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

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.

Crystal structure, Hirshfeld surface analysis and interaction energy calculation of 1-decyl-2,3-dihydro-1H-benzimidazol-2-one

The title molecule, C17H26N2O, adopts an L-shaped conformation, with the straight n-decyl chain positioned nearly perpendicular to the dihydrobenzimidazole moiety. The dihydrobenzimidazole portion is not quite planar as there is a dihedral angle of 1.20 (6)° between the constituent planes. In the crystal, N—H...O hydrogen bonds form inversion dimers, which are connected into the three-dimensional structure by C—H...O hydrogen bonds and C—H...π(ring) interactions. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H...H (75.9%), H...C/C...H (12.5%) and H...O/O...H (7.0%) interactions. Based on computational chemistry using the CE–B3LYP/6–31 G(d,p) energy model, C—H...O hydrogen bond energies are −74.9 (for N—H...O) and −42.7 (for C—H...O) kJ mol−1.

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Intramolecular NH…O,S,N interactions in non-tautomeric systems are reviewed in a broad range of compounds covering a variety of NH donors and hydrogen bond acceptors. 1H chemical shifts of NH donors are good tools to study intramolecular hydrogen bonding. However in some cases they have to be corrected for ring current effects. Deuterium isotope effects on 13C and 15N chemical shifts and primary isotope effects are usually used to judge the strength of hydrogen bonds. Primary isotope effects are investigated in a new range of magnitudes. Isotope ratios of NH stretching frequencies, νNH/ND, are revisited. Hydrogen bond energies are reviewed and two-bond deuterium isotope effects on 13C chemical shifts are investigated as a possible means of estimating hydrogen bond energies.

Hyperhomogeneity of hydrogen-disordered ice and its origin: the residual entropy compatible with the disparity in hydrogen bond energy

The residual entropy is one of the most crucial properties for the existence of a large number of ice polymorphs. The residual entropy has been estimated by Pauling assuming that there is no large difference between the hydrogen bond energies in ice. This simple model accurately predicts the entropy change of the phase transition between a hydrogen-disordered ice phase and its hydrogen-ordered counterpart. This fact is, however, incompatible with another fact that the difference in the pair interaction energies involved in hydrogen bonds in an ice phase can be larger than the thermal energy of a few kJ/mol. Here we propose a mechanism that reconciles them by considering the equality of the binding energy in each molecule rather than the pair interaction energy of the proximate pair. The topological feature of ice, called the ice rules, allows us to replace the interactions of a water molecule with the other individual molecules by that with the collections of the dipoles represented by directed cycles consisting of O-H vectors. This resummation reveals that molecular environments in ice are extremely homogeneous thereby providing a solid basis for Pauling's model.

Crystal structure, Hirshfeld surface analysis and interaction energy and DFT studies of 1-(1,3-benzothiazol-2-yl)-3-(2-hydroxyethyl)imidazolidin-2-one

In the title molecule, C12H13N3O2S, the benzothiazine moiety is slightly non-planar, with the imidazolidine portion twisted only a few degrees out of the mean plane of the former. In the crystal, a layer structure parallel to the bc plane is formed by a combination of O—HHydethy...NThz hydrogen bonds and weak C—HImdz...OImdz and C—HBnz...OImdz (Hydethy = hydroxyethyl, Thz = thiazole, Imdz = imidazolidine and Bnz = benzene) interactions, together with C—HImdz...π(ring) and head-to-tail slipped π-stacking [centroid-to-centroid distances = 3.6507 (7) and 3.6866 (7) Å] interactions between thiazole rings. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (47.0%), H...O/O...H (16.9%), H...C/C...H (8.0%) and H...S/S...H (7.6%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. Computational chemistry indicates that in the crystal, C—H...N and C—H...O hydrogen-bond energies are 68.5 (for O—HHydethy...NThz), 60.1 (for C—HBnz...OImdz) and 41.8 kJ mol−1 (for C—HImdz...OImdz). Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state.

Fragmentation method reveals a wide spectrum of intramolecular hydrogen bond energies in antioxidant natural products

Very strong and weak IHBs in curcumin.