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11.
Yao Chang Jiayue Yang Zhichao Chen Zhiguo Zhang Yong Yu Qingming Li Zhigang He Weiqing Zhang Guorong Wu Rebecca A. Ingle Matthew Bain Michael N. R. Ashfold Kaijun Yuan Xueming Yang Christopher S. Hansen 《Chemical science》2020,11(19):5089
Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH2, CH3 and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini–Huygens fly-by of Jupiter.The vacuum ultraviolet photodissociation dynamics of ethane provide clues for modelling the atmospheric chemistry of the gas giants. 相似文献
12.
Gupta Madan Mohan Srivastava Alpana Tripathi Arvind Kumar Misra Himanshu Verma Ram Kishore 《平面色谱法杂志一现代薄层色谱法》2006,19(4):282-287
JPC – Journal of Planar Chromatography – Modern TLC - High-performance thin-layer chromatography (HPTLC) has been used for normal-phase separation of the components of hexane,... 相似文献
13.
John B. Hynes Alenka Tomai
Arvind Kumar Veena Kumar James H. Freisheim 《Journal of heterocyclic chemistry》1991,28(8):1981-1986
A series of thirty eight 2,4-diaminoquinazolines having diverse substitution patterns on the aromatic ring was evaluated for inhibitory activity against dihydrofolate reductase (DHFR) obtained from a human lymphoblast cell line. Many of these compounds were also evaluated as inhibitors of rat liver DHFR under the same experimental conditions. In most instances the results obtained with each enzyme were comparable indicating that the rodent enzyme is a suitable model for the human DHFR as far as the determination of I50 values is concerned. The results demonstrate that relatively simple 5-substituted- or 5,6-disubstituted-2,4-diaminoquinazolines can be potent DHFR inhibitors. The presence of a nonpolar substituent at position 7 or 8 was highly detrimental to inhibitory potency. 相似文献
14.
The kinetic determination of total ascorbic acid with a flow-injection analysis system is described. The sample is loaded into two serial sample injection valves and injected into a carrier system containing mercuric chloride and o-phenylenediamine. The formation of a fluorescent product is monitored. The single-point and double-point kinetic methods are compared by using both peak height and peak area as the analytical signal. A detection limit of 0.1 mu/ml for vitamin C was achieved with a sample throughput rate of 30 per hour. 相似文献
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Brandall L. Ingle 《Journal of Coordination Chemistry》2014,67(23-24):3920-3931
Within the ATP-grasp family of enzymes, divalent alkaline earth metals are proposed to chelate terminal ATP phosphates and facilitate the formation of peptide bonds. Density functional theory methods are used to explore the impact of metal ions on peptide bond formation, providing an insight into experimental metal substitution studies. Calculations show that alkaline earth and transition metal cations coordinate with an acylphosphate reactant and aid in the separation of the phosphate leaving group. The critical biochemical reaction is proposed to proceed through the formation of a six-membered transition state in the relatively nonpolar active site of human glutathione synthetase, an ATP-grasp enzyme. While the identity of the metal ion has a moderate impact on the thermodynamics of peptide bond formation, kinetic differences are much sharper. Simulations indicate that several transition metal ions, most notably Cu2+, may be particularly advantageous for catalysis. The detailed mechanistic study serves to elucidate the vital role of coordination chemistry in the formation of peptide bonds. 相似文献
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19.
Arvind Samariya S.N. Dolia Arun S. Prasad P.K. Sharma S.P. Pareek M.S. Dhawan Sudhish Kumar 《Current Applied Physics》2013,13(5):830-835
CaFe2O4 nanocrystalline powders were synthesized through sol–gel treatment in which the stoichiometric mixing of various nitrates involving calcium and iron in presence of citric acid was performed. Subsequently, the as prepared sample was annealed at various temperatures in order to obtain the fine distribution of size including the bulk counterpart. The samples were then characterized using powder X-ray diffraction followed by 57Fe Mössbauer spectroscopy, SQUID as well as vibrating sample magnetometry. The results of spectroanalyses revealed that the samples were formed in single phase cubic spinel structure and exhibits room temperature superparamagnetism, except the bulk one, which crystallizes in characteristic orthorhombic structure of CaFe2O4 and displays trivial coercivity and remanent magnetization at room temperature. 相似文献
20.
Eric C. Chi Liuyi Hu Arvind K. Saibaba Arvind U. K. Rao 《Journal of computational and graphical statistics》2019,28(1):36-47
We consider the problem of performing matrix completion with side information on row-by-row and column-by-column similarities. We build upon recent proposals for matrix estimation with smoothness constraints with respect to row and column graphs. We present a novel iterative procedure for directly minimizing an information criterion to select an appropriate amount of row and column smoothing, namely, to perform model selection. We also discuss how to exploit the special structure of the problem to scale up the estimation and model selection procedure via the Hutchinson estimator, combined with a stochastic Quasi-Newton approach. Supplementary material for this article is available online. 相似文献