Stereoisomers enantiomers and diastereoisomers

One of the problems attaching to the HPLC separation of peptides is the analysis of stereoisomers (enantiomers and diastereoisomers), that is, of peptides that differ only in the configuration of their amino acid residues. 

Generally, in liquid crystals, it is only phases that contain optically active materials that exhibit chiral liquid crystal modifications. Thus at least one substance in the liquid crystal system must be a stereoisomer that contains at least one asymmetrically substituted atom, and which is present in a greater concentration than its opposite enantiomer. It is the configurational isomers in the system that give rise to chiral properties. Included in configurational isomers are two distinct classes of stereoisomers enantiomers and diastereoisomers [2]. Enantiomers are two molecules that are related to one another as object and nonsuperimposable mirror image, as shown in the upper part of Fig. 1. Diastereoisomers usually contain more than one asymmetric atom, and pairs of diastereoisomers do not share a superim-posable mirror image, as shown in the lower part of Fig. 1 [1, 2]. 

Isomers that differ from each other only in the way atoms are oriented in space. There are two types of stereoisomers enantiomers and diastereoisomers. 

Some Physical Properties of Selected Stereoisomers (Enantiomers and Diastereoisomers)... 

---