Hydrolytic Dephosphorylation of p-Nitrophenyl Diphenyl Phosphate by Alkyl Hydroxamate Ions

The kinetics of the hydrolysis of p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions (R'(CO)N(RO-) such as octanohydroxamate (OHA(-)) and decanohydroxamate (DHA(-)) was investigated in dioctadecyldimethylammonium chloride (DODAC) and didodecyldimethylammonium bromide (DDAB) vesicles. The physicochemical properties of these surfactants were studied by conductivity and fluorescence measurements at 300K. The hydrolysis of PNPDPP was studied in a vesicular system by using hydroxamate ions (OHA(-) and DHA(-)) at 300K. The different catalytic effects of hydroxamate ions for the hydrolysis of PNPDPP in the vesicles were determined. All reactions followed pseudofirst-order kinetics. The reactivity of DHA(-) was found to be higher than that of OHA(-) in the vesicular system toward the cleavage of phosphate ester. Further, the binding constants (K) and free energy change (G) for the associations of PNPDPP with DODAC and DDAB vesicles were determined spectrophotometrically as well as from the Benesi-Hildebrand (B-H) plots. The pseudophase model was applied for the quantitative treatment of the kinetic data in the vesicle systems.