Astatine Standard Redox Potentials and Speciation in Acidic Medium

Abstract

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.

Effective bond orders from two-step spin–orbit coupling approaches: The I2, At2, IO+, and AtO+ case studies

“…11 Among the recent experimental highlights, it is worth quoting the determination of the ionization potential of the free atom, 12 or the determination of predominance domains in the Pourbaix diagram (E-pH) of At in aqueous solution. [13][14][15] One should also mention the theoretical prediction of a metallic behavior for condensed astatine, unlike the other halogens. 16 Furthermore, stable At cationic forms (At + and AtO + ) exist in aqueous solution and their coordination chemistry has been experimentally explored by reporting complexation constants with various inorganic ligands.…”

Radiopharmaceutical chemistry of targeted radiotherapeutics, part 4: Strategies for 211At labeling at high activities and radiation doses of 211At α-particles

“…Although it possibly could be a component of the At(1) peak, its presence becomes important only at pH much lower than those present in our experiments [21]. Moreover, although AtO+ can produce astatination reactions in trycyanomethanide and azide compounds [22], its suitability for the electrophilic astatination of organostannyl derivatives like BuSTB has not been documented.…”

Evaluation of a Wet Chemistry Method for Isolation of Cyclotron Produced [211At]Astatine

“…The fact that the 211 At species produced is not volatile indicates that may be the case. In addition to the oxidized forms of 211 At, use of 8 M HCl may produce a number of interhalogen species [24,36,38,39]. There was concern that oxidized forms of 211 At might be obtained in the final isolated solution (except where the distillation was conducted under reductive conditions).…”