Astatine standard redox potentials and speciation in acidic medium.
A combined experimental and theoretical approach is used to define astatine (At) speciation in acidic aqueous solution and to answer the two main questions raised from literature data: does At(0) exist in aqueous solution and what is the chemical form of At(+III), if it exists. The experimental approach considers that a given species is characterized by its distribution coefficient (D) experimentally determined in a biphasic system. The change in speciation arising from a change in experimental conditions is observed by a change in D value. The theoretical approach involves quasi-relativistic quantum chemistry calculations. The results show that At at the oxidation state 0 cannot exist in aqueous solution. The three oxidation states present in the range of water stability are At(-I), At(+I), and At(+III) and exist as At(-), At(+), and AtO(+), respectively, in the 1-2 pH range. The standard redox potentials of the At(+)/At(-) and AtO(+)/At(+) couples have been determined, the respective values being 0.36 +/- 0.01 and 0.74 +/- 0.01 V vs NHE.
Champion
J
J
Laboratoire SUBATECH, IN2P3/CNRS/EMN Nantes/Universite de Nantes, 4 rue A. Kastler, BP 20722, 44307 Nantes Cedex 03, France.
Alliot
C
C
Renault
E
E
Mokili
B M
BM
Chérel
M
M
Galland
N
N
Montavon
G
G
D001246:Astatine / Q000737:chemistry*; D017942:Nitric Acid / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D012996:Solutions
D012996:Solutions; D017942:Nitric Acid; D001246:Astatine