Konstantin E. German

Speciation of heptavalent technetium in sulfuric acid: structural and spectroscopic studies

The speciation of Tc(vii) was studied in 12 M H(2)SO(4) by NMR, UV-visible and XAFS spectroscopy. Experimental results and density functional calculations show the formation of TcO(3)(OH)(H(2)O)(2).

Macrocyclic receptor for pertechnetate and perrhenate anions

The design and synthesis of a neutral macrocyclic host that is capable of perrhenate and pertechnetate recognition is described. The anion affinities and underlying coordination modes were estimated by several experimental and theoretical methods including a new technique--reverse (99)Tc NMR titration.

Characterization of technetium(vII) reduction by cell suspensions of thermophilic bacteria and archaea

Washed cell suspensions of the anaerobic hyperthermophilic archaea Thermococcus pacificus and Thermoproteus uzoniensis and the anaerobic thermophilic gram-positive bacteria Thermoterrabacterium ferrireducens and Tepidibacter thalassicus reduced technetium [99Tc(VII)], supplied as soluble pertechnetate with molecular hydrogen as an electron donor, forming highly insoluble Tc(IV)-containing grayish-black precipitate. Apart from molecular hydrogen, T. ferrireducens reduced Tc(VII) with lactate, glycerol, and yeast extract as electron donors, and T. thalassicus reduced it with peptone. Scanning electron microscopy and X-ray microanalysis of cell suspensions of T. ferrireducens showed the presence of Tc-containing particles attached to the surfaces of non-lysed cells. This is the first report on the reduction in Tc(VII) by thermophilic microorganisms of the domain Bacteria and by archaea of the phylum Euryarchaeota.

Oxygen isotope effect on NMR parameters of pertechnetate anion TcO 4

The effects of oxygen isotope substitution 16O ↔ 17O ↔ 18O in the coordination sphere of the pertechnetate anion (TcO4−) on the NMR 99Tc chemical shifts and 99Tc-17O and 17O-99Tc spin coupling constants have been studied by 17O and 99Tc NMR. The isotope shifts 16/17Δ and 16/18Δ in 99Tc NMR and the spin coupling constants of the Tc16O217O2−, Tc 16O318O−, Tc 16O317O−, Tc 16O217O18O−, and Tc16O218O2− isotopomers have been measured. For the Tc 16O318O− and Tc 16O317O− anions in an ammonium pertechnetate solution, the temperature dependences of the isotope shift in the temperature range 278–333 K are described by linear relationships 16/18Δ = −0.616 + 6.45 × 10−4T (ppm) and 16/17Δ = −0.302 + 2.67 × 10−4T (ppm), respectively. For the Tc16O317O− anion in a sodium pertechnetate solution, the magnitude of the 1Δ(16/17O) isotope shift nonlinearly decreases with increasing temperature. The nonlinear temperature dependence of the J(99Tc-17O) spin coupling constant and the extreme point on the curve of the 1Δ(16/18O) isotope shift versus temperature for the isotopomers in an NaTcO4 solution are presumably related to equilibrium between contact and water-separated ion pairs.

Structure and Solubility of Tetrapropylammonium Pertechnetate and Perrhenate

The crystal structure was determined and the physicochemical properties were studied for tetrapropylammonium pertechnetate and perrhenate. Pr4NMO4 (M = Tc, Re) are isostructural and crystallize as colorless prismatic crystals in the orthorhombic system, space group Pna21, Z = 4. For M = Tc at 25°C, a = 13.22(4) Å, b = 12.35(3) Å, c = 10.13(4) Å; for M = Re at −120°C, a = 13.169(2) Å, b = 12.311(2) Å, c = 10.107(1) Å. The Re-O distances are 1.677(12), 1.704(5), 1.719(4), and 1.739(11) Å. Each anion in this structure has four neighboring cations with Re…N distances of 5.06–5.34 Å. The solubility product of Pr4NTCO4 is (6.19 ± 0.50) × 10−5 mol2/L2. The Gibbs energy of dissolution of [(C3H7)4N]TcO4 in dilute aqueous solutions is 24.0 ± 0.5 kJ/mol. The association constant K1 for (Pr4N+)…(TcO4−) in water and aqueous solutions is 10.8 ± 0.7 L/mol. The solubility of Pr4NTcO4 increases with the solution acidity, similarly to the solubility of Bu4NTcO4. Upon precipitation of Pr4NTcO4 from model solutions containing (2.0–7.5) × 10−2 mol/L Tc in 3–4 M HNO3, (2.0–7.5) × 10−8 mol/L 239PuO2(NO3)2, and 5.7 mCi/L 106Ru(NO)(NO3)3, the technetium decontamination factors from 239Pu and 106Ru were (0.5–1.5) × 102 and (6.0–7.5) × 102, respectively.

