Mononuclear and binuclear ruthenium(II) heteroleptic complexes based on 1,10-phenanthroline ligands. Part II: Spectroscopic and photophysical study in the presence of DNA.

Photophysical and photochemical properties of a series of mononuclear and binuclear ruthenium(II) complexes of phen (phen=1,10-phenanthroline), in the absence or in the presence of calf-thymus DNA have been investigated by steady-state as well as time-resolved methods. The complexes of this series are [Ru(x)(phen)(2x)(L)](2x+) (x=1 or 2) type, where L is a bpy (4,4'-dimethyl-2,2'-bypiridine, with x=1) or a bis-bpy covalently linked by flexible chains including either polymethylene groups or polyamine functions (with x=2). Upon addition of DNA, the most important increasing luminescence and change of emission maxima wavelength are observed for the bimetallic compounds having amine functions in their spacer. A biexponential decay in luminescence is found with emission lifetimes of the complexes upon binding to DNA. Moreover, these complexes induce efficient photocleavage of DNA by irradiation at 450 nm. This efficiency is particularly important when the binuclear complexes include amino groups. Topoisomerization experiments have pointed out a similarity between the DNA cleaving ability of these complexes and their intercalation into DNA. Scavenging experiments have shown that the oxidative species involved in DNA cleavage was mainly (1)O(2), via a type II mechanism.

Temperature and pH Dependence XAFS Study of Gd(DOTA)(-) and Gd(DTPA)(2)(-) Complexes: Solid State and Solution Structures.

We present an X-ray absorption spectroscopy study of the local structures of Gd(DTPA)(2)(-) and Gd(DOTA)(-) complexes in the crystalline state (at room and low temperatures) and in aqueous solutions exhibiting various pH values (0.15-7) at different temperatures (25-90 degrees C). Using X-ray absorption fine structure (XAFS) analysis procedures and ab initio multiple scattering calculations of XAFS spectra at the Gd L(3) edge, we reconstructed the Gd(3+) local environment, and compared it with existing structural models. From neutral pH to a value of 1.5, we found that the local environment and complex dynamics around the gadolinium ions were conserved up to 4.5 Å, and the structure agreed well with the known crystallographic data. In these solutions, the gadolinium ions in the complex Gd(DOTA)(-) are bonded to the four carboxylate oxygen atoms [R(Gd-O(av)) 2.38 Å, Debye-Waller (DW) factor 0.006 Å(2)], to the four nitrogen atoms [R(Gd-N(av)) 2.65 Å, DW factor 0.006 Å(2)] and to one water molecule [R(Gd-O(w)) 2.46 Å, DW factor 0.012 Å(2)]. Concerning the complex Gd(DTPA)(2)(-), the gadolinium ions are bonded to the five carbonyl oxygen atoms [R(Gd-O(av)) 2.39 Å, DW factor 0.007 Å(2)], to the three nitrogen atoms [R(Gd-N(av)) 2.64 Å, DW factor 0.006 Å(2)], and to one water molecule [R(Gd-O(w)) 2.47 Å, DW factor 0.018 Å(2)]. In the range of pH (0.15-1.5) for the Gd(DTPA)(2)(-) complexes, thanks to the pH strong dependence of the XAFS signals, we observed a progressive complex dissociation. On the other hand, the XAFS signals of Gd(DOTA)(-) complexes exhibited only a slight pH (1-1.5) dependence. Concerning both complexes, we noted just a slight temperature dependence.