pH and salt-induced reversible aggregation of nonionic synthetic glycolipid vesicles

Salt and pH can induce reversible aggregation of vesicles composed of a nonionic synthetic glycolipid, 1,3-di-o-phytanyl-2-o-(β-maltotriosyl) glycerol. The aggregation of the vesicles appears reversible with respect to a change in the pH value of the medium as seen from the reversible change in the turbidity. It was also found that in an acidic region (pH 4–6), the size of the aggregated vesicles are well above 1000 nm, an indication of vesicle aggregation. But in an alkaline region (pH 8–10), the sizes are 110–130 nm, close to their original size of 100–110 nm, which strongly suggests the reversible disaggregation and also confirms the lack of vesicle fusion. The ζ-potentials of vesicles are measured in the presence of NaCl with the pH changes of the vesicle suspension. It is seen that the ζ-potential of vesicles changes with the pH value. The surface charges of the Mal3(Phyt)2 vesicles arise from two independent mechanisms; one is excess ‘adsorption’ of OH− ions at the vesicle–water interfaces and the other is dissociation of hydroxyl groups in a high pH region (pH >11). The changes of the surface charges are thought to be the major factor which induces the aggregation and disaggregation of this nonionic glycolipid vesicle.