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[en] The mutual separation of Am, Cm and lanthanides (Ln) by the hydrophilic and lipophilic ligands present in both aqueous and organic phases was studied. The hydrophilic ligands used here are DTPA (diethylene-triamine-N,N,N’,N’’,N’’-pentaacetic acid), malonamide, amic acid, TEDGA (N,N,N’,N’-tetraethyl-diglycolamide) and DOODA(C2) (N,N,N’,N’-tetraethyl-3, 6-dioxaoctanediamide) and four types of extractants, TODGA (N,N,N’,N’-tetraoctyl-diglycolamide), TDdDGA (N,N,N’,N’-tetradodecyl-diglycolamide), DOODA(C8) (N,N,N’,N’-tetraoctyl-3, 6-dioxaoctanediamide) and DOODA(C12) (N,N,N’,N’-tetradodecyl-3, 6-dioxaoctanediamide). DOODA(C8, 12) can extract light lanthanides with high D values into the organic phase. On the other hand (TO, TDd)DGA shows the opposite trend for Ln extraction. The high separation factor, over 1000, between D for La and that for Gd can be seen in the extraction using the extractant, TDdDGA, and DOODA(C2) as the masking agent in the aqueous phase. The separation factors for Am/Cm by DOODA(C8, C12) and (TO, TDd)DGA are 1.51-1.94, while values over 3 can be obtained by the conditions introduced in this work. (author)
[en] In this study, we report the first direct observation of the transient spin-state in the disordered system by time-resolved XAFS (X-ray absorption fine structure) using a pulsed hard X-ray beam. By detecting the evolution of the inner-atomic transition of the divalent iron ion, the transient spin-crossover transition from 1A1 low spin state to 5T2 high spin state has been directly observed on the picosecond timescale. Furthermore, the time-resolved investigation in the X-ray absorption near-edge structure and the extended X-ray absorption fine structure provided dynamic information on the altered electronic states of the iron as well as information on the structural change in the Fe-N bond elongation of 0.17 A resulting from the formation of the high-spin excited state. This unique experimental technique probes the excited states and provides a new level of understanding of ultrafast reactions in spin crossover transitions as well as in magnetic photocatalysts, nanomagnets, biological magnetic systems, and photo-induced phase transition. (author)
[en] Since the discovery of the fact that compounds bearing a vinylic fluoride moiety often exhibit remarkable biological activities such as enzyme inhibitors, many synthetic methods for fluorine-substituted vinylic compounds have been developed. The synthesis of selectively fluorinated building blocks, such as arylsubstituted fluoro-alkenes, also has become an area of interest in recent years. Herein we describe a novel and practical method for the synthesis of 1,1-difluoro- and 1-fluoroalkenes starting from easily accessible trifluoroacetophenone derivatives. Various 1,1-difluoro- and 1-fluoroalkenes were prepared by the reaction of the corresponding tosyl hydrazones that were derived from trifluoroacetophenone derivatives by treating with alkyl or aryllithium reagents via addition-elimination and single electron transfer (SET) mechanism
[en] The materials composed of the 3d series transition metals are introduced into the hydrocarbon steam-reforming reaction in order to enhance the H2 production and abruptly depress the catalytic deactivation resulting from the strong sintering between the Ni component and the γ-Al2O3 support. The conventional impregnation method is used to synthesize the Ni/3d series metal/γ-Al2O3 materials through the sequentially loading Ni source and the 3d series metal (Ti, V, Cr, Mn, Fe, Co, Cu, and Zn) sources onto the γ-Al2O3 support. The Mnloaded material exhibits a significantly higher reforming reactivity than the conventional Ni/γ-Al2O3 and the other Ni/3d series metal/γ-Al2O3 materials. Particularly the addition of Mn selectively improves the H2 product selectivity by eliminating the formation of CH4 and CO. The H2 production is maximized at a value of 95% over Ni(0.3)/Mn(0.3)/γ-Al2O4(1.0) with a butane conversion of 100% above 750 .deg. C for up to 55 h
[en] We fabricated ceria (CeO2) nanofibers by applying a mixed solution of polyvinylpyrrolidone (PVP) and various concentrations of cerium nitrate hydrate (Ce(NO3)3) ranging from 15.0 to 26.0 wt % by the electrospinning process. Ceria nanofibers were obtained after calcining PVP/Ce(NO3)3 nanofiber composites at 873 and 1173 K. The SEM images indicated that the diameters of CeO2 nanofibers calcined at 873 and 1173 K were smaller than those of nanofibers obtained at RT. As the amount of cerium increased, the diameter of CeO2 nanofibers increased. XRD analysis revealed that the ceria nanofibers were in cubic form. TEM results revealed that the ceria nanofibers were formed by the interconnection of Ce oxide nanoparticles. The ceria nanofibers obtained at low concentrations of Ce (CeL) showed spotty ring patterns indicated that the ceria nanofibers were polycrystalline structure. And the ceria nanofibers obtained at high concentration of Ce (CeH) showed fcc (001) diffraction pattern. XPS study indicated that the oxidation of Ce shifted from Ce3+ to Ce4+ as the calcination temperature increased
