Pourbaix Diagram of Astatine Revisited: Experimental Investigations

Abstract

The Pourbaix diagram of an element displays its stable chemical forms with respect to the redox potential and pH of the solution, whose knowledge is fundamental for understanding and anticipating the chemistry of the element in a specified solution. Unlike most halogens, the Pourbaix diagram in the aqueous phase for astatine (At, Z = 85) is still under construction. In particular, the predominant domains of two astatine species assumed to exist under alkaline conditions, At − and AtO(OH) 2 − , need to be refined. Through high-performance ion-exchange chromatography, electromobility measurements, and competition experiments, the existence of At − and AtO(OH) 2 − has been confirmed and the associated standard potential has been determined for the first time (0.86 ± 0.05 V vs the standard hydrogen electrode). On the basis of these results, a revised version of astatine's Pourbaix diagram is proposed, covering the three oxidation states of astatine that exist in the thermodynamic stability range of water: At(−I), At(I), and At(III) (as At − , At + , AtO + , AtO(OH), and AtO(OH) 2 − ).211

In vivo stability of 211At-radiopharmaceuticals: on the impact of halogen bond formation

“…ethyl 3-astatobenzoate, EAB in Chart 1). 12 At is indeed much more sensitive to oxidation than other halogens, 13,14 and the negative impact of oxidation on the in vivo stability of At–C Ar bonds was recently confirmed. 9 A third hypothesis is investigated in this work, where the deastatination mechanism is governed by specific interactions with protein functional groups.…”

Ion exchange behavior of astatine and bismuth

“…[5][6][7] However, the aqueous chemistry of astatine deals with À1, +1, and +3 states only. 8 The astatine neutral species, oxidation state 0, is believed to escape aqueous media. 9 To confirm the two highest oxidation states, +5 and +7, the presence of aggressive oxidizing agent xenon difluoride is required.…”

“…10,11 And this means that these species exist outside of the window of stability for water. 8,12 It is believed that AtO + is the most stable species in the aqueous phase, representing the +3 oxidation state. [13][14][15][16][17] However, At + can also be found in acidic solutions.…”