Conformational and H‐Bonding Preferences for Facile Racemate Crystallization of Ribose

Abstract

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 β-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.

On the Plausibility of Pseudosugar Formation in Cometary Ices and Oxygen-rich Tholins

“…Pure enantiomers are difficult to obtain and, as paradigmatic example, D-ribose (for which at least two polymorphs exist) resisted all attempts to generate suitable crystals for X-ray diffraction studies until a few years ago (Šišak et al 2010). Racemic DL-ribose crystallizes easily instead due to conformational preferences and H-bonding interactions (Patyk and Katrusiak 2014).…”