Isomers are compounds with the same molecular formula. Components which only differ in the arrangement of their substituents in space are called stereoisomers. One of the geometrical possibilities for the existence of stereoisomers are enantiomers. Enantiomers are defined as (one pair of) molecules which behave as picture and mirror image. This is valid when the molecules do not possess any symmetry elements, which can transfer the one form into the other (such as the famous example of left and right hand):
Enantiomers exhibit identical physical properties (for instance, both enantiomers have identical mass spectra, the same retention times on nonchiral stationary phases, and identical melting points - however, the melting point of the individual enantiomers is different to the melting point of the racemate), but their biological properties (for instance the stability in a chiral environment) can be different. Interaction of enantiomers with a chiral selector (for instance an enzyme system or a chiral stationary phase used in chromatography) may yield associates, which behave as diastereomers. In contrast to enantiomers, diastereomers have different physical and chemical properties. Such different interactions of optical antipodes with a chiral selector can be accompanied with different biological properties such as bioavailability, toxicity, and metabolism of enantiomers.
In the worst case, the two enantiomers of a chiral molecule can have opposing biological properties while interacting with a chiral selector. Therefore, the gaining of pure enantiomers, the control of enantiopurity, and the investigation of the fate of chiral compounds play important roles in almost all disciplines of natural science which are dealing with "chiral systems" (food chemistry, chemistry, environmental chemistry, pharmacy, life sciences, biology, biochemistry, nutritional sciences among others).
The major substance class of our previous enantioselective studies with the help of chromatographic methods have been the chlorinated hydrocarbons. Many chloropesticides (for instance components of chlordane and toxaphene), by-products in technical grade products (α-HCH, o,pī-DDT), or important metabolites (oxychlordane, p,pī-DDD among others) are chiral. In addition there are chiral PCBs (for instance PCB 149 and PCB 132), PBBs and other compounds, which are chiral due to the hindered rotation about single bonds and their unsymmetrical composition (atropisomers). We have applied different chiral stationary phases on the basis of modified cyclodextrins in order to study the following points: