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41.
We present a detailed account of the technical aspects of stochastic quantum molecular dynamics, an approach introduced recently by the authors [H. Appel, M. Di Ventra, Phys. Rev. B 80 (2009) 212303] to describe coupled electron-ion dynamics in open quantum systems. As example applications of the method we consider both finite systems with and without ionic motion, as well as describe its applicability to extended systems in the limit of classical ions. The latter formulation allows the study of important phenomena such as decoherence and energy relaxation in bulk systems and surfaces in the presence of time-dependent fields. 相似文献
42.
43.
K. Bernhauer F. Mayer L. Zechmeister H. Appel 《Analytical and bioanalytical chemistry》1935,103(5-6):239-239
44.
Functionalized 2,3-benzoxepins were prepared by cyclopropanation of benzopyrylium triflates with diazoesters and subsequent TFA-mediated ring enlargement. 相似文献
45.
Eva Vergucht Björn De Samber Andrei Izmer Bart Vekemans Karen Appel Sergei Tolmachev Laszlo Vincze Frank Vanhaecke 《Analytical and bioanalytical chemistry》2015,407(6):1559-1566
This study aims at evaluating the capabilities of synchrotron radiation micro X-ray fluorescence spectrometry (SR micro-XRF) for qualitative and semi-quantitative elemental mapping of the distribution of actinides in human tissues originating from individuals with documented occupational exposure. The investigated lymph node tissues were provided by the United States Transuranium and Uranium Registries (USTUR) and were analyzed following appropriate sample pre-treatment. Semi-quantitative results were obtained via calibration by external standards and demonstrated that the uranium concentration level in the detected actinide hot spots reaches more than 100 μg/g. For the plutonium hot spots, concentration levels up to 31 μg/g were found. As illustrated by this case study on these unique samples, SR micro-XRF has a high potential for this type of elemental bio-imaging owing to its high sensitivity, high spatial resolution, and non-destructive character.
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相似文献
46.
To address the impact of electron correlations in the linear and non-linear response regimes of interacting many-electron systems exposed to time-dependent external fields, we study one-dimensional (1D) systems where the interacting problem is solved exactly by exploiting the mapping of the 1D N-electron problem onto an N-dimensional single electron problem. We analyze the performance of the recently derived 1D local density approximation as well as the exact-exchange orbital functional for those systems. We show that the interaction with an external resonant laser field shows Rabi oscillations which are detuned due to the lack of memory in adiabatic approximations. To investigate situations where static correlations play a role, we consider the time-evolution of the natural occupation numbers associated to the reduced one-body density matrix. Those studies shed light on the non-locality and time-dependence of the exchange and correlation functionals in time-dependent density and density-matrix functional theories. 相似文献
47.
Sindbert S Kalinin S Nguyen H Kienzler A Clima L Bannwarth W Appel B Müller S Seidel CA 《Journal of the American Chemical Society》2011,133(8):2463-2480
In Fo?rster resonance energy transfer (FRET) experiments, the donor (D) and acceptor (A) fluorophores are usually attached to the macromolecule of interest via long flexible linkers of up to 15 ? in length. This causes significant uncertainties in quantitative distance measurements and prevents experiments with short distances between the attachment points of the dyes due to possible dye-dye interactions. We present two approaches to overcome the above problems as demonstrated by FRET measurements for a series of dsDNA and dsRNA internally labeled with Alexa488 and Cy5 as D and A dye, respectively. First, we characterize the influence of linker length and flexibility on FRET for different dye linker types (long, intermediate, short) by analyzing fluorescence lifetime and anisotropy decays. For long linkers, we describe a straightforward procedure that allows for very high accuracy of FRET-based structure determination through proper consideration of the position distribution of the dye and of linker dynamics. The position distribution can be quickly calculated with geometric accessible volume (AV) simulations, provided that the local structure of RNA or DNA in the proximity of the dye is known and that the dye diffuses freely in the sterically allowed space. The AV approach provides results similar to molecular dynamics simulations (MD) and is fully consistent with experimental FRET data. In a benchmark study for ds A-RNA, an rmsd value of 1.3 ? is achieved. Considering the case of undefined dye environments or very short DA distances, we introduce short linkers with a propargyl or alkenyl unit for internal labeling of nucleic acids to minimize position uncertainties. Studies by ensemble time correlated single photon counting and single-molecule detection show that the nature of the linker strongly affects the radius of the dye's accessible volume (6-16 ?). For short propargyl linkers, heterogeneous dye environments are observed on the millisecond time scale. A detailed analysis of possible orientation effects (κ(2) problem) indicates that, for short linkers and unknown local environments, additional κ(2)-related uncertainties are clearly outweighed by better defined dye positions. 相似文献
48.
