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281.
282.
Trilisa M. Perrine Rajat K. Chaudhuri Karl F. Freed 《International journal of quantum chemistry》2005,105(1):18-33
Simple and quadratic Padé resummation methods are applied to high‐order series from multireference many‐body perturbation theory (MR‐MBPT) calculations using various partitioning schemes (Møller–Plesset, Epstein–Nesbet, and forced degeneracy) to determine their efficacy in resumming slowly convergent or divergent series. The calculations are performed for the ground and low‐lying excited states of (i) CH2, (ii) BeH2 at three geometries, and (iii) Be, for which full configuration interaction (CI) calculations are available for comparison. The 49 perturbation series that are analyzed include those with oscillatory and monotonic divergence and convergence, including divergences that arise from either frontdoor or backdoor intruder states. Both the simple and quadratic Padé approximations are found to speed the convergence of slowly convergent or divergent series. However, the quadratic Padé method generally outperforms the simple Padé resummation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
283.
E. T. Denisov 《Russian Chemical Bulletin》2004,53(8):1602-1608
The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E
e0) and the elongation of the attacked and formed bonds (r
e) in the transition state were calculated from the experimental data (activation energy (E
e) and enthalpy of reaction (H
e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH3 to the C=O and CC bonds. Analysis of the data obtained showed that E
e0 depends linearly on the |H
e| + Ee sum, i.e., Ee0/kJ mol–1 = 14.2 + 0.61 · (Ee – H
e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004. 相似文献
284.
Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)mn+ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)mn+ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH4OH also promotes the formation of (Cyt c)mn+. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)mn+ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS. 相似文献
285.
Solid state synthesis and structure of two novel polyoxometalates [(n-Bu)4N]4[M6O19][Ag2I4](M?Mo,W)†
Hou Hong-Wei Xin Xin-Quan Yu Kai-Bei Wang Zhe-Min Liu Shi-Xiong Huang Jin-Ling 《中国化学》1996,14(2):123-130
The reaction of [NH4]2[MO2S2], AgI and (n-Bu)4NBr in solid state produced the polyoxometalates [(n-Bu)4N]4[M6O19][Ag2I4] (1, M? Mo; 2, M? W) which were structurally determined. The crystals of 1 and 2 are isomorphous, monoclinic, space group P21/c. 1, a = l.6624(2), b=1.6699(3), c=l.7217(2) nm, β=98.29(1)°, V=4.729(1) nm3, Z=2, R=0.040, Rw“0.037; 2, a = 1.6636(3), b = 1.6733(3), c = 1.7190(3) nm, β=98.25(1)°, V=4.736(l) nm3, Z = 2, R = 0.038, Rw = 0.047. The results of the structure determination showed that the two compounds had the same structures whose skeletons are composed of [Ag2I4]2. and [M6O19]2-. The difference of them and heteropolymetalate compounds synthesized in solution is that the title compounds contain cluster. ion, heteropolymetalate and organic cations, while the latter is only composed of heteropolymetalate and organic cations. 相似文献
286.
MA Jianhua LIN Weizhen DU Fuqiang HAN Zhenhui YAO Side & LIN Nianyun .College of Biology Engineering Jimei University Xiamen China .Laboratory of Nanobiomedicine & Laboratory of Radiation Chemistry Shanghai Institute of Applied Physics Chinese Acade Sciences Shanghai China 《中国科学B辑(英文版)》2005,48(4):292-296
Quinones including menadione are ubiquitous in nature. They play important roles in aerobic respira- tion and photosynthesis[1,2]. In addition, exogenous quinones are used as antibiotics and anticancer drugs. Their function is closely related to their red… 相似文献
287.
Muliadi Ramli Nasrullah Idris Kenichi Fukumoto Hideaki Niki Fujio Sakan Tadashi Maruyama Koo Hendrik Kurniawan Tjung Jie Lie Kiichiro Kagawa 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1379-1389
A TEA CO2 laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO2 laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO2 laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO2 laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens. 相似文献
288.
M.E. Kletskii A.A. Millov A.V. Metelitsa M.I. Knyazhansky 《Journal of photochemistry and photobiology. A, Chemistry》1997,110(3):857-270
The mechanism of light-induced transformation in the salicylideneaniline molecule was studied by semiempirical PM3 calculations. The structures and energies of the minima and saddle points (transition states) on the S0, S1 and T1 potential energy hypersurfaces (PESs) were obtained, together with the gradient lines on the PESs. The structure-energy scheme was compared with the experimental findings. According to the results obtained, the following principle processes are observed: fast S1 excited state intramolecular proton transfer (ESIPT), followed by typical ESIPT fluorescence; the formation of two S1 twisted intramolecular charge transfer (TICT) structures which quench the ESIPT fluorescence; the diabatic formation of two ground state metastable coloured “post-TICT” structures responsible for photochromism. 相似文献
289.
E. Tomaszewicz 《Thermochimica Acta》2006,447(1):69-74
Reactivity in the solid state between CoWO4 and some rare-earth metal tungstates RE2WO6 (RE = Sm, Eu, Gd) was investigated by the XRD method. Two families of new isostructural cobalt and rare-earth metal tungstates, Co2RE2W3O14 and CoRE4W3O16, were synthesized. The Co2RE2W3O14 phases are formed by heating in air the CoWO4 and RE2WO6 compounds mixed at the molar ratio 2:1, while the CoRE4W3O16 phases are synthesized at the molar ratio of CoWO4/RE2WO6 equals to 1:2. The Co2RE2W3O14 phases as well as the CoRE4W3O16 compounds crystallize in the orthorhombic system. The Co2RE2W3O14 and CoRE4W3O16 compound melt above 1150 °C. A melting manner of the Co2RE2W3O14 and CoRE4W3O16 compounds was determined in an inert atmosphere. The formation of CoWO4−x phase was observed during heating in an inert atmosphere. 相似文献
290.
Using synthetic substrates, an uncomplicated and sensitive procedure for the identification and determination of extracellular
aminopeptidase was developed. The β-naphthylamides of the amino acids were applied for the identification of extracellular
aminopeptidase, whereas the 4-(phenylazo) phenylamides of the amino acids were used for the determination of intra-and extracellular
aminopeptidase activity. The results show a 81.8–88.9% intracellular and 11.1–18.2% extracellular distribution of the studied
enzyme activity.
Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 167–169, March–April, 2007. 相似文献