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Experimental evidence of solvent effect on oligosaccharide conformational equilibria

3 EXPERIMENTAL EVIDENCE OF SOLVENT EFFECT ON OLIGOSACCHARIDE CONFORMATIONAL EQUILIBRIA [Pg.711]

From comparison of experimental data and theoretical results (using quantum-mechanical and semi-empirical methods) on model compounds,the angular dependence of the coupling constants, Jcjj, on the anomeric and aglycon torsional angles q) and and [Pg.714]

Only for a linear dependence of Jc on x, the equation could hold the equals sign. Because of the simultaneous dependence of the property on % and on the complexity of potential energy function, E(x), the ensemble average of as well as of any property of [Pg.714]

Apart from NMR and die mefliods suitable for characterization of overall chain dimensions (which we will touch on below), fliere are not many simple experimental techniques that can be used to study sugar conformation and that are directly correlated to theoretical results based on calculated potential energy surfaces or force fields. An exception is given by chiro-optical techniques, which provide important (although empirical) structural information as optical rotation experiments have been shown to be very useful and informative in flic study of saccharides in solution. Literature gives die experimental evidence for the effects of the external conditions (solvent and temperature) on the optical rotation. The additivity mediods, proposed in the Fifties by Whiffen and Brewster, were [Pg.714]

Experimental Jc,h values for conformationally rigid carbohydrate derivatives allow to calculate the constant values of Aj and Bj in equations [12.2.1], The major practical use of these equations is their ability to estimate the glycosidic dihedral angles from experimental Jqh in combination with other complementary results, for example, from NOESY, X-ray and chiro-optical experiments. Since the experimental values are averaged over all the accessible conformational states in solution, they do not necessary reflect the property of only the most probable conformer but they nevertheless include contributions of all the conformers, each one taken with its proper statistical weight. Thus, the quantitative interpretation of experimental data in terms of accessible conformational states of flexible molecules requires the additional theoretical evaluation of the energy of the molecule as a function of internal coordinates. Since the dependence of the observed coupling constants on the conformation is non-linear, it derives that  [Pg.714]




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Conformation solvent

Conformation, effect

Conformational effect

Conformational equilibria, solvent effects

Conformational equilibrium

Conformic equilibrium

Effect of solvent

Effect on equilibria

Effects of experimental

Effects on Conformation

Evidence of conformity

Experimental evidence

Experimenter effects

Of oligosaccharides

Oligosaccharides, conformers

Solvent Effects on

Solvent Effects on Conformational Equilibria

Solvent Effects on Equilibria

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