Interglycolipid membrane interactions: pH-dependent aggregation of nonionic synthetic glycolipid vesicles

Large unilamellar vesicles composed of a nonionic synthetic glycolipid, 1,3 -di-O-phytanyl-2-O-(beta-D-maltotriosyl) exhibited a pH-dependent aggregati on-disaggregation process; vesicle aggregation occurred in a lower pH regio n and vesicle disaggregation occurred in a higher pH region. This process w as almost reversible and the aggregation threshold pH increased as NaCl con centration increased. Electrophoretic mobility measurements revealed that t he glycolipid vesicles are negatively charged in the range pH 1.6-13. The c hange in zeta-potentials as functions of pH and NaCl concentration could be well described by the Gouy-Chapman expression of the surface charges with an assumption that the interfacial charges arise from the "adsorption" of O H- at the vesicle-water interface and the dissociation of hydroxyl groups o f the sugar headgroup in a higher pH regime (>pH 10). The pH-dependent aggr egation process was reasonably well described by the classical DLVO theory. Thus, the double-layer repulsive forces appear to be a major factor in sta bilizing the glycolipid vesicle suspension. (C) 2000 Academic Press.