Dithiocarbazate based oxidomethoxidovanadium(V) and mixed-ligand oxidovanadium(IV) complexes: Study of solution behavior, DNA binding, and anticancer activity.

In this work, one oxidomethoxidovanadium(V) [V ^V O(L)(OMe)] (1) and two mixed-ligand oxidovanadium(IV) [V ^IV O(L)(phen)] (2), and [V ^IV O(L)(bipy)] (3) complexes have been synthesized using a tridentate bi-negative ONS donor dithiocarbazate as main ligand, H ₂ L [where, H ₂ L = S-benzyl-3-(2-hydroxy-3-ethoxyphenyl)methylenedithiocarbazate] along with 1,10-phenanthroline (phen) (for 2) and 2,2'-bipyridine (bipy) (for 3) as co-ligands. The ligand and complexes have been characterised by FT-IR, UV-vis, NMR, and HR-ESI-MS techniques. Distorted square pyramidal for 1, and distorted octahedral geometry for 2 and 3 was confirmed by single crystal X-ray crystallography. The behavior of 1-3 in solution medium has been investigated through various physicochemical techniques. It is observed that 1 completely and 2-3 partially decomposes and converts into a penta-coordinated species, [V ^IV O(L)(DMSO/H ₂ O)] after the release of the methoxido group (1) or breaking of the diimine based co-ligands (2 and 3) in DMSO/aqueous solution. Interestingly, in DMSO/aqueous solution, 1 gets completely reduced and converted into the corresponding oxidovanadium(IV) species. Interaction of 1-3 with calf thymus DNA (CT-DNA) was investigated and the results show, complex 2 exhibited the maximum binding constants, K _b  = 7.12 × 10 ⁴  M ^-1 . The anticancer potential of 1-3 was evaluated by cell viability assay against human breast carcinoma cell, MCF-7, and noncancerous mouse embryonic cell, NIH-3T3 and 2 was found to be the most cytotoxic complex (IC ₅₀  = 6.73 ± 0.36 μM) in the series. In addition, 2 selectively inhibit colony formation compared to the rest complexes. Also, the cell cycle studies of the complexes were performed using flow cytometry analysis.
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