Cobalt(II)Schiff base complexes bearing aza crown ether pendants as synthetic hydrolase catalyzing PNPP hydrolysis

摘要

Two Co~(II)complexes with aza crown ether substituted salicylaldimine Schiff base,CoL_2~1 and CoL2,have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of a carboxylic ester.The specific change of u.v.-vis.absorption spectra of the hydrolytic reactive systems has been observed,which indicates that key intermediates are formed by PNPP and Co~(II)complexes.The kinetics and the mechanism of PNPP hydrolysis have been investigated.The kinetic mathematical model for PNPP cleavage catalyzed by the Co~(II)complexes has been proposed.The results show that,compared with the crown-free analogous CCoL_2~3 ,the bis(aza crown ether)s Co~(II)complexes CoL_2~1 and CoL_2~2 exhibit high activity in the PNPP catalytic hydrolysis;the rate of the PNPP hydrolysis catalyzed by the complexes increases with the increase of pH of the buffer solution;the pseudo-first-order rate constants(K_(ob))of PNPP hydrolysis catalyzed by the complexes is 1000 times more than that of spontaneous hydrolysis of PNPP.