Chemical behaviors of tritium produced by the 6Li(n, α)T reaction in lithium oxide

The chemical forms of tritium released from neutron-irradiated crystalline powders of Li₂O, LiOH and Li₂CO₃ have been investigated over the temperature range of 100–600°C with radio-gas chromatography and mass spectrometry. When the target materials are heated to 600°C under vacuum after the irradiation, more than 96% of tritium is released as hydrogen oxide, HTO, and collected in the cold trap cooled at −72°C. Tritium is also released in forms such as HT (and T₂), CH₃T and C_nH_2n+x − T (n = 2, x = 0, 1, 2), although their percentages are rather low. The release of HTO is interpreted by supposing that recoil tritium produced by the ⁶Li(n, α)T reaction is first stabilized as LiOT in the solids and then released by the reaction LiOT·LiOH(c)→Li₂O(c)+HTO(g) at a temperature between 250 and 400°C.     

Extraction of U(VI), Th(IV) and some fission products from nitric acid by n,n-disubstituted amides and effect of γ-ray irradiation on the extraction

In this work, ten disubstituted amides have been synthesized and the extracting ability for U and Th fission products (mainly Zr, Nb and Ru) and the tendency of third phase formation have been studied. From the preliminary studies, two disubstituted amides, N-octylcaprolactam (OCLA) and N-(2-ethyl) hexylcaprolactam (EHCLA) were chosen for further studies. All studies were compared with those obtained by using TBP under exactly the same conditions. The dependence of aqueous nitric acid concentration, extractant concentration, temperature, -ray irradiation on extraction of Th, U and some fission products were studied. Back extraction of Th and U from organic phases and third phase formation were also studied. The studies of the reaction mechanism indicate that Th and U are extracted as disolvates, whereas HNO₃ is extracted as monosolvate. Extraction distribution of Th and U decrease with increase of temperature, indicating the extraction reaction to be exothermic. Preliminary studies show that OCLA and EHCLA have better -irradiation stabilities compared with TBP.     

Influence of α- and β-Cyclodextrins on the Separation of Positional Isomers of Benzoic Acid Nitro, Amino, Chloro, and Hydroxy Derivatives by Capillary Electrophoresis

The positional isomers of nitro-, amino-, chloro-, and hydroxybenzoic acids were separated by capillary electrophoresis. The introduction of 1 to 10 mM of natural - and -cyclodextrins into the background electrolyte significantly enhanced the resolution of the capillary electrophoresis system in its zone version, while the isomers were not separated in the absence of cyclodextrins (CDs). Additives of both individual CDs and their mixtures were used. Micellar electrokinetic chromatography with or without CD additives was used for the separation of analytes along with capillary zone electrophoresis.     

Changes in the phase composition of oxide layers produced by microarc oxidation on Al–Si and Mg alloys induced by additions of SiO<Subscript>2</Subscript> nanoparticles to the electrolyte

In oxide layers produced by microarc oxidation on Al–Si- and Mg-based alloys, addition of nano-dispersed silicon dioxide to the electrolyte was found to cause a shift in the phase composition toward high-temperature phases and ultra-high-pressure phases. For the first time, ultra-high-pressure phases were detected in oxide layers formed by microarc oxidation on AK6M2 alloy (stishovite) and commercially pure magnesium MG96 (wadsleyite).     

Conformational, steric and electronic effects on the site- and chemoselectivity of the metal-catalyzed reaction of N-bis(trimethylsilyl)methyl, N-(2-indolyl)methyl α-diazoamides

