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21.
Versatile synthesis of some analogues of the naturally-occurring α-glucosidase inhibitor salacinol (1), involving thioanhydro alditol moieties with erythro, d,l-threo, xylo, ribo, d-arabino and d-manno configurations is described. Nucleophilic attack at the least-hindered carbon atom of an l- or d-protected erythritol cyclic sulfate by the thioanhydro alditol sulfur atom yielded the desired zwitterionic compounds. In addition, the preparation of the cyclic sulfates of 2,4-O-benzylidene-d-erythritol and 2,4-O-isopropylidene-l-erythritol was improved. Enzyme inhibition tests showed that most of the new compounds were weak but specific inhibitors, while good inhibitory activity was found for a six-membered ring analogue (β-glucosidase: Ki=16 μM). 相似文献
22.
Marielle Christiansen Kjetil Fagerholt Bjørn Nygreen David Ronen 《European Journal of Operational Research》2013
We review research on ship routing and scheduling and related problems during the new millennium and provide four basic models in this domain. The volume of research in this area about doubles every decade as does the number of research outlets. We have found over a hundred new refereed papers on this topic during the last decade. Problems of wider scope have been addressed as well as more specialized ones. However, complex critical problems remain wide open and provide challenging opportunities for future research. 相似文献
23.
Mentré O Ketatni el M Colmont M Huvé M Abraham F Petricek V 《Journal of the American Chemical Society》2006,128(33):10857-10867
The BiCu(2)(P(1-x)V(x))O(6) system shows the appearance of various phenomena that progressively change as a function of the average (P/V)O(4) groups size. Then, from x = 0 to x approximately 0.7, a solid solution exists with respect to the basic orthorhombic unit cell of BiCu(2)PO(6). For greater x values (0.7 < x <0.96), structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatment of single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K (orthorhombic, a = 12.379(3)Angstrom, b = 5.2344(9) Angstrom, c = 7.8270(14) Angstrom, q = 0.268(3) b*, super space group: Xbmm(0gamma0) s00, X stands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)(overall) = 5.27%, R(obs)(fundamental) = 4.48%, R(obs)(satellite) = 6.58%) has evidenced strong positional modulated effects within the [BiCu(2)O(2)](3+) ribbons while three XO(4) configurations compete along the x(4) fourth dimension. There is no P/V segregation along x(4) in good agreement with steric-only origins of the modulation. Finally for 0.96 < x <1, two phases coexist, i.e., BiCu(2)VO(6) (X = 1) and a modulated phase of the previous domain.The BiCu(2)VO(6) crystal structure shows a unit cell tripling associated with monoclinic symmetry lowering. The VO(4) orientations between two ribbons proceed with respect to the interribbon distance. Then the full system shows flexible interactions between modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the average XO(4) size. Furthermore, between two ribbons the Cu(2+) arrangement forms magnetically isolated zigzag copper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence of true S = (1)/(2) Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement with band-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution of Cu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magnetic change. 相似文献
24.
From the study of molybdenum oxidation in aqueous solutions we developed a semi-autonomous method to detect silicate in aqueous samples. Molybdenum oxidation was used to form molybdate in acidic media. The silicomolybdic complex formed with silicate is detectable by amperometry or cyclic voltammetry. The new electrochemical method is in good agreement with the method conventionally used for environmental water silicate analysis. In the second stage, a completely reagentless method was developed using molybdate and proton produced during molybdenum oxidation. Reproducibility tests show a precision of 2.6% for a concentration of 100 μmol L−1. This new method will be very suitable for the development of new autonomous silicate sensors easy to handle and without reagents. In this paper we present the analytical and chemical aspects necessary for a complete documentation of the method before the development of a new reagentless sensor. 相似文献
25.
Guillaume Renaud Samuel Callé Jean-Pierre Remenieras Marielle Defontaine 《International Journal of Non》2008,43(3):194-200
Three methods to measure qualitative and quantitative aspects of bone non-linearity were investigated in the context of diagnosis of bone “biomechanical health”: i.e. harmonic generation, parametric emission and parametric reception using phase modulation. Trabecular bone exhibited hysteretic non-linear behavior due to microcracks in bone tissue, and parametric reception using phase modulation seemed to be the best configuration for in vivo application. However, the relationship between level of non-linearity and crack density needs to be validated by histological analysis. 相似文献
26.
Sharma Adhikarimayum S. Buti B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1977,5(4):293-296
The effects of collisions and oblique modulation on Langmuir waves are studied. The nonlinear Schrondinger equation for these waves are derived by using the Krylov-Bogoliubov-Mitropolsky method. The collisions damp the envelope of these waves and the obliqueness of the modulation effects the dispersion of the system. The Langmuir waves are found to modulationally stable as in the collisionless and parallel modulation case. However, the width of the envelope hole state of these waves is found to increase due to the oblique modulation. 相似文献
27.
Buti B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1976,4(4):292-295
Nonlinear ion-acoustic waves, which in the absence of collisions are moderately stable in the long wave length limit, become modulationally unstable due to presence of collisions. These waves are unstable in the wave number range kmin < k < kmax. 相似文献
28.
The nonlinear Schrödinger equation describing the evolution of the plane wave solutions of the Hirota equation and of the Boussinesq equation are obtained. The conditions for modulational instability and the localised stationary solutions are derived. 相似文献
29.
30.
Engineering the Donor Selectivity of D‐Fructose‐6‐Phosphate Aldolase for Biocatalytic Asymmetric Cross‐Aldol Additions of Glycolaldehyde
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Dr. Anna Szekrenyi Anna Soler Dr. Xavier Garrabou Dr. Christine Guérard‐Hélaine Dr. Teodor Parella Dr. Jesús Joglar Prof. Dr. Marielle Lemaire Dr. Jordi Bujons Prof. Dr. Pere Clapés 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12572-12583
D ‐Fructose‐6‐phosphate aldolase (FSA) is a unique catalyst for asymmetric cross‐aldol additions of glycolaldehyde. A combination of a structure‐guided approach of saturation mutagenesis, site‐directed mutagenesis, and computational modeling was applied to construct a set of FSA variants that improved the catalytic efficiency towards glycolaldehyde dimerization up to 1800‐fold. A combination of mutations in positions L107, A129, and A165 provided a toolbox of FSA variants that expand the synthetic possibilities towards the preparation of aldose‐like carbohydrate compounds. The new FSA variants were applied as highly efficient catalysts for cross‐aldol additions of glycolaldehyde to N‐carbobenzyloxyaminoaldehydes to furnish between 80–98 % aldol adduct under optimized reaction conditions. Donor competition experiments showed high selectivity for glycolaldehyde relative to dihydroxyacetone or hydroxyacetone. These results demonstrate the exceptional malleability of the active site in FSA, which can be remodeled to accept a wide spectrum of donor and acceptor substrates with high efficiency and selectivity. 相似文献