Abstract
The liquid crystalline behaviour of methyl-6-O-(n-dodecanoyl)--D-glucopyranoside, 1, has been characterised using X-ray diffraction and variable temperature Fourier transform infrared (FTIR spectroscopy). 1 exhibits a monotropic interdigitated smectic A phase consisting of bilayers in which the alkyl chains are overlapped. The crystal-isotropic transition is accompanied by a pronounced decrease in the strength of the hydrogen bonding network involving the sugar groups resulting in a marked change in the environment of the alkyl chains. The isotropic phase consists of disordered smectic-like domains stabilised via hydrogen bonding between the sugar groups. At the transition to the smectic A phase, a subtle change in hydrogen bonding is observed which is manifested by a change in the temperature dependence of the OH stretching peak position in the FTIR spectrum. On crystallisation, the strong hydrogen bonding network is re-established accompanied by a change in the conformational distribution of the alkyl chains. A model is proposed in which a combination of hydrogen bonding (enthalpic effects) and conformational arrangements (entropic effects) promotes initially the formation of smectic-like domains in the isotropic phase and subsequently stabilises the smectic A phase by inhibiting the microphase separation leading to the crystal phase.
Original language | English |
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Pages (from-to) | 1817-1827 |
Number of pages | 11 |
Journal | Liquid Crystals |
Volume | 40 |
Issue number | 12 |
Early online date | 1 Nov 2013 |
DOIs | |
Publication status | Published - 1 Dec 2013 |
Keywords
- carbohydrate liquid crystal
- smectic A phase
- variable temperature FTIR
- hydrogen bonding
- transform infrared-spectroscopy
- liquid-crystalline glycolipids
- beta-D-glucopyranoside
- homologous series
- phase-transitions
- sugar glasses
- IR-spectrum
- D-glucose
- chain
- mesomorphism