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

Abstract Two mononuclear iron complexes, [Fe(tppz) 2 ](PF 6 ) 2 ·H 2 O ( 1 ) and Fe(tppz)Cl 3 ·2CHCl 3 ( 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 ](NO 3 ) 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 ](NO 3 ) 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 ](NO 3 ) 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.