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  • Author: Bohumir Grüner x
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Abstract

An industrial liquid–liquid extraction process for reprocessing of spent nuclear fuel will inevitably lead to radiolysis of the phases, since the process streams contain highly radioactive species. Solvents containing one of the BTBP (6,6′-bis(5,6-dialkyl-[1,2,4]-triazin-3-yl)-2,2′-bipyridine) molecules intended for the separation of trivalent actinides (An) from lanthanides (Ln), the so called C5-BTBP, have shown a dramatic decrease in both distribution ratios and An/Ln separation factor when irradiated; hence, the molecule is highly unstable towards radiolysis.

HPLC-, APCI(+)-MS and LC-MS analyses were performed on irradiated solvents containing initially 0.005 M C5-BTBP dissolved in either hexanol or cyclohexanone. The decrease in concentration of starting molecule as well as the increase in concentration of various degradation products were studied with quantitative and semi-quantitative measurements. Structures were suggested for the degradation products produced in highest yields and these were compared to previously proposed structures for the same products.

A synthesis of the first double-decker sandwich ion [(1',2'-C2B9H11)-3,3'-Co-(1,2-C2B8H10)-6,3"-Co-(1",2"-C2B9H11)]2– (DD 2–) derivatives is described, having been developed in connection with our search for biologically active substances. A series of B-substituted hydroxyl derivatives was prepared by direct hydroxylation of the ion using aqueous sulfuric acid. Two isomers of monohydroxy derivatives were isolated. The main product was substituted at the central “canastide” ion fragment, whereas the substitution site for the minor isomer corresponded to a B(8) atom of one of the terminal 11-vertex dicarbollide parts. Similarly, the disubstitution occurred slightly more preferentially on the “canastide” fragment providing the main isomeric derivative with a symmetric structure. The cesium salt of this ion was characterized by X-ray diffraction. Two other isomeric species have one substituent sitting on the “canastide” ion and the second present on the dicarbollide ligand in apart or syn-geometric arrangement. A new zwitterion anion [(1',2'-C2B9H11)-3',3-Co-(8-(CH2)4O-1,2-C2B8H9)-6,3"-Co-(1",2"-C2B9H11)-]1– was prepared by the reaction of the parent ion with tetrahydrofuran (THF), activated by BF3·OEt2. This new compound serves as a versatile building block for constructing organic derivatives, as exemplified by the ring cleavage by various amines or phenolate ions and the synthesis of a basic series of compounds of general formulation [(1',2'-C2B9H11)-3',3-Co-(8-X-(CH2)4O-1,2-C2B8H9)-6,3"-Co-(1",2"-C2B9H11)]n where the organic end-groups X adjacent to the “canastide” moiety via a B-oxatetramethylene spacer corresponds to C4H9NH2, NC5H5, N(C2H5)3, (C6H5)3P (n = 1), or (4-t-Bu-C6H4-1-O) and (2-CH3O-C6H4O) (n = 2). We show that dicluster compounds with two identical DD 2– anion units or asymmetric molecules containing two different clusters, the cobalt bis(dicarbollide) and the DD 2– anion, are accessible using this building block. All compounds were characterized by high-resolution NMR (1H, 13C, and 11B) and mass spectrometry. Some of the compounds were tested by in vitro assay for their ability to inhibit the HIV-protease (HIV-PR) enzyme. The majority of the tested species proved substantially high activity toward the HIV-PR, exhibiting on the other hand a noncompetitive mechanism of the inhibition.

Abstract

Spent nuclear fuel contains many highly radioactive species; hence solvents used in reprocessing will be subjected to radiolysis. In this study, solvents containing one of the BTBP molecules intended for the separation of trivalent actinides and lanthanides, the so called C5-BTBP, have been subjected to radiolysis and hydrolysis. We present here that this compound shows a dramatic decrease in both distribution ratios and separation factor when irradiated with higher doses up to 50 kGy; particularly in the presence of an aqueous phase. Furthermore, fast hydrolytic degradation is observed, which significantly contributes to the overall degree of decomposition. This is supported by speciation studies performed by HPLC and LC-MS methods. Proposed structures of the highest-yield degradation products are presented and they seem to confirm previously drawn structures for these products. From these studies it can be concluded that the presence of nitric acid or nitrate during irradiation leads to higher content of species containing keto groups.

Abstract

The highly selective nitrogen donor ligand CyMe4BTBP for An(III) separation by solvent extraction was irradiated in a 60Co γ-source under varying conditions. Organic solutions of 10 mmol/L ligand in 1-octanol were contacted with different concentrations of nitric acid to observe the influence of an aqueous phase during irradiation. In subsequent liquid-liquid extraction experiments, distribution ratios of 241Am and 152Eu were determined. Distribution ratios decreased with increasing absorbed dose when irradiation was performed in the absence of nitric acid. With addition of nitric acid, initial distribution ratios remained constant over the whole examined dose range up to 300 kGy. For qualitative determination of radiolysis products, HPLC-MS measurements were performed. The protective effect of nitric acid was confirmed, since in samples irradiated with acid contact, no degradation products were observed, but only addition products of the 1-octanol molecule to the CyMe4BTBP molecule.

Abstract

Radiation stability of CyMe4-BTPhen was examined in systems with three selected cyclohexanone-based diluents. Accelerated electrons were used as a source of ionizing radiation. The CyMe4-BTPhen radiation degradation identification and characterization of the degradation products were performed by high performance liquid chromatography (HPLC) and mass spectrometry (MS) analyses. Residual concentrations of tested ligand were determined. Moreover, extraction properties of the solvents irradiated at two different doses were compared with the extraction properties of non-irradiated solvents to estimate the influence of the presence of degradation products in the organic phase.