The antimicrobial properties of some copper(ii) and platinum(ii) 1,10-phenanthroline complexes

Abstract

Copper(II) (1_CuCu–21_CuCu) and previously established experimental anticancer platinum(II) metallointercalator complexes (1_PtPt–16_PtPt) have been prepared and investigated for their antimicrobial properties. These complexes are of the general structure [M(I_L)(A_L)]²⁺ where I_L represents functionalised 1,10-phenanthrolines (1_ILIL–10_ILIL), and A_L represents 1,2-diaminoethane, 1S,2S- or 1R,2R-diaminocyclohexane. The structures of synthesised complexes were confirmed using a combination of elemental analysis, UV spectrometry, circular dichroism, ¹H and [¹H–¹⁹⁵Pt]-HMQC NMR, X-ray crystallography, and electrospray ionisation mass spectrometry and where appropriate. Crystallisation attempts yielded single crystals of [Cu(4-methyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)](ClO₄)₂ (4_CuCu), [Cu(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)(H₂O)](ClO₄)₂·1.5H₂O (10_CuCu) and [Cu(5,6-dimethyl-1,10-phenanthroline)₃](ClO₄)₂·5,6-dimethyl-1,10-phenanthroline·2H₂O (21_CuCu). Growth inhibition of liquid cultures of bacteria (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa), and yeast (Saccharomyces cerevisiae) discerned the most antimicrobially potent metal complexes ≤20 μM, as well as that of their intercalating ligands alone. To further investigate their mode of antimicrobial activity, membrane permeabilisation caused by selected complexes was visualised by means of a cell viability kit under fluorescence microscopy.