Institution: | a Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, 224 Cary Hall, Buffalo, NY, USA b Faculty of Pharmaceutical Sciences, Science University of Tokyo, Shinjuku-ku, Tokyo, Japan |
Abstract: | Interaction and aggregation of acidic phospholipid (phosphatidylserine) vesicles were studied with variation of cation species and their concentrations in vesicle suspensions, and of vesicle sizes. Aggregation was determined by measuring turbidity of vesicle suspension. The experimental results of aggregation of vesicles induced by monovalent cations (Na+, K+, Cs+ and TMA+) were explained well in terms of the interaction energy of two interacting vesicles using the ordinary Derjaguin–Landau–Verwey–Overbeek (DLVO) theory for both small and large lipid vesicles. However, the experimental results of aggregation of vesicles induced by divalent cations (Ca2+, Mg2+ and Ba2+) were not explained by the ordinary DLVO theory. In order to explain the experimental results of these vesicle aggregation phenomena, it was necessary to modify the theory by including hydration interaction energies which are due to hydrated water at membrane surfaces, and their magnitude and sign depend upon the nature (hydrophobicity) of the membrane surface. |