PH EFFECTS ON PROPERTIES OF DIHEXADECYL PHOSPHATE VESICLES

Vesicle size (S) and bilayer structure and function as well as colloidal stability were assessed in large dihexadecyl phosphate (DHP) vesicles on the basis of turbidity spectra, phase transition temperature (T(c)) determinations, water permeation rates (upsilon-s), and initial flocculation rates (upsilon-0), respectively, for a range of NaCl concentration (C) or pH. S, T(c), upsilon-s, and log 1/upsilon-0 display a bell-shaped profile as a function of pH for a given C. In water, the maximal S, T(c), upsilon-s, and log 1/upsilon-0 values occur at pH 6.0-7.0, i.e., around the apparent pK value of the phosphate polar head at the membrane/water interface. The results emphasize the importance of the extent of surface hydration in determining the total surface area of the dispersion and thereby the vesicle size and phase behavior.