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The different steps leading to oligosaccharide synthesis on polymeric support have been studied in the case of a functionalized ”popcorn” polystyrene: anchoring of the first glucidic group, unblocking of a selectively protected hydroxyl group, glycosylation and cleavage of the glucide support bond. The first glucidic unit is attached by a benzoic ester bond cleaved by methanolysis (Zemplén's method); β-benzoylpropionic ester was used as temporary protecting group. The synthesis of benzyl - 2 - acetamido - 4,6 - di - O - acetyl - 3 - O - (2 - acetamido - 3,4,6 - tri - O - acetyl - 2 - deoxy - β - D - glucopyranosyl) - 2 - deoxy - α - D - glucopyranoside is described as an example. 相似文献
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The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
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Jérôme JP. Leon 《Letters in Mathematical Physics》1981,5(1):75-80
We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems. 相似文献
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Besombes S Utille JP Mazeau K Robert D Taravel FR 《Magnetic resonance in chemistry : MRC》2004,42(3):337-347
Intramolecular H-bonding interactions were investigated in solution for the threo and erythro diastereomeric forms of a guaiacyl beta-O-4 lignin model compound by using the NMR data obtained from hydroxyl protons. Temperature coefficients of the chemical shifts (ddelta/dT) and coupling constants (3J(HCOH)) were measured in aprotic and protic solutions: DMSO-d6, acetone-d6 and acetone-d6-water. The NMR parameters do not support the existence of strong and persistent intramolecular H-bonds that could participate in the stabilization of the guaiacyl beta-O-4 structure in solution, but instead indicate that intermolecular H-bonds to solvent predominate. 1D NOE experiments nevertheless revealed the presence of a direct chemical exchange between the hydroxyl protons, suggesting the possible existence of weak and transient intramolecular H-bonding interactions. The conformational flexibility of the threo structure was also investigated in acetone solution from the measurement of long-range 1H, 1H and 1H, 13C coupling constants and from NOESY experiments. The NMR data are not consistent with any single conformation, indicating that different conformers co-exist in solution. The experimental results support the conformational flexibility predicted by molecular dynamics simulations performed in a previous study. Finally, both experimental and theoretical approaches indicate that weak intramolecular H-bonds can exist transiently in solution, breaking and reforming as the beta-O-4 molecule undergoes conformational interconversion, but cannot be invoked as possible means of conferring rigidity to the beta-O-4 structure. 相似文献
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