title: DNA binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline.
abstract: 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.
authors.affiliation: Department of Chemistry, Gadjah Mada University, Yogyakarta, Indonesia.
authors.lastname: Mudasir
authors.forename: N
authors.initials: N
authors.lastname: Yoshioka
authors.forename: H
authors.initials: H
authors.lastname: Inoue
mesh_terms: 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*
chemical_list: D005296:Ferrous Compounds; D008024:Ligands; D010618:Phenanthrolines; D014475:Uncoupling Agents; C006686:bathophenanthroline; D004247:DNA; C025205:1,10-phenanthroline