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141.
O.N. Ulenikov E.S. Bekhtereva T.D. Homiak T.R. Huet F. Herregodts W. Jerzembeck 《Journal of Molecular Spectroscopy》2003,222(2):153-158
The high resolution spectrum of a phosphine gas mixture containing PHD2 was recorded at room temperature in the 12 550-12 770 cm−1 region. A high sensitivity laser photoacoustic spectrometer consisting of a longitudinal resonant cell coupled to a Ti:sapphire ring laser was employed. More than 600 transitions were assigned to the 6ν1 overtone band of PHD2 up to Jmax=20, Kamax=6. A Hamiltonian model developed up to the octic centrifugal distortion terms was used. Seven rotational and centrifugal distortion parameters were fitted, the other ones being fixed to their values linearly extrapolated from ν1 and 2ν1. The derived parameters reproduce the initial data within the experimental uncertainties. The isolated character of the P-H bond is confirmed. 相似文献
142.
Marion Scheepers 《Proceedings of the American Mathematical Society》1997,125(9):2719-2724
An open cover of an infinite separable metric space is an -cover of if and for every finite subset of there is a such that . Let be the collection of -covers of . We show that the partition relation holds if, and only if, the partition relation holds.
143.
Comparison of different extraction techniques for the determination of chlorinated pesticides in animal feed 总被引:2,自引:0,他引:2
Gfrerer M Chen S Lankmayr EP Quan X Yang F 《Analytical and bioanalytical chemistry》2004,378(7):1861-1867
The performances of Soxhlet extraction, dive-in Soxhlet extraction, microwave-assisted extraction (MAE), accelerated solvent extraction (ASE), fluidized-bed extraction (FBE), and ultrasonic extraction (UE) for the analysis of organochlorine pesticides in animal feed have been investigated. ASE and MAE provided significantly better extraction efficiency than Soxhlet extraction. The concentrations were 126.7 and 114.8%, respectively, of the values obtained by classical Soxhlet extraction, whereas the results from FBE and dive-in Soxhlet were comparable with those from the standard Soxhlet procedure. The reproducibility of FBE was the best, with RSDs ranging from 0.3 to 3.9%. Under the investigated operation conditions UE was not efficient, with the recoveries of target compounds being about 50% less than Soxhlet. Additionally, the performances of Soxhlet, dive-in Soxhlet, MAE, ASE and FBE were validated by determination of the certified reference material BCR-115. The results from the extraction techniques were in good agreement with the certified values. 相似文献
144.
Reactions of Undecacarbonyl(acetonitrile)triiron with Alkyne Ethers (CO)11(CH3CN) 1 reacts with the alkyne ethers H3C? C?C? OC2H5 2a , H? C?C? OC2H5 2b , H3C? O? CH2? C?C? CH2? O? CH3, 2c and H3C? O? C(CH3)H? C?C? C(CH3)H? O? CH3 2d forming different cluster products depending on the substituents and the reaction conditions. The product obtained with 2a is the bisalkylidyne cluster Fe3(CO)9(m?3-C? CH3)(m?3-C? OC2H5) 3 which results from the cleavage of the carbon carbon triple bond. The alkyne 2b however yields the vinylidene cluster Fe3(CO)10(m?3-η2-C? C(H)OC2H5) 4 by 1,2 proton shift. The alkyne clusters Fe3(CO)10(m?3-η2-C? C(H)OC2H5) 4 by 1,2 proton shift. The alkyne clusters Fe3(CO)10(m?3-η2- H3 C? O? CH2? C?C? CH2? O? CH3) 6 and Fe3(CO)9(m?-η2-H3C? O? CH2? C?C? CH2? O? CH3) 7 are the isolated products obtained from 2c . Thermolysis of 7 results in the formation of the dinuclear butatrien complex Fe2(CO)6 (H2C? C? C? CH2) 8a . The analogous compound Fe2(CO)6[H(H3C)C ? C ? C ? C(CH3)H] 8b is the only product of 2d and 1 . The structures of 4, 5 , and 6 have been determined by crystal structure determinations. 相似文献
145.
Poluektov OG Paschenko SV Utschig LM Lakshmi KV Thurnauer MC 《Journal of the American Chemical Society》2005,127(34):11910-11911
Efficient charge separation occurring within membrane-bound reaction center proteins is the most important step of photosynthetic solar energy conversion. All reaction centers are classified into two types, I and II. X-ray crystal structures reveal that both types bind two symmetric membrane-spanning branches of potential electron-transfer cofactors. Determination of the functional roles of these pairs of branches is of fundamental importance. While it is established that in type II reaction centers only one branch functions in electron transfer, we present the first direct spectroscopic evidence that both cofactor branches are active in the type I reaction center, photosystem I. 相似文献
146.
