DOUBLE-CHAIN SURFACTANTS WITH 2 CARBOXYLATE HEAD GROUPS THAT FORM VESICLES

Double-chain, double-head group surfactants, 1, were prepared by dispe rsal of a 1:1 mixture of diastereomeric diacids 3a -5-dipentadecyl-c-4 -(carboxymethyl)-1,3-dioxolane) and -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, a nd gel filtration chromatography. The vesicles at pH 9.2 were larger a nd had a greater phase transition temperature than those at pH 10.7. T hese differences were attributed to a greater fraction of carboxyl gro ups among the carboxyl and carboxylate head groups at the lower pH.