Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH) sub(2) super(-) over At super(-) in Basic Conditions

• Published in: Chemistry : a European journal 2016-02, Vol.22 (9), p.2964-2971
• Main Authors: Sergentu, Dumitru-Claudiu, Teze, David, Sabatie-Gogova, Andrea, Alliot, Cyrille, Guo, Ning, Bassal, Fadel, Da Silva, Isidro, Deniaud, David, Maurice, Remi, Champion, Julie, Galland, Nicolas, Montavon, Gilles
• Format: Article
• Language: English
• Subjects: Astatine; Chromatography; Competition; Constants; Formations; Mathematical analysis; Pourbaix diagrams; Quantum mechanics
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201504403

It is generally assumed that astatide (At super(-)) is the predominant astatine species in basic aqueous media. This assumption is questioned in non-complexing and non-reductive aqueous solutions by means of high-pressure anion-exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10 super(-6.9) has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH) sub(2) super(-), is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO sub(2) super(-) species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH) sub(2) super(-) species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of super(211)At radiolabeling protocols. Where it's At: The outcomes of chromatography, competition experiments, and quantum mechanical calculations are combined to demonstrate that the predominant astatine species in basic and non-reductive conditions is not At super(-), but actually AtO(OH) sub(2) super(-).