Photodynamic action of bis(tertiary arsine (diars)) metal(III) complexes trans-[M(diars)2X2]+ (X = Cl, Br, I); M = Co3+, Cr3+, Rh3+: Optical and EPR spin-trapping studies

Photodynamic properties of series of metal complexes having the general formula [M(diars)2X2]ClO4 or BF4 where M = Co3+, Cr3+, Rh3+; X = Cl, Br, I, diars = o-phenylene bis(dimethylarsine) are studied. Photogeneration of singlet oxygen is monitored by both optical and EPR methods. In comparison with rose bengal (ϕ(1O2) for RB = 0.76), singlet oxygen generating efficiencies of these complexes are determined. Rate of N,N-dimethyl-4-nitrosoaniline (RNO) bleaching is found to be retarded by specific 1O2 quencher NaN3, confirming the involvement of 1O2 as an active intermediate. Photolysis of these complexes in the presence of spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generates 12-line EPR spectra, characteristic of O2− adduct. Photogeneration of O2− is also monitored by optical spectroscopy using superoxide dismutase (SOD) inhibitable cytochrome c reduction assay. The results indicate that the [Co(diars)2Br2]ClO4 complex possesses high ability to generate reactive oxygen species (ROS). Both Type I and II paths are involved in the photosensitisation of the metal complexes. The antimicrobial activity of the complexes against selected bacteria is estimated. The relationship between the enzymatic production of ROS and antimicrobial activity of the complexes is examined and a good correlation between two factors is found. The [CoBr2(diars)2]ClO4 complex investigated in this study effect photo cleavage of the plasmid DNA (pUC18).