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951.
Hakemian AS Tinberg CE Kondapalli KC Telser J Hoffman BM Stemmler TL Rosenzweig AC 《Journal of the American Chemical Society》2005,127(49):17142-17143
The oxidation state of copper bound to methanobactin, a small siderophore-like molecule from the methanotroph Methylosinus trichosporium OB3b, was investigated. Purified methanobactin loaded with Cu(II) exhibits a weak EPR signal probably due to adventitious Cu(II). The EPR signal intensity increases significantly upon addition of the strong oxidant nitric acid. Features of the X-ray absorption near edge spectrum, including a 1s --> 4p transition at 8985 eV, further indicate the presence of Cu(I). EXAFS data were best fit using a multiple scattering model generated from previously reported crystallographic parameters. These results establish definitively that M. trichosporium OB3b methanobactin binds Cu(I) and suggest that methanobactin itself reduces Cu(II) to Cu(I). 相似文献
952.
The degree of interfacial structuring of n-hexadecane and octamethylcyclotetrasiloxane (OMCTS) was measured within a nanometer boundary regime to silicon surfaces. Boundary-layer effects on lubricating sliding (in terms of a thermodynamic stress activation parameter) and the layer thickness were determined by scanning force microscopy. A 2.0+/-0.3 nm thick, entropically cooled layer was found for n-hexadecane. Measurements on spherically shaped OMCTS molecules exhibited only an interfacial "monolayer," and identified the molecular shape of n-hexadecane responsible for augmented interfacial structuring. Interfacial liquid structuring was found to reduce friction. 相似文献
953.
A novel porous framework polymer with expandable structure, over 8% volume expansion upon inclusion, has been characterized. 相似文献
954.
Thallapally PK Katz AK Carrell HL Desiraju GR 《Chemical communications (Cambridge, England)》2002,(4):344-345
Conformational flexibility in a symmetrical tris-phenol leads to close packed structures that are also characterised by an extended though finite cooperative chain of hydrogen bonds. 相似文献
955.
Stockert AL Shinde SS Anderson RF Hille R 《Journal of the American Chemical Society》2002,124(49):14554-14555
Current research on xanthine oxidase has favored a mechanism involving base-catalyzed proton abstraction from a Mo-OH group, allowing nucleophilic attack on the substrate and hydride transfer from the substrate to Mo=S group in the active site. During the course of this reaction mechanism, the molybdenum redox cycles from MoVI to MoIV, with reoxidation of the MoIV speices to form the EPR active MoV intermediate. However, it has also been suggested that the reaction occurs in two subsequent one-electron steps. We have determined kinetic parameters kred and kred/Kd for a variety of plausible substrates as well as the one-electron reduction potentials for these substrates. Our data indicate no correlation between these kinetic parameters and their one-electron reduction potentials, as would be expected if the enzyme were using two subsequent one-electron reduction steps. Our results provide additional support to current evidence for the favored two-electron reduction mechanism. 相似文献
956.
957.
J. H. Beynon J. E. Corn W. E. Baitinger J. W. Amy R. A. Benkeser 《Journal of mass spectrometry : JMS》1970,3(2):191-198
A new method of general applicability for determining the percentage deuterium labeling in organic compounds is described. It uses the heights of ‘metastable peaks’ in the mass spectrum to determine the relative amounts of deuterated and undeuterated species. The method is illustrated by describing the analysis of mixtures of toluene-o-d1 and toluene, of toluene α-d1 and toluene, and of toluene-2,6-d2, toluene-o-d1 and toluene. 相似文献
958.
[structure: see text] Intramolecular [4 + 2] cycloaddition using alpha,beta-unsaturated oximes was explored. The reactions proceeded under unusually facile conditions to furnish the nitrones. The latter were subsequently reacted with DMAD to afford [3 + 2] cycloaddition products. 相似文献
959.
Matthew?GouldEmail author Karen Ann?LintonEmail author Amy Wildsmith?Nelson 《Semigroup Forum》2004,68(2):186-201
Given a monogenic semigroup, (S, ·) , we characterize all interassociates of
(S, ·) . We determine necessary and sufficient conditions under which an interassociate
of (S, ·) is isomorphic to (S, ·) . Finally, we find necessary and
sufficient conditions under which two interassociates of (S, ·) are isomorphic. 相似文献
960.
We demonstrate a high-power laser system that employs a new scheme in which pulses with negative chirp are amplified and then recompressed by dispersion in a block of transparent material. This scheme has significant advantages for amplification of intermediate energy pulses at high average power, including insensitivity to small misalignments of the pulse compressor, elimination of compressor gratings and their thermal loading issues, low compressor energy and bandwidth throughput losses, and a simplified optical design. Using this scheme, we demonstrate what we believe is the highest-average-power single-stage Ti:sapphire amplifier system with 11-W compressed output. 相似文献