Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium in fast breeder reactors (FBRs) fuel reprocessing

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium is developed for the recovery of uranium and plutonium present in spent fuel of fast breeder reactors (FBRs). Effect of pH on the solubility of carbonates of uranium and plutonium in ammonium carbonate medium is studied. Effect of mole ratios of uranium and plutonium as a function of uranium and plutonium concentration at pH 8.0–8.5 for effective separation of uranium and plutonium to each other is studied. Feasibility of reconversion of plutonium in carbonate medium is also studied. The studies indicate that uranium is selectively precipitated as AUC at pH 8.0–8.5 by adding ammonium carbonate solution leaving plutonium in the filtrate. Plutonium in the filtrate after acidified with concentrated nitric acid could also be precipitated as carbonate at pH 6.5–7.0 by adding ammonium carbonate solution. A flow sheet is proposed and evaluated for partitioning and reconversion of uranium and plutonium simultaneously in the FBR fuel reprocessing.     

Research status in preparation of FePO4: a review

The cathode is the most important component of a lithium-ion battery. The olivine structure lithium iron phosphate (LiFePO₄) with its numerous appealing features, such as high theoretical capacity, acceptable operating voltage, increased safety, environmental benignity, and low cost, has attracted extensive interest as a potential cathode material for Li-ion batteries. As a precursor, FePO₄ can be used to produce LiFePO₄ on a large scale with high bulk density, discharge rate, and capacity. This can be realized by controlling the crystal size and morphology of FePO₄. The characteristics, structure, and synthesis methods of FePO₄ are discussed in this review. The relative merits of these synthetic methods, as well as some suggestions on how to improve them, are also presented.     

Bio-inspired phosphole-lipids: from highly fluorescent organogels to mechanically responsive FRET

Sensitive gels: the amphiphilic features of phosphole-lipids lead to intriguing self-assembly properties and the formation of highly fluorescent organogels. Moreover, the dynamic structural features of the system make it possible to amplify the mechanochromic emission shifts (100 nm) in a donor-acceptor system through thermally and mechanically responsive fluorescence resonance energy transfer (FRET).     

Free Energy Calculations Give Insight into the Stereoselective Hydroxylation of α-Ionones by Engineered Cytochrome P450 BM3 Mutants

Previously, stereoselective hydroxylation of α-ionone by Cytochrome P450 BM3 mutants M01 A82W and M11 L437N was observed. While both mutants hydroxylate α-ionone in a regioselective manner at the C3 position, M01 A82W catalyzes formation of trans-3-OH-α-ionone products whereas M11 L437N exhibits opposite stereoselectivity, producing trans-(3S,6S)-OH-α-ionone and cis-(3S,6R)-OH-α-ionone. Here, we explore the stereoselective C3 hydroxylation of α-ionone by Cytochrome P450 BM3 mutants M01 A82W and M11 L437N using molecular dynamics-based free energy calculations to study the interaction between the enzyme and both the substrates and the products. The one-step perturbation approach is applied using an optimized reference state for substrates and products. While the free energy differences between the substrates free in solution amount to ～0 kJ mol(-1), the differences in mutant M01 A82W agree with the experimentally obtained dissociation constants K(d). Moreover, a correlation with experimentally observed trends in product formation is found in both mutants. The trans isomers show the most favorable relative binding free energy in the range of all four possible hydroxylated diastereomers for mutant M01 A82W, while the trans product from (6S)-α-ionone and the cis product from (6R)-α-ionone show highest affinity for mutant M11 L437N. Marcus theory is subsequently used to relate the thermodynamic stability to transition state energies and rates of formation.     

Bromenium‐Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal‐Free [3+2+1]/[4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation

We present a detailed study of a [3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Br^δ+? X^δ?) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one‐pot operation. The formation of amidines involves the ring‐opening of VCPs with Br? X, followed by a Ritter‐type reaction with chloramine‐T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a [4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo[4.3.0]‐, ‐[4.3.1]‐ and ‐[4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a π‐stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6‐311+G** and M06‐2X/6‐31+G* levels of theory in gas‐phase calculations suggest the ring‐opening of VCP is initiated at the π‐complex stage (between the double bond and Br? X). This can be clearly perceived from the solution‐phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero‐bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity.     

