Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(L)(B)] (1–3), where H2L is a Schiff base ligand 2-(2-hydroxybenzylideneamino)phenol and B is 1,10-phenanthroline (phen for 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq for 2) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO3N3 coordination geometry. The complexes show a d–d band within 800–850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)–V(IV) and a reductive response within −1.1 to −1.3 V due to V(IV)–V(III) couple in DMF–0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 × 104 to 1.2 × 105 M−1. The complexes do not show any “chemical nuclease” activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via 1O2 pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO• pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC50 value of 13 μM, while it is less toxic in dark (IC50 = 97 μM).