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Speciation 98: Abstracts
Carlos Kremer1, Julia Torres1, Sixto Domínguez2, Alfredo Mederos2, Eduardo Kremer1
1 Cátedra de Química Inorgánica,
Facultad de Química, CC 1157, Montevideo, Uruguay;
2 Departamento de Química Inorgánica,
Universidad de La Laguna, Tenerife, Canary Islands, Spain
Metal complexes of b- emitter radionucleides have been widely developed for the radiotherapy treatment of diseases. Among them, 153Sm presents desirable nuclear properties. Design of new radiotherapeutic agents implies the formation of chelates, stable enough to reach malignant sites on the target organs and to deposit high doses of radiation there. It is well known that cancer cells adopt accelerated growth patterns. This fact enhances the requirement for biomolecules like aminoacids. With this in mind, this communication reports the study about the stability of Sm(III)-aminoacid complexes.
Potentiometric studies in aqueous solution (I = 0.5 and 0.15 mol dm-3 in NaClO4; 25 oC and 37 oC) were performed for Sm(III) alone and Sm(III) in presence of the aminoacids glycine, alanine, cysteine and glutamic acid. The potentiometric experimental data were analyzed using the SUPERQUAD program1.
In absence of other ligands, results show that Sm(III) only forms Sm(OH)2+ before precipitation as Sm(OH)3. In presence of the aminoacids, the metal mostly forms 1:1 species. However, they are not stable enough to prevent Sm hydrolysis over pH 6. This is a serious problem if the complex is intended to be assayed as a radiopharmaceutical for therapy.
In a second stage of this work, we studied the system Sm-edta. It is formed a single and very stable species, [Sm(edta)]-, in aqueous solution. X-ray diffraction measurements show that Sm in nine-coordinate with three coordination positions occupied by water molecules. So, it is reasonable to suppose that some of the water molecules can be substituted by aminoacids, if present in solution.
Potentiometric experiments in aqueous solution show that mixed ligand species are formed with Sm, edta and aminoacids. They are stable enough at physiological conditions.
As a consequence, these complexes have optimal properties to be assayed as radiopharmaceuticals for therapy.
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