Temperature and pH dependence of Gd-DOTA and Gd-DTPA complexes dissociation studied by EXAFS

The Gd L3-edge of Gd(DTPA)^2- and Gd(DOTA)^- complexes, in crystalline state and aqueous solutions presenting various pH (0.15-8) at different temperatures (25-90 °C), are investigated by XAFS experiments. For the Gd(DTPA)^2- complexes we observe a strong pH (0.15-1.5) dependence of XAFS signals. On the other hand, the XAFS signals of Gd(DOTA)^- complexes exhibit a light pH (1-1.5) dependence and for pH<1 we observe a ligand decomposition. Concerning both complexes, we note just a light temperature dependence. To obtain information about the short and medium range order (up to 5 Å), multiple scattering calculation is performed. For the first coordination shell, we apply multi-shell fitting and RDF reconstruction. The comparative XAFS and XRD results are discussed, and some discrepancies with previous RMN experiments are underlined.