Astatine species

It might be of interest to recall here the time-of-flight MS investigation by Appelman and coworkers14 from the sixties which allowed direct identification of the At+ ion—among other astatine species—owing to the extreme sensitivity of the method. 

Another controversial issue is the chemical form of astatine in neutral solutions. On the basis of extensive studies on extractability and complex formation, Visser23 has come to far reaching conclusions concerning the chemical and oxidation state of astatine species in neutral aqueous solutions. Rejecting the previously accepted assumption of the At(0) -... 

Linear dependence has been obtained for the experimental points (see Figure 1) giving a reaction constant p = -3.4, which confirms the electrophilic character of the astatine species replacing hydrogen in the above mixtures. The authors50 suggest protonated hypoastatite [AcOHAt]+ to be responsible for the substitution in these systems. 

Preliminary results from the on-line separation of At from molten ThF4,LiF in the 600 MeV C.E.R.N. synchrotron have been reported by Ravn et a/. The energies and intensities of y-rays and internal-conversion electrons from the electron capture and from the particle decay of "At have been measured. The rates of exchange of iodine and astatine species between submonolayers on Pt and aqueous solution have been compared. ... 

Serov, A., Aksenov, N., Bozhikov, G., Eichler, R., Dressier, R., Lebedev, V., Petrushkin, O., Piguet, D., Tiirler, A., Vogele, A., Wittwer, D., Gaggeler, H.W. Adsorption interaction of astatine species with quartz and gold surface. Radiochim. Acta 99, 593-599 (2011)... 

Only limited information about the electrochemical properties of astatine is available. The formation of a singly positively charged cation, At+, in aqueous and other solvent environments has been observed. A study in a nitric acid environment investigated the adsorption into ion exchange materials of this cation [206]. In a similar study in aqueous perchloric acid, the mobility of At+ was found to change with pH and the presence of a strongly water bound species, At(H20)2", with a pA of ca. 1.5 was proposed [207]. 

A separate section is devoted to the biomedical applications of 211At-labelled species because of their increased role in astatine research. 

Despite Visser s convincing results and argumentation, ready reactions of astatine with organic species cannot be excluded. 

An important conclusion drawn from the last two studies is that, with the help of trialkylstannyl derivatives, astatine can easily be incorporated into compounds with an aromatic ring or with an olefinic bond. This enables the method to be applicable for labelling a wide variety of biologically active species, drugs or proteins. 

The combination of triphenylphosphine with esters of trihaloacetic acids provides a reagent system for the stereo- and regio-selective conversion of alcohols into alkyl halides.The bromine-triphenylphosphine adduct has been used at low temperatures (-50 C in dichloromethane) for the removal of the tetrahydropyranyl protecting group from tetrahydropyranyl ethers derived from secondary and tertiary alcohols.The reactions of tertiary phosphines (and other trivalent phosphorus compounds) with iodine in aprotic solvents have received further study, a range of species being identified.The first reported study of the reactions of trivalent phosphorus compounds with monopositive astatine has led to the identification of stable complexes with triphenylphosphine, trioctylphosphine, and triethylphosphite. 

Ozone is formed by the photolytic decomposition of NO2 yielding oxygen radicals and by the reaction sequence NO2 — HNO3 — NO3 O3. In particular, the reaction of NO2 with hydroxyl radicals to form HNO3 increases ozone concentration because two radicals, NO2- and -OH, which catalyze ozone decomposition, are removed. Other radicals are also important for ozone destruction in the stratosphere, especially chlorine oxides see Chlorine, Bromine, Iodine, Astatine Inorganic Chemistif). The mechanism of ozone destruction is complicated as there many compounds involved. Chlorine nitrate and dinitrogen pentoxide can act as reservoir species for CIO-, NO2-, and NO3- radicals. 

A quick word about astatine may be of interest here. All isotopes of astatine are intensely radioactive even the most stable, At, has a half-life of only 8.1 h. Astatine chemistry is therefore understandably relatively little explored. It is utterly fascinating, however. Thus, condensed, bulk astatine (which is yet to be prepared) has been predicted to be metallic. Experimentally, there is significant evidence for At+ cations in aqueous solution. Two possible closed-shell structures for such species are the following ... 

He studied chemistry at the Technical University Dresden from 1976 to 1981. His diploma work was on the Production of At and investigations on cationic species of Astatine and their reactions and his PhD thesis 1984 On the chemistry of At(l)-complex formations. 

Champion J, Sabatie-Gogova A, Bassal F, Ayed T, Alliot C et al (2013) Investigation of astatine (III) hydrolyzed species experiments and relativistic calculations. J Phys Chem A 117(9) 1983-1990... 

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