Kinetics and Mechanism of Hydrolysis of P-Nitrophenyl Picolinate by Transition-Metal Hydroxamate Containing Benzo-15-Crown-5

Abstract

Two hydroxamic acids HL 1 and HL 2 containing benzo-15-crown-5 have been synthesised and their transition metal (Cu 2+ , Co 2+ , Zn 2+ , Mn 2+ ) complexes have been employed as models to mimic hydrolase in catalytic hydrolysis of p-nitrophenyl picolinate(PNPP). The kinetics and mechanism of PNPP hydrolysis have been investigated. A kinetic mathematical model of PNPP cleavage catalysed by these complexes is proposed. The effects of reactive temperature and metal ion in complexes on the rate of catalytic PNPP hydrolysis are discussed. The results show that the transition-metal hydroxamates (ML 1 2 , ML 2 2 , M= Cu 2+ , Co 2+ , Zn 2+ , Mn 2+ ) containing benzo-15-crown-5 exhibit high activity in catalytic PNPP hydrolysis. The rate of PNPP hydrolysis catalysed by these complexes increased along with the increase of pH values of the buffer solution; the catalytic activity of different metal ions in complexes of the same ligand deceased in the order Cu 2+ > Co 2+ >Zn 2+ > Mn 2+ ; the pseudo-first-order-rate constants of PNPP hydrolysis catalysed by the complexes are over 1000 times more than that of spontaneous hydrolysis of PNPP.