KINETICS AND MECHANISM OF HYDROLYSIS OF UREA AND N, N′-DIACETYL UREA IN PRESENCE OF COBALT(II), COPPER(II), ZINC(II)-SCHIFF BASE COMPLEXES.

Solid aquo CoII, CuII and ZnII complexes of Schiff bases derived from amino acids and salicylaldehyde had been prepared, characterized and used as model enzymes of Urease. Using a pH-stat method, the kinetics of acid hydrolysis of urea and its derivative N,N′-diacetyl urea in the presence of the complexes had been studied in pH range of 4.91?6.19 at 300C and I = 0.10 mol dm-3 (KNO3). It was found that the hydrolytic reactions followed first order kinetics (pseudo-unimolecular) with respect to urea or N,N′-diacetyl urea concentration. The complexes enhanced the rate of hydrolysis markedly; the values of the second-order rate constants (kH) being 106 times greater than those found in the absence of the catalysts. Comparison showed that the complexes acted as better catalysts for urea [kH = (0.79?2.34)?102 dm3 mol-1 s-1] than N,N′-diacetyl urea [kH = (0.36?1.19)?102 dm3 mol-1 s-1] towards the hydrolysis reactions. The catalytic performance of the complexes was 30-100% greater in urea than in N,N′-diacetyl urea. The proposed mechanism involved the formation of mixed ligand chelate complex by replacement of two coordinated labile water molecules by NHR′ (R′= H or COCH3) and carbonyl group of urea or N,N′-diacetyl urea followed by nucleophilic and electrohilic attacks by H2O and H+ respectively. The average half-life period (t?) ranges for urea and N,N′-diacetyl urea hydrolysis were 450?676 and 529?807 seconds respectively. [CoII(Gly)(Sal)(H2O)3] was found as the most efficient catalyst towards urea hydrolysis reactions. This investigation would establish the potential catalytic role of the complexes in hydrolyzing urea and its derivative, and thereby would throw more light on hydrolytic mechanism of urease enzyme.