Dielectric spectroscopy in aqueous solutions of oligosaccharides: Experiment meets simulation

Abstract

We report the frequency-dependent complex dielectric permittivity of aqueous solutions of the homologous saccharides D(+)-glucose, maltose, and maltotriose in the frequency range 200 MHz⩽ν⩽20 GHz. For each solute, solutions having concentrations between 0.01 and 1 mol dm−3 were studied. In all measured spectra two dispersion/loss regions could be discerned. With the exception of the two most concentrated maltotriose solutions, a good description of the spectra by the superposition of two Debye processes was possible. The amplitudes and correlation times of the glucose and maltose solutions determined from fits of the experimental data were compared to those obtained in an earlier molecular dynamics study of such systems; the overall agreement between experiment and simulation is quite satisfactory. A dielectric component analysis of the simulation results permitted a more detailed assignment of the relaxation processes occurring on the molecular level. The physical picture emerging from this analysis is compared with traditional hydration models used in the interpretation of measured dielectric data. It is shown that the usual standard models do not capture an important contribution arising from cross terms due to dipolar interactions between solute and water, as well as between hydration water and bulk water. This finding suggests that conventional approaches to determine molecular dipole moments of the solutes may be problematic. This is certainly the case for solutes with small molecular dipole moments, but strong solute–solvent interactions, such as the saccharides studied here.

Terahertz Absorption Spectroscopy of a Liquid Using a Polarity Probe: A Case Study of Trehalose/Water Mixtures

“…When the trehalose concentration is raised to 0.5 m and then to 1.0 m, characteristic changes are observed: 1) A new relaxational mode S appears at 7.1 GHz. It is assigned to rotational relaxation of the hydrated trehalose solute by analogy to results from dielectric relaxation of maltotriose [25] and glucose [26,27] solutions, which were confirmed by depolarized Rayleigh scattering. [28] 2) The dynamics of the solution differ from those of pure water.…”

Hydration Dynamics of Water near an Amphiphilic Model Peptide at Low Hydration Levels: A Dielectric Relaxation Study

“…We have recently addressed hydration dynamics by dielectric spectroscopy [17,18,30] in terms of a dielectric component analysis developed by Steinhauser and co-workers in conjunction with results from molecular dynamics (MD) simulations. [16,30] However, decisive studies of the state of water at the protein/water interface are not trivial.…”

Electric field inside a “Rossky cavity” in uniformly polarized water

“…(16) and (18) to solutions of ionic and hydrogen-bonding substances in water. [29][30][31] The closed squares in the figure show the relative dielectric constant increment ∆ǫ/ǫ, ∆ǫ = ǫ mix − ǫ for hydrated lysozyme. 29 At the pH of the measurements the protein carries the total charge of +10 electron units.…”

“…30 Dioxane offers strong hydrogen-bond acceptor sites. Finally, diamonds and triangles show, respectively, hydrated glucose 31 and maltotriose, 31 both offering multiple hydrogen-bonding sites. The results for lysozyme and for two saccharides refer to dielectric increments of the loss peak of the water component of the solution.…”

“…The results for lysozyme and for two saccharides refer to dielectric increments of the loss peak of the water component of the solution. 29,31 This approach has allowed us to eliminate the contribution of the permanent dipole moment of the solute, characterized by a much longer relaxation time. The increment of the water loss peak reflects only the interfacial polarization described by the present model.…”