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

A new ligand (L), 6-mono-(2-(2-hydroxy-3-(hydroxymethyl)-5-methyl benzylamino)-ethylamino)-beta-cyclodextrin, based on beta-cyclodextrin derivatives with dinucleating units was synthesized and used to prepare a trimetallic bis-ligands zinc complex (Zn-3(L2-)(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 x 10(3)-fold rate enhancement over uncatalyzed hydrolysis and 1.62 x 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 x 10(-8)s(-1) at pH = 8.50 and 35 degrees C, which is a 731-fold acceleration over uncatalyzed hydrolysis. The second rate constant (k(BNPP)) was found to be 1.22 x 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 beta-cyclodextrin with substrates. (C) 2010 Elsevier B.V. All rights reserved.