Sviatoslav Baranets Marion Schfer Svilen Bobev 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(11):1535-1540
Exploratory studies in the systems A–Al–Sn (A = K and Rb) yielded the clathrates K8AlxSn46–x (potassium aluminium stannide) and Rb8AlxSn46–x (rubidium aluminium stannide), both with the cubic type‐I structure (space group Pmn, No. 223; a ? 12.0 Å). The Al:Sn ratio is close to the idealized A8Al8Sn38 composition and it is shown that it can be varied slightly, in the range of ca ±1.5, depending on the experimental conditions. Both the (Sn,Al)20 and the (Sn,Al)24 cages in the structure are fully occupied by the guest alkali metal atoms, i.e. K or Rb. The A8Al8Sn38 formula has a valence electron count that obeys the valence rules and represents an intrinsic semiconductor, while the experimentally determined compositions A8Al8±xSn38?x suggest the synthesized materials to be nearly charge‐balanced Zintl phases, i.e. they are likely to behave as heavily doped p‐ or n‐type semiconductors. 相似文献
147.
[reaction: see text] A new generation of 2,5-dimethylthiolanes with a locked conformation was developed to promote the asymmetric addition of chiral sulfonium ylides to aldehydes. The novel chiral sulfur derivative 4 succeeded the synthesis of trans-stilbene oxide derivatives with enantiomeric ratios ranging from 95:5 to 98:2. This user-friendly organocatalytic process proved to be efficient with 20-10% of sulfide 4 in 1 or 2 days of reaction. An insight into the ylide intermediate conformation is given on the basis of a computational ab initio study. 相似文献
148.
The electrophoretic separation of high-molecular-weight proteins (> 500 kDa) using polyacrylamide is difficult because gels with a large enough pore size for adequate protein mobility are mechanically unstable. A 1% vertical sodium dodecyl sulfate (SDS)-agarose gel electrophoresis (VAGE) system has been developed that allows titin (a protein with the largest known SDS subunit size of 3000-4000 kDa) to migrate over 10 cm in a approximately 13 cm resolving gel. Such migration gives clear and reproducible separation of titin isoforms. Proteins ranging in size from myosin heavy chain ( approximately 220 kDa) up to titin can be resolved on this gel system. Electroblotting of these very large proteins was nearly 100% efficient. This VAGE system has revealed two titin size variants in rabbit psoas muscle, two N2BA bands in rabbit cardiac muscle, and species differences between titins from rat and rabbit muscle. Agarose electrophoresis should be the method of choice for separation and blotting of proteins with very large subunit sizes. 相似文献
149.
Dr. Dominique Marion Dr. Diego F. Gauto Isabel Ayala Karine Giandoreggio-Barranco Dr. Paul Schanda 《Chemphyschem》2019,20(2):276-284
Studying protein dynamics on microsecond-to-millisecond (μs-ms) time scales can provide important insight into protein function. In magic-angle-spinning (MAS) NMR, μs dynamics can be visualized by rotating-frame relaxation dispersion experiments in different regimes of radio-frequency field strengths: at low RF field strength, isotropic-chemical-shift fluctuation leads to “Bloch-McConnell-type” relaxation dispersion, while when the RF field approaches rotary resonance conditions bond angle fluctuations manifest as increased rate constants (“Near-Rotary-Resonance Relaxation Dispersion”, NERRD). Here we explore the joint analysis of both regimes to gain comprehensive insight into motion in terms of geometric amplitudes, chemical-shift changes, populations and exchange kinetics. We use a numerical simulation procedure to illustrate these effects and the potential of extracting exchange parameters, and apply the methodology to the study of a previously described conformational exchange process in microcrystalline ubiquitin. 相似文献
150.
The detection of food allergens has been a challenge because of the increasing need to ensure the absence of undeclared allergens in foods. The current trend in the detection of some food allergens, like peanuts, is based on the detection of multiple allergenic and nonallergenic proteins, and this is the approach that kit manufacturers have adopted. Because commercial kits differ in their ability to detect allergens, regulatory agencies, the food industry, and kit manufacturers are working together to standardize the detection methods. Three kits for the detection of peanuts have been evaluated for performance by the AOAC Research Institute. For this evaluation, a peanut butter suspension was used as a reference material. Several kit components contribute to between-kit analytical variation, even when the same sample is used. One component of commercial kits, which may be contributing to this variability, is the sample extraction buffer. In this study, differences in extractability of 3 allergenic foods were evaluated by using 4 different extraction buffers. The conclusion is that optimum allergen extractability was buffer-dependent, and no single buffer is appropriate for use as a universal extraction solution for all allergenic foods. Therefore, a thorough evaluation of sample preparation buffers needs to be performed for every individual allergenic food. In light of the results obtained, the current approach used for detection of peanut allergens based on the detection of multiple allergenic and nonallergenic proteins is being analyzed. 相似文献