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)-β-cyclodextrin, based on β-cyclodextrin derivatives with dinucleating units was synthesized and used to prepare a trimetallic bis-ligands zinc complex (Zn3(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 × 103-fold rate enhancement over uncatalyzed hydrolysis and 1.62 × 102-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 (kBNPP) 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.

A new ligand (L) with dinucleating units based on β-cyclodextrin was synthesized. Its trimetallic bis-cyclodextrins zinc complex (Zn3(L2−)2) was demonstrated as a potent catalyst for ester hydrolysis.Figure optionsDownload high-quality image (113 K)Download as PowerPoint slideResearch highlights▶ Trinuclear zinc complex based β-cyclodextrins catalyzed ester hydrolysis. The complex displayed good hydrolytic activities for monoester and diesters. The cooperation of metal centers and β-cyclodextrin was important for ester cleavage.