Linear alkyl diamine-uranium-phosphate systems: U(VI) to U(IV) reduction with ethylenediamine

Mild-hydrothermal reactions in acidic medium using 1,3-diaminopropane, 1,4-diaminobutane, and 1,5-diaminopentane as structure directing agents led to three-dimensional (3D) uranyl phosphates (CH?)?(NH?)?{[(UO?)(H?O)][(UO?)(PO?)]?} (C3U5P4), (CH?)?(NH?)?{[(UO?)(H?O)][(UO?)(PO?)]?} (C4U5P4) and (CH?)5(NH?)?{[(UO?)(H?O)][(UO?)(PO?)]?} (C5U5P4). The structures of (C4U5P4) and (C5U5P4) were solved in the space group Cmc2? using single-crystal X-ray diffraction data. The compounds are isostructural to the corresponding uranyl vanadates and contain the same 3D inorganic framework built from uranyl-phosphate layers of uranophane-type anion topology pillared by [UO?(H?O)] pentagonal bipyramids. In neutral or basic medium the alkyl diamines decompose to give ammonium uranyl phosphate trihydrate. In the same conditions by using ethylenediamine, unexpected reduction of uranium(VI) to uranium(IV) occurs leading to the formation of (CH?)?(NH?)?[U(PO?)?] (C2UP2) single crystals. C2UP2 undergoes a reversible phase transition from triclinic to monoclinic symmetry at about 230 °C. The structure of the two forms results from the stacking of inorganic layers (∞)1[U(PO?)?]2?, and organic layers containing ethylene diammonium ions, the two layers being linked by hydrogen bonds. Single crystals of (CH?)?(NH?)?[PO?OH] (C2HP) are formed by evaporation of the solution after filtering of C2UP2 single crystals. The structure of C2HP contains infinite (∞)1[PO?OH]2? chains connected by (CH?)?(NH?)?2? ions through hydrogen bonds.     

STUDIES OF THE ROLE OF THE COAT PROTEIN IN THE U.V. PHOTOINACTIVATION OF U(1) AND U(2) STRAINS OF TMV*

Abstract— Two properties of the u.v. inactivation process in the u.v. sensitive U(2) strain have been investigated: (1) The increased binding of protein to RNA induced by irradiation of the virus at 254 nm; (2) The action spectrum for u.v. inactivation of U(2) between 250 nm and 285 nm. The extent of the u.v. induced binding of protein to RNA is similar to that previously found in the resistant U(1) strain, thereby eliminating the possibility that the capacity for this binding phenomenon bears any correlation to the difference in u.v. sensitivities of these two viruses at 254 nm. The results indicate that the radiation induced interaction of protein and RNA in U(1) and U(2) are probably similar. The action spectrum for U(2) resembles the absorption spectrum of the RNA between 250 nm and 285 nm implicating the RNA as the primary absorber leading to inactivation of the virus in this region of the spectrum. Quantum yields calculated for U(2) virus and free TMV-RNA irradiated at 254 nm reveal that the irradiated free RNA may be as much as 1–4 times more sensitive to inactivation at this wavelength than RNA in the intact virus. It is concluded that the coat protein of U(2) probably offers some protection to the enclosed RNA against u.v. damage at 254 nm, therefore, the difference in u.v. sensitivity between U(1) and U(2) TMV at this wavelength is a consequence of a difference in the degree of protection offered by the respective coat proteins to the enclosed RNA.     

Palladium catalyzed oxidation of allylsilanes with U.V. light and molecular oxygen (1)

Photolysis of oxygenated acetone solutions of allylsilanes containing small amounts of palladium led to α,β-ethylenic alcohols, aldehydes or ketones. Efficient regiospecific oxidation can be observed when the allylsilane was substituted by an arylsulphonyl group.     

High-energy (neodymium) laser pyrolysis of U.S. coals

As part of a study exploring conditions that influence coal pyrolysis, the effects of neodymium laser heating upon five different rank coals have been studied. Gaseous products from neodymium-laser pyrolysis of all coal types can be explained by condensation reactions during the cooling of high-temperature systems. The use of neutral or reducing atmospheres (helium, hydrogen or deuterium at two atmospheres) does not significantly alter the product distributions, although some deuteration of products was observed. High-speed photography was used to determine the dynamics of the laser interactions.     

Extraction of U(VI) with Cyanex 302

U(VI) was quantitatively extracted from 1·10⁻³M HNO₃ using 5·10⁻³M Cyanex 302 in xylene and was stripped from organic phase with 5M HCl. The optimum extraction conditions have been evaluated by studying parameters like acidity, effect of diluents, extractant concentration and period of equilibration. Based on this data, the separations of uranium from binary and complex metal mixtures and its recovery from uranmicrolite tailings (leachate) were successfully tested. Uranium can be determined with a relative standard deviation of 0.4%.     

