DNA binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and 4,7-diphenyl-1, 10-phenanthroline

摘要

Absorption spectroscopy and circular dichroism (CD) have been used to characterize the DNA binding of [Fe(phen)_3]~(2+), [Fe(phen)_2(DIP)]~(2+) and [Fe(phen)_2(DIP)]~(2+) where phen and DIP stand for 1,10-phenanthroline and 4,7-diphenyl-1, 10-phenanthroline, respectively. Both [Fe(phen)_3]~(2+) and [Fe(phen)_2(DIP)]~(2+) bind weakly to calf thymus DNA (CT-DNA) in an electrostatic mode, while [Fe(phen)_2(DIP)]~(2+) binds more strongly to CT-DNA, possibly in an intercalation mode. The hypochromicity. red shift and K_b increase in the order [Fe(phen)_3]~(2+) K< [Fe(phen)_2(DIP)]~(2+)<[Fe(phen)_2(DIP)]~(2+) in accordance with the increase in size and hydrophobicity of the iron(II) complexes. The thermodynamic parameters obtained suggest that the DNA binding of both [Fe(phen)_3]~(2+) and [Fe(phen)_2(DIP)]~(2+) is entropically driven, while that of [Fe(phen)_2(DIP)]~(2+) is enthalpically driven. A strong CD spectrum in the UV and visible region develops upon addition of CT-DNA into the racemate solution of each iron(II) complex (Pfeiffer effect). This has revealed that a shift in diastereomeric inversion equilibrium takes place in the solution to yield an excess of one of the DNA-complex diastereomers. The striking resemblance of the CD spectral profiles to those of the pure #DELTA#-enantiomer indicates the the #DELTA#-enantiomer of the iron(II) complexes is preferentially bound to CT-DNA. The mechanism of the development of Pfeiffer CD is proposed on the basis of kinetic studies on the DNA binding of the racemic iron(II) complexes.