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121.
Schleicher E Kowalczyk RM Kay CW Hegemann P Bacher A Fischer M Bittl R Richter G Weber S 《Journal of the American Chemical Society》2004,126(35):11067-11076
The blue-light sensitive photoreceptor, phototropin, is a flavoprotein which regulates the phototropism response of higher plants. The photoinduced triplet state and the photoreactivity of the flavin-mononucleotide (FMN) cofactor in two LOV domains of Avena sativa, Adiantum capillus-veneris, and Chlamydomonas reinhardtii phototropin have been studied by time-resolved electron paramagnetic resonance (EPR) and UV-vis spectroscopy at low temperatures (T < or = 80 K). Differences in the electronic structure of the FMN as reflected by altered zero-field splitting parameters of the triplet state could be correlated with changes in the amino acid composition of the binding pocket in wild-type LOV1 and LOV2 as well as in mutant LOV domains. Even at cryogenic temperatures, time-resolved EPR experiments indicate photoreactivity of the wild-type LOV domains, which was further characterized by UV-vis spectroscopy. Wild-type LOV1 and LOV2 were found to form an adduct between the FMN cofactor and the functional cysteine with a yield of 22% and 68%, respectively. The absorption maximum of the low-temperature photoproduct of wild-type LOV2 is red-shifted by about 15 nm as compared with the FMN C(4a)-cysteinyl adduct formed at room temperature. In light of these observations, we discuss a radical-pair reaction mechanism for the primary photoreaction in LOV domains. 相似文献
122.
123.
Federrath C Chabrier G Schober J Banerjee R Klessen RS Schleicher DR 《Physical review letters》2011,107(11):114504
We study the growth rate and saturation level of the turbulent dynamo in magnetohydrodynamical simulations of turbulence, driven with solenoidal (divergence-free) or compressive (curl-free) forcing. For models with Mach numbers ranging from 0.02 to 20, we find significantly different magnetic field geometries, amplification rates, and saturation levels, decreasing strongly at the transition from subsonic to supersonic flows, due to the development of shocks. Both extreme types of turbulent forcing drive the dynamo, but solenoidal forcing is more efficient, because it produces more vorticity. 相似文献
124.
Maeda K Neil SR Henbest KB Weber S Schleicher E Hore PJ Mackenzie SR Timmel CR 《Journal of the American Chemical Society》2011,133(44):17807-17815
The study of radical pair intermediates in biological systems has been hampered by the low sensitivity of the optical techniques usually employed to investigate these highly reactive species. Understanding the physical principles governing the spin-selective and magneto-sensitive yields and kinetics of their reactions is essential in identifying the mechanism governing bird migration, and might have significance in the discussion of potential health hazards of electromagnetic radiation. Here, we demonstrate the powerful capabilities of optical cavity-enhanced techniques, such as cavity ring-down spectroscopy (CRDS) in monitoring radical recombination reactions and associated magnetic field effects (MFEs). These include submicrosecond time-resolution, high sensitivity (baseline noise on the order of 10(-6) absorbance units) and small (μL) sample volumes. Combined, we show that these represent significant advantages over the single-pass flash-photolysis techniques conventionally applied. The studies described here focus on photoinduced radical pair reactions involving the protein lysozyme and one of two possible photosensitizers: anthraquinone-2,6-disulphonate and flavin mononucleotide. CRDS-measured MFEs are observed in pump-probe experiments and discussed in terms of the sensitivity gains and sample-volume minimization afforded by CRDS when compared with flash photolysis methods. Finally, CRDS is applied to an in vitro MFE study of intramolecular electron transfer in the DNA-repair enzyme, Escherichia coli photolyase, a protein closely related to cryptochrome which has been proposed to mediate animal magnetoreception. 相似文献
125.
