Racemic Mixture

Nature is chiral exemplified by the fact that molecules of living organisms (both plants and animals) such as amino acids, peptides, proteins, enzymes, carbohydrates and nucleic acids are chiral. 

Enantiomers: Non - superimposable mirror images 

Chiral (Enantiomers): Different from its mirror image 

Chiral VS Achiral

However, not only these biomolecules ( living organisms (both plants and animals) such as amino acids, peptides, proteins, enzymes ) are chiral 

Many other molecules we find on a daily basis are chiral. Most of these molecules are artificial coming from the human activity who synthesized these compounds in order to be used as agrochemicals, or pharmaceuticals

Independently of its origin (natural or artificial) these chiral molecules (namely, their enantiomers) may have different biological activity. This can be illustrated by means of the following examples:

The enantiomers of limonene, both formed naturally, smell differently. One of the enantiomers (S)-limonene smells of lemon while its mirror image compound (R)-limonene smells of oranges. We distinguish between these two enantiomers because our nasal receptors are also made up of chiral molecules that recognise the difference.

Chirality also plays a role on odorants such as (4S)-(+)-carvone, which has a distinct caraway odour, as compared to (4R)-(-)-carvone which has a characteristically sweet spearmint odour. Again our nasal receptors let us to allow us to distinguish the difference in smell. These two odorants possess different odours due to the role of chirality on bioactivity.

Thus, biology is very sensitive to chirality 

   

Activity of pharmaceuticals depends on which enantiomer is used. 

Most drugs consist of chiral molecules. 

One of the earliest known uses of a chiral compound to cure a disease is the case of Quinine (and other Cinchona alkaloids). 

Cinchona extracts and quinine are also used in tonic waters, which were popularized in the British colonies as both a malaria prophylactic and for enjoyment in the form of a “Gin & Tonic”. Tonic water is now one of the largest industrial uses of quinine.

Racemic Mixture

Equal quantities of d- and l- enantiomers a 50/50 mixture

Racemic Mixture ( Drugs)

                                                        Enantiomers (Harmful)

In certain cases, one of the enantiomers may even be harmful. This was the case, for example, with the drug thalidomide, which was sold in the 1960s to pregnant women. One of the enantiomers of thalidomide helped against nausea, while the other one could cause fetal damage.

Racemic Mixture (Snapshot)