Solution and solid-state structural chemistry of actinide hydrates and their hydrolysis and condensation products.

Oxo ligand functionalization in the uranyl ion (UO22

Actinide oxalates, solid state structures and applications

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.

/pdf/immobilization-of-metal-hexacyanoferrate-ion-exchangers-for-3qpcn1ccd8.pdf

Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents--A Mini-Review.

The use of radiopharmaceuticals for molecular imaging of biochemical and physiological processes in vivo has evolved into an important diagnostic tool in modern nuclear medicine and medical research. Positron emission tomography (PET) is currently the most sophisticated molecular imaging methodology, mainly due to the unrivalled high sensitivity which allows for the studying of biochemistry in vivo on the molecular level. The most frequently used radionuclides for PET have relatively short half-lives (e.g. 11C: 20.4 min; 18F: 109.8 min) which may limit both the synthesis procedures and the time frame of PET studies. Iodine-124 (124I, t1/2 = 4.2 d) is an alternative long-lived PET radionuclide attracting increasing interest for long term clinical and small animal PET studies. The present review gives a survey on the use of 124I as promising PET radionuclide for molecular imaging. The first part describes the production of 124I. The second part covers basic radiochemistry with 124I focused on the synthesis of 124I-labeled compounds for molecular imaging purposes. The review concludes with a summary and an outlook on the future prospective of using the long-lived positron emitter 124I in the field of organic PET chemistry and molecular imaging.

https://www.mdpi.com/1420-3049/15/4/2686/pdf

Iodine-124: A Promising Positron Emitter for Organic PET Chemistry

The behavior of Pu(VI) and Pu(V) in CH3COOH (HAc)-H2O solutions was studied by spectrophotometry. The absorption spectrum of Pu(VI) does not change on adding HAc to a concentration of 5 M in the presence of 0.5–1.0 M HClO4, but in solutions containing less than 0.001 M mineral acid, changes in the spectrum are observed at HAc concentration of 0.6 M.he major absorption band of PuO
 2
 2+
 ions, caused by an f-f transition, with increasing [HAc] is shifted from 830.6 to 836 nm, with a simultaneous decrease in the absorption intensity, which is due to formation of 1: 1 complexes of Pu(VI) with Ac− ions. In anhydrous HAc, the peak intensity increases again, owing to total change in the composition of the solvation shell. Pu(V) is unstable in 1–17 M HAc solutions and disproportionates to form Pu(VI) and Pu(IV). The Pu(V) loss follows a second-order rate law with respect to [Pu(V)] and accelerates with increasing HAc concentration. The reaction products exert opposite effects on the reaction rate: Pu(IV) accelerates the consumption of Pu(V), whereas Pu(VI) does not affect the process in dilute HAc solutions but decelerates the disproportionation in concentrated solutions owing to formation of a cation-cation complex with Pu(V).

Disproportionation of Pu(V) in the CH3COOH-H2O system

Capture of Pu(V), Np(V) and Pu(VI) from alkaline solutions by hydroxides of Pu(IV), Th(IV) and La(III)

The behavior of Pu(VI), Pu(V), and Pu(IV) in K(Li,Na)HCO2 and HCOOH + Li(Na)HCO2 solutions was studied by spectrophotometry. Changes in the spectra of a Pu(VI) solution, observed on adding alkali metal formates, suggest formation of Pu(VI) formate complexes. Changes in the absorption spectra of Pu(V), observed with an increase in the concentration of LiHCO2 or NaHCO2, suggest the appearance of Pu(V) formate complexes. The absorption spectra of Pu(IV) indicate that, in a wide range of formate concentrations, the composition of the Pu(IV) formate complexes under the examined conditions is constant. The Pu(VI) content in formate solutions decreases at a rate exceeding the rate of the Pu(VI) disappearance in 0.5–2 M HClO4 under the action of the 239Pu α-radiation. The tendency of Pu(V) to reduction and disproportionation in formate solutions depends in a complex fashion on the formate ion concentration and kind of the alkali metal. The kinetics of the Pu(V) consumption in HCOOH + Li(Na)HCO2 solutions was studied. The reaction starts with the formation of a Pu(V) formate complex, which interacts with Pu(V) aqua ions and Pu(V) formate complex to form dimers, with their subsequent protonation and transformation into Pu(VI) and Pu(IV).

Stability of Pu(VI) and Pu(V) in aqueous formate solutions

The radiolytic behavior of FNS composite ferrocyanide sorbent based on potassium nickel ferrocyanide and silica gel was studied. γ-Irradiation of the sorbent results in formation of hydrogen due to radiolytic decomposition of water in the solid phase. The hydrogen yield (molecules/100 eV) is 0.02 for the dry sorbent and 0.07 for the wet sorbent. The amount of hydrogen formed in the course of storage of the sorbent saturated with 137Cs was calculated. On irradiation of the dry sorbent in the potassium form to a dose of 4 MGy, the 137Cs distribution coefficient Kd decreases by a factor of 2.5. However, Kd of 137Cs on irradiated sorbents remains sufficiently high (>104), i.e., the FNS ferrocyanide sorbent shows high functional resistance to radiation. γ-Irradiation of dry and wet samples of the ferrocyanide sorbent to a dose of 4 MGy does not lead to oxidation of Fe(II) to Fe(III) in [Fe(CN)6] groups. Thus, FNS ferrocyanide sorbent is a radiation-resistant material suitable for recovery of cesium radionuclides from liquid radioactive wastes and the subsequent long-term and safe storage.

Radiation resistance of a composite ferrocyanide-silica gel sorbent

Complexes of 1,10-phenanthroline (phen) with Np(V) and Pu(V) benzoates of the compositions NpO2(phen)(OOCC6H5) and PuO2(phen)(OOCC6H5) were synthesized. A powder X-ray diffraction study showed that these compounds, depending on the preparation conditions, exist in the form of two phases having essentially the same composition but different powder patterns. The phases isolated from hot (70–100°C) solutions are isostructural with the previously described complexes AnO2(bipy)(OOCC6H5) (An = Np and Pu, bipy = 2,2′-bipyridine), i.e., in their structure there are dimeric (AnO2)22+ cations formed by mutual coordination of two AnO2+ ions via “yl” oxygen atoms. The compounds AnO2(phen)(OOCC6H5) prepared by slow crystallization in the cold or at weak (up to 45°C) heating are isostructural with each other but appreciably differ in the structure from the high-temperature phases. The electronic absorption spectra of the compounds and their thermal behavior were examined.

A. A. Bessonov

Papers

Disproportionation of Pu(V) in the CH3COOH-H2O system

Capture of Pu(V), Np(V) and Pu(VI) from alkaline solutions by hydroxides of Pu(IV), Th(IV) and La(III)

Stability of Pu(VI) and Pu(V) in aqueous formate solutions

Radiation resistance of a composite ferrocyanide-silica gel sorbent

Synthesis and properties of complexes of Np(V) and Pu(V) benzoates with phenanthroline