Aminopeptidase function of dinuclear zinc(II) complexes of phenol-based dinucleating ligands: effect of p-substituents

Abstract

The aminopeptidase functions of newly obtained dinuclear zinc(II) complexes [Zn 2(bonp)(MeCO 2) 2]BPh 4 ( 1) and [Zn 2(bocp)(MeCO 2) 2]BPh 4 ( 2) were estimated using l-leucine– p-nitroanilide as a substrate [H(bonp): 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-nitrophenol; H(bocp): 4-chloro-2,6-bis[bis(2-methoxyethyl)aminomethyl]phenol]. Both complexes showed aminopeptidase activities, and a second-order rate equation was obtained as v= k[complex][substrate]. The second-order rate constants k were 5.9(5)×10 −1 for complex 1, and 2.7(1)×10 −2 dm 3 mol −1 s −1 for complex 2. Compared to the previously reported complex, [Zn 2(bomp)(MeCO 2) 2]BPh 4 ( 3) [H(bomp): 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol], the aminopeptidase activity was improved 250 times by the substitution of the p-methyl group into p-nitro group. The rate constants were found to be ordered as 1> 2> 3 (250:10:1), and this order is a decreasing order of the electron-withdrawing effect of the p-substituents of the dinucleating ligands 1(–NO 2)> 2(–Cl)> 3(–CH 3).