Nickel(II) complexes with a flexible piperazinyl moiety: Studies on DNA and protein binding and catecholase like properties

Abstract

Four new mononuclear Ni(II) complexes [Ni(L1)]ClO4 (1a), [Ni(L2)]ClO4(1b), [Ni(SCN)3(CH3OH)(aminoethylpiperazineH)] (2a), and [Ni(DMSO)4(aminoethylpiperazineH)](ClO4)3(2b)have been synthesized from two Schiff base ligands [L1 = 1-phenyl-3-((2-(piperidin-4-yl)ethyl)imino)but-1-en-1-ol and L2 = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] by exploiting the flexibility of the piperazinyl moiety. Structural analysis reveals that 1a and 1b are square planar complexes with piperazine rings in boat conformations whereas hydrolysis of Schiff bases (L1 and L2) occurs during formation of octahedral complexes (2a and 2b) with piperazine rings in chair conformations. Screening tests were conducted to quantify the binding ability of complexes (1a, 1b and 2a) towards DNA, BSA and HSA and it was found that square planar complexes (1a and 1b) showed more effective binding properties over octahedral complex (2a). Furthermore, enzyme kinetic studies reflect that square planar complexes (1a and 1b) are also effective in mimicking catecholase like activities over octahedral complex (2a). Among all the complexes, 1a was found to be the most promising molecule among the series due to its large binding affinity towards different bio-macromolecules and higher T.O.N in the catechol oxidation reaction. © The Royal Society of Chemistry 2015.