The Rh(II)- and Cu(II)-catalyzed reactions of N-bis(trimethylsilyl)methyl, N-(2-indolyl)methyl α-diazoamides are investigated to delineate how conformational, steric and electronic factors influence the site- and chemoselectivity of the metallocarbenoid reaction. The N-bis(trimethylsilyl)methyl (N-BTMSM) group is found to be essential in promoting the metallocarbenoid reaction at the N-(2-indolyl)methyl moiety as well as providing subtle but effective conformational influence about the amide N-C(α) sigma bond in diazoamides carrying an N-C(α) alkoxymethyl side-chain, to afford excellent site- and chemoselectivity. In general, the metal-catalyzed reactions are found to favor metallocarbenoid addition to the indole C(2)-C(3) double bond over C-H insertion to give cyclopropanated products (tetracyclic γ-lactams); however, chemoselectivity is also affected by steric effects, as revealed in the N-[2-(3-methylindolyl)]methyl diazoamides, and to some extent by the nature of the catalyst employed, as seen in the N-C(α)-alkoxymethyl diazoamides. The tetracyclic γ-lactams are found to rearrange to give good to high yields of the tricyclic indole derivatives under the metallocarbenoid reaction conditions or under acidic conditions. The propensity of the tetracyclic γ-lactams to undergo rearrangement is found to be dependent on the nature of the α-substituent on the original diazo carbon and the indole N-substituent.     

Effect of P-Containing Ligands on the Structural and Optical Properties of (CdSe)<Subscript>n</Subscript> (n = 3, 6, 10) Clusters

The effect of phosphorus-containing ligands on the structure, energetics and properties of the (CdSe)_n clusters (n = 3, 6, and 10) with different number of PH₃ and PMe₃ ligands were studied by using density functional theory calculations. The P atom in the ligand interacts with Cd and forms a strong Cd–P coordination bond. The introduction of ligands does not change the cluster architecture, but leads to considerable changes in Cd–Se bondlength, charge distribution, binding energy, HOMO–LUMO gap and optical absorption. The ligand influence is enhanced with increasing ligand coverage. A blueshift in absorption band was predicted for the clusters with increasing ligands, resulting from the electron donating characteristics of the ligands that hamper electron transition from Se to Cd. As P-containing ligands are often used in the preparation of CdSe nanocrystals, our calculations reveal the influence of ligand-cluster interaction on the cluster geometrical and electronic properties, which would be helpful for the nanocrystal design and synthesis.     

Design, synthesis and evaluation of new α-nucleophiles for the hydrolysis of organophosphorus nerve agents: application to the reactivation of phosphorylated acetylcholinesterase

A series of new α-nucleophiles including oximes and amidoximes have been synthesized, and their ability to efficiently and selectively cleave the P-S bond of organophosphorus nerve agents has been evaluated. The relationship between the chemical structure of the α-nucleophiles and their reactivity towards PhX hydrolysis is reported. A significant effect induced by an ortho-hydroxyl group of aryl- and pyridyl-oximes, amidoximes on their organo-phosphono-thioase reactivity was discovered. The evaluation of the initial rates of PhX hydrolysis reaction in the presence of α-nucleophiles allowed the discovery of new uncharged molecules with increased reactivity compared to positively charged 2-pralidoxime used as antidote. The mechanism of their action was studied in details by kinetic analysis, HPLC and LC-MS methods. The most promising structures were then considered as potent in vitro reactivators of phosphylated acetylcholinesterase (AChE), which was confirmed by the preliminary results of AChE reactivation initially inhibited by VX.     

Effects of the alkali-metal cation size on molecular and extended structures: formation of coordination polymers and hybrid materials in the homologous series [(4-Et-C6H4OM)·(diox)n], M = Li, Na, K, Rb, Cs

The complete series of group 1 metal 4-ethylphenoxide (4-Et-C(6)H(4)O(-)) networks have been synthesized using 1,4-dioxane (diox) as a neutral linker. [{(4-Et-C(6)H(4)OLi)(4)·(diox)(2.5)}·diox](∞) (1) and [{(4-Et-C(6)H(4)ONa)(6)·(diox)(3)}(∞)] (2) form 2D and 3D networks, respectively, composed of discrete aggregates linked by diox. Compound 1 forms a hexagonal layered structure with Li(4)O(4) cubanes acting as nodes, whereas compound 2 forms a primitive cubic network (pcu) with Na(6)O(6) hexameric nodes. [{(4-Et-C(6)H(4)OK)(3)·diox}(∞)] (3), [{(4-Et-C(6)H(4)ORb)(2)·(diox)(0.5)}(∞)] (4), and [{(4-Et-C(6)H(4)OCs)(2)·(diox)(0.5)}(∞)] (5) are composed of isostructural 1D inorganic rods that are linked through diox to form pcu-type networks. Compound 5 is the first example of a network built from cesium inorganic rods.     

