Supersaturated solution preferential enrichment

Usual standard recrystallization conditions have been applied to the Preferential Enrichment experiment, except that highly supersaturated solutions are employed, because the supersolubility (a solubility obtained by dissolving the sample in a solvent on heating followed by being cooled) of the compounds showing Preferential Enrichment is considerably higher than that of the usual solubility at 25°C. 

Preferential Enrichment is a secondary phenomenon caused by a polymorphic transition occurring during crystallization from a highly supersaturated solution. This unique dynamic enantiomeric resolution phenomenon has proved to be observable for a fairly ordered racemic mixed crystal showing a polymorphism a solvent-assisted solid-to-sohd type of polymorphic transition from the kinetically-formed metastable crystalline phase comprising homochiral R and S chains into the thermodynamically stable crystalline phase consisting of a heterochiral 2D sheet structure during crystallization is responsible for this phenomenon. That is, it is essential that homochiral R and S ID chain structures are stable in solution while a heterochiral 2D sheet structure is stable in the crystal. 

Apart from the significance as a novel enantiomeric resolution phenomenon, the investigation on the mechanism of Preferential Enrichment has also shed light on the hitherto unknown mechanism of a polymorphic transition occurring during crystallization from a supersaturated solution. A combination of several techniques employed here would also be useful to elucidate the unknown mechanism of another type of polymorphic transition... 

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