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91.
Methylperoxy radicals, CH3O2 · have been detected by UV light absorption in the photolysis of azomethane, oxygen and nitrogen mixtures using the technique of molecular modulation spectrometry. The radical concentration is shown to be governed by second-order kinetics. The results give the extinction coefficient, o (exponential), at the peak (λ = 240 nm) = 4.4 × 10?18 molecule?1 cm2 and a value for the rate constant of mutual recombination, k, which lies between 2.2 × 10?13 and 4.4 × 10?13 molecule?1 cm3 sec?1. Similar results have been obtained when the azomethane was replaced by azoethane, suggesting the formation of C2H5O2. 相似文献
92.
93.
Sample controlled thermal analysis (SCTA) is the generic name used to describe a family of techniques where the heating rate is not pre-determined as in conventional thermal analysis, but altered as some function of a property of the sample (i.e. mass loss, rate of gas evolution, etc.). We demonstrate here a new form of SCTA, where the reaction rate for gas–solid reactions can be controlled by programming the concentration of the reactive gas whilst keeping the temperature constant. 相似文献
94.
E.W. Parkes 《International Journal of Solids and Structures》1975,11(9):1017-1022
An objection to the Michell theory of optimum frameworks is that many of the forms achieved embody large numbers of joints, and the theory ignores the penalty in material or fabrication cost which these entail. The paper investigates the forms of the optimum frameworks for some simple load systems when the cost of joints is taken into account. 相似文献
95.
Michelle A. Harris Tuba Sahin Jianbing Jiang Pothiappan Vairaprakash Pamela S. Parkes‐Loach Dariusz M. Niedzwiedzki Christine Kirmaier Paul A. Loach David F. Bocian Dewey Holten Jonathan S. Lindsey 《Photochemistry and photobiology》2014,90(6):1264-1276
Biohybrid light‐harvesting antennas are an emerging platform technology with versatile tailorability for solar‐energy conversion. These systems combine the proven peptide scaffold unit utilized for light harvesting by purple photosynthetic bacteria with attached synthetic chromophores to extend solar coverage beyond that of the natural systems. Herein, synthetic unattached chromophores are employed that partition into the organized milieu (e.g. detergent micelles) that house the LH1‐like biohybrid architectures. The synthetic chromophores include a hydrophobic boron‐dipyrrin dye (A1) and an amphiphilic bacteriochlorin (A2), which transfer energy with reasonable efficiency to the bacteriochlorophyll acceptor array (B875) of the LH1‐like cyclic oligomers. The energy‐transfer efficiencies are markedly increased upon covalent attachment of a bacteriochlorin (B1 or B2) to the peptide scaffold, where the latter likely acts as an energy‐transfer relay site for the (potentially diffusing) free chromophores. The efficiencies are consistent with a Förster (through‐space) mechanism for energy transfer. The overall energy‐transfer efficiency from the free chromophores via the relay to the target site can approach those obtained previously by relay‐assisted energy transfer from chromophores attached at distant sites on the peptides. Thus, the use of free accessory chromophores affords a simple design to enhance the overall light‐harvesting capacity of biohybrid LH1‐like architectures. 相似文献
96.
Christopher J. R. Illingworth Paul D. Scott Kevin E. B. Parkes Christopher R. Snell Matthew P. Campbell Christopher A. Reynolds 《Journal of computational chemistry》2010,31(15):2677-2688
Here, we describe a family of methods based on residue–residue connectivity for characterizing binding sites and apply variants of the method to various types of protein–ligand complexes including proteases, allosteric‐binding sites, correctly and incorrectly docked poses, and inhibitors of protein–protein interactions. Residues within ligand‐binding sites have about 25% more contact neighbors than surface residues in general; high‐connectivity residues are found in contact with the ligand in 84% of all complexes studied. In addition, a k‐means algorithm was developed that may be useful for identifying potential binding sites with no obvious geometric or connectivity features. The analysis was primarily carried out on 61 protein–ligand structures from the MEROPS protease database, 250 protein–ligand structures from the PDBSelect (25%), and 30 protein–protein complexes. Analysis of four proteases with crystal structures for multiple bound ligands has shown that residues with high connectivity tend to have less variable side‐chain conformation. The relevance to drug design is discussed in terms of identifying allosteric‐binding sites, distinguishing between alternative docked poses and designing protein interface inhibitors. Taken together, this data indicate that residue–residue connectivity is highly relevant to medicinal chemistry. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
97.
Michael A. Parkes Jessica F. Lockyear Stephen D. Price 《International journal of mass spectrometry》2009,280(1-3):85
The reaction between Ar2+ and C2H2 has been studied, at centre-of-mass collision energies ranging from 3 to 7 eV, using a position-sensitive coincidence technique to detect the monocation pairs, which are formed. Sixteen different reaction channels generating pairs of monocations have been observed, these channels arise from double-electron-transfer, single-electron-transfer and chemical reactions forming ArC+. Examination of the scattering diagrams and energetic information extracted from the coincidence data indicate that double-electron-transfer is a direct process, which does not involve a collision complex, and the derived energetics point towards a concerted, not stepwise, mechanism for the two-electron-transfer. As is commonly observed, single-electron-transfer from C2H2 to Ar2+ takes place via a direct mechanism, again not involving complexation. Most of the C2H2+ products that are formed in the single-electron-transfer reactions possess significant (12–15 eV) internal energy and fragment rapidly within the electric field of the partner Ar+ ion. The chemical reactions appear to proceed via a direct mechanism involving the initial formation of ArCH+, which subsequently fragments to form ArC+. 相似文献
98.
Dawson E. A. Parkes G. M. B. Barnes P. A. Chinn M. J. Norman P. R. 《Journal of Thermal Analysis and Calorimetry》1999,56(1):267-273
A constant rate method involving the control of the concentration of evolved CO2 at a constant level was used to study the air activation of pure and copper-doped carbon prepared from sodium carboxymethylcellulose.
Whereas under a linear heating regime, both types of carbon reacted suddenly and quickly with O2, under constant rate conditions this violent reaction was avoided and oxidation proceeded steadily at a lower temperature
until complete burn off of the carbon was achieved. The catalytic effect of the copper on carbon gasification was noted with
lower reaction temperatures for both linear heating (380°C compared to 500°C) and for the constant rate experiments (320°C
compared to 400°C).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献