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91.
用水合五氧化二锑分离放射性母子体的研究─—一个新的~(201)Pb—~(201)T1发生器的制备 总被引:1,自引:0,他引:1
本文研究了无机离子交换剂—水合五氧化二锑(Sb2O5·nH2O)的制备,并用它分离了放射性母子体,制备了一个新的201Pb—201Tl放射性发生器。结果表明,末发生器具有高效、快速、简便的特点,此外还讨论了离子交换反应的机理。 相似文献
92.
Minoru Isobe Prof. Dr. Masakuni Kurono Dr. Katsunori Tsuboi Dr. Akira Takai Prof. Dr. 《化学:亚洲杂志》2007,2(3):377-385
We have accomplished the synthesis of 13C‐labeled tautomycin at the C18, C19, C21, and C22 positions starting from 100 % [13C]triethylphosphonoacetate for the purpose of elucidating the dynamics and conformation of the C17–C26 moiety. NMR spectroscopy of 13C‐labeled tautomycin revealed strong binding with protein phosphatase type 1 and new features in the 13C NMR spectrum, such as the very small three‐bond coupling constants (2J). 相似文献
93.
Even systems in which strong electron correlation effects are present, such as the large near-degeneracy correlation in a
dissociating electron pair bond exemplified by stretched H2, are represented in the Kohn–Sham (KS) model of non-interacting electrons by a determinantal wavefunction built from the
KS molecular orbitals. As a contribution to the discussion on the status and meaning of the KS orbitals we investigate, for
the prototype system of H2 at large bond distance, and also for a one-dimensional molecular model, how the electron correlation effects show up in the
shape of the KS σ
g
orbital. KS orbitals φHL and φFCI obtained from the correlated Heitler-London and full configuration interaction wavefunctions are compared to the orbital
φLCAO, the traditional linear combination of atomic orbitals (LCAO) form of the (approximate) Hartree-Fock orbital. Electron correlation
manifests itself in an essentially non-LCAO structure of the KS orbitals φHL and φFCI around the bond midpoint, which shows up particularly clearly in the Laplacian of the KS orbital. There are corresponding
features in the kinetic energy density t
s
of the KS system (a well around the bond midpoint) and in the one-electron KS potential v
s
(a peak). The KS features are lacking in the Hartree-Fock orbital, in a minimal LCAO approximation as well as in the exact
one.
Received: 11 December 1996 / Accepted: 10 January 1997 相似文献
94.
This paper reports our results for the direct experimental determination of the equilibrium constant for the hydrogen-isotope-exchange
reaction, 1/2D2(g)+HCl(hexOH)=1/2H2(g)+DCl(hexOD), where hexOH isn-hexanol and hexOD isn-hexanol with deuterium substitution in the alcohol function. The reaction was studied in electrochemical double cells without
liquid junction for which the net cell reaction is the above isotope-exchange reaction. The experimentally determined value
of ε° (296.0°K) for this cell is 4.03±0.95 mV (strong electrolyte standard states, mole-fraction composition scale); the value
of the equilibrium constant for the reaction is 1.17±0.05. The contributions of isotope-exchange and transfer effects to the
magnitude of the standard Gibbs energy change for the above reaction and for the analogous reaction 1/2D2(g)+HCl(aq)=DCl(daq)+1/2H2(g) are considered. Our results support the conclusion of Heinzinger and Weston that the formulation of the solvated proton
in water as H3O+, as opposed to H9O4
+, is sufficient for the interpretation of the thermodynamics of hydrogen-isotope-exchange reactions in water. We also find
that the formulation of the solvated proton inn-hexanol as ROH
2
+
is sufficient for the interpretation of our results on the thermodynamics of hydrogen-isotope-exchange inn-hexanol. 相似文献
95.
Samuel C. Perry Pui-ki Leung Ling Wang Carlos Ponce de León 《Current Opinion in Electrochemistry》2020
CO2 reduction processes continue to be developed for electrosynthesis, energy storage applications, and environmental remediation. A number of promising materials have shown high activity and selectivity to target reduction products. However, the progress has been mainly at a small laboratory scale, and the technical challenges of large scale CO2 reduction have not been considered adequately. This review covers recent advancements in catalyst materials and cell designs. The leading materials for CO2 reduction to a number of useful products are presented with their corresponding cell and reactor designs. The latest efforts to progress to industrially relevant scales are discussed, along with the challenges that must be met for carbon dioxide reduction to be a viable route for mass scale production. 相似文献
96.
