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2,5-Diphenyl-2,5-dipotassiohexane, 2-lithio-4,4-dimethyl-2-phenylpentane, and 1-lithio-2,5,5-trimethylhexene-2 have been prepared, all labelled with13C in the position adjacent to the alkali metal atom. The13C NMR spectra of these compounds have been measured and the13CC coupling constants found for the charged atom. The first two compounds have coupling constants consistent with an sp2 hybridized Cα, with relatively little effect of the charge on the coupling constant. The third compound, when dissolved in either THF or benzene, gave much smaller coupling constants, which are more difficult to interpret. 相似文献
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A comparison is made between the distribution of residue preferences, three dimensional nearest neighbour contacts, preferred rotamers, helix-helix crossover angles and peptide bond angles in three sets of proteins: a non-redundant set of accurately determined globular protein structures, a set of four-helix bundle structures and a set of membrane protein structures. Residue preferences for the latter two sets may reflect overall helix stabilising propensities but may also highlight differences arising out of the contrasting nature of the solvent environments in these two cases. The results bear out the expectation that there may be differences between residue type preferences in membrane proteins and in water soluble globular proteins. For example, the -branched residue types valine and isoleucine are considerably more frequently encountered in membrane helices. Likewise, glycine and proline, residue types normally associated with `helix-breaking' propensity are found to be relatively more common in membrane helices. Three dimensional nearest neighbour contacts along the helix, preferred rotamers, and peptide bond angles are very similar in the three sets of proteins as far as can be ascertained within the limits of the relatively low resolution of the membrane proteins dataset. Crossing angles for helices in the membrane protein set resemble the four helix bundle set more than the general non-redundant set, but in contrast to both sets they have smaller crossing angles consistent with the dual requirements for the helices to form a compact structure while having to span the membrane. In addition to the pairwise packing of helices we investigate their global packing and consider the question of helix supercoiling in helix bundle proteins. 相似文献
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S. Bywater 《Journal of polymer science. Part A, Polymer chemistry》1999,37(24):4467-4477
The determination of the individual rate constants in a reaction involving more than a single step is part of the basic knowledge required to understand the process itself. The history of the chain mechanism of vinyl polymerization is presented briefly. The techniques needed to measure the chain propagation step are discussed for the three basic mechanisms: free-radical, cationic, and anionic polymerization. Illustrative examples of the rate constants obtained are given, with stress placed on the monomers styrene and methyl methacrylate, which have the advantage of being able to be polymerized by all three or two of the mechanisms, respectively. This allows a comparison of propagation constants between mechanisms. Some factors influencing the magnitudes of the constants are mentioned, and some problems involved in specific cases are discussed. © 1999 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4467–4477, 1999 相似文献
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Seddon G Lounnas V McGuire R van den Bergh T Bywater RP Oliveira L Vriend G 《Journal of computer-aided molecular design》2012,26(1):137-150
In its first 25 years JCAMD has been disseminating a large number of techniques aimed at finding better medicines faster.
These include genetic algorithms, COMFA, QSAR, structure based techniques, homology modelling, high throughput screening,
combichem, and dozens more that were a hype in their time and that now are just a useful addition to the drug-designers toolbox.
Despite massive efforts throughout academic and industrial drug design research departments, the number of FDA-approved new
molecular entities per year stagnates, and the pharmaceutical industry is reorganising accordingly. The recent spate of industrial
consolidations and the concomitant move towards outsourcing of research activities requires better integration of all activities
along the chain from bench to bedside. The next 25 years will undoubtedly show a series of translational science activities
that are aimed at a better communication between all parties involved, from quantum chemistry to bedside and from academia
to industry. This will above all include understanding the underlying biological problem and optimal use of all available
data. 相似文献
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