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Studies of artificial hydrolytic metalloenzymes: the catalytic carboxyester hydrolysis by new macrocyclic polyamine zinc(II) complexes with a phenolic-pendant as novel nucleophile by Shourong Zhu; Wandong Chen; Huakuan Lin; Xiangchen Yin; Kou Fuping; Lin Meirong; Chen Yunti is a Chemistry article available to read on EtoBox.

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Akstract--Zinc(II) complexes of new macrocyclic tetraamines (cyclam derivatives) having a strategically appended phenolic group, 6-(2'-hydroxy)-benzyl-l,4,8,11-tetraazacyclotetradecane (LA), 6-(2'-hydroxy-5'bromo)-benzyl-l,4,8,11-tetraazacyclotetradecane (LB) and 6-(2'-hydroxy-3',5'-dibromo)-benzyl-l,4,8,11tetraazacyclotetradecane (Lc), have been examined as catalysts for the hydrolyses of 4-nitrophenylacetate (NA). The phenolic functionalized macrocycles form 1 : 1 ZnL complexes at pH ca 5. The potentiometric pH titration of LA, LB and Lc-Zn tE complexes showed dissociation of a phenolic proton with pKa values of 8, 8, 8.7 and 8.5 at 298 K and I = 0.10 mol.1-1 KNO 3 for LA, LB and Lc-Zn H complexes respectively. In the kinetic studies using the zinc complex in 10% (v/v) CH3CN at 298 K, I = 0.10 mol.1-1 KNO 3 and pH 7.(~9.5, we proved that the coordinated phenolate can serve as a good nucleophile that effectively catalyzes NA hydrolysis. The hydrolysis rate follows the law v = (kcat [complex]+koH[OH-]+ko) [NA]. The pH rate profile gave a sigmoidal curve with inflection points at pH 8.8, 8.7 and 8.6 for LA, LB and Lc, respectively, which correspond to the pKa value of the complex. T

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Author

Shourong Zhu; Wandong Chen; Huakuan Lin; Xiangchen Yin; Kou Fuping; Lin Meirong; Chen Yunti

Publisher

Elsevier Science; Elsevier ; Elsevier Ltd.; Elsevier BV (ISSN 0277-5387)

Published

1997

Language

EN

Field

Chemistry (Physical Sciences)