An effective metallohydrolase model with a supramolecular environment: Structures, properties, and activities

作者:Zhou, Ying Hua; Fu, Heng; Zhao, Wei Xi; Tong, Ming Liang; Su, Cheng Yong; Sun, Hongzhe; Ji, Liang Nian; Mao, Zong Wan*
来源:Chemistry - A European Journal, 2007, 13(8): 2402-2409.
DOI:10.1002/chem.200601302

摘要

A supramolecular inclusion complex, [Zn(L-1)(H2O)(2)(beta-CD)]-(ClO4)(2)center dot 9.5H(2)O (1) was synthesized and characterized structurally and its first-order active species for hydrolysis of esters, [Zn(L-1)(H2O)(OH)(beta-CD)]-(ClO4) (2), was isolated (L-1=4-(4'-tert-butylbenzyl)diethylenetriamine; beta-CD=beta-cyclodextrin). The apparent inclusion stability constant of the host and the guest measured in aqueous solution was (5.91 /- 0.03) x 10(3) for 1. The measured values of the first- and second-order pK(a) values of coordinated water molecules were 8.20 /- 0.08 and 10.44 /- 0.08, respectively, and were assigned to water molecules occupying the plane and remaining axial positions in a distorted trigonal bipyramid of the [Zn(L-1)(H2O)(2)(mu-CD)}(2)] sphere according to the structural analysis of [Zn(L-2)(H2O)}(2)(mu-OH)] (ClO4)(3) (3) (L-2 = 4-benzyldiethylenetriamine). p-water molecules were 8.20 /- 0.08 and 10.44 /- 0.08, respectively, and were assigned to water molecules occupying the plane and remaining axial positions in a distorted trigonal bipyramid of the [Zn(L-1)(H2O)2(P-CD)]21 sphere according to the structural analysis of [Zn(L-2)(H2O)}(2)(mu-OH)](ClO4)(3) (3) (L-2=4-benzyldiethylenetriamine). p-Nitrophenyl acetate (pNA) hydrolysis catalyzed by 1 at pH 7.5-9.1 and 25.0 /- 0.1 degrees C exhibited a first-order reaction with various concentrations of pNA and 1, but the pH profile did not indicate saturated kinetic behavior. Second-order rate constants of 0.59 and 24.0 M-1 s(-1) were calculated for [Zn(L-1)(H2O)(OH)(beta-CD)]( ) and [Zn(L-1)(OH)(2)(beta-CD)], respectively; the latter exhibited a potent catalytic activity relative to the reported mononuclear and polynuclear Zn-II species.