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Kinetics and mechanism of the catalytic dehydration of HCO 3 − by zinc(II) complexes of tripod ligands
Author(s) -
Ge Qingchun,
Guo Yanhe,
Lin Hai,
Lin Huakuan,
Zhu Shourong
Publication year - 2004
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.10190
Subject(s) - chemistry , dehydration , deprotonation , zinc , kinetics , catalysis , titration , reaction rate constant , aqueous solution , medicinal chemistry , inorganic chemistry , carbonic anhydrase ii , carbonic anhydrase , organic chemistry , ion , biochemistry , physics , quantum mechanics , enzyme
The kinetics of the catalyzed dehydration of HCO 3 − by zinc(II) containing tripod complexes has been studied at 25°C using the stopped‐flow technique. The direction of reaction curve was changed in aqueous solution when the pH of the solution was greater than 7.5. The pH‐profile of rates of the dehydration reactions indicates that only the aqua complex catalyzes the dehydration of HCO 3 − via a ligand substitution process. The second‐order rate constants for the dehydration of HCO 3 − catalyzed by complexes Zn 3 L1, Zn 3 L2, Zn 3 L3, and Zn 3 L4 are 0.96, 2.53, 12.05, and 6.99 mol −1 dm 3 s −1 respectively. At the same time, the p K a values 7.60, 7.16, 7.51, and 7.42 for the deprotonation of the Zn(II)‐bound water in the four catalysts were obtained, which are consistent with those that resulted from pH titrations, i.e. 7.47, 7.25, 7.52, and 7.38 respectively. The mechanism is proposed and the results are compared with other model complexes of carbonic anhydrase. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 197–203, 2004