| Summary: | Six new copper(II) complexes were prepared: [Cu(ClBrQ)<sub>2</sub>] (<b>1a</b>, <b>1b</b>), [Cu(ClBrQ)<sub>2</sub>]·1/2 diox (<b>2</b>) (diox = 1,4-dioxane), [Cu(BrQ)<sub>2</sub>] (<b>3</b>), [Cu(dNQ)<sub>2</sub>] (<b>4</b>), [Cu(dNQ)<sub>2</sub>(DMF)<sub>2</sub>] (<b>5</b>) and [Cu(ClNQ)<sub>2</sub>] (<b>6</b>), where HClBrQ is 5-chloro-7-bromo-8-hydroxyquinoline, HBrQ is 7-bromo-8-hydroxyquinoline, HClNQ is 5-chloro-7-nitro-8-hydroxyquinoline and HdNQ is 5,7-dinitro-8-hydroxyquinoline. Prepared compounds were characterised by infrared spectroscopy, elemental analysis and by X-ray structural analysis. Structural analysis revealed that all complexes are molecular. Square planar coordination of copper atoms in [Cu(XQ)<sub>2</sub>] (XQ = ClBrQ (<b>1a</b>, <b>1b</b>), BrQ (<b>3</b>) and ClNQ (<b>6</b>)) and tetragonal bipyramidal coordination in [Cu(dNQ)<sub>2</sub>(DMF)<sub>2</sub>] (<b>5</b>) complexes were observed. In these four complexes, bidentate chelate coordination of XQ ligands via oxygen and nitrogen atoms was found. Hydrogen bonds stabilizing the structure were observed in [Cu(dNQ)<sub>2</sub>(DMF)<sub>2</sub>] (<b>5</b>) and [Cu(ClNQ)<sub>2</sub>] (<b>6</b>), no other nonbonding interactions were noticed in all five structures. The stability of the complexes in DMSO and DMSO/water was evaluated by UV-Vis spectroscopy. Cytotoxic activity of the complexes and ligands was tested against MCF-7, MDA-MB-231, HCT116, CaCo2, HeLa, A549 and Jurkat cancer cell lines. The selectivity of the complexes was verified on a noncancerous Cos-7 cell line. Antiproliferative activity of the prepared complexes was very low in comparison with cisplatin, except complex <b>3</b>; however, its activity was not selective and was similar to the activity of its ligand HBrQ. Antibacterial potential was observed only with ligand HClNQ. Radical scavenging experiments revealed relatively high antioxidant activity of complex <b>3</b> against ABTS radical.
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