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41.
Bright orange (CuBr)3P4Se4 is obtained from the reaction of CuBr, P, and Se in stoichiometric amounts (CuBr : P : Se = 3 : 4 : 4). The composition and the crystal structure of the compound were determined from single crystal X‐ray diffraction data. Lattice constants are a = 33.627(2) Å, b = 6.402(1) Å, c = 19.059(1) Å, β = 90.19(3) °, V = 4103.2(3) Å3, and Z = 12. The compound crystallizes in a structure that is related to (CuI)3P4Se4. Cages of β‐P4Se4 are stacked along the b‐axis and are separated by columns of copper(I) bromide. However, the coordination of the β‐P4Se4 cage molecules to the copper atoms in the CuBr columns in (CuBr)3P4Se4 is quite different from (CuI)3P4Se4. The monoclinic compound (space group: P21, no. 4) has an almost orthorhombic metric in combination with a threefold superstructure in [100]. Structural aspects of (CuBr)3P4Se4 are discussed with respect to the heavier homologue (CuI)3P4Se4. 相似文献
42.
De Vriendt K Sandra K Desmet T Nerinckx W Van Beeumen J Devreese B 《Rapid communications in mass spectrometry : RCM》2004,18(24):3061-3067
The use of electrospray ionization mass spectrometry (ESI-MS) for studying non-covalent interactions between macromolecules and ligands is well established. ESI-MS can be a useful tool for the determination of dissociation constants between molecules in the gas phase. We validate this method by studying the binding of the catalytic domain of cellobiohydrolase I (CBH I) from Trichoderma reesei to the disaccharide inhibitor cellobiose. The method was further applied to study two newly synthesized cellobiose derivatives (m-iodobenzyl 2-deoxy-2-azido-beta-cellobioside and p-benzyloxybenzyl beta-cellobioside). In a titration experiment, peak areas of different charge states of the free enzyme and the complex were summed in order to determine the dissociation constant. For cellobiose and m-iodobenzyl 2-deoxy-2-azido-beta-cellobioside, the calculated values are in good agreement with those reported from either displacement titration or equilibrium binding experiments in solution. Due to non-specific binding, the dissociation constant of p-benzyloxybenzyl beta-cellobioside does not correspond with the solution-based value. Our results indicate the need for careful interpretation of data sets when using nanoESI to study non-covalent interactions. 相似文献
43.
[reaction: see text] Continuing from the syntheses and the antibacterial studies of a library of pyranmycins, we further probed the proximity around ring III of pyranmycin by introducing an "extended arm" that has hydroxyethyl or aminoethyl groups at the O-2' ', O-3' ', or O-4' ' positions. The results from the antibacterial studies reveal the optimal structural motif is the attachment of an extended arm with a terminal hydroxyl group at the O-3' ' position. 相似文献
44.
Battle PD Blundell SJ Brooks ML Hervieu M Kapusta C Lancaster T Nair SP Oates CJ Pratt FL Rosseinsky MJ Ruiz-Bustos R Sikora M Steer CA 《Journal of the American Chemical Society》2004,126(39):12517-12527
The temperature dependence of the crystal structure and electronic properties of brownmillerite-like Ca(2.5)Sr(0.5)GaMn(2)O(8) has been studied by neutron powder diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO(6) octahedra approximately 50 K above the 3D Néel temperature of approximately 150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO(4) layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn(3+) and Mn(4+) cations in a 1:1 ratio, and the behavior in the region of the Néel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO(4) tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers. 相似文献
45.
Cofino et al. have put forward a method for the analysis of data from interlaboratory studies. The method uses ideas and notation from quantum chemistry, and is quite sophisticated. A critical examination shows that it has some relationship with both kernel density estimation and robust estimation methods. The quantitative results it provides are not founded on any statistical probability model, and it is not at all clear how the variance in particular is to be interpreted. There is no clear argument for adopting Cofino statistics in preference to simple problem-free methods that are at least as effective in estimating a concensus value.This report was prepared for the Statistical Subcommittee by Professor T. Fearn, with the assistance of Mr T. Robinson, and approved by the AMC on 25/11/03. The Statistical Subcommittee comprised: Dr. S.L.R. Ellison, Professor T. Fearn, Mr M. Gardner, Dr. F. Hollywood, Professor R.J. Howarth, Dr. P. Lowthian, Professor J.N. Miller, Dr. E.J. Newman, Professor B.D. Ripley, Professor M. Thompson (Chair), Dr. R. Wood, Dr. A. Williams and Mr J.J. Wilson (Secretary). 相似文献
46.
Mei Y Wu T Xu C Langenbach KJ Elliott JT Vogt BD Beers KL Amis EJ Washburn NR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(26):12309-12314
A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region. 相似文献
47.
[reaction: see text] A microwave-assisted reaction was developed to facilitate the construction of 4,5-disubstituted pyrazolopyrimidines. This one-pot two-step process involves a sequential S(N)Ar displacement of the C4 chloro substituent with various anilines and amines, followed by a Suzuki coupling reaction with different boronic acids. Using microwave irradiation leads to high product conversion, low side product formation, and shorter reactions. 相似文献
48.
Rozing G van de Goor T Yin H Killeen K Glatz B Kraiczek K Lauer HH 《Journal of separation science》2004,27(17-18):1391-1401
A systematic investigation of the influence of the perimeter shape of open and particle packed fused silica capillaries on chromatographic properties such as resistance to flow and dispersion of solutes propelled through these channels has been conducted. Verifications of these uncommon experiments with existing theoretical treatments are presented and the insights transferred to a novel polymer chip design with integrated facilities for complex separations. A comparison of the chromatographic performance of a real life proteomics sample on this chip with a capillary column of "similar" dimensions is presented. 相似文献
49.
Glyoxaldiimines (I) RN=CHCH=NR show in the NMR a downfield shift of glyoxalic protons (Hgly) when complexed to (II: M = Mo, W), but increasing high field shifts when going to (III) and complexes (IV). In the tungsten complexes II HglyW coupling satellites are resolved (J(WH) ≈4–6 Hz); in the phosphine compounds III, IV long range PHgly coupling is clearly visible. Mechanisms of spinspin interaction are briefly discussed in connection with the EPR results on monoanionic radicals of II–IV. 相似文献
50.