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Transcript of Chirality
June 15, 2013
"chiral" = hand in Greek
What is chirality?
Chiral molecules are a type of
They are non-superimposable mirror images.
A chiral atom and its mirror image are called
Enantiomers share the same physical properties and the same chemical properties (in a chiral environment).
Enantiomers can be right or left "handed".
In a solution, chiral substances can rotate a plane of polarized light. Such chiral molecules are
Optical Activity in Action
Uses: polarized sunglasses
Solutions that contain R and S enantiomers in equal quantities are
They cannot rotate the plane of polarized light because the rotations of each enantiomer cancel each other out.
A chemical reaction that creates a chiral product will yield a racemate. This makes the production of a racemate cheaper and easier than that of a pure enantiomer.
Many substances, such as tartaric acid, are found in nature as pure enantiomers.
Many biological molecules, such as DNA, amino acids, and enzymes, are chiral.
Chirality of Biological Molecules
Enzymes are chiral catalysts. Their chirality contributes to the "lock and key fit" with their substrate.
All amino acids (except glycerine) are chiral.
All amino acids in proteins are "left handed".
This consistent chirality leads to the double helix structure of DNA.
carbon center bonded to four DIFFERENT atoms or groups of atoms
The enantiomer that rotates light to the right is
and is labeled
The enantiomer that rotates light to the left is called
and is labeled
Many pharmecutical drugs consist of chiral molecules. When these drugs are administered as racemic mixtures, one enantiomer is beneficial and the other is inactive or harmful.
When a racemic mixture is placed in a chiral environment, the two isomers can be seