Experimental and molecular modeling studies of the interaction of the polypyridyl Fe(II) and Fe(III) complexes with...

Two mononuclear iron complexes, [Fe(tppz)₂](PF₆)₂·H₂O (1) and Fe(tppz)Cl₃·2CHCl₃ (2) where tppz is (2,3,5,6-tetra(2-pyridyl)pyrazine), have been synthesized and characterized by elemental analysis, spectroscopic methods (UV-Vis and IR) and single crystal X-ray structure analysis. The interaction of (1) as the nitrate salt ([Fe(tppz)₂](NO₃)₂) with calf-thymus DNA (CT-DNA) has been monitored by UV-Vis spectroscopy, competitive fluorescence titration, circular dichroism (CD), voltammetric techniques, viscosity measurement, and gel electrophoresis. Gel electrophoresis of DNA with [Fe(tppz)₂](NO₃)₂ demonstrated that the complex also has the ability to cleave supercoiled plasmid DNA. The results have indicated that the complex binds to CT-DNA by three binding modes, viz., electrostatic, groove and partial insertion of the pyridyl rings between the base stacks of double-stranded DNA. Molecular docking of [Fe(tppz)₂](NO₃)₂ with the DNA sequence d(ACCGACGTCGGT)₂ suggests the complex fits into the major groove. The water-insoluble complex (2) can catalyze the cleavage of BSA at 40 °C. There are no reports of the catalytic effect of polypyridyl metal complexes on the BSA cleavage. Molecular docking of (2) with BSA suggests that, when the chloro ligands in the axial positions are replaced by water molecules, the BSA can interact with the Fe(III) complex more easily.