; Vol. 3 (4) Duchene, D. 1991 (5) Ward, S.; Calderon, O; Zhang, P.; Sobchuk, M.; Keller, S. N.; Williams, V. E.; Ling, C. C. J. Mater. Chem. C. 2014, 2.4928
Figure 2: Derivatives Synthesized in Previous Work
Figure 3: Target Product: Compound (11)
Results Initially, a synthesis was carried out to produce a brominated β-cyclodextrin (7). The bromine was used as a leaving group, which was displaced by the azide in order to protect the C6 position during the acylation of the C2 and C3 positions. Both bromine and NBS were successful reagents in producing the brominated CD. The bromine was successfully displaced by the azide to produce a pure azido compound. The acylation was carried out with a hexanoic anhydride as well as a lauroyl chloride (C12). The hexanoic anhydride successfully acylated the CD and formed a semi pure product, however, the lauroyl chloride was not successful. The optimization of the reduction reaction with a palladium catalyst is still underway.
Scheme 3: Overall Synthesis
O
O
O O
OH2N
OO O
O
NH2O
O
O
O
NH2
O
O
O
O NH2
O
OO
O
NH2
OOO O
H2N O
O
OH2N
O
O
O
OO
OO
O
O
O
OO O
O
Project Goals The initial goal of this project is to successfully synthesize a 6 carbon derivative of β-cyclodextrin with an amine in the primary hydroxyl group position. This can be accomplished by introducing a good leaving group (halogen) in order for a good nucleophile to be installed (azide). The secondary hydroxyl groups are more hindered due to steric crowding and twice as many reactive sites. Therefore, the azide on the primary face will serve as a protecting group while acylating the secondary hydroxyl groups before reducing the azide to an amine. The amine will serve as the hydrophilic group at the primary face and the hydrophobic group will be kept at the secondary face. I am interested in how this will affect the physical properties, such as the phase change temperatures and liquid crystalline characteristics.
Future Work In addition to compound 11 we are also interested in synthesizing and characterizing derivatives with longer hydrophobic chains such as C-12 and possibly a C-14 derivative. The LC properties of our final compounds will be characterized by the temperature and enthalpy of the phase changes by differential scanning calorimetry (DSC) as well as using polarized optical microscopy (POM). Once the LC properties are characterized we are interested in inclusion complexes with guest molecules in order to observe any possible changes to the physical properties of the CDs by non-covalently making new compounds, without a lengthy synthesis. 5-amino-1-naphthol (Figure 5) has been chosen as a guest molecule due to its hydrogen bonding abilities. We predict the guest may disrupt the hydrogen bonding between the smectic layers of the host, similar to how the methyl groups decreased the hydrogen bonding network and a lower melting temperature was observed. No CD inclusion complexes have been reported to be LC in literature and we want to explore the results of these inclusion complexes to determine if guest molecules can allow LC properties.
OH
NH2
Figure 5: 5-amino-1-napthol
Figure 1: Liquid Crystalline Phases
OSC18H37
HO
OMeO
7
OSC18H37
HO
OAllylO
7
OSC18H37
HO
OBnO
7
OSC18H37
OH
OOH
7
OSC18H37
MeO
OMeO
72 3
4 5
n-octadecylthio β-CD per-2,3-di-O-methylated β-CD per-2-O-methylated β-CD
per-2-O-benzylated β-CDper-2-O-allylated β-CD
Sm 57-280 °C No LC properties Sm 68-110 °C
No LC properties No LC properties
1
O
OH
HO
OOH
7
6
O
Br
HO
OOH
7
NBS, PPh3
DMF
O
N3
HO
OOH
7
NaN3
DMF
O
N3
O
OO
7O
O
Hexanoic Anhydride
O
NH2
O
OO
7
11
OO
Pd/C
H2
7 (100%) 8 (70%)
10 (74%)
Figure 4: H-NMR of product 10
