**3. Enantioselective crystallization**

The crystallization of racemic molecules is very similar to the crystallization of achiral molecules. However, because of their chirality, racemic molecules can form different types of crystals with different compositions. If the crystal lattice contains equal left and right handed molecules arranged in an ordered manner, the crystal is heterochiral and referred to as a racemic compound. In the case where the crystal lattice is composed of only one enantiomer (left or right), the crystal is homochiral and referred to as a conglomerate. In nature, racemic compounds greatly outnumber conglomerates.

Chiral resolution is the process of the separation of racemates into their enantiomers. Many methods have been developed for this purpose. The most common is the use of chiral stationary phases in HPLC. However, large scale chiral separation is based on the classical crystallization method, which incorporates diasteriomeric transformation and chiral seeding. Even today, new methods of chiral crystallization are being designed. Lahav et al. developed a method, called "tailor-made" additives, which has been exploited for the kinetic resolution of conglomerates (Addadi, 1982). These additives have molecular structures which are very similar to one of the enantiomorphs of the substrate crystals. Consequentially, the inhibitors stereoselectively adsorb to the surfaces of one of the enantiomorphs, delaying or preventing its growth. As a result, enantiomeric excess is achieved. It is important to mention that in order to acheive chiral resolution by crystallization, the racemate system must spontaneously resolve upon crystallization to a conglomerate.
