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 crystalli ne state and aqueous solutions presenting various pH (0.15-8) at diffe rent temperatures (25-90 degrees C), are investigated by XAFS experime nts. 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 s hort and medium range order (up to 5 Angstrom), multiple scattering ca lculation is performed. For the first coordination shell, we apply mul ti-shell fitting and RDF reconstruction. The comparative XAFS and XRD results are discussed, and some discrepancies with previous RMN experi ments are underlined.