Comparison of the effects of ionization mechanism, analyte concentration, and ion “cool-times” on the internal energies of peptide ions produced by electrospray and atmospheric pressure matrix-assisted laser desorption ionization

The propensities of a series of peptide ions produced by both electrospray and atmospheric pressure matrix assisted laser desorption ionization (AP-MALDI) to fragment in an ion trap mass spectrometer under various conditions were studied in detail by measuring the extent of fragmentation of precursor ions by collision induced dissociation (CID) as a function of applied resonance excitation RF voltage. For the most basic peptides, the energy required to fragment MH+ ions generated by electrospray exceeded that required to fragment equivalent AP-MALDI ions under identical instrumental conditions; the reverse was observed for a peptide incorporating no basic residues, while peptides of intermediate basicity showed little difference between the ionization methods. This correlation between peptide basicity and the difference in the energy required to induce fragmentation of MH+ ions generated by AP-MALDI and electrospray is attributed primarily to a trend in the internal energies of the ions generated by AP-MALDI (the greater the difference in gas-phase basicities between the matrix and the analyte the greater the internal energy of the analyte ions produced). Furthermore the internal energies of ions produced by AP-MALDI, but not the equivalent ions formed by electrospray, were observed to decrease with decreasing analyte concentration. We attribute this finding to the cooling effect of endothermic dissociation of analyte ion/matrix molecule clusters following the matrix assisted laser desorption step. Time-resolved analyses (measurement of extent of fragmentation of precursor ions by CID as a function of pre-CID "cool times") revealed that cooling periods in excess of 250 ms were required to achieve internal energy equilibrium through cooling collisions with the helium buffer gas. Furthermore, these analyses demonstrated that, even after these extended cooling times, equivalent ions formed by the two ionization techniques showed different propensities to fragment. We conclude that the two different ionization techniques produce ion populations that may differ in their three-dimensional structure.     

Measurement of the 238U(n,γ)239U reaction cross sections in the energy range of 2.0–5.0 MeV by using a neutron activation technique

The neutron capture cross-sections of ²³⁸U at the neutron energies of 4.38?±?0.05 MeV, 3.02?±?0.49 MeV and 2.04?±?0.26 MeV have been measured using the activation method and off-line gamma-ray spectrometric technique. The effects of neutron flux fluctuation, multiple scattering, flux self-shielding and gamma-ray self-absorption were corrected. The excitation function of the ²³⁸U(n,γ)²³⁹U reaction was also calculated using the TALYS-1.9 code. The experimental results were compared with the evaluated data, the theoretical data and the previous experimental data.

     

The relevance of the nuclearity of the metal in the cocyclization of α, ω-diynes and nitriles catalyzed by mesitylene solvated cobalt atoms; preliminary EPR studies

The clustering when mesitylene-solvated cobalt atoms are allowed to warm from the cocondensation temperature, affords cobalt compounds of both low and high nuclearity which have different catalytic properties in the synthesis of pyridines from α, ω-dialkynes and nitriles.     

Activation cross sections for the 110Pd(n,2n) reaction and the isomeric cross-sections ratio of 109m,gPd in the neutron energy range of 13–15 MeV

Journal of Radioanalytical and Nuclear Chemistry - The 110Pd(n,2n)109m,gPd reaction cross-sections and the isomeric cross section ratios (σm/σg) in the neutron energy range of...     

Formation of defect,oxygen vacancy creation,and shifting of phonon mode by Li3+ swift heavy ion irradiation on Zn1 − x Mn x O thin films

Journal of Solid State Electrochemistry - Thin films of pure, Mn-substituted ZnO were synthesized by dip coating technique and irradiated thin films by Li3+ swift heavy ions (SHIs) with fluence...     

Measurement of the neutron activation constants Q 0 and k 0 for the 27Al(n, γ)28Al reaction at the JSI TRIGA Mark II reactor

Measurements of the neutron activation constants Q ₀ and k ₀ for the ²⁷Al(n, γ)²⁸Al reaction have been performed in two irradiation channels with different spectral characteristics at the JSI TRIGA Mark II reactor. In the determination of Q ₀ the fission spectrum contribution to the reaction rates has been corrected for. The final experimental value of the Q ₀ factor was found to differ significantly from the adopted value in the k ₀-database. The experimental value of the k ₀ factor is in agreement with the recommended value in the k ₀-database. The thermal cross-section and resonance integral for the reaction were found to be in good agreement with the values calculated from the cross-sections from the ENDF/B-VII.1 library.     

