Research on Zn(II) complexes with diaminodiphenol ligand as carbonic anhydrase model

Chain ligand N, N' - bis(2 - hydroxylbenzyl) - propylenediamine (H2L) and i ts Zn(II) complex (ZnL) were synthesized and characterized by elemental ana lysis, IR and H-1 MMR, By pH titration at 25 +/- 0.1 degrees C and I = 0.1 mol . dm(-3)(KNO3), protonation constants of the ligand and equilibria cons tants of Zn(II) complexation with the ligand have been determined. Modes of the ligand coordination to Zn(II) were discussed, and the dissociation con stant for the phenoxyl in complex ZnHL+ was obtained. The kinetics of p - n itrophenyl acetate (NA) hydrolysis catalyzed by the complexes as carbonic a nhydrase models was determined spectrophotometrically at 25 +/- 0.1 degrees C and I = 0.1 mol . dm(-3) (KNO3) in 10%(v/v) CH3CN at pH 5.5 similar to 9 .0 (50mmol . dm(-3) buffers), and the second - rate constants for NA hydrol ysis were obtained. The experimental results indicate that the dissociation constant pKa value for the phenoxyl in complex ZnHL+ is 6.83. The pH - k(N P) profile does not exhibit a Sigmoidal curve and the k(NP) reaches a maxim um point around neutral pH. The complex ZnHL+ has very strong catalytic abi lity around neutral pH following the double - catalysis mechanism, and ther efore is a good carbonic anhydrase model.