Segregation into Chiral Enantiomeric Conformations of an Achiral Molecule by Concomitant Polymorphism

An analogue of the green fluorescent protein (GFP) luminophore
crystallizes from a methanol solution impregnated with dichloromethane,
into a pair of chiral crystals. Thermal analysis, fluorescence emission
studies, and crystal packing analysis show that the two crystals are
different materials. The two polymorphs arise from the rotation of
a monosubstituted benzene ring about a C–N bond which results
in the formation of two strong bifurcated C–H···O
intermolecular bonds to oxygen O(6). The color difference has been
ascribed to a difference in the packing of the two crystal forms.
Theoretical studies supported by low temperature NMR show low kinetic
energy barriers (∼10 kJ mol–1) separating
the asymmetric units of the two crystal structures, suggesting that
the driving force for the polymorphism could be the result of packing
of two different asymmetric units.