Double-chain, double-head group surfactants, 1, were prepared by dispersal of a 1:1 mixture of diastereomeric diacids 3a (r-2-(carboxymethyl)-2,t-5-dipentadecyl-c-4-(carboxymethyl)-1,3-dioxolane) and 3b(r-2-(carboxymethyl)-2,c-5-dipentadecyl-t-4-(carboxymethyl)-1,3-dioxolane) into pH 9.2 and 10.7 carbonate buffers. The resultant small unilamellar vesicles were characterized by H-1 NMR spectroscopy, dynamic laser light scattering, differential scanning calorimetry, and gel filtration chromatography. The vesicles at pH 9.2 were larger and had a greater phase transition temperature than those at pH 10.7. These differences were attributed to a greater fraction of carboxyl groups among the carboxyl and carboxylate head groups at the lower pH.