Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes

Two ruthenium(II) polypyridyl complexes were prepared with the {Ru(phen)(2)}(2+) moiety and a third sterically non-hindering bidentate ligand, namely 2,2'-dipyridylamine (dpa) and N-benzyl-2,2'-dipyridylamine (Bndpa). Hence, complexes [Ru(phen)(2)(dpa)](PF6)(2) (1) and [Ru(phen)2(Bndpa)](PF6) 2 (2) were characterized and their photochemical behaviour in solution (acetonitrile and water) was subsequently investigated. Compounds 1 and 2, which do not exhibit notably distorted octahedral coordination environments, contrarily to the homoleptic parent compound [Ru(phen)(3)](PF6)(2), experience two-step photoejection of the dpa and Bndpa ligand upon irradiation (1050-430 nm) for several hours. DNA-binding studies revealed that compounds 1 and 2 affect the biomolecule differently upon irradiation; while 2 solely modifies its electrophoretic mobility, complex 1 is also capable of cleaving it. In vitro cytotoxicity studies with two cancer-cell lines, namely A549 (lung adenocarcinoma) and A375 (melanoma), showed that both 1 and 2 are not toxic in the dark, while only 1 is significantly cytotoxic if irradiated, 2 remaining non-toxic under these conditions. [GRAPHICS] .

Automated summary

Two ruthenium(II) polypyridyl complexes, [Ru(phen)(2)(dpa)](PF6)(2) and [Ru(phen)2(Bndpa)](PF6)2, were synthesized with the {Ru(phen)(2)}(2+) moiety and different bidentate ligands. The photochemical behavior of these complexes in acetonitrile and water was investigated, showing that they undergo two-step photoejection of the ligands upon irradiation. Furthermore, these complexes exhibit different effects on DNA and cytotoxicity when irradiated.