Giant strain geared to transformable H-bonded network in compressed ß-D-mannose.

Networks of OH···O bonds in sugars and H2O ices are hardly affected by temperature, but transform under pressure. Such a transition at 1.95 GPa in ß-D-mannose induces strong strain, non-destructive for the single crystal and easily visible in its shape deformation. This transition occurs at the lowest pressure of all sugars investigated at high pressure so far. The giant strain propagates perpendicular to the clearly visible zero-strain planes. The transition reconstructs the 3-dimensional pattern of OH···O hydrogen bonds, changes the conformation of molecules and preserves the space-group symmetry, like the analogous transitions of α-D-glucose and D-sucrose. However, new repulsing O···O contacts have been generated at high pressure in D-mannose only.

Conformational and H-bonding preferences for facile racemate crystallization of ribose.

Recalcitrant crystallization and syrup formation are frequent features of natural sugars. This is the case of D-ribose, yielding low-quality crystals of mixed α- and ß-pyranose anomers. However, large crystals of DL-ribose can be grown easily. The crystal structures of stable D-ribose forms I and II as well as DL-form II have been analyzed in terms of their compatibility with the molecular aggregation. The comparison of the potential energy of all conformers and their OH···O hydrogen-bonding patterns is consistent with the preferential racemate crystallization in terms of departures from the optimized isolated ribose molecule and its directional interactions. This analysis is aimed at rationalizing the interplay between the molecular structure and spontaneous crystallization of chiral compounds.

Transformable H-bonds and conformation in compressed glucose.

In response to external stimuli the α-d-glucose molecule extensively transforms its H-bonding pattern and conformation. High-pressure reverses the linear compressibility and changes the hierarchy of intermolecular interactions in crystalline α-d-glucose. At 5.40(2) GPa it undergoes an isostructural phase transition rearranging the OH···O hydrogen bonds, promoting the role of CH···O contacts and eliminating voids in the structure. Such monotonic and abrupt transformations may be characteristic of sugars and polysaccharides.

Isothermal and isochoric crystallization of highly hygroscopic pyridine N-oxide of aqueous solution.

Highly hygroscopic pyridine N-oxide, C5H5NO, dissolves in water absorbed from atmospheric air, but it crystallizes in the neat form of the aqueous solution under high pressure. The crystals grown at high-pressure isochoric conditions are of the same phase as that obtained from anhydrous crystallization at ambient pressure. This feature can be employed for retrieving compounds highly soluble in water from their aqueous solutions. The crystal structure is strongly stabilized by CH...O contacts. The crystal compression and thermal expansion as well as three shortest H...O distances comply with the inverse-relationship rule of pressure and temperature changes.