Measurements of activation cross-sections for the 101Ru(n,p)101Tc reaction for neutrons with energies between 13 and 15 MeV

In this study, activation cross-sections were measured for the ¹⁰¹Ru(n,p)¹⁰¹Tc reaction at three different neutron energies from 13.5 to 14.8 MeV. The fast neutrons were produced via the ³H(d,n)⁴He reaction on K-400 neutron generator. Induced gamma activities were measured by a high-resolution gamma-ray spectrometer with high-purity germanium detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The data for ¹⁰¹Ru(n,p)¹⁰¹Tc reaction cross-sections are reported to be 15.7 ± 2.0, 18.4 ± 2.7 and 22.0 ± 2.4 mb at 13.5 ± 0.2, 14.1 ± 0.2, and 14.8 ± 0.2 MeV incident neutron energies, respectively. Results were compared with the previous works.     

Characterization of the fluxes of neutral and positively charged clusters (Agn and Agn+; n≤4) produced by argon ion sputtering of silver

The emission of neutral and positively charged silver clusters during sputtering of a polycrystalline silver target by 5 keV Ar⁺ ion bombardment has been studied and the sputter ejected silver flux has been characterized. As a result, the silver flux is found to be strongly dominated byneutral clusters rather than cluster ions. The contribution of neutral clusters in the overall silver flux decreases rapidly and monotonically with increasing cluster size n and decreases, in addition, with decreasing bombarding energy. The well known alternation of the secondary ion intensities of Ag _n ⁺ as a function of cluster size (higher intensities for odd n) is found to be correlated with the effective ionization potentials of the corresponding sputtered neutral clusters.     

Regioselective CC bond formation between ethylene and α-naphthylcarbaldimines catalyzed by Ru3(Co)12: NMR spectroscopic investigations on the proceeding of the reaction

The reaction of ethylene with imines derived from α-naphthylcarbaldehyde catalyzed by Ru₃(CO)₁₂ leads to the selective and quantitative formation of products in which one molecule of ethylene has been inserted into the CH bond in ortho position with respect to the exocyclic imine substituent. The stoichiometric reaction of the same ligands with Ru₃(CO)₁₂ leads to dinuclear ruthenium carbonyl complexes showing the same regioselectivity of CH activation but the hydrogen atom is shifted in an intramolecular hydrogen transfer reaction towards the former imine carbon atom. If the catalytic alkylation of α-naphthylcarbaldimines is monitored by NMR the occurrence of the dinuclear product of the stoichiometric reaction is observed before the reaction again quantitatively yields the imines bearing an ethyl group in 2-position of the naphthalene core. This proofs that there must be an equilibrium between the dinuclear ruthenium carbonyl complex which is also observed if α-naphthylcarbaldimines are treated with an equimolar amount of Ru₃(CO)₁₂ and another ruthenium compound where the ethylene might be inserted catalytically into a ruthenium carbon bond.     

Photo-induced reduction of Cr<Superscript>6+</Superscript> by the hybrid systems “Cu<Superscript>II</Superscript> complex with Schiff base and TiO<Subscript>2</Subscript>”: dependence on irradiation wavelength

The synthesis of novel Cu^II complexes with a Schiff base obtained by condensation of salicylaldehyde and an l-aspartic acid ester are described. The physicochemical properties of the complexes were compared with those of related Cu^II complexes obtained earlier. All the complexes studied were characterized by elemental analysis as well as by IR, UV-Vis, and EPR spectroscopies. The activity of the complexes and their hybrid systems (HS) with TiO₂ in visible-light-driven photocatalysis in organic solvents was investigated. After irradiation with visible light, the complexes and corresponding HS reduce Cr⁶⁺ to Cr³⁺ more efficiently than bare TiO₂. To determine the molecular orbital compositions and energies and to explain the electronic spectra and redox properties of the systems studied, density functional calculations of the optimized structures of representative model complexes were performed.