Photocytotoxic ferrocene-appended (l-tyrosine)copper(II) complexes of phenanthroline bases

Abstract

Copper(II) complexes of ferrocene(Fc)-conjugated reduced Schiff base of l-tyrosine (Fc-TyrH), viz., [Cu(Fc-Tyr)(L)](ClO4), where L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3) and 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (nip, 4), were prepared and tested for their photocytotoxicity in cancer cells. [Cu(Fc-Phe)(phen)](ClO4) (5) of l-phenylalanine and [Cu(Ph-Tyr)(L)(ClO4)] of the reduced Schiff base Ph-TyrH derived from benzaldehyde and l-tyrosine having phen (6) and dppz (7), and [Cu(Ph-Phe)(phen)(ClO4)] (8) using l-phenylalanine were prepared and used as controls. Complexes 5 and 6 were structurally characterized by X-ray crystallography. A copper(II)-based d–d band near 600 nm and a ferrocenyl band at ∼450 nm were observed in DMF–Tris–HCl buffer (1:4 v/v) in respective complexes. The complexes are photocleavers of pUC19 DNA in visible light forming •OH radicals. They are cytotoxic in HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells showing an enhancement of cytotoxicity in visible light. Fluorescence imaging shows nuclear localization of the complexes.