Lithium pertechnetate trihydrate LiTcO4 · 3H2O: Synthesis and crystal structure

Lithium pertechnetate trihydrate was obtained and its crystal structure was examined; LiTcO4 · 3H2O crystallizes in hexagonal crystal system as colorless elongated prismatic crystals (space group P63/mc, Z = 2; at 100 K: a = 7.8604(1) Å, c = 5.4164(1) Å). This compound is isostructural with LiClO4 · 3H2O, LiBrO4 · 3H2O, and LiMnO4 · 3H2O.

Synthesis and crystal structure of anilinium pertechnetate and perrhenate at low and room temperatures

Anilinium pertechnetate (I) and perrhenate (II) salts were synthesized for the first time and their crystal structure was studied. The crystals of the compounds are isostructural (monoclinic system, space group P21/c). On cooling from 293 to 100 K, both compounds undergo a phase transition with doubling of the parameter a, the isostructural character being retained and the space group remaining the same. The phase transitions are accompanied by strengthening and change in the H-bond system.

Electrochemical Studies of Technetium–ruthenium Alloys in HNO3: Implications for the Behavior of Technetium Waste Forms

The electrochemical behavior of Tc–Ru alloys (Ru content, at. %: 3.2, 5.2, 20.1, 24.7) in 1 M HNO3 was studied. The transpassivation potentials (Etp) of Tc–Ru alloys were determined by linear voltammetry. The results show that the transpassivation potentials of the alloys increase with the Ru content. To understand the dissolution mechanism, electrolysis experiments at 1.2 V vs. Ag/AgCl were performed; the corrosion products of the alloys were characterized in solution by UV-visible spectroscopy and electrospray ionization mass spectrometry (ESI-MS). For Ru, a polymeric Ru(IV) species was detected, while for Tc the speciation was dominated by TcO4–.

Kinetics of the formation of precipitates and the physicochemical properties of technetium-99 and rhenium sulfides according to small-angle X-ray scattering and ultramicrocentrifugation data

The interaction of technetium and rhenium with sulfides in aqueous solutions was studied by small-angle X-ray scattering and ultramicrocentrifugation. It was shown that, although the stoichiometry of technetium sulfide corresponds to the formula Tc2S7–x, the oxidation state of technetium in it is +4 and the excess sulfur is bound into a disulfide group so that its formula can correctly be written as [Tc3(µ3-S)(µ2-S2)3(S2)(3n–n)/n)]n. The determination of the solubility of technetium sulfide is complicated by its tendency to form colloids, which was the reason why the above methods were chosen to find features of its formation and describe its solubility in solutions.

Technetium sulfide – formation kinetics, structure and particle speciation

Abstract Technetium sulfide formation kinetics was studied in the pH range 8 − 12 in presence of Na2S and phosphate buffer solution. The conditions for separation of Tc sulfide micro and nanoparticles were found with ultramicrocentifugation and the values of Tc sulfide solubility were demonstrated to be dependent on the Na2S concentration as C(Tc3S10+x) =− 9E − 5 ln [Na2S] − 2 · 10–5 M. The composition of Tc sulfide precipitate was elucidated with EXAFS, RBS and chemical analyses as Tc3S10+x or [Tc3(μ3 − S)(S2)3(S2)3/3]n in agreement with recent Lukens data.