Generation of chirality in two-component molecular crystals from achiral molecules

Chiral co-crystals by the self-assembly of two different achiral molecules through hydrogen bonding are reviewed. The chiral crystals involve propeller-type and helical-type crystals. The chirality of the propeller-type crystals of diphenylacetic acid and aza aromatic compounds is generated from the propeller-like conformation of phenyl and carboxyl groups in the lattice. In a series of helical-type crystals of tryptamine and Various achiral carboxylic acids, their chirality is generated by the formation of unidirectional two-fold helix between both components through quaternary ammonium salt bridge and hydrogen bonding. Both enantiomorphous crystals were obtained by spontaneous crystallization to give the discrimination of handedness by the solid state CD spectrometry. (C) 2000 Elsevier Science B.V. All rights reserved.