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51.
Emmanuel Mikros George Labrinidis Serge Pérez 《Journal of carbohydrate chemistry》2013,32(9):1319-1349
ABSTRACT Relaxed-residue energy maps based on the MM3 force field were computed for the methyl glycosides of eight C-linked D-glucosyl disaccharides: the two-bond axial-equatorial linked disaccharides β-kojibioside [(1→2)α–], β-nigeroside [(1→3)α–] and β-maltose [(1→4)α–], the two-bond equatorial-equatorial linked disaccharides β-sophoroside [(1→2)β–], β–laminarabioside [(1→3)β-], β–cellobioside [(1→4)β–] and the three-bond-linked (1→6) disacharides C-isomaltoside and C-gentiobioside. Optimized structures were calculated on a 20° grid spacing of the torsional angles about the C-glycosidic bonds and the final isoenergy surfaces were based on 11664 conformations, for the two-bond-linked disaccharides and 69984 conformations for the three-bond-linked disaccharides. Boltzmann-weighted 3J coupling constants were calculated and compared to the experimental values. They are satisfactory except for maltose where hydrogen bonds cause an over-estimation of the energy differences between the conformers. The energy maps are similar to maps of the corresponding O-disaccharides, but there are differences in the locations and the relative energies of the minima. The preferred conformations of the C-glycosidic bonds are as if they were conforming to the exo-anomeric effect but are closer to staggered conformations than shown by the MM3 results for the O-linkages. 相似文献
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Mikhail H. Klin Serge S. Tratch Nikolai S. Zefirov 《Journal of mathematical chemistry》1991,7(1):135-151
We give a necessary and sufficient condition for a reaction graph of a degenerate rearrangement to be connected. This condition is formulated in terms of vertex stabilizers of the automorphism group of a molecular graph. The condition is illustrated on several examples, including the reaction graph of bullvalene. We consider different mathematical models for the construction of reaction graphs and state the problem: which of the models is more adequate? 相似文献
54.
The esterfication of ethylene glycol (EG) with benzoic acid (BA) is an acid-catalyzed reaction which leads, as a first intermediate, to ethylene glycol monobenzoate (EGMB). This compound has an ? OH group which is more active towards carboxylic groups than the first ? OH group of EG. Moreover, it is a key intermediate in the formation of sideproducts containing diethylene glycol (DEG) moieties. The condensation reaction of EGMB was particularly studied in the presence of carboxylic acids or metal derivatives as catalysts. Titanium is the most active. Sb, which is widely used in the industrial synthesis of PET, needs to be present at a high level of concentration to show an activity. The presence of carboxylic groups in the reaction medium does not affect its activity, but it is necessary to remove the ethylene glycol as soon as it is formed in order to keep it active during the condensation reaction. 相似文献
55.
Boris Gouilleux Benoît Charrier Serge Akoka Patrick Giraudeau 《Magnetic resonance in chemistry : MRC》2017,55(2):91-98
Benchtop NMR emerges as an appealing alternative to widely extend the scope of NMR spectroscopy in harsh environments and for on‐line monitoring. Obviously, the use of low‐field magnets induces a dramatic reduction of the spectral resolution leading to frequent peak overlaps. This issue is even more serious because applications such as chemical process monitoring involve the use of non‐deuterated solvents, leading to intense and broad peaks overlapping with the signals of interest. In this article, we highlight the need for efficient suppression methods compatible with flowing samples, which is not the case of the common pre‐saturation approaches. Thanks to a gradient coil included in our benchtop spectrometer, we were able to implement modern and efficient solvent suppression blocks such as WET or excitation sculpting to deliver quantitative spectra in the conditions of the on‐line monitoring. While these methods are commonly used at high field, this is the first time that they are investigated on a benchtop setting. Their analytical performance is evaluated and compared under static and on‐flow conditions. The results demonstrate the superiority of gradient‐based methods, thus highlighting the relevance of implementing this device on benchtop spectrometers. The comparison of major solvent suppression methods reveals an optimum performance for the WET‐180‐NOESY experiment, both under static and on‐flow conditions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
56.
Serge Crouzy Jerme Baudry Jeremy C. Smith Benoît Roux 《Journal of computational chemistry》1999,20(15):1644-1658
Accurate calculation of potential energy and free-energy profiles along reaction coordinates of biological processes such as enzymatic reactions or conformational changes is fundamental to the obtention of theoretical insight into protein function. We describe here the practical implementation of the Automatic Map Refinement Procedure (AMRP) and two-dimensional Weighted Histogram Analysis Method (WHAM) for efficient computation of adiabatic potential energy and free-energy maps, respectively. Methods for efficiently sampling configuration space with high-energy barriers and for removing hysteresis in the case of periodic reaction coordinates are presented. The application of these techniques to the isomerization of the C13C14 and C15N16 bonds in the retinal of bacteriorhodopsin is described. In dark-adapted bacteriorhodopsin (bR), the retinal moiety exists in two conformers, all-trans and (13,15)cis, with the latter making ≃67% of the population. This experimental free energy difference is reproduced here to within kBT. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1644–1658, 1999 相似文献
57.
Christine Mousty Arielle Lepellec Serge Cosnier Andres Novoa Robert S. Marks 《Electrochemistry communications》2001,3(12):727-732
We describe herein, the creation of an organic phase enzyme electrode (OPEE) via avidin–biotin interactions built over an electrogenerated polymer. Multilayered polyphenol oxidase (PPO) assemblies were transferred into an organic solvent (chloroform) for the catechol detection at −0.2 V. In conjunction with an alginate gel, as a hydrophilic additive, the biosensor performance was widely enhanced. The effects of biotinylated polypyrrole film and alginate gel on the diffusion process through the biosensor coating are studied by rotating disk electrode experiments carried out in chloroform with hydroquinone as electroactive permeant. 相似文献
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In this paper we consider approximations of the occupation measure of the Fractional Brownian motion by means of some functionals
defined on regularizations of the paths. In a previous article Berzin and León proved a cylindrical convergence to a Wiener
process of conveniently rescaled functionals. Here we show the tightness of the approximation in the space of continuous functions
endowed with the topology of uniform convergence on compact sets. This allows us to simplify the identification of the limit. 相似文献