Volume 60, Nº 1 (2018)

Coordination of Np(III–VII) atoms in the crystal structures of all the oxygen-containing compounds characterized with the R-factor lower than 0.1 was analyzed with the aid of Voronoi–Dirichlet polyhedra (VDPs). Nine types of NpO_n coordination polyhedra (6 ≤ n ≤ 12) are realized. The most characteristic of them are trigonal dodecahedra [Np(IV)], penta- and hexagonal bipyramids [Np(V) and Np(VI)], and octahedra [Np(VII)] based on square NpO₄^– cores. For Np atoms of a fixed oxidation state, the volume of their VDPs in the NpO_n complexes is virtually independent of the coordination number n. The VDP parameters can be used for determining the valence state of the Np atoms, finding compounds with the maximal nonlinearity of the NpO₂⁺ and NpO₂²⁺ dioxocations, and revealing errors in the crystal structure data. Anion–anion interactions involving NpO₄^– and OH^– ions are an important structure-forming factor in Np(VII) compounds. In sublattices consisting of Np atoms only (Np sublattices), the rule of 14 neighbors is fulfilled. Compounds in which binding Np···Np 5f interactions in crystal structures are possible were revealed by analysis of the VDPs of the atoms in the Np sublattices. In such compounds, the metal atoms form bent Np=O–Np bridging fragments and the Np^VO₇ bipyramids are combined in dimers sharing a common axial edge, with the Np atoms of the dimers being also bound via two carboxylate bridges.

Trivalent transplutonium (TPE) and rare earth (REE) elements are extracted to more than 80% with 30% TBP in Isopar M from solutions containing 0.06–0.5 M HNO₃ and a salting-out agent, NH₄NO₃, in a concentration of ≥6 M. The elements are stripped from the organic phase with 0.1 M HNO₃. The Am(III)/Eu separation factors vary from 1.8 to 2, which can be used for their extraction separation. The Cm/Am(III) separation factors in 0.06–3 M HNO₃ are in the range from 1.1 to 1.2; therefore, to separate these elements, higher oxidation states of Am, Am(VI) and Am(V), should be used. The effect of various factors on the stability of Am(VI) was examined, and the conditions of the existence of Am(VI) and Am(V) in ≤0.1 M HNO3 solutions containing ~8 M NH₄NO₃ were determined. Curium is extracted with 30% TBP in Isopar M virtually completely, whereas americium only partially (≤30%) passes into the organic phase in the form of Am(III). In the process, high degree of separation of Cm from Am(V) remaining in the aqueous phase is reached (≥99.9%).

The kinetics of the ⁹⁹Мо sorption onto T-5 sorbent at different pH values of the nitric acid solution was studied. The previously suggested limiting steps of the ⁹⁹Мо sorption onto Т-5 sorbent were confirmed. The effective rate constant of the molybdenum sorption onto titanium hydroxide (fast step) as a function of pH passes through a maximum at pH from 4.5 to 5.5, which does not correspond to the maximum of the pH dependence of the distribution coefficient but correlates with the maximal content of one of the sorbable species, НМоО₄^–, in the solution. Thus, the rate of Mo sorption onto titanium hydroxide as a function of pH passes through a maximum at a minimal negative charge of the sorbate near pH of the isoelectric point of the sorbent. The kinetic studies confirm the scheme of the sorption of molybdenum hydroxo complexes onto titanium hydroxide, suggested previously on the basis of the logk_d–рН and log ε–log[m] sorption isotherms. According to this scheme, simultaneous redistribution and sorption of sorbable molybdenum species, МоО₂ОН⁺, Н₂МоО₄, and НМоО₄^–, are possible.

A convenient synthetic pathway for ¹⁴C labeling of fentanyl [N-(1-phenethyl-4-piperidinyl)- propionanilide], a widely used narcotic analgesic agent, with good radiochemical yield was developed.

Uridine, a pyrimidine nucleoside essential for the synthesis of RNA and biomembranes, was radiolabeled with ^99mTc to obtain a potential tumor imaging agent. The maximal radiochemical yield of about 96.5%, as determined by paper chromatography and instant thin-layer chromatography, was reached under the following optimum conditions: 1 mg of uridine, 20 μg of SnCl₂·2H₂O as reducing agent, 20 mg of mannitol as a stabilizer, and pH 8. ^99mTc-uridine is stable in vitro at room temperature for up to 6 h post labeling. The biodistrbution study in tumor-bearing mice shows high target-to-nontarget ratio. These results match with the high docking score of the complex on uridine phosphorylase enzyme. ^99mTc-uridine shows promise as a tumor imaging agent.

Ni and Ni/Pd nanoparticles stable in the liquid phase and in the adsorbed state were prepared by radiation-chemical reduction of metal ions in aqueous-organic inverse micellar solutions. The optical absorption and luminescence spectra of nanoparticle solutions were studied immediately after preparation in the presence of oxygen and without it. Changes in these spectra, resulting from evolution of the nanoparticles in the course of storage and from pH variation, were examined.

A natural polymineral compound in which the major uranium-containing mineral is polycrase (Ti- Ta-niobate) described by the formula АВ₂О₆ was chosen as a model for studying the behavior of recoil atoms produced by α-decay of actinides. Polycrase, despite its metamict structure, is characterized by the following features distinguishing it from Ti-Ta-niobates of the formula А₂В₂О₇ (pyrochlore and betafite): (1) 1/3 of uranium atoms preserve the initial valence state, U(IV); (2) the U(IV) fraction is characterized by the isotope activity ratio AR(²³⁴U/²³⁸U) close to that at secular equilibrium; (3) the uranium atoms that underwent oxidation “memorize” their radiogenic origin; as a result, the AR(²³⁴U/²³⁸U) ratio in the U(VI) fraction is 0.90, and in the most altered part of the mineral it decreases to 0.77; (4) the parent uranium is relatively stable in the metamict structure of polycrase: The half-leaching time for ²³⁸U atoms is 2 times longer than that in betafite, zircon, or sphene.

The radiocesium interception potential (RIP) characterizing the ability of a sorbent to retain ¹³⁷Cs⁺ cations in the presence of competing K⁺ or NH₄⁺ cations [RIP(K) or RIP(N)] under the conditions controlled by selective sorption was determined for various materials. RIP(K) (mg-equiv kg^–1) is 44–720 and 260–1200, and RIP(N), 21–189 and 96–250 for sapropels of the organic and silica types, respectively. For sapropels of the organic type, the selectivity coefficient K_s(N/K) for the ¹³⁷Cs-selective sorption sites varies from 2.1 to 3.8, and for silica sapropels (Lake Dobeevskoe) it reaches 4.5–4.8, suggesting the presence of illite-type particles, which significantly influence the ¹³⁷Cs uptake by these types of sapropels. The highest RIP(K) values for the sapropels studied are reached at the organic to mineral matter ratios in the interval 0.43–0.61.