Structure and hydrolysis of the U(IV), U(V), and U(VI) aqua ions from ab initio molecular simulations

Ab initio molecular dynamics simulations at 300 K, based on density functional theory, are performed to study the hydration shell geometries, solvent dipole, and first hydrolysis reaction of the uranium(IV) (U(4+)) and uranyl(V) (UO(2)(+)) ions in aqueous solution. The solvent dipole and first hydrolysis reaction of aqueous uranyl(VI) (UO(2)(2+)) are also probed. The first shell of U(4+) is coordinated by 8-9 water ligands, with an average U-O distance of 2.42 ?. The average first shell coordination number and distance are in agreement with experimental estimates of 8-11 and 2.40-2.44 ?, respectively. The simulated EXAFS of U(4+) matches well with recent experimental data. The first shell of UO(2)(+) is coordinated by five water ligands in the equatorial plane, with the average U═O(ax) and U-O distances being 1.85 ? and 2.54 ?, respectively. Overall, the hydration shell structure of UO(2)(+) closely matches that of UO(2)(2+), except for small expansions in the average U═O(ax) and U-O distances. Each ion strongly polarizes their respective first-shell water ligands. The computed acidity constants (pK(a)) of U(4+) and UO(2)(2+) are 0.93 and 4.95, in good agreement with the experimental values of 0.54 and 5.24, respectively. The predicted pK(a) value of UO(2)(+) is 8.5.     

Isotope exchange and separation factor of238U/235U for the system U(III)/U(IV) in aqueous/organic phases

A study of the isotope exchange reaction U(III)_org/U(IV)_aq in the extraction system: 7M HCl — tributyl phosphate (TBP) — toluene has been performed. For 20 s of contact the results show a separation factor²³⁵U/²³⁸U of 1.014. This large separation factor is explained by the oxidation reaction of²³⁵U(III) and²³⁸U(III).     

英国的国家理科课程研究（一）──国家理科课程的由来及演变

本文对英国国家理科课程的提出、设置和框架、及其演变等,作了较为详细的研究;分析了理科课程成为国家核心课程的原因;对“理科课程在学校课程中的地位”、“为哪些人的理科”、“广泛和平衡的理科课程”、“持续和进步”等国家理科课程的基本理念,进行了探讨。     

Polymer battery R&D in the U.S.

Polymer electrolytes that have been developed for battery applications fall into two general classes, neat or “pure” polymer and plasticized or gel in which the polymer is combined with a conducting organic electrolyte. The polyethylene oxide (PEO) and its modifications are typical of the “pure” polymer electrolytes. They have poor conductivity at room temperatures, but at elevated temperatures, their conductivity is of the order of 10⁻³ to 10⁻⁴ S/cm. The PEO electrolytes have found application in the high temperature (>60°C) lithium metal anode battery systems. The high temperature necessary for good operation makes them unsuitable for use in small consumer appliances. The polymer electrolyte battery development activities have resulted in several high performance battery systems now just entering the market. Not all of the developments have resulted in commercial cell production. The commercialization activities of high performance lithium‐ion (Li‐Ion) batteries have been based on two general plastic polymer systems: poly‐vinylidene difluoride‐hexafluoropropylene copolymer (PVdF‐HFP) and polyacrylates. The polymer cells are expected to have advantages in manufacturing, flexibility, thin cell formats and lightweight packaging. Important parameters in PVdF gel electrolyte performance include the electrolyte type (combination of organic carbonates), temperature, and HFP copolymer content. Li‐Ion coin cells fabricated with a polyolefin separator with either liquid electrolyte or with the PVdF gel polymer electrolyte have equivalent performance.     

Catalytic reduction of U(VI) to U(IV) using hydrogen with platinum loaded on alumina and silica

During the reprocessing of spent nuclear fuel, uranium (U) and plutonium (Pu) are together extracted by employing tri-n-butyl phosphate (TBP)/dodecane mixture and their partitioning is achieved by adding uranous nitrate. The partitioning agent, uranous is conventionally produced by the electrolytic reduction of uranyl nitrate. An alternate route for the reduction of U from (VI) to (IV) using hydrogen (H₂) as reductant was developed using platinum (Pt) based catalyst. Improvements in the development of the catalyst have been carried out in order to reduce the requirement of Pt without affecting the reduction performance. Experiments using 2 wt% Pt loaded on alumina beads and alumina powder have been performed and results are discussed. As the catalyst supported on alumina was found to be unstable in acidic environment, Pt loaded on silica powder has also been developed. Pt loaded on alumina and silica substrates have been tried to envisage the reduction behaviour using H₂ as reductant in presence of hydrazine nitrate which acts as U(IV) stabiliser as well as reductant. Parametric studies have been carried out to optimise the process parameters namely pressure, temperature, U concentration, free acidity, hydrazine concentration and catalyst to U (C/U) ratio. 2 wt% Pt loaded on silica has been selected for further scale up studies for making uranous.     

