R. Dreyer

Synthesis and characterization of cationic astatine compounds with sulphur-containing ligands stable in aqueous solutions

The formation of cationic astatine compounds with thiourea, thiourea derivatives and some N-acylthioureas was investigated in aqueous solutions. The ion mobilities in free electrolytes were determined for the detection of carrier-free astatine compounds and their characterization. Informations about the stability of this group of compounds could be given after investigations in the presence of halogenide and pseudo halogenide ions /Cl−, Br−, I−, SCN−/. First results on the reaction of At/θ/+ with thiourea derivatives and N-acylthioureas in acid and neutral solutions are reported. The cationic astatine compound formation with representatives of this group is shown.

Pseudohalogen compounds of astatine: synthesis and characterization of At/I/-tricyanomethanide- and At/I-azide-compounds

Reactions of At/⊖/+, “Ato.H2O”, AtCl2− and AtBr2 with the pseudohalogenides tricyanomethanide and azide are described. Information on the compound formation of astatine with C/CN/3− and N3− could be obtained on the basis of electromigration investigations under variation of the conditions /composition of the electrolyte, pH, exchange reactions of ligands/. For the reaction: [At/H2O/C/CN/3]+C/CN/3−⇆[At/C/CN/3/2]+H2O at 301 K and u=0.075 mol.l−1 K2=/675±25/ [1.mol−1] and uo=−/3.50±0.10/×10−4 [cm2.s−1.V−1]. According to this astatine/I/-tricyanomethanide is classified between AtI2− and At/SCN/2−. First investigations in azid-containing systems confirm the formation of astatine/I/-azide-compounds. Their composition is probably At/N3/2−. There is no dependence of the ion mobility of astatine/I/-azide in the investigated range on azide concentration which is due to its high stability.

COMPLEX FORMATION EQUILIBRIA BETWEEN ASTATINE(I) AND SULPHUR-CONTAINING CHELATING LIGANDS

Abstract Complex compounds between [ 211 At] astatine(I) and chelating ligands were characterized by electromigration in free electrolytes. O, S and N served as donor atoms in the ligands. Complexes of the type (AtXL) (X − = Cl − and Br − ) are formed in ligand exchange reactions, and their stability constants were assessed for X − being Br − . In the case of astatine(I) the stability depends on the kind and number of donor atoms, as well as on substituents at the nitrogen and on the basicity of the ligand. The behaviour of astatine(I) is typical for a strongly polarizable acceptor. The experiments were carried out at 298 K in anhydrous ethanolic solutions at constant ionic strength adjusted to 0.05±0.01 M with Na(H)ClO 4 .

Characterization of99mTc/99Tc-hydroxycarboxylic acid chelates by high voltage electrophoresis without supporting material

Ion mobilities of different99mTc- and99Tc chelates prepared by reduction of pertechnetate by Sn(II) in the presence of citric, malic, tartaric, gluconic, and α-hydroxyisobutyric acid as ligands have been measured by means of electrophoresis without supporting material. All the chelates investigated proved to be anions in the pH range of 2–7. Both the Tc(V)- and Tc(IV) compounds with the same ligand including the99mTc preparation show identical ion mobilities and dissociation characteristics.

Zur anorganischen Chemie des monovalenten Astats

There is given a review on the level of astatine chemistry in oxydation state +1. According to the position of astatine in the periodic system At(I) has “metallic” properties. They may be seen in the existence of similar changed cation At(0)+ in acid water solutions and in complex formation reactions with halogenides to anionic forms and with thioureas its derivates and N-acylthioureas to cationic forms which are almost very stable in water solutions. The information on optimal synthese conditions, composition, existence and stability area of At(I)-complexes and on the calculation of stability constants mainly based on electromigration in free electrolys solutions.

Stability constants of At(I)-complexes with thiourea, iodide and mixed ligands in ethanol and water

The ion mobilities of [211At] At(I) in dependence on thiourea (tu) concentration, iodide concentration and a mixture of both ligands were measured by the electromigration method in free electrolytes. An equilibrium model was developed for the characterization of electromigration curves which permitted the calculation of stability constants and ion mobilities of the complexes [AtI], [AtI2]−, [Attu]+, [Attu2]+ and [AtItu] existing in these solutions. Ethanol and water served as solvents. The temperature was 298 K and the ionic strength was about 0.05 mol/dm3.

Optimization of bombardment conditions of the209Bi/α, 2n/ cyclotron production of211At

The production of astatine isotope 211 for nuclear therapeutic applications requires to minimize its210At contaminations. This work provides a numerical programme, allowing an optimization of bombarding conditions of the cyclotron isotope production in order to obtain high yields of the mean isotope as well as lowest contaminations of other by-produced nuclides. Finally, results are compared with experimental values.

Investigation of the complex formation of technetium with thiourea by spectrophotometry and electromigration

TcO4− is reduced by thiourea /tu/ to Tc/III/ in 6N HCl. By capillar electrophoresis three different cations have been identified with electrophoretic mobilities of u=/4.3−4.8/x10−4 u=/3.2−3.8/x10−4, and u=/2.2−2.8/x10−4 cm2 v−1s−1. These species were assigned to complex cations [Tc/tu/6]3+, [Tc/tu/5Cl]2+, and [Tc/tu/4Cl2]+, respectively. [Tc/tu/6]3+ was identified by spectrophotometry according to recently published data. [Tc/tu/5Cl]2+ was isolated and chemically characterized. The formation of the monovalent cation [Tc/tu/5Cl2]+ was concluded from spectrophotometrical measurements.

Electromigration of carrier-free radionuclides

Using a special type of on-line electromigration measurements of γ-emitting radio-nuclides in homogeneous aqueous electrolytes free of supporting material, complex formation of carrier-free241Am-Am(III) has been studied in perchlorate electrolytes, T=298.1 (1) K. Stoichiometric stability constants for oxalate ligand of log K1=5.01 (13), 5.11 (13) and 5.38 (18) as well as log K2=3.15 (15), 3.19 (14) and 3.58 (26) were obtained at the overall ionic strength of μ=0.10, 0.05 and 0.01, respectively. The corresponding thermodynamic stability constants are log K10=5.90 (15) and log K20=3.73 (18). The sulfate ligand values of log K1=2.5 (2) were obtained both in acidic and neutral solutions, μ=0.10.

Electromigration of carrier-free radionuclides. XIII: Ion mobilities and hydrolysis of 241Am-Am(III) in aqueous inert electrolytes

The electromigration behaviour of carrier-free241Am−Am(III) in inert electrolytes, μ=0.1 (C104−), T=298.1(1) K, was studied. On the basis of the overall ion mobilities of241Am−Am(III) on pH between pH 5.5 and 12.9, the stoichiometric hydrolysis constants p3β3=23.8(9), and pK1=6.9(2) were obtained. For K4 a limitation of pK4≧14.4(3) was possible, because no formation of anionic hydrolysis products in solutions pH≦12.9 was registered. The individual ion mobility of the241Am−Am3+ decrease in the range pH 5.5–3 from +6.85(15) up to +5.50(15)·10−4 cm2·s−1·V−1. Dependences of this effect on overall ionic strength, inert electrolyte anion, and the temperature of the electrolytes were studied in acidic and neutral solutions.