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排序方式: 共有143条查询结果,搜索用时 62 毫秒
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THREE EXPONENTIAL FLUORESCENCE DECAY OF HORSE LIVER ALCOHOL DEHYDROGENASE REVEALED BY IODIDE QUENCHING 总被引:1,自引:0,他引:1
David R. Demmer † Douglas R. James † Ronald P. Steer Ronald E. Verrall 《Photochemistry and photobiology》1987,45(1):39-48
Abstract— The time resolved fluorescence decay of horse liver alcohol dehydrogenase was measured using a frequency doubled picosecond dye laser and time-correlated single-photon counting detection. A flow-cell technique is described which eliminates the photodegradation artifacts which commonly occur with laser excitation. A procedure is introduced which uses fluorescence quenching to reveal minor fluorescence lifetime components. The decay of the unquenched tryptophanyl fluorescence could be described by a double exponential decay law, but experiments conducted in the presence of iodide ion showed that the fluorescence decay must be more complex than this. A model is presented in which the fluorescence decay consists of three exponential components, only two of which are susceptible to quenching by iodide ion. Several possibilities are presented for the origin of this minor decay component, the most reasonable of which is that it arises from conformational heterogeneity in the solvent-exposed tryptophanyl residue. 相似文献
3.
Nikhil M. Kriplani David P. Nackashi Christian J. Amsinck Neil H. Di Spigna Michael B. Steer Paul D. Franzon Ramon L. Rick Gemma C. Solomon Jeffrey R. Reimers 《Chemical physics》2006
Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6–8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol. 相似文献
4.
Battle PD Blundell SJ Brooks ML Hervieu M Kapusta C Lancaster T Nair SP Oates CJ Pratt FL Rosseinsky MJ Ruiz-Bustos R Sikora M Steer CA 《Journal of the American Chemical Society》2004,126(39):12517-12527
The temperature dependence of the crystal structure and electronic properties of brownmillerite-like Ca(2.5)Sr(0.5)GaMn(2)O(8) has been studied by neutron powder diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO(6) octahedra approximately 50 K above the 3D Néel temperature of approximately 150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO(4) layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn(3+) and Mn(4+) cations in a 1:1 ratio, and the behavior in the region of the Néel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO(4) tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers. 相似文献
5.
H. K. Sinha O. K. Abou-Zied M. Ludwiczak A. Maciejewski R. P. Steer 《Chemical physics letters》1994,230(6):547-554
The S2-S0 fluorescence excitation spectra ofxanthione (XT) and azulene (AZ) complexed with 1 or 2 molecules of the C1 to C10 n-alkanes and the C1 to C6 perfluoro-n-alkanes have been measured. The 1:1 complexes exhibit microscopic solvent shifts, Δ
gn, which are larger for the alkanes than the corresponding perfluoroalkanes, despite the larger molecular polarizability of the latter. The values of Δ
gn increase monotonically with carbon number of the adduct to C10 in 1:1 n-alkane complexes with XT and to C5 in 1:1 n-alkane complexes with AZ. However, Δ
gn exhibits no further increase beyond C2 in 1:1 perfluoro-n-alkane complexes with XT and beyond C3 in 1:1 perfluoro-n-alkane complexes with AZ. The results are interpreted in terms of a model in which the n-alkanes stretch out along the long axis of the chromophore and ‘wet’ its surface whereas the perfluoro-n-alkanes with carbon numbers 3 away from the surface of the chromophore and are ‘non-wetting’. 相似文献
6.
Alfredo E. Bruno Ronald P. Steer Paul G. Mezey 《Journal of computational chemistry》1983,4(1):104-109
Approximate minimum energy reaction paths have been calculated for two thioketone–enethiol tautomeric systems using an ab initio SCF–MO method. The calculations indicate nearly equal stabil ties of the isolated tautomers in both systems and an energy barrier of ca. 85 kcal/mol for their interconversion. This barrier is expected to be significantly lower in solution as a result of solvent–solute interactions. 相似文献
7.
Peter D. Battle Anthony M.T. BellStephen J. Blundell Amalia I. ColdeaDaniel J. Gallon Francis L. PrattMatthew J. Rosseinsky Christopher A. Steer 《Journal of solid state chemistry》2002,167(1):188-195
The room-temperature crystal structure of the brownmillerite SrCaMnGaO5+δ (δ=0.035) has been refined from neutron powder diffraction data; space group Ima2, a=15.7817(6), b=5.4925(2), c=5.3196(2)> Å. Mn and Ga occupy 99.0(2)% of the 6- and 4-coordinate sites, respectively. A combination of magnetometry, neutron diffraction and μSR spectroscopy has shown that the compound orders magnetically at 180 K, and that the low-temperature phase has a G-type antiferromagnetic structure, with an ordered magnetic moment of 3.30(2) μB per Mn at 2 K. Displaced hysteresis loops provide evidence that the atomic moment has an additional, glassy component. Magnetometry shows that significant short-range magnetic interactions persist above 180 K, and μSR that the spin fluctuations are thermally activated in this temperature region. The compound is an electrical insulator which at 159 K shows an unusually large magnetoresistance of 85% in 6 T, increasing to 90% in 13 T. 相似文献
8.
The S2 → S0 fluorescence spectra and quantum yields and the S2 lifetimes of 2,2,3,3-tetramethylindanethione (TMIT) have been measured in several solvents using a synchronously pumped picosecond dye laser excitation system. The S2 nonradiative decay rate is markedly solvent dependent. In inert perfluoroalkane solvents remarkably large S2-S0 fluorescence quantum yields (θf = 0.14) and long S2 lifetimes (τ = 880 ps) are measured. Hydrocarbons are efficient excited-state quenchers. 相似文献
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10.
硅基材料是新一代高容量锂离子蓄电池负极材料的典型代表,近年来已成为理论研究和应用研究的热点.本文介绍了锂离子电池硅基负极材料的制备方法、电化学性能及其研究现状,分析了硅材料作为锂离子电池负极材料存在的问题;讨论了硅材料作为锂离子电池负极材料的研究前景.并指出若能克服目前存在问题,将有望成为新一代锂离子电池负极材料. 相似文献