Reversible crystal-to-crystal chiral resolution: making/breaking non-bonding S⋯O interactions

What is it about?

An achiral organic molecule adopts a chiral conformation, due to rotation about sigma bonds, when it crystallizes. At low temperatures (below 70 deg C), there is a 50:50 (i.e., racemic) mixture of the two possible enantiomers in the crystal. Above 70 deg C, there is a phase transition to a new crystal structure in which all the molecules in a single crystal are of only one enantiomer (i.e., there is chiral resolution). This phase transition is completely reversible.

Featured Image

Why is it important?

"Handedness" (i.e., chirality) can have an enormous impact on the physiological effects of a pharmaceutical chemical. Crystal morphology can have a huge impact on solubility, bioavailability, and efficacy of a pharmaceutical chemical. The system reported in this paper represents a unique combination of attributes associated with morphological behaviour and chirality. It can be used as a benchmark example of how supramolecular interactions can be used to understand/manipulate chiral resolution and phase behaviour.