A Hydrolytic Reporter of Cu(II) Availability in Artificial Liposomes

Article abstract of DOI:10.1021/jo00063a020

The dioctadecyl ammonium surfactant 1, functionalized with a p-nitrophenyl ester of picolinic acid has been synthesized and its hydrolysis in covesicular blends of nonfunctional surfactants dihexadecyldimethylammonium bromide, 3, dioctadecyldimethylammonium bromide, 4, and racemic 1,2-bis(palmitoyloxy)-3-(trimethylammonium)propyl bromide, 5, studied after addition of Cu(II) ions pH=5.0 and different temperatures.The cleavage of 1 gives the p-nitrophenoxide surfactant 2, which shows a strong absorption band at 400 nm.Clear biphasic kinetics were observed for all vesicular systems at a temperature below the gel-liquid crystal phase transition temperature (T_c) of the membrane; the first, faster process (ca. 60percent ester cleaved) was associated with the Cu(II)-catalyzed hydrolysis of the exovesicular ester; the slower one (the remaining ca. 40percent of the ester cleaved) was associated with the uncatalyzed hydrolysis of the endovesicular ester.Above T_c only a monoexponential process was observed.Variable temperature experiments allowed one to conclude that the cationic vesicles studied are totally impermeable to Cu(II) ions either below or above their T_c which controls the rate of the transbilayer movements of the lipids.