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Kinetics and mechanism of the catalytic dehydration of HCO3− by zinc(II) complexes of tripod ligands

✍ Scribed by Qingchun Ge; Yanhe Guo; Hai Lin; Huakuan Lin; Shourong Zhu

Publisher
John Wiley and Sons
Year
2004
Tongue
English
Weight
146 KB
Volume
36
Category
Article
ISSN
0538-8066

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✦ Synopsis

Abstract

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

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