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51.
Elise Champion Isabelle André Laurence A. Mulard Pierre Monsan Magali Remaud-Siméon Sandrine Morel 《Journal of carbohydrate chemistry》2013,32(3):142-160
Transglucosylation reactions using sucrose as glucosyl donor and either N-acetyl-D-glucosamine, L-rhamnose, or methyl α -L-rhamnopyranoside as acceptors were carried out with recombinant glucansucrases from families 70 and 13 of glycoside-hydrolases. Depending on the enzyme specificity, various carbohydrate structures were synthesized and characterized including α -D-glucopyranosyl-(1 → 6)-N-acetyl-D-glucosamine, α -D-glucopyranosyl-(1 → 4)-N-acetyl-D-glucosamine, α -D-glucopyranosyl-(1 → 1)-β -L-rhamnopyranoside, α -D-glucopyranosyl-(1 → 4)-α -D-glucopyranosyl-(1 → 1)-β -L-rhamnopyranoside, methyl α -D-glucopyranosyl-(1 → 4)-α -L-rhamnopyranoside, and methyl α -D-glucopyranosyl-(1 → 3)-α -L-rhamnopyranoside. Disaccharides were obtained with yields going up to 64%. The structural diversity generated as well as the obtained yields appear to be related to enzyme active site architecture, which can be modulated and improved by enzyme engineering. Several of the obtained disaccharides enter in the composition of surface polysaccharides of pathogenic bacteria, among which is Shigella flexneri. Our results outline the potential of glucansucrases in the chemo-enzymatic synthesis of complex carbohydrates of biological interest whose chemical synthesis may be seen as a limitation. 相似文献
52.
Fu W Zhang J Fuhrer T Champion H Furukawa K Kato T Mahaney JE Burke BG Williams KA Walker K Dixon C Ge J Shu C Harich K Dorn HC 《Journal of the American Chemical Society》2011,133(25):9741-9750
The dimetallic endohedral heterofullerene (EHF), Gd(2)@C(79)N, was prepared and isolated in a relatively high yield when compared with the earlier reported heterofullerene, Y(2)@C(79)N. Computational (DFT), chemical reactivity, Raman, and electrochemical studies all suggest that the purified Gd(2)@C(79)N, with the heterofullerene cage, (C(79)N)(5-) has comparable stability with other better known isoelectronic metallofullerene (C(80))(6-) cage species (e.g., Gd(3)N@C(80)). These results describe an exceptionally stable paramagnetic molecule with low chemical reactivity with the unpaired electron spin density localized on the internal diatomic gadolinium cluster and not on the heterofullerene cage. EPR studies confirm that the spin state of Gd(2)@C(79)N is characterized by a half-integer spin quantum number of S = 15/2. The spin (S = ?) on the N atom of the fullerene cage and two octet spins (S = 7/2) of two encapsulated gadoliniums are coupled with each other in a ferromagnetic manner with a small zero-field splitting parameter D. Because the central line of Gd(2)@C(79)N is due to the Kramer's doublet with a half-integer spin quantum number of S = 15/2, this relatively sharp line is prominent and the anisotropic nature of the line is weak. Interestingly, in contrast with most Gd(3+) ion environments, the central EPR line (g = 1.978) is observable even at room temperature in a toluene solution. Finally, we report the first EHF derivative, a diethyl bromomalonate monoadduct of Gd(2)@C(79)N, which was prepared and isolated via a modified Bingel-Hirsch reaction. 相似文献
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The global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm−1 is reported. This work incorporates and extends to the fifth polyad, the preliminary study of the lower four polyads published by [J. Mol. Spectrosc. 221 (2003) 199]. More than 20 000 transitions (including numerous hot bands) for each isotopomer 12CH335Cl and 12CH337Cl have been assigned and fitted with a standard deviation of about 3 × 10−4 cm−1 close to the experimental precision. A common set of 288 (resp. 303) effective parameters was determined for each isotopomer. Our global model allowed us to reproduce simultaneously and accurately the resonances already encountered in Polyad 3 and the new ones involved in Polyad 5. 相似文献
56.
Singlet oxygen regiospecifically oxidizes 1-benzyl-3,4-dihydroisoquinoline. Mechanistic studies do not distinguish between a dioxetane or the alternative zwitterionic peroxide intermediate. 相似文献
57.
Transmission probability and energy distribution of electrons impinging on indium thin film targets
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M. Hannachi Z. Rouabah N. Bouarissa C. Champion 《Surface and interface analysis : SIA》2017,49(6):570-572
Based on a home‐made Monte Carlo simulation, the electron backscattering coefficient, mean penetration depth, transmission probability, and transmission energy distribution of 1–5 keV electron normally incident penetrating in indium thin film targets have been computed. The trend of all features of interest as a function of the indium film thickness at both nanometric scale region and bulk material region has been examined and discussed. The present predictions may be seen as the first investigation regarding 1–5 keV electrons impinging on indium thin film targets. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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From light-scattering studies on polybutylmethacrylate, a polymeric glass, the variation of the velocity and attenuation of thermally excited hypersonic phonons with temperature has been measured. Measurement of the temperature dependence of the ratio of the intensity of the Rayleigh line to the Brillouin lines is interpreted as due to a configurational rearrangement within the glass above the glass transition temperature, Tg . Only light scattered from longitudinal phonons was observed. The distinct change in the temperature dependence of the velocity, attenuation and intensity ratio identified the glass transition. For samples annealed well above Tg, Tg was found to be about 0°C from the light-scattering studies, 12°C from differential scanning calorimetry (DSC), and 20°C from refractive index measurements. For an unannealed sample the behaviour of the above parameters with temperature was found to be different. Tg for the unannealed sample was 14°C from light-scattering, 18°C from DSC and 20°C from index of refraction measurements. 相似文献
60.
Felipe Alvarez Miguel Carrasco Thierry Champion 《Journal of Optimization Theory and Applications》2012,153(2):388-407
Algorithms for convex programming, based on penalty methods, can be designed to have good primal convergence properties even
without uniqueness of optimal solutions. Taking primal convergence for granted, in this paper we investigate the asymptotic
behavior of an appropriate dual sequence obtained directly from primal iterates. First, under mild hypotheses, which include
the standard Slater condition but neither strict complementarity nor second-order conditions, we show that this dual sequence
is bounded and also, each cluster point belongs to the set of Karush–Kuhn–Tucker multipliers. Then we identify a general condition
on the behavior of the generated primal objective values that ensures the full convergence of the dual sequence to a specific
multiplier. This dual limit depends only on the particular penalty scheme used by the algorithm. Finally, we apply this approach
to prove the first general dual convergence result of this kind for penalty-proximal algorithms in a nonlinear setting. 相似文献