Aggregation/precipitation enantioselectivity

Enantioselectivity in Aggregation/Precipitation Induced Fluorescence Emission. 203... 

Cyclic dipeptides, especially cyclo[(S)-phenylalanyl-(S)-histidyl], are efficient and selective catalysts for the hydrocyanation of aromatic aldehydes (Fig. 5) [41]. The catalysts are not available commercially but can be synthesized by conventional methods and their structure can be varied easily (Fig. 5) [41,42,43]. The catalysts are only selective in a particular heterogeneous state, described as a clear gel [41,43]. It seems that their method of precipitation is crucial [41,44] and that reproducing literature results is not always easy [42]. A recent study confirmed the importance of the aggregate formation and reported a second order rate dependence on the concentration of the cyclic dipeptide [45]. These findings indicate that the enantioselective catalytic species is not monomeric but either a dimer or polymer. 

Albert, A. H. and Wynberg, H. (1990) Enantioselective autoinduction in the aldol condensation of ethyl acetate and benzaldehyde selective precipitation of an optically inactive Li-O aggregate, J. Chem. Soc. Chem. Commun, 453-454. 

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