To model active site structure of carbonic anhydrase (CA), we synthesized a series of metal complexes supported by tris (substituted pyrazolyl) hydroborato ligands [T~p^R^,^R^1]MX[R=Ph, 2'- thie, Me; R^1=Ph, 2'-thie, Me; M=Co, Ni, Cu, Zn, Cd; X=Cl, NO~3, CH~3COO]. These complexes were all characterized by elemental analysis, IR, and ^1H NMR spectroscopy. Activity of five representatives selected from these complexes in catalyzing reversible hydration reaction of CO~2 were investigated by the stopped-flow technique. It was showed that the reaction had general dynamic characteristics of enzyme-catalyzed reaction. The activity varied with the pH of reaction system, the structure (especially electric structure of metal ion) and concentration of the model complexes, along with some other important results were obtained. The activation energy of dehydration reaction in the presence and absence of model complexes were calculated, which may interpret well that the higher reaction rate essentially resulted from the decrease in activation energy of the reaction.

Key words: CARBONIC ANHYDRASE, MODEL COMPOUND, CATALYTIC BEHAVIOUR, PYRAZOLE P, THIOPHENE P, COBALT COMPLEX, NICKEL COMPLEX, COPPER COMPLEX, ZINC COMPLEX, CADMIUM COMPLEX