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

The aminopeptidase functions of newly obtained dinuclear zinc(II) complexes [Zn2(bonp)(MeCO2)2]BPh4 (1) and [Zn2(bocp)(MeCO2)2]BPh4 (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 dm3 mol−1 s−1 for complex 2. Compared to the previously reported complex, [Zn2(bomp)(MeCO2)2]BPh4 (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(–NO2)>2(–Cl)>3(–CH3).