Abstract:

The protonation constant of TPA and, in its 1:2 (Zn(II):L) complex, the deprotonation constant of H2O coordinated to Zn(II) have been determined by pH titration at 25±0.1℃, I=0.1 mol•dm-3 KNO3. They are 4.29 and 7.8, respectively. It is worthy to be noted that the H2O bound to Zn(II) could deprotonate easily near physiology pH. A kinetic study of 4-nitrophenyl acetate(NA) hydrolysis by Zn(II)(TPA)2•H2O complex in 10%(v/v) CH3CN at 25±0.1℃, I=0.1 mol•dm-3 NaClO4, and pH range 6~9(20mmol•dm-3 Tris buffer)，has been carried out. The maximum value of second-order rate constant k((mol•dm-3)-1•s-1) obtained is 3.32×10-2. Thus, Our present model study shows that, like the Zn(II)-enzymes, the Zn(II)-bound OH- in complex can act as a good nucleophile agent to the carbonyl carbons, the Zn(II) complex of TPA is a good model for carbonic anhydrase.

Key words: Carbonic anhydrase, Model, Nucleophile agent, Rate constant