Relationships between Molecular Structure of Carbohydrates and Their Dynamic Hydration Shells Revealed by Terahertz Time-Domain Spectroscopy.

Nikita V Penkov

doi:10.3390/ijms222111969

Abstract

Despite more than a century of research on the hydration of biomolecules, the hydration of carbohydrates is insufficiently studied. An approach to studying dynamic hydration shells of carbohydrates in aqueous solutions based on terahertz time-domain spectroscopy assay is developed in the current work. Monosaccharides (glucose, galactose, galacturonic acid) and polysaccharides (dextran, amylopectin, polygalacturonic acid) solutions were studied. The contribution of the dissolved carbohydrates was subtracted from the measured dielectric permittivities of aqueous solutions based on the corresponding effective medium models. The obtained dielectric permittivities of the water phase were used to calculate the parameters describing intermolecular relaxation and oscillatory processes in water. It is established that all of the analyzed carbohydrates lead to the increase of the binding degree of water. Hydration shells of monosaccharides are characterized by elevated numbers of hydrogen bonds and their mean energies compared to undisturbed water, as well as by elevated numbers and the lifetime of free water molecules. The axial orientation of the OH(4) group of sugar facilitates a wider distribution of hydrogen bond energies in hydration shells compared to equatorial orientation. The presence of the carboxylic group affects water structure significantly. The hydration of polysaccharides is less apparent than that of monosaccharides, and it depends on the type of glycosidic bonds.

Highlights

It is well known that hydration shells are an important factor determining the structure and function of biological molecules [1,2,3,4]
An approach based on the THz time-domain spectroscopy (THz-TDS) assay was suggested in the current work for studying the dynamic hydration shells of the carbohydrates in aqueous solutions
Complex dielectric permittivities of the water phase were calculated from recorded spectra of carbohydrate solutions in the THz area using the corresponding effective medium models

Summary

Introduction

It is well known that hydration shells are an important factor determining the structure and function of biological molecules [1,2,3,4]. More and more modern experimental methods capable of analyzing hydration were used, such as the measurement of vapour water pressure above an aqueous solution [12], densitometry [13], viscometry [14], measurement of water sorption [15], differential scanning calorimetry [16,17,18], X-ray diffraction method [19], compressibility measurement [20], ultrasonic techniques [21,22], NMR-spectroscopy [23,24], neutron scattering [25,26,27,28], extended depolarized light scattering [29,30], dynamic light scattering [31,32], IR-spectroscopy [33,34,35], Raman spectroscopy [27,36], polarization-resolved femtosecond-infrared spectroscopy [37], dielectric spectroscopy [38,39,40], terahertz (THz) spectroscopy [39,41,42,43,44,45,46,47], and molecular modeling [9,42,48,49,50,51,52] Despite such a rich history of studying carbohydrate hydration, we are still far from a complete understanding of this process. There is no clear answer to a simple question: are the sugars cosmotropic or chaotropic agents [16,39,53]? the studies by currently available methods and the development of novel approaches should be continued

Methods

Findings

Discussion

Conclusion