The special case of Actinide(IV) complexation by the carboxylic function of small and large organic ligands

Accidental release of radionuclides from mining activities, nuclear energy production, and radioactive waste storage sites requires research to predict the fate and mobility of these contaminants in the environment and more specific in organisms. To date, the interaction of actinides with biological systems is widely unkown, due to the lack of structural information on the molecular level. The aim of this presentation is to summarize recently explored coordination principles of tetravalent actinides with small carboxylic and aminocarboxylic ligands as well as the interaction with proteins.
Tetravalent actinides form with carboxylate ligands in aqueous solutions at low pH values usually monomeric complexes. They show at the other hand a strong tendency toward hydrolysis already at low pH. As the pH reaches the onset of An(IV) hydrolysis, olation and oxolation occur as competing reactions to the carboxylate complexation. We observed under these circumstances the formation of several well-defined polynuclear species. The carboxylic group acts in such systems as a terminating ligand and stabilizes nanosized polynuclear clusters in solution and in the solid state. It is important to note that this reaction prevents widely the formation of polynuclear hydrolysis species as well as the formation of An(IV) hydrous oxide colloids.