Inhibition of Ester Hydrolysis by a Lipid Vesicle Membrane

Article abstract of DOI:10.1021/jo00159a020

The second-order rate constants for the imidazole- or hydroxide-mediated hydrolysis of <3-nitro-4-(palmitoyloxy)phenyl>trimethylammonium iodide (1), <11-(4-nitrocarbophenoxy)undecyl>trimethylammonium bromide (2), and <5-nitro-2-(palmitoyloxy)benzyl>trimethylammonium halide (3) were obtained in the absence and presence of phospholipid vesicles.The rate data were obtained under conditions where only bound ester contributed to the kinetics.In general, small retardations of the hydrolysis rates were effected by binding of the substrates to lipid bilayers with cholinephosphate headgroups.The imidazole rates appear to be more sensitive to the depth within the bilayer of the reaction center.The relative rates also can be interpreted in terms of an intramolecular electrostatic acceleration of the hydroxide rate for 3 in aqueous solution, which is inhibited upon binding of this amphiphilic ester to the lipid bilayer membrane.