Water-in-trichloroethylene emulsions stabilized by uniform carbon microspheres

Uniform hard carbon spheres (HCS), synthesized by the hydrothermal decomposition of sucrose followed by pyrolysis, are effective at stabilizing water-in-trichloroethylene (TCE) emulsions. The irreversible adsorption of carbon particles at the TCE-water interface resulting in the formation of a monolayer around the water droplet in the emulsion phase is identified as the key reason for emulsion stability. Cryogenic scanning electron microscopy was used to image the assembly of carbon particles clearly at the TCE-water interface and the formation of bilayers in regions of droplet-droplet contact. The results of this study have potential implications to the subsurface injection of carbon submicrometer particles containing zero-valent iron nanoparticles to treat pools of chlorinated hydrocarbons that are sequestered in fractured bedrock.     

Chiroptical dissymmetries in fluorescence excitation from single molecules of (M-2) helicene dimers

We report on the single-molecule chiroptical properties of "right"-handed bridged triaryl amine helicene dimers, MH2. Using an experimental setup to precisely define the circular excitation polarization at the sample plane, we investigated the circular dichroic response in luminescence from individual molecules in which induced ellipticity from microscope optics is minimized. Our results comparing circular anisotropies in fluorescence excitation from MH2 and perylene diimide (PDI), an achiral, centrosymmetric chromophore, demonstrate a significant reduction in the breadth of the distribution of circular dissymmetry parameters obtained from modulation of the circularly polarized excitation source (457 nm). For PDI, we observe a symmetric distribution of circular anisotropy parameters centered about zero, with a fwhm of 0.25. For MH2, we observe an asymmetric distribution peaked at g = -0.09, with a slightly larger width as the corresponding PDI distribution. These results indicate that the large dissymmetry parameters (|g| > 0.5) in fluorescence excitation described in our original report (Hassey, R.; et al. Chirality 2008, 20, 1039-1046 and Hassey, R.; et al. Science 2006, 314, 1437-1439) were indeed affected by (at the time, unknown) linear polarization artifacts. However, the present results on MH2 provide compelling evidence for single-molecule circular dissymmetries much larger than solution or thin-film ensemble values, defined primarily by the enhanced rotatory strength (relative to the monomer), and restricted orientation at the sample surface.     

Conductive molecular silicon

Bulk silicon, the bedrock of information technology, consists of the deceptively simple electronic structure of just Si-Si σ bonds. Diamond has the same lattice structure as silicon, yet the two materials have dramatically different electronic properties. Here we report the specific synthesis and electrical characterization of a class of molecules, oligosilanes, that contain strongly interacting Si-Si σ bonds, the essential components of the bulk semiconductor. We used the scanning tunneling microscope-based break-junction technique to compare the single-molecule conductance of these oligosilanes to those of alkanes. We found that the molecular conductance decreases exponentially with increasing chain length with a decay constant β = 0.27 ± 0.01 ?(-1), comparable to that of a conjugated chain of C═C π bonds. This result demonstrates the profound implications of σ conjugation for the conductivity of silicon.     

Application of Cu·FeHCF coated acrylic fibre for the separation of Cs isotopes in drinking water to determine fallout 137Cs

Ten fresh water samples of wells and rivers from the environment of Tarapur Maharashtra Site were analyzed to evaluate and establish the fall out level of ¹³⁷Cs activity concentration using large volume of water samples. A radiochemical separation method suitable for the analysis of large volume of water sample based on the adsorption of Cs isotopes on coated acrylic fibres was standardized. ¹³⁴Cs isotope was used for monitoring the radiochemical recovery of the analysis. Radiochemical recovery was obtained in the range of 74?C98% for a sample volume of 250?L or more. The fall out level ¹³⁷Cs concentration in river/dam water was found to be in the range of 0.205 to 0.268?mBq?L^?1. The fall out level annual effective dose through water ingestion pathway for a member of public was evaluated to be 2.27?×?10^?9?Sv.     

Synthesis of γ-Fe2O3 by Thermal Decomposition of Ferrous Gluconate Dihydrate

Ferrous gluconate dihydrate (FeC₁₂H₂₂O₁₄⋅2H₂O), was prepared and its thermal decomposition was studied by means of simultaneous thermal analysis, supplemented with a two probe d.c. electrical conductivity measurements under the atmospheres of static air, dynamic air and dynamic nitrogen. Under all the atmospheres final product was found to be α-Fe₂O₃ with FeO, γ-Fe₂O₃, Fe₃O₄ etc. as probable intermediates. γ-Fe₂O₃ was formed under the atmosphere of dynamic air containing water vapour. γ-Fe₂O₃ thus synthesised was characterised for its structure, morphology, thermal and magnetic behaviour. This revised version was published online in August 2006 with corrections to the Cover Date.