Deuterium NMR studies ofn-octyl α andβ–glucopyranoside liquid-crystalline systems

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Abstract
Deuterium NMR measurements have been performed on mixtures of n-octyl-α-D-glucopyranoside (αOG) and n-octyl-β-D-glucopyranoside (βOG) with deuteriated water or benzene. The phase diagrams, at high αOG concentrations (lamellar phases), are similar to those reported previously for the β anomer. Deuterium NMR measurements of D2O in mixtures with αOG or βOG at lower concentrations show the existence of additional hexagonal and isotropic (including possibly cubic) phases. Some differences were noted between the phase diagrams of α and βOG at these concentrations. The sign of the diamagnetic anisotropy, Δ χ , of the SA lamellar phase of αOG/D2O and αOG/C6D6 was found to be negative. Slow exchange between the sugar hydroxyl deuterons and water in αOG enabled us to measure their quadrupolar splittings at different temperatures. Using a simple model, where rotation of the polar head as a rigid unit around a single axis is assumed, we have calculated the direction of this axis relative to a molecular axis. The results show that this axis is approximately parallel to the C4[sbnd]C8 axis.