DNA binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline.
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)(DIP)2]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)(DIP)2]2+ binds more strongly to CT-DNA, possibly in an intercalation mode. The hypochromicity, red shift and Kb increase in the order [Fe(phen)3]2+ < [Fe(phen)2(DIP)]2+ < [Fe(phen)(DIP)2]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)(DIP)2]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 that 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.
Mudasir
Department of Chemistry, Gadjah Mada University, Yogyakarta, Indonesia.
Yoshioka
N
N
Inoue
H
H
D002942:Circular Dichroism; D004247:DNA / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism*; D008024:Ligands; D008956:Models, Chemical; D010618:Phenanthrolines / Q000378:metabolism*; D013054:Spectrophotometry, Atomic; D013816:Thermodynamics; D014475:Uncoupling Agents / Q000378:metabolism*
D005296:Ferrous Compounds; D008024:Ligands; D010618:Phenanthrolines; D014475:Uncoupling Agents; C006686:bathophenanthroline; D004247:DNA; C025205:1,10-phenanthroline