Role of carboxamido nitrogen in mononuclear manganese complex: Superoxide scavenging activity and nuclease activity

Three new ligands Pyimpy (2-((2-phenyl-2-(pyridin-2-yl)hydazono)methyl)pyridine), Me-Pyimpy (1-phenyl-1-(pyridin-2-yl)-2-(1-(pyridin-2-yl)ethylidene)hydrazine) and PampH (N′-phenyl-N′-(pyridin-2-yl)picolinohydrazide) were synthesized. Hexa-coordinated mononuclear complexes [Mn(Pyimpy)2](ClO4)2 (1), [Mn(Me-Pyimpy)2](ClO4)2 (2), and [Mn(Pamp)2](ClO4)·CH3OH, (3·CH3OH) were synthesized and characterized. The molecular structure of [Mn(Pamp)2](ClO4)·CH3OH, (3·CH3OH) was determined by single crystal X-ray diffraction, which afforded distorted octahedral coordination sphere having meridionally spanning ligands. The redox properties were exploited to examine superoxide dismutase (SOD) activity using Mn(II)/Mn(III) couple. The complex 3 having ligands containing carboxamido nitrogen (Nam) donor, has been revealed to catalyze more effectively the dismutation of superoxide (O2-) ions in xanthine–xanthine oxidase–nitro blue tetrazolium assay as compared to 1 and 2. Among the three complexes, complex 3 was found to be most effective in nuclease activity in the presence of H2O2.

The graphical abstract represents two important aspects of our manuscript namely, SOD activity and nuclease activity. Complex 3·CH3OH, which was structurally characterized (shown in the graphical abstract), possesses E1/2 value for MnII/MnIII couple which is in the proper range (between two arrows, −0.375 V ⩽ E1/2 ⩽ +0.605 V vs Ag/AgCl) to exhibit SOD activity. In the redox potential value scale, values for complexes 1 and 2 are beyond the proper range and show very poor SOD activity. In terms of nuclease activity complex 3·CH3OH was more efficient as compared to complexes 1 and 2. Schiff base complexes 1 and 2 afforded lower activity for SOD as well as nuclease activity due to the lack of Nam donor in the ligand frames.Figure optionsDownload as PowerPoint slide