Nucleophilic Cleavage of Phosphate Triesters in Dialkylammonium Bilayer Membranes

Article abstract of DOI:10.1246/bcsj.54.2072

A study was carried out on the reaction of p-nitrophenyl phosphates with hydroxamate nucleophiles in water in the presence of dialkylammonium bilayer membranes.With ethyl bis(p-nitrophenyl) phosphate, clean second-order kinetics was observed for all the hydroxamate nucleophiles, two equivalents of p-nitrophenol being released in most cases.In contrast, a complex kinetics was observed for octadecylbis(p-nitrophenyl)phosphate.The second cleavage process of this long-chain substrate by a long-chain hydroxamate was affected by the fluidity of the matrix membrane, an inflection region being present in the Arrhenius plots near the phase transition temperature (T_c) of the 2C16N⁺2C1 membrane.The activation energy was 14 and 21 kcal/mol at temperatures above and below T_c, respectively.Similar changes in the activation energy had been observed for decarboxylation and proton abstraction.