Deniz Zengel Pirmin Koch Bentolhoda Torkashvand Jan‐Dierk Grunwaldt Maria Casapu Olaf Deutschmann 《Angewandte Chemie (International ed. in English)》2020,59(34):14423-14428
Reducing greenhouse gas and pollutant emissions is one of the most stringent priorities of our society to minimize their dramatic effects on health and environment. Natural gas (NG) engines, in particular at lean conditions, emit less CO2 in comparison to combustion engines operated with liquid fuels but NG engines still require emission control devices for NOx removal. Using state‐of‐the‐art technologies for selective catalytic reduction (SCR) of NOx with NH3, we evaluated the interplay of the reducing agent NH3 and formaldehyde, which is always present in the exhaust of NG engines. Our results show that a significant amount of highly toxic hydrogen cyanide (HCN) is formed. All catalysts tested partially convert formaldehyde to HCOOH and CO. Additionally, they form secondary emissions of HCN due to catalytic reactions of formaldehyde and its oxidation intermediates with NH3. With the present components of the exhaust gas aftertreatment system the HCN emissions are not efficiently converted to non‐polluting gases. The development of more advanced catalyst formulations with improved oxidation activity is mandatory to solve this novel critical issue. 相似文献
126.
W. Muchlinsky E. Rother G. Jander O. Pfundt E. Göte W. Schramek L. W. Janssen J. A. C. Teegan A. Schleicher W. Lüdicke E. Denina J. M. Preston N. Rae J. K. Rummel K. Schierjott J. M. Kolthoff T. Kameda L. Blumen J. Pucherna Fr. Hein und H. Pauling 《Fresenius' Journal of Analytical Chemistry》1932,89(3-4):128-135
Ohne Zusammenfassung 相似文献
127.
The fast Fourier transform and the numerical solution of one-dimensional boundary integral equations
Summary Here we present a fully discretized projection method with Fourier series which is based on a modification of the fast Fourier transform. The method is applied to systems of integro-differential equations with the Cauchy kernel, boundary integral equations from the boundary element method and, more generally, to certain elliptic pseudodifferential equations on closed smooth curves. We use Gaussian quadratures on families of equidistant partitions combined with the fast Fourier transform. This yields an extremely accurate and fast numerical scheme. We present complete asymptotic error estimates including the quadrature errors. These are quasioptimal and of exponential order for analytic data. Numerical experiments for a scattering problem, the clamped plate and plane estatostatics confirm the theoretical convergence rates and show high accuracy. 相似文献
128.
Ramon M. Barnes Robert G. Schleicher 《Spectrochimica Acta Part B: Atomic Spectroscopy》1975,30(4):109-134
Models of induction coupled plasma (ICP) discharges are developed for arrangements important in spectrochemical analysis. These models account for the spatial distribution of gas properties and major energy losses found in high temperature discharges. Realistic gas flows, and sample particle motion and decomposition are incorporated into the models. Computer simulations based on these models provide spatial temperature, gas velocity, sample concentration, and radiation distributions for a number of experimental ICP discharge configurations. The alteration of these distributions for various operational parameters permits evaluation of some important factors in developing spectroohemical analysis with the ICP source. Recognized differences between theory and experiment are discussed. 相似文献
129.
The Newton map Nf of an entire function f turns the roots off into attracting fixed points. Let U be the immediate attractingbasin for such a fixed point of Nf. We study the behavior ofNf in a component V of \U. If V can be surrounded by an invariantcurve within U and satisfies the condition that for all z , Nf–1({z}) V is a finite set,then it is shown that V contains another immediate basin ofNf or a virtual immediate basin. 相似文献
130.
[reaction: see text] The nickel(0)-catalyzed coupling of alpha-olefins and isocyanates proceeds in the presence of the N-heterocyclic carbene ligand IPr to provide alpha,beta-unsaturated amides. Carbon-carbon bond formation occurs preferentially at the 2-position of the olefin. The N-tert-butyl amide products can be converted to the corresponding primary amides under acidic conditions. 相似文献