Ternary copper(II) complexes of salicylaldehyde-histamine Schiff base (HL) and pyridyl ligands, viz. [Cu(bpy)(L)](ClO₄) (1) and [Cu(dppz)(L)](ClO₄) (2), where bpy is 2,2′-bipyridine (in 1) and dppz is dipyrido[3,2-a:2′,3′-c]phenazine (in 2), were synthesized, characterized and their DNA binding, photo-activated DNA cleavage activity and photocytotoxicity studied. The 1:1 electrolytic one-electron paramagnetic complexes showed a d-d band near 670 nm in aqueous DMF (1:1 v/v). The crystal structure of complex 1 showed the metal in CuN₄O distorted square-pyramidal geometry. Complex 2 intercalatively binds to calf-thymus (ct) DNA with a binding constant (𝐾_b) of ∼10⁵ M⁻¹. It exhibited moderate chemical nuclease activity but excellent DNA photocleavage activity in red light of 647 nm forming $^{\bullet}\text{OH}$ radicals. It showed remarkable photocytotoxicity in human cervical cancer cells (HeLa) giving IC₅₀ of 1.6 𝜇M in visible light (400-700 nm) with low dark toxicity. The photo-induced cell death is via generation of oxidative stress by reactive oxygen species.

Several amino acid-based photo-active monomeric iron(III) complexes of the general formula,[Fe(L)₂]PP^-, where L= Schiff base ligands (salisalidene arginine, salicylidenetryptophan, 3,5-di-tert-butyl benzalidine arginine and salicylidene tryptophan) were synthesized, characterized and explored for photoactivated anticancer activity to Chang Liver Cells, HeLa and MCF-7 cells. Complexes exhibited remarkable photo-cytotoxicity with IC₅₀ value to the extent of 0.7 μM to Chang Liver Cells in visible light and there wasa 40-fold enhancement in cytotoxicity in comparison to the cytotoxicity in dark. Complexes were non-toxic to MCF-10A (normal cells) in dark and visible light (IC₅₀ > 100 μM in dark; IC₅₀ > 80 μM in visible light) signifying target-specific nature of the anti-tumour activity of the complexes. Increased ROS concentration,as probed by DCFDA assay, in the cancer cells was responsible for apoptotic cell death. Decarboxylation or phenolate-Fe(III) charge transfer of photo-activated iron(III) complexes generating • OH radicals (ROS) were responsible for the apoptosis. Overall, the tumour-selective photo-activated anticancer activity of the amino acidbased iron(III) complexes have shown a promising aspect in developing iron-based photo-chemotherapeutics as the next generation PDT agents.