Long-Range Influence of Carbohydrates on the Solvation Dynamics of Water—Answers from Terahertz Absorption Measurements and Molecular Modeling Simulations

Abstract

We present new terahertz (THz) spectroscopic measurements of solvated sugars and compare the effect of two disaccharides (trehalose and lactose) and one monosaccharide (glucose) with respect to the solute-induced changes in the sub-picosecond network dynamics of the hydration water. We found that the solute affects the fast collective network motions of the solvent, even beyond the first solvation layer. For all three carbohydrates, we find an increase of 2-4% in the THz absorption coefficient of the hydration water in comparison to bulk water. Concentration-dependent changes in the THz absorption between 2.1 and 2.8 THz of the solute-water mixture were measured with a precision better than 1% and were used to deduce a dynamical hydration shell, which extends from the surface up to 5.7 +/- 0.4 and 6.5 +/- 0.9 A for the disaccharides lactose and trehalose, respectively, and 3.7 +/- 0.9 A for the glucose. This exceeds the values for the static hydration shell as determined, for example, by scattering, where the long-range structure was found to be not significantly affected by the solute beyond the first hydration shell. When comparing all three carbohydrates, we found that the solute-induced change in the THz absorption depends on the product of molar concentration of the solute and the number of hydrogen bonds between the carbohydrate and water molecules. We can conclude that the long-range influence on the sub-picosecond collective water network motions of the hydration water is directly correlated with the average number of hydrogen bonds between the molecule and adjacent water molecules for carbohydrates. This implies that monosaccharides have a smaller influence on the surrounding water molecules than disaccharides. This could explain the bioprotection mechanism of sugar-water mixtures, which has been found to be more effective for disaccharides than for monosaccharides.

Analysis of Water and Hydrogen Bond Dynamics at the Surface of an Antifreeze Protein

“…The differences among the power spectra for the water molecules hydrogen bonding to each of the three planes are influenced by mutation. We expect that THz measurements, which are highly sensitive to the hydration water [48,[51][52][53][54][55], will reveal differences between the wild type and mutant. Recent THz experiments [49] on a λ-repressor fragment indicate that only a few point mutations can give rise to very different THz spectra.…”

Perspective: Watching low-frequency vibrations of water in biomolecular recognition by THz spectroscopy

“…This allowed us to deduce the size and the absorption coefficient of the dynamical hydration shell around the carbohydrates. 34 The hydration shell of the monosaccharide glucose was found to extend to approximately 4 Å from the carbohydrate surface and around 6-7 Å for the disaccharides lactose and trehalose. Accompanying molecular dynamics simulation on the spatial dependence of the hydration water on the solutes also showed quantitatively similar trends, evidencing a significant correlation between the carbohydrates and the hydration water due to the hydrogen bonding.…”

Critical Droplet Theory Explains the Glass Formability of Aqueous Solutions

“…For example, glucose and trehalose have Stokes radii of 3.5 and 4.7 Å , respectively. When probed on the picosecond time scale [23], corresponding to that for rearrangements of the hydrogen bonding network [24] that might be expected to impact nucleation, their hydration shell thicknesses are 3.7 and 6.5 Å , respectively. The sum of these hydration shell radii and the corresponding Stokes radii (which include a contribution from hydration [22]) is indicated by the open symbols in Fig.…”