[en] We have studied the relative stability and atomic structures of five C20X2 regioisomers obtained as diadducts of a C20 cage (X = H, F, Cl, Br, and OH). All the regioisomers are geometric isomers, i.e., they differ in their spatial arrangement. Full-geometry optimizations of the regioisomers have been performed using the hybrid density-functional (B3LYP/6-31G(d, p)) method. Our results suggest that the cis-1 regioisomer (the 1,2- diadduct) is the most stable and that the second most stable is the trans-2 (1,13-diadduct) regioisomer, implying that the long-range interaction between the two adducts and the resonance effect are more pronounced than the diadduct-induced strain in the C20 cage. The HOMO and LUMO characteristics of each regioisomer with the same symmetry of structural regioisomers except C20(OH)2 are topologically same. This suggests that by using an entirely different set of characteristic chemical reactions for each regioisomer, we can distinguish between the five regioisomers for each C20 diadduct derivative
[en] We developed a simple, convenient, one-pot synthetic method to synthesize phosphoramides and phosphates. This protocol has many attractive features, such as mild reaction conditions, short reaction times, and operational simplicity. In organophosphorous chemistry, phosphoryl amides and esters are important due to their broad ranges of biological properties and presence in bioactive molecules, such as natural products, amino acid analogues, pharmacological agents, and synthetic precursors. These phosphate motifs are often used as prodrugs to enhance the water solubility or therapeutic potential of parent drugs. Phosphoramides play significant roles in modern organic chemistry, as they can be used in enantioselective catalytic processes that are activated by Lewis bases, including aldol additions and allylation reactions. An important use of dialkyl, dibenzyl, and diphenyl phosphoramidates is protecting amino groups. Phosphoric acid esters are among the most valuable substances in material and medicinal chemistry. Owing to their widespread use, general and convenient access to these compounds is desirable
[en] A prototype instrument with an inclined ferromagnetic foil was built which was capable of π-flipping over a broad wavelength range of polarised thermal neutrons in a time-of-flight beam. It was found that, for a single foil, polarised neutrons could be flipped in a wavelength range of 0.2–0.5 nm with an efficiency of 93%. With improved mechanical setup this range probably can even be extended to 0.1–1.0 nm. Foil flippers can have some major advantages for polychromatic SESANS over resonance flippers, but the technical realisation with four foils in series will be challenging.
[en] By co-deposition via RF-Sputtering and RF-PECVD methods and using Cu target and acetylene gas, we prepared [email protected]2O core–shell nanoparticles on the a-C:H thin film at room temperature. Mie absorption of Cu cores, scattering from Cu2O shell and luminescence that rises from carrier transfer in [email protected]2O interface were employed to fit the whole range of visible extinction spectrum of these core–shells. From simulation it was found that scattering and luminescence have an important effect on the energy, width and shape of LSPR absorption peak. Shift of LSPR peak is more affected by the dielectric coefficient of shell than Cu core size particularly for Cu core diameter above 4 nm. Also, the LSPR absorption peak is damped by decreasing Cu core size and dielectric coefficient of shell. The energy of LSPR absorption peak is independent of shell thickness and host dielectric coefficient. The LSPR peak is damped by increasing shell thickness and host dielectric coefficient too. The scattering contribution in extinction spectra was affected more by shell size than dielectric coefficient. These points are important for detection techniques based on LSPR peak.
[en] Atomic mechanism of the heating-induced phase transitions of the monatomic Lennard-Jones (LJ) glass has been studied via molecular dynamics (MD) simulations. Monatomic LJ glass was heated up at two different heating rates, crystallization occurs at the lowest one and further heating leads to the melting of LJ crystal. Thermodynamics of the phase transitions and corresponding evolution of structural properties upon heating have been analyzed in details. Atomic mechanism of a crystallization of the glassy state was monitored via spatio-temporal arrangements of the atoms involved in the 1421 bond-pair of the fcc crystalline structure. The 1421 bond-pair was detected via the Honeycutt–Andersen analysis [J.D. Honeycutt, H.C. Andersen, J. Phys. Chem. 91 (1987) 4950]. We found that crystallization of the monatomic LJ glass occurs via homogeneous local rearrangements of atoms in the glassy matrix and we found an important role of the liquid-like atoms (existed in the glassy state) in crystallization of the system. In addition, spatio-temporal arrangements of the liquid-like atoms in the system upon further heating were shown in order to clarify the atomic mechanism of a melting of the obtained LJ crystal. Liquid-like atoms were defined by the Lindemann melting criterion. Our results provide previously un-reported data and give deeper understanding of the heating-induced phase transitions in the less stable metallic glasses, which have been observed in practice.