Dielectric constant, carbohydrates

Since both molar volume and refractive index are influenced by the actual molecular species present in a solution, molar refraction has some potential value for studying association equilibria. Giles and co-workers (65-68) correlated the method with dielectric constant measurements, and have been the most active users of refractive index for studying compound formation. Reference 68 reviews earlier work (which is sketchy) and lists about forty systems (mostly oxygen containing compounds) that were studied. References 65-67 deal with amide, amine, and azo compounds, plus esters and additional work on alcohols, aldehydes, ketones, and carbohydrates. The method is simple the refractive index of a series of mixtures of varying composition but constant concentration in a solvent is measured. Compound formation is shown by a change in the slope of the n vs. mole fraction plot, such as in Fig. 2-15. 

We also are interested in this equilibrium as a function of dielectric constant (D), since for simple compounds, gas phase and solution data are often available, and for more complex compounds, particularly carbohydrates, the measurements are usually... 

PEF employs partial atomic charges (identical for related atom types) selected from a Mulliken population analysis of a minimal basis set wavefunction computed for a-D-Glcp. Although the relatively low magnitude of these partial atomic charges renders them unsuitable for applications with common models for explicit water, the PEF422 parameters were optimized for modeling isolated carbohydrates, in vacuo, with a dielectric constant (e) of 3 Debye. ... 

A CHARMm-type parameter set for carbohydrates was reported by Ha and co-workers in 1988, and remains the standard for application with CHARMm. The internal force constants, and Ke. and equilibrium parameter values, r q and 0eq were derived by fitting to the experimental vibrational and structural properties of a representative monosaccharide, a-D-Glcp. The fitting was performed with the parameter optimization capability of CHARMm on the isolated monosaccharide with a dielectric value of unity. Partial charges were... 

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