Manganese (II) complexes of tridentate ligands having NNN donors: Structure, DFT calculations, superoxide dismutase, DNA interaction, nuclease and protease activity studies

A new family of manganese complexes Mn(H-N3L)Cl-2 (1), [Mn(H-N3L)(2)](ClO4)(2) (2), Mn(Me-N3L)Cl-2 (3) and [Mn(Me-N3L)(2)](ClO4)(2) (4) where H-N3L is 1-phenyl-1-(pyridine-2-ylmethyl)-2-(pyridine-2-ylmethylene)hydrazine and Me-N3L 1-phenyl-2-(1-(pyridin-2-yl)ethylidene)-1-(pyridin-2-ylmethyl)hydrazine, have been synthesized and characterized by various spectroscopic techniques such as ESI-mass, IR, UV-vis etc. X-ray crystal structure of complex 3 contains monomeric penta-coordinated complex having square pyramidal geometry (tau = 0.22). Redox properties were investigated for all the complexes. Theoretical calculations (DFT and TD-DFT) were performed using complexes 1 and 3. Geometrical, structural and electronic parameters demonstrated good agreement with the experimental data. TD-DFT calculations revealed nature of electronic transition in the complexes 1 and 3. This work mainly focuses on a series of manganese complexes to assess their potential activity on reactions performed by enzymes. SOD activities of all the complexes were studied via indirect method using NBT (nitro blue tetrazolium) assay. The interaction of the complexes (1-4) with calf thymus DNA was examined using UV-visible, fluorescence and circular dichroism spectral studies to understand the mode and extent of DNA binding. DNA interaction studies indicated partial intercalation as probable mode of interaction. In addition to this complex 1 exhibited oxidative nuclease as well as protease activities in presence of oxidising agent (H2O2).