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

Abstract

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 1H 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.