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

Copper(II) (1(Cu)-21(Cu)) and previously established experimental anticancer platinum(II) metallointercalator complexes (1(Pt)-16(Pt)) 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(IL)-10(IL)), 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, (1)H and [(1)H-(195)Pt]-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)](ClO(4))(2) (4(Cu)), [Cu(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)(H(2)O)](ClO(4))(2)·1.5H(2)O (10(Cu)) and [Cu(5,6-dimethyl-1,10-phenanthroline)(3)](ClO(4))(2)·5,6-dimethyl-1,10-phenanthroline·2H(2)O (21(Cu)). 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.