Deuterium NMR studies of n-octyl α and β–glucopyranoside liquid-crystalline systems

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 S_A 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.