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

Two Co-II complexes with aza crown ether substituted salicylaldimine Schiff base, CoL21 and CoL22, 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 CoL23, the bis(aza crown ether)s Co-II complexes CoL21 and CoL22 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.