Terpyridine oxovanadium(IV) complexes of phenanthroline bases for cellular imaging and photocytotoxicity in HeLa cells

Abstract

Oxovanadium(IV) complexes [VO(N-N-N)(N-N)](NO₃)₂ (1-4) 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 2-4 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.