Chiral recognition molecule chemical structures

Chiral recognition in complexes, linked by hydrogen bonds, has been studied experimentally and theoretically. In some cases, chiral systems can aggregate and form long chains or helix shape structures. The subsequent chemical processes along the chains can invert the chirality of the molecules producing what we have called racemization waves [37]. The control and rationalization of these processes are of the utmost importance in the development of novel molecules designed as switches. 

Multiple Chiral Centers. The number of stereoisomers increases rapidly with an increase in the number of chiral centers in a molecule. A molecule possessing two chiral atoms should have four optical isomers, that is, four structures consisting of two pairs of enantiomers. However, if a compound has two chiral centers but both centers have the same four substituents attached, the total number of isomers is three rather than four. One isomer of such a compound is not chiral because it is identical with its mirror image it has an internal mirror plane. This is an example of a diaster-eomer. The achiral structure is denoted as a meso compound. Diastereomers have different physical and chemical properties from the optically active enantiomers. Recognition of a plane of symmetry is usually the easiest way to detect a meso compound. The stereoisomers of tartaric acid are examples of compounds with multiple chiral centers (see Fig. 1.14), and one of its isomers is a meso compound. 

The general idea that biochemical processes follow specific chemical recognition/response events was first proposed by Emil Fischer, who used the term "lock and key." The implication here is that a specific chemical compound "fits" into a specific location in a biochemical and that this then initiates a certain biochemical response. The term "lock and V.ey is stiU widely used today, but there is a much better appreciation nowadays that there are a range of responses to chemicals, and that many different molecules with similar, but not necessarily identical, structures can initiate similar biochemical responses. However, the chirality of the interacting species is important in almost all examples of this principle. 

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