排序方式: 共有71条查询结果,搜索用时 15 毫秒
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Carlos Calle Anandaram Sreekanth MatveyV. Fedin Jrg Forrer Ins Garcia‐Rubio IgorA. Gromov Dariush Hinderberger Besnik Kasumaj Patrick Lger Bruno Mancosu George Mitrikas MariaGrazia Santangelo Stefan Stoll Arthur Schweiger Ren Tschaggelar Jeffrey Harmer 《Helvetica chimica acta》2006,89(10):2495-2521
This review discusses the application of pulse EPR to the characterization of disordered systems, with an emphasis on samples containing transition metals. Electron nuclear double‐resonance (ENDOR), electron‐spin‐echo envelope‐modulation (ESEEM), and double electron–electron resonance (DEER) methodologies are outlined. The theory of field modulation is outlined, and its application is illustrated with DEER experiments. The simulation of powder spectra in EPR is discussed, and strategies for optimization are given. The implementation of this armory of techniques is demonstrated on a rich variety of chemical systems: several porphyrin derivatives that are found in proteins and used as model systems, otherwise highly reactive aminyl radicals stabilized with electron‐rich transition metals, and nitroxide–copper–nitroxide clusters. These examples show that multi‐frequency continuous‐wave (CW) and pulse EPR provides detailed information about disordered systems. 相似文献
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Robert George Acres Sarah Louise Harmer Hung Wei Shui Chia‐Hao Chen David Allan Beattie 《Journal of synchrotron radiation》2011,18(4):649-657
Scanning photoemission microscopy (SPEM) has been applied to the investigation of homogeneous and heterogeneous metal sulfide mineral surfaces. Three mineral samples were investigated: homogeneous chalcopyrite, heterogeneous chalcopyrite with bornite, and heterogeneous chalcopyrite with pyrite. Sulfur, copper and iron SPEM images, i.e. surface‐selective elemental maps with high spatial resolution acquired using the signal from the S 2p and Cu and Fe 3p photoemission peaks, were obtained for the surfaces after exposure to different oxidation conditions (either exposed to air or oxidized in pH 9 solution), in addition to high‐resolution photoemission spectra from individual pixel areas of the images. Investigation of the homogeneous chalcopyrite sample allowed for the identification of step edges using the topography SPEM image, and high‐resolution S 2p spectra acquired from the different parts of the sample image revealed a similar rate of surface oxidation from solution exposure for both step edge and a nearby terrace site. SPEM was able to successfully distinguish between chalcopyrite and bornite on the heterogeneous sample containing both minerals, based upon sulfur imaging. The high‐resolution S 2p spectra acquired from the two regions highlighted the faster air oxidation of the bornite relative to the chalcopyrite. Differentiation between chalcopyrite and pyrite based upon contrast in SPEM images was not successful, owing to either the poor photoionization cross section of the Cu and Fe 3p electrons or issues with rough fracture of the composite surface. In spite of this, high‐resolution S 2p spectra from each mineral phase were successfully obtained using a step‐scan approach. 相似文献
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W. M. Bright E. L. Miller C. E. ZoBell S. C. Rittenberg P. Wulff O. Lazar A. H. Meyling E. G. Voiret Y. Kauko A. Airola W. J. Harmer A. E. Cameron K. Schwabe G. Parsy P. A. Krjukow A. A. Krjukow H. Bender D. J. Pye M. J. Dallemagne G. Haugaard M. Dole B. Z. Wiener J. L. Gabbard E. S. Amis J. Powney D. O. Jordan W. S. Finkelstein I. S. Tartakowski D. I. Hitchcock Alice C. Taylor H. S. Ilarned R. W. Ehlers L. F. Nims B. B. Owen R. Rosenthal A. E. Lorch L. P. Hammett 《Analytical and bioanalytical chemistry》1939,118(9-10):322-332
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Finazzo C Harmer J Bauer C Jaun B Duin EC Mahlert F Goenrich M Thauer RK Van Doorslaer S Schweiger A 《Journal of the American Chemical Society》2003,125(17):4988-4989
Methyl-coenzyme M reductase (MCR) catalyzes the reaction of methyl-coenzyme M (CH3-S-CoM) with coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. At the active site, it contains the nickel porphinoid F430, which has to be in the Ni(I) oxidation state for the enzyme to be active. How the substrates interact with the active site Ni(I) has remained elusive. We report here that coenzyme M (HS-CoM), which is a reversible competitive inhibitor to methyl-coenzyme M, interacts with its thiol group with the Ni(I) and that for interaction the simultaneous presence of coenzyme B is required. The evidence is based on X-band continuous wave EPR and Q-band hyperfine sublevel correlation spectroscopy of MCR in the red2 state induced with 33S-labeled coenzyme M and unlabeled coenzyme B. 相似文献
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Grain boundary segregation of Y and Zr in -Al2O3 and the atomic structural environment around the Y and Zr atoms have been investigated using high resolution STEM and EXAFS. At dilute concentrations, the Y ions in -Al2O3 grain boundaries, on average, are coordinated by 4 oxygens, at a distance of 2.30 Å, which corresponds nearly to the Y-O bond length in cubic Y2O3, and Zr ions are coordinated by 5 oxygens at a distance of 2.14 Å, which is approximately the same as the average Zr-O bond length in monoclinic ZrO2. However, in the EXAFS radial distribution function, the Y-cation and Zr-cation next nearest neighbor shell cannot be clearly identified. These results suggest that Y and Zr at dilute concentrations in -Al2O3 occupy grain boundary sites with well defined nearest neighbor cation-oxygen bond lengths similar to those in their parent oxides, but with the next nearest neighbor cation-cation distances varying considerably from site to site. Grain growth can cause grain boundaries to become supersaturated by Y. In this case, both the Y-O nearest neighbor coordination number and the ordering of Y with respect to Al ions beyond nearest neighbor O are increased. This Y-Al distance is the same as that expected for the Y-Al distance when Y substitutes for Al while relaxing the Y-O distance to that in Y2O3. This may indicate that as the Y concentration increases, Y begins to occupy near-boundary sites in planes on each side of the geometrical boundary. In these near-boundary planes, the nearest neighbor ordering extends at least to nearest neighbor cations. Nucleation of the YAG phase leads to the depletion of these partially ordered layers. 相似文献
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N. S. Scott V. Faro-Maza M. P. Scott T. Harmer J. -M. Chesneaux C. Denis F. Jézéquel 《Physics of Particles and Nuclei Letters》2008,5(3):150-156
We describe a computational science research program primarily aimed at engineering numerically robust software that can exploit
high performance on distributed computers in the study of electron collisions with atoms and ions. In particular, we describe
the development of 2DRMP-G, a Grid aware 2-dimensional R-matrix propagator and its numerical validation using CADNA, a software tool based on discrete stochastic arithmetic.
The text was submitted by the authors in English. 相似文献
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