Carboxy and diphosphate ester hydrolysis promoted by di- or tri-nuclear zinc(II) complexes based on β-cyclodextrin

• DOI: 10.1016/j.molcata.2010.11.037
• Publication Date: 2010-12-09T10:21:41Z
• Authors: Si-Ping Tang; Ping Hu; Huo-Yan Chen; Sha Chen; Zong-Wan Mao; Liang-Nian Ji
• Keywords: Hydroxymethyl; Esterase

Abstract A new ligand (L), 6-mono-(2-(2-hydroxy-3-(hydroxymethyl)-5-methyl benzylamino)-ethylamino)-β-cyclodextrin, based on β-cyclodextrin derivatives with dinucleating units was synthesized and used to prepare a trimetallic bis-ligands zinc complex (Zn 3 (L 2− ) 2 ). The esterase activity of the complex was investigated by the hydrolysis of two carboxylic acid esters, bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA), and a DNA model bis(4-nitrophenyl)phosphate (BNPP) as a phosphate ester. The catalytic rate for BNPC was very high, which was found to be a 5.63 × 10 3 -fold rate enhancement over uncatalyzed hydrolysis and 1.62 × 10 2 -fold rate enhancement over uncatalyzed hydrolysis for NA hydrolysis at pH = 7.0. For the catalytic hydrolysis of BNPP, the initial first-order rate constant of 0.1 mM catalyst was 5.85 × 10 −8 s −1 at pH = 8.50 and 35 °C, which is a 731-fold acceleration over uncatalyzed hydrolysis. The second rate constant ( k BNPP ) was found to be 1.22 × 10 −3 M −1 s −1 at pH = 10.0. According to the potentiometric titration study, the zinc complex exists in a dinuclear single ligand coordinated mode and a trinuclear bis-ligands system at pH ≥ 7.0. The ester hydrolysis activity was attributed to the cooperative interaction of the two metal centers and the hydrophobic cavity of β-cyclodextrin with substrates.