Copper complexes with a flexible piperazinyl arm: nuclearity driven catecholase activity and interactions with biomolecules

<p>Three new Cu(II) complexes, [Cu(HL<sup>1</sup>)(pyridine)(H<sub>2</sub>O)](ClO<sub>4</sub>)<sub>2</sub>·2MeOH (<b>1</b>), [Cu<sub>2</sub>(HL<sup>1</sup>)<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>](NO<sub>3</sub>)<sub>2</sub>·3H<sub>2</sub>O (<b>2</b>) and [Cu(HL<sub>2</sub>)(NO<sub>3</sub>)<sub>2</sub>]·MeCN (<b>3</b>), have been synthesized from two Schiff base ligands [HL<sup>1</sup> = 1-phenyl-3-((2-(piperazin-4-yl)ethyl)imino)but-1-en-1-ol and HL<sup>2</sup> = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] using the chair conformer of a flexible piperazinyl moiety. Structural analysis reveals that <b>1</b> and <b>3</b> are monomeric Cu(II) complexes consisting of five- and six-coordinate Cu(II), respectively, whereas <b>2</b> is a dinuclear Cu(II) complex consisting of two different Cu(II) centers, one square planar with the other distorted octahedral. Screening tests were conducted to quantify the binding of <b>1</b>–<b>3</b> towards DNA and BSA as well as the DNA cleavage activity of these complexes using gel electrophoresis. Enzyme kinetic studies were also performed for the complexes mimicking catecholase-like activities. Antibacterial activities of these complexes were also examined towards Methicillin-Resistant <i>Staphylococcus aureus</i> bacteria. The results reflect that <b>2</b> is more active than the monomeric complexes, which is further corroborated by density functional theory study.</p>