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

Four new mononuclear Ni(ii) complexes [Ni(L(1))]ClO4 (), [Ni(L(2))]ClO4(), [Ni(SCN)3(CH3OH)(aminoethylpiperazineH)] (), and [Ni(DMSO)4(aminoethylpiperazineH)](ClO4)3()have been synthesized from two Schiff base ligands [L(1) = 1-phenyl-3-((2-(piperidin-4-yl)ethyl)imino)but-1-en-1-ol and L(2) = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] by exploiting the flexibility of the piperazinyl moiety. Structural analysis reveals that and are square planar complexes with piperazine rings in boat conformations whereas hydrolysis of Schiff bases (L(1) and L(2)) occurs during formation of octahedral complexes ( and ) with piperazine rings in chair conformations. Screening tests were conducted to quantify the binding ability of complexes (, and ) towards DNA, BSA and HSA and it was found that square planar complexes ( and ) showed more effective binding properties over octahedral complex (). Furthermore, enzyme kinetic studies reflect that square planar complexes ( and ) are also effective in mimicking catecholase like activities over octahedral complex (). Among all the complexes, 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.