Double-Chain Surfactants with Two Carboxylate Head Groups That Form Vesicles

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 1 H 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.