Chirality and its impact on daily life
- Georgina Griffiths
- Jan 5, 2021
- 3 min read
Chirality is a form of stereoisomerism which relates to how the molecule itself is structured. Chirality is caused by whether the molecule can be reflected or not, i.e. can you superimpose the mirror image of itself on top of it and still have the same image. An example of this is the hands with which you are scrolling through this web-page. For two molecules to be chiral to each other they must include the same atoms and of course be mirror images of the other.
Discovery
In winemaking, tartaric acid is formed and builds up on the walls of the container. Some factory workers accidentally boiled the wine for too long and produced paratartaric acid which of course acts differently than wine does. The nature of this "new" compound intrigued many scientists, including Louis Pasteur. The study of the acid involved the crystals and the way in which they interact with light.
When scientist Jean-Baptiste Biot shined polarised light through the crystals he noticed that the crystals rotated the light both clockwise and anticlockwise. From this he concluded that tartaric acid was optically active.
When studying paratartaric acid Louis Pasteur noticed that it formed two types of crystal; one which resembled the crystals of tartaric acid and another which was mirror opposite to it. He also noticed that the crystals no longer rotated polarised light contrary to the property of tartaric acid. Pasteur concluded that the two opposing crystals cancelled each other out and caused the light to appear as if it had not been rotated at all. Pasteur's progression in this area is commonly attributed to his interest in art.
In Nature
Chirality can also be observed in nature, for example in Bindweed, a form of seaweed, it only ever winds as a right handed helix and honeysuckle grows as a left handed helix. Chirality has also been found in some forms of bacteria, some scientists from the university of Arizona investigated Bacillus subtilis which usually forms right handed chiral colonies however as they increased the temperature of the conditions the bacteria was under they became increasingly more left hand chiral.
Naturally molecules are able to be chiral and the existence of life as we know it relies upon chiral molecules, mainly proteins including DNA. All amino acids are chiral but one (glycine), the catalytic capabilities of enzymes also relies upon the molecules being chiral.
The human sensory organs are also chiral, so they can sense the difference between two enantiomers can be distinguished by smell, for example Carvone, which in one direction it’s the smell of spearmint oil, and in the other is caraway oil.
In Medicine
A key example of the impact of chirality is the incident with Thalidomide. Thalidomide was a medication used in West Germany to treat anxiety, insomnia and morning sickness. While one enantiomer (one of the two mirror images) did this very successfully the other did not, and as the pregnant women who took this "wonder drug" would discover caused birth defects. This drug is on the WHO's list of essential medicines but is no longer given to pregnant women.
The difference between each chiral isomer, which is what caused these unexpected symptoms, is the way in which they interact with the drug binding site, if the atoms do not match up with the corresponding receptor then it will not work. When the active enantiomer interacts with the binding site it will react as expected while the inactive enantiomers do nothing.
References:
•"Organic Synthesis III Stereoselective Organic Synthesis" by Francis A. Carey, Richard J. Sundberg, Jonathan Clayden, Nick Greeves, Stuart Warren, Peter Wothers, Ernest L. Eliel, Samuel H. Wilen, Robert S. Ward, Garry Procter
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