Deuterium NMR Investigation of the Lyotropic Phasesof Alkyl β-Glycoside/D2O Systems.

We have investigated the phase behaviorof four glycosides (βC8OGlc, βC8SGlc, βC10OGlc,βC8OGal) in water and D2O by optical polarizingmicroscopy and deuterium NMR. Previously published phase diagramswere evaluated by deuterium NMR, via monitoring D2O spectra,and confirmed the presence of the hexagonal, bicontinuous cubic, andlamellar phases in these glycosides. We have also shown the presenceof the gel phase in (βC10OGlc) and observed the extensivesupercooling of the lamellar phase to temperatures well below theKraft line. While the main features of the phase diagrams were confirmed,some phase boundaries were found to be slightly different. Magneticallyaligned spectra were also observed for relatively dilute samples forthe hexagonal phase (βC8OGlc and βC8OGal) and the lamellar phase (βC8SGlc and βC10OGlc). The average number of bound water molecules per headgroupin the lamellar phase for the glycosides was determined by the systematicmeasurement of the quadrupolar splitting of D2O over awide range of values of the (glycoside/water) molar ratio. The numberof water molecules bound to the headgroup was found on average tobe about 1.6–1.7 water molecules with no significant differencesin this value for the different glycosides (and over the temperaturerange investigated), indicating that the bound water content is predominatelyinfluenced by the number of hydroxyl groups of the headgroup only.However, this bound water content of only 1.6–1.7 water moleculesper sugar headgroup is surprisingly low, suggesting strong intermolecularinteractions of the OH groups of headgroup sugars. The results arein line with computational results reported earlier for the octyl-β-glucosideand β-galactoside, which show the presence of strong intralayerhydrogen bonding. [ABSTRACT FROM AUTHOR]