LYOTROPIC PHASE-BEHAVIOR OF N-OCTYL-1-O-BETA-D-GLUCOPYRANOSIDE AND ITS THIO DERIVATIVE N-OCTYL-1-S-BETA-D-GLUCOPYRANOSIDE

We have determined the phase diagrams of n-octyl- 1-0-beta-D-glucopyra noside and its thio derivative n-octyl- 1 -S-beta-D-glucopyranoside in water, using polarizing microscopy and X-ray diffraction. Comparison of the two compounds gives us an insight into the complex interactions which determine phase behaviour. Both compounds form type I (normal) lyotropic phases, with the adoption of a fluid lamellar phase at low h ydrations and a cubic phase at higher hydrations. However, the hexagon al phase observed in the n-octyl-1-O-beta-D-glucopyranoside/water syst em adjacent to the micellar solution is suppressed in the n-octyl-1-S- beta-D-glucopyranoside/water system. In addition, we have found that i n both systems the cubic phase spontaneously grows into large monodoma ins, as revealed by faceting of entrapped air bubbles. Indexing of the monodomain diffraction patterns shows that in both cases the space gr oup of the cubic phase is Ia3d (no. 230).