Segregation into chiral enantiomeric conformations of an achiral molecule by concomitant polymorphism

摘要

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.