A scheme of time-dependent density functional theory (TDDFT) combined with single-excitation configuration interaction (CIS) approach was employed to make a detailed investigation of the emitting energy for fifteen well-known coumarin derivatives. The results showed that the predicted emitting energies as well as the absorption ones were dominated mainly by the exchange-correlation (XC) functional to be used. So long as a functional is properly chosen, the experimental emitting energy of most derivatives can be accurately reproduced within 0.16 eV by a calculation at the TDDFT/6-31G(d)//CIS/3-21G(d) theoretical level. It was found that, nevertheless, the hybrid functional, B3LYP, well predicted the absorption energies for all the fifteen coumarin derivatives but none of the functionals could work equally well for the emitting energy calculations. Two pure functionals, OLYP and BLYP, yield good emitting energies for the 7-aminocoumarins or derivatives with a N atom connected to 7-position, which exhibit inconspicuous charge transfer (CT) in their excited states, whereas the B3LYP hybrid functional, with 20% Hartree-Fock (HF) exchange energy, performs significantly better than OLYP and BLYP for those 3-substituted coumarins with larger CT in excited states. Thus, in comparison with the absorption energies, the selection of proper functionals for the emitting energy calculations becomes more complex. In all probability, it is effective and doable to choose an XC-functional with alterable fraction of HF exchange energy according to the composition and structure characteristics of molecule. 相似文献
97.
The role of achiral sorbent matrix in chiral recognition of amino acid enantiomers in ligand-exchange chromatography 总被引:2,自引:0,他引:2
Summary As an alternative to the known three-point interaction model describing recognition of optical isomers by a chiral resolving agent, a new concept has been developed stating that two interaction points between the resolving agent and the enantiomers are also sufficient for achieving chiral recognition of the latter, provided that the diastereomeric adducts formed by the resolving agent with the enantiomers additionally interact with a non-chiral chromatographic sorbent. This concept is based on the results of ligand-exchange chromatography of -amino acid enantiomers with copper(II) complexes of chiral bifunctional ligands as the resolving agents in chromatographic systems. 相似文献
98.
Fe(CN)4?6, Cu(CN)3?4, Co(CN)3?6, Fe(CN)3?6, Ni(CN)2?4 and Cr(CN)3?6 are determined by ion-interaction chromatography using a C18 column and methanol-tetrahydrofuran-10 mM phosphate buffer (pH 7.9) (25 + 1 + 74, v/v/v) containing 5 mM tetrabutylammonium hydroxide as mobile phase, with spectrophotometric detection at 214 nm. Detection limits are in the range 0.01–0.5 mg 1?1. In an alternative approach, an automated on-line sample preconcentration technique is used wherein a 2-ml volume of sample containing metallo-cyanides is loaded onto a C18 precolumn which has been equilibrated with the above mobile phase. The bound solutes are then eluted from the precolumn to a C18 analytical column where they are separated using the same mobile phase as employed to equilibrate the precolumn. Detection limits are in the rate 0.08–1.58 μg 1?1 and calibration graphs are linear up to 200 μg 1?1. The preconcentration step is shown to give quantitative recoveries for all species except Fe(CN)4?6 and (CN)3?4. The iron(II) complex does not bind quantitatively to the precolumn, and extensive studies with the copper complex suggested that low recoveries were due to dissociation and ligand-exchange reactions occurring during the chromatographic separation process. Negative interference effects were observed for Cl? and SO2?4 when present at a level of 250 mg 11?, and UV-absorbing anions such as Br?, SCN?, NO?2 and NO?3 caused positive interference when present at concentrations as low as 1 mg 1?1. The negative interferences could be reduced by diluting the sample and the positive interferences could be eliminated by incorporating an additional step in the preconcentration process, in which UV-absorbing anions bound to the precolumn after sample loading were eluted selectively using an eluent consisting of 10 mM NaCl in phosphate buffer (pH 6.7). 相似文献
99.
Alfonso Loaiza Dan Borchardt Francisco Zaera 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2481-2493
13C NMR at 125.76 MHz with 1H and 2H decoupling, 2H NMR at 76.77 MHz with 1H decoupling, and 1H NMR at 500.14 MHz with 2H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H–D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-dn (n=1–6) were used to identify the peak positions in the 13C, 2H, and 1H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both 1H and 2H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to 1H–1H (1H NMR) and 2H–2H (2H NMR) couplings. 13C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the 13C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that 13C NMR with 1H and 2H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures. 相似文献
100.
采用量子化学GAUSSIAN94abinitioUHF方法和STO-3G基组设计一系列三氮宾分子,讨论分子的几何结构和取代基对其磁性的影响,计算结果表明,这些分子都具有铁磁性并有高自旋基态,有效交换积分值随代基的变化而变化,其中一种具有较代的总能量和高的有效交换积分值的分子,可期望被合成。 相似文献