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 and Hirshfeld surface analysis of the product of the ring-opening reaction of a dihydrobenzoxazine: 6,6′-[(cyclohexylazanediyl)bis(methylene)]bis(2,4-dimethylphenol)

In the title unsymmetrical tertiary amine, C24H33NO2, which arose from the ring-opening reaction of a dihydrobenzoxazine, two 2,4-dimethylphenol moieties are linked by a 6,6′-(cyclohexylazanediyl)-bis(methylene) bridge: the dihedral angle between the dimethylphenol rings is 72.45 (7)°. The cyclohexyl ring adopts a chair conformation with the exocyclic C—N bond in an equatorial orientation. One of the phenol OH groups forms an intramolecular O—H...N hydrogen bond, generating an S(6) ring, and a short intramolecular C—H...O contact is also present. In the crystal, O—H...O hydrogen bonds link the molecules into C(10) chains propagating along the [100] direction. The Hirshfeld surface analysis of the title compound confirms the presence of these intra- and intermolecular interactions. The corresponding fingerprint plots indicate that the most significant contacts in the crystal packing are H...H (76.4%), H...C/C...H (16.3%), and H...O/O...H (7.2%).

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

Regioselective glycosylations allow planning simpler strategies for the synthesis of oligosaccharides, and thus reducing the need of using protecting groups. With the idea of gaining further understanding of such regioselectivity, we analyzed the relative reactivity of the OH-3 and OH-4 groups of 2,6-diprotected methyl α- and β-galactopyranoside derivatives in glycosylation reactions. The glycosyl acceptors were efficiently prepared by simple methodologies, and glycosyl donors with different reactivities were assessed. High regioselectivities were achieved in favor of the 1→3 products due to the equatorial orientation of the OH-3 group. A molecular modeling approach endorsed this general trend of favoring O-3 substitution, although it showed some failures to explain subtler factors governing the difference in regioselectivity between some of the acceptors. However, the Galp-(β1→3)-Galp linkage could be regioselectively installed by using some of the acceptors assayed herein.

The first structural characterization of the protonated azacyclam ligand in catena-poly[[[(perchlorato)copper(II)]-μ-3-(3-carboxypropyl)-1,5,8,12-tetraaza-3-azoniacyclotetradecane] bis(perchlorate)]

The asymmetric unit of the title compound, catena-poly[[[(perchlorato-κO)copper(II)]-μ-3-(3-carboxypropyl)-1,5,8,12-tetraaza-3-azoniacyclotetradecane-κ4 N 1,N 5,N 8,N 12] bis(perchlorate)], {[Cu(C13H30N5O2)(ClO4)](ClO4)2} n , (I), consists of a macrocyclic cation, one coordinated perchlorate anion and two perchlorate ions as counter-anions. The metal ion is coordinated in a tetragonally distorted octahedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the perchlorate anion and the carbonyl O atom of the protonated carboxylic acid group of a neighbouring cation. The average equatorial Cu—N bond lengths [2.01 (6) Å] are significantly shorter than the axial Cu—O bond lengths [2.379 (8) Å for carboxylate and average 2.62 (7) Å for disordered perchlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans-III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carboxylic acid group of the cation to a neighbouring complex unit results in the formation of infinite chains running along the b-axis direction, which are crosslinked by N—H...O hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the perchlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra- and interchain C—H...O contacts.

3-Acetyl-7-[2-(morpholin-4-yl)ethoxy]chromen-2-one

In the title compound, C17H19NO5, the morpholine ring adopts a chair conformation with the exocyclic N—C bond in an equatorial orientation. In the crystal, the molecules are linked by C—H...O and weak aromatic π–π stacking interactions, thereby generating a layered structure.

1,1′-[(2,3,5,6-Tetramethyl-1,4-phenylene)bis(methylene)]dipiperidine

The asymmetric unit of the title compound, C22H36N2, comprises one half-molecule, the other half being generated by a center of inversion. The piperidine ring adopts a chair conformation, with the exocyclic N—C bond in an equatorial orientation. A short intramolecular C—H...N hydrogen bond occurs and forms an S(6) motif. No directional interactions beyond van der Waals contacts are observed between the molecules, which form a wave-like supramolecular architecture.

3-Chloro-r-2,c-6-bis(4-fluorophenyl)-3-methylpiperidin-4-one

The title compound, C18H16ClF2NO, contains one independent molecule in the asymmetric unit, with the piperidin-4-one ring adopting a slightly distorted chair conformation and an equatorial orientation of all the substituents except chlorine. A single weak intermolecular C—H...O interaction influences the crystal packing, forming infinite one-dimensional zigzag chains along the a axis. The structure was refined as a two-component inversion twin.

Crystal structure of 3,4-dimethyl 2-(tert-butylamino)-5-[2-oxo-4-(thiomorpholin-4-yl)-2H-chromen-3-yl]furan-3,4-dicarboxylate ethyl acetate hemisolvate

In the title hemisolvate, C25H28N2O7S·0.5C4H8O2, the thiomorpholine ring adopts a chair conformation, with the exocyclic N—C bond in an equatorial orientation. The dihedral angle between the coumarin ring system (r.m.s. deviation = 0.044 Å) and the furan ring is 64.84 (6)°. An intramolecular N—H...O hydrogen bond closes anS(6) ring. The ethyl acetate solvent molecule is disordered about a crystallographic inversion centre. In the crystal, the components are linked by C—H...O and C—H...S hydrogen bonds, generating a three-dimensional network.