Catalytic hydrolysis of p-nitrophenyl picolinate by copper(II) and zinc(II) complexes of N-(2-deoxy-β-D-glucopyranosyl-2-salicylaldimino)

D-glucosamine Schiff base N-(2-deoxy-β-D-glucopyranosyl-2-salicylaldimino) and its Cu(II) and Zn(II) complexes were synthesized and characterized. The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by ligand and complexes was investigated kinetically by observing the rates of the release of p-nitrophenol in the aqueous buffers at 25°C and different phs. The scheme for reaction acting mode involving a ternary complex composed of ligand, metal ion, and substrate was established and the reaction mechanisms were discussed by metal-hydroxyl and Lewis acid mechanisms. The experimental results indicated that the complexes, especially the Cu(II) complex, efficiently catalyzed the hydrolysis of PNPP. The catalytic reactivity of the Zn(II) complex was much smaller than the Cu(II) complex. The rate constant k_N showing the catalytic reactivity of the Cu(II) complex was determined to be 0.299 s^-1 (at pH 8.02) in the buffer. The pK_a of hydroxyl group of the ternary complex was determined to be 7.86 for the Cu(II) complex.