McIntosh CL Germer F Schulz R Appel J Jones AK 《Journal of the American Chemical Society》2011,133(29):11308-11319
Protein film electrochemistry (PFE) was utilized to characterize the catalytic activity and oxidative inactivation of a bidirectional [NiFe]-hydrogenase (HoxEFUYH) from the cyanobacterium Synechocystis sp. PCC 6803. PFE provides precise control of the redox potential of the adsorbed enzyme so that its activity can be monitored under changing experimental conditions as current. The properties of HoxEFUYH are different from those of both the standard uptake and the "oxygen-tolerant" [NiFe]-hydrogenases. First, HoxEFUYH is biased toward proton reduction as opposed to hydrogen oxidation. Second, despite being expressed under aerobic conditions in vivo, HoxEFUYH is clearly not oxygen-tolerant. Aerobic inactivation of catalytic hydrogen oxidation by HoxEFUYH is total and nearly instantaneous, producing two inactive states. However, unlike the Ni-A and Ni-B inactive states of standard [NiFe]-hydrogenases, both of these states are quickly (<90 s) reactivated by removal of oxygen and exposure to reducing conditions. Third, proton reduction continues at 25-50% of the maximal rate in the presence of 1% oxygen. Whereas most previously characterized [NiFe]-hydrogenases seem to be preferential hydrogen oxidizing catalysts, the cyanobacterial enzyme works effectively in both directions. This unusual catalytic bias as well as the ability to be quickly reactivated may be essential to fulfilling the physiological role in cyanobacteria, organisms expected to experience swings in cellular reduction potential as they switch between aerobic conditions in the light and dark anaerobic conditions. Our results suggest that the uptake [NiFe]-hydrogenases alone are not representative of the catalytic diversity of [NiFe]-hydrogenases, and the bidirectional heteromultimeric enzymes may serve as valuable models to understand the diverse mechanisms of tuning the reactivity of the hydrogen activating site. 相似文献
49.
The rates of the epoxidation reactions of aldehydes, of the aziridination reactions of aldimines, and of the cyclopropanation reactions of α,β-unsaturated ketones with aryl-stabilized dimethylsulfonium ylides have been determined photometrically in dimethyl sulfoxide (DMSO). All of these sulfur ylide-mediated cyclization reactions as well as the addition reactions of stabilized carbanions to N-tosyl-activated aldimines have been shown to follow a second-order rate law, where the rate constants reflect the (initial) CC bond formation between nucleophile and electrophile. The derived second-order rate constants (log k(2)) have been combined with the known nucleophilicity parameters (N, s(N)) of the aryl-stabilized sulfur ylides 4a,b and of the acceptor-substituted carbanions 4c-h to calculate the electrophilicity parameters E of aromatic and aliphatic aldehydes (1a-i), N-acceptor-substituted aromatic aldimines (2a-e), and α,β-unsaturated ketones (3a-f) according to the linear free-energy relationship log k(2) = s(N)(N + E) as defined in J. Am. Chem. Soc.2001, 123, 9500-9512. The data reported in this work provide the first quantitative comparison of the electrophilic reactivities of aldehydes, imines, and simple Michael acceptors in DMSO with carbocations and cationic metal-π complexes within our comprehensive electrophilicity scale. 相似文献
50.
Almstetter MF Appel IJ Dettmer K Gruber MA Oefner PJ 《Journal of chromatography. A》2011,1218(39):7031-7038
The alignment algorithm Statistical Compare (SC) developed by LECO Corporation for the processing of comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) data was validated and compared to the in-house developed retention time correction and data alignment tool INCA (Integrative Normalization and Comparative Analysis) by a spike-in experiment and the comparative metabolic fingerprinting of a wild type versus a double mutant strain of Escherichia coli (E. coli). Starting with the same peak lists generated by LECO's ChromaTOF software, the accuracy of peak alignment and detection of 1.1- to 4-fold changes in metabolite concentration was assessed by spiking 20 standard compounds into an aqueous methanol extract of E. coli. To provide the same quality input signals for both alignment routines, the universal m/z 73 trace of the trimethylsilyl (TMS) group was used as a quantitative measure for all features. The performance of data processing and alignment was evaluated and illustrated by ROC curves. Statistical Compare performed marginally better at the lower fold changes, while INCA did so at the higher fold changes. Using SC, quantitative precision could be improved substantially by exploiting the signal intensities of metabolite-specific unique (U) m/z ion traces rather than the universal m/z 73 trace. A list of 56 features that distinguished the two E. coli strains was obtained by the SC alignment using m/z U with an estimated false discovery rate (FDR) of <0.05. Ultimately, 23 metabolites could be identified, one additional and five less than with INCA due to the failure of SC to extract unitized m/z U's across all fingerprints with suitable spectral intensities for the latter metabolites. 相似文献