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Terpyridine Oxovanadium(IV) Complexes of Phenanthroline Bases for Cellular Imaging and Photocytotoxicity in HeLa Cells



Oxovanadium(IV) complexes [VO(N-N-N)(N-N)](NO3)2 (14) of (4′-phenyl)-2,2′:6′,2″-terpyridine (ph-tpy in 1 and 2) or (4′-pyrenyl)-2,2′:6′,2″-terpyridine (py-tpy in 3 and 4) having N-N as 1,10-phenanthroline (phen in 1 and 3) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 2 and 4) are prepared and characterized. The crystal structure of 1 has VO2+ group in VN5O coordination geometry. The terpyridine ligand coordinates in a meridional binding mode. The phen ligand displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo group. The complexes show a d-d band in the range of 710–770 nm in aqueous DMF (4:1 v/v). The complexes exhibit an irreversible VIV/VIII redox response near –1.0 V vs. SCE in aqueous DMF/0.1 M KCl. The complexes bind to CT DNA giving Kb values within 3.5 × 105 to 1.2 × 106M–1. The complexes show poor chemical nuclease activity in dark. Complexes 24 show photonuclease activity in UV-A light of 365 nm forming 1O2 and ·OH. Complex 4 shows DNA photocleavage activity at near-IR light of 785 nm forming ·OH radicals. Complexes 2 and 4 show significant photocytotoxicity in HeLa cancer cells. Uptake of the complexes in HeLa cells, studied by fluorescence imaging, show predominantly cytosolic localization inside the cells.