Spectrophotometric (U.V.) investigation on Metal Biguanidinium Complexes

From the U.V. spectra study of series of metal biguanides, attempt has been made to find out any interaction between the filled ligand orbital with the vacant metal orbital which may give rise to delocalisation of electron system over the whole complex molecule. This type of interaction may develop aromatic character in metal biguanide ring. The benzenoid character of the metal acetylacetonate can be cited as parallel to that of the metal biguanide. The U.V. study of metal biguanides concludes that there is a definite indication of the suggested overlap of the ligand and metal orbitals with consequent shifting of absorption bands with different substitutions.     

Calculation of the U.V. Spectrum of p-disilylbenzene

The electronic spectrum of p-disilylbenzene has been calculated by the Pariser-Parr-Pople method in order to test theoretical methods of including the d type orbitals of silicon.

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Zusammenfassung Das Elektronenspektrum des p-Disilylbenzols wurde nach der Pariser-Parr-Pople-Methode berechnet, um theoretische Methoden zu prüfen, die die d -Orbitale des Siliziums berücksichtigen.

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Résumé Le spectre électronique du p-disilylbenzène a été calculé par la méthode de Pariser-Parr-Pople afin d'éprouver l'inclusion dans la méthode des orbitales de type d du silicium.

     

Kinetics of the reaction of U(VI) with benzene-1,2-diphosphonic acid

The kinetics of the reaction between dioxouranium(VI) and benzene-1,2-diphosphonic acid (BzDPA) has been investigated by stopped-flow spectrophotometry. The rate of reaction of uranyl ions with Arsenazo III (2,7-bis(2,2'-arsonophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid) in 50:50 methanol-water solutions was also determined. Both formation and dissociation rate constants for the 1:1 complex between uranyl-BzDPA in acidic solutions were resolved. To gain insight into the effect of solvation on the progress of the reaction, the system was studied in triply distilled water, in 50:50 methanol-water, 80:20 methanol-water and in 50:50 tert-butanol-water as a function of temperature at pH 1.0. The rates of complex formation and dissociation reactions decrease as methanol substitutes for water in the medium and further decrease as tert-butanol replaces methanol as co-solvent. Activation parameters are most consistent with an associative process governing the progress of both complex formation and dissociation reactions. Introduction of alcoholic co-solvents results in notably more negative activation entropies for both complex formation and dissociation reactions, while the activation enthalpies are only slightly reduced in the mixed methanol-water medium. These results are compared with the kinetic features of other U(VI) systems.     

Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex

Reaction of the N-heterocylic carbene ligand ⁱPrIm (L¹) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl₄ resulted in U(IV) and U(V) complexes. Uranium's +V oxidation state in (HL¹)₂[U(V)(TMSI)Cl₅] (TMSI=trimethylsilylimido) ( 2 ) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L¹)₂(TMSA)Cl₃] ( 1 ) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.     

Unitary group approach to the many-electron problem. II. Adjoint tensor operators for U(n)

In this paper we present a derivation of the U(n) adjoint coupling coefficients for the representations appropriate to many-electron systems. Since the states of a many-fermion system are to comprise the totally antisymmetric Nth rank tensor representation of U(2n), the work of this paper enables the matrix elements of the U(2n) generators to be evaluated directly in the U(n) × U(2) (i.e., spin orbit) basis using their transformation properties as adjoint tensor operators. A connection between the adjoint coupling coefficients, as derived in this paper, and the matrix elements of certain (spin independent) two-body operators is also presented. This indicates that in CI calculations, one may obtain the matrix elements of spin-dependent operators from the known matrix elements of certain spin-independent two-body operators. In particular this implies a segment-level formula for the matrix elements of the U(2n) generators in the spin-orbit basis.     

Order parameters from U.V. spectra with incompletely polarized absorption bands

A new method is developed for the determination of Saupe's order parameters S* and D* from I.R. or U.V. spectra and the temperature dependence of their degree of anisotropy R. This method can be applied to molecules with one uniformly polarized band and another band of mixed polarization if all bands concerned are polarized in the same plane. For that a relation D* = f(S*) between the order parameters as a function of temperature is necessary, which can be obtained from the lines of constant entropy in the order triangle. These isentropics are calculated from the orientational distribution function of the ordered system. The resulting function D* = f(S*) is equal to that of the mean field theory given by Luckhurst et al., but can be derived here in a very easy way. The method is applied to diaminoanthraquinones with a point symmetry C_2v.     

Adsorption of U(VI) on montmorillonite pillared with hydroxy-aluminum

Hydroxy-aluminum pillared Na-montmorillonite(OH–Al-MT) was prepared for studying sorption of U(VI) in the existence of soluble calcium (Ca²⁺), carbonate ion (CO₃^2?) and humic acid. Various characterizations confirm that hydroxy-aluminum was successfully pillared into Na-montmorillonite (Na-MT). The effects of pH, concentration of Ca²⁺ and CO₃^2? as well as HA on the sorption capacity of Na-MT and OH–Al-MT for U(VI) has been investigated by batch experiments. Additionally, the kinetics, isotherms and thermodynamics of adsorption of U(VI) were discussed in detailed. The study indicates that OH–Al-MT can be a potentially promising low-cost adsorbent for removal of U(VI) in wastewaters.