Kinetic studies of manganese(III) and cobalt(II) Schiff base complexes as synthetic hydrolases for p-nitrophenyl picolinate in CTAB surfactant micellar solution

Abstract

Four symmetrical bis-Schiff bases with either benzo-10-aza-crown ether or morpholino pendants and their Mn(III) and Co(II) complexes have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in buffered CTAB micellar solution. A kinetic model of PNPP cleavage catalysed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit higher catalytic activity in the buffered CTAB micellar solution and the rate increases with pH of the buffer at 25 °C. The complexes containing two crown ether group exhibit higher catalytic activities than their crown-free analogues, and the catalytic activity of the phenyl-bridged Schiff base complex is larger than that of the ethyl-bridged Schiff base complex for the same substituents and metal. The catalytic activity of the manganese(III) complex exceeds that of the cobalt(II) complex in catalysing hydrolysis of PNPP under the same ligand.