Cyclometalated Pt(II) complexes as photosensitizers for DNA damaging
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In solution at room temperature, several mixed-ligand cyclometalated Pt(II) (unlike Pd(II) or Au(III)) complexes exhibit long-lived luminescence, which is effectively quenched by dioxygen. This led us to hypothesize that active oxygen species can be engendered in these conditions. Indeed, here we revealed at least one of them: when UV-illuminating (370 nm) aqueous solutions of cyclometalated ethylenediamine Pt(II) complexes with 2-phenylpyridine, 2-phenyl-1,3-benzothiazole, and 2-(2-thienyl)-pyridine we detected singlet oxygen luminescence. DNA intercalation of these complexes by itself did not affect plasmid DNA gel-electrophoretic mobility; however, upon UV irradiation (365 nm) it led to a slowdown in plasmid DNA migration. Such a slowdown can be explained by breaks induced in DNA by active oxygen species generated in collisions between excited-state Pt (II) complexes and triplet dioxygen. The property discovered allows considering cyclometalated Pt(II) complexes useful as promising photosensitizers in the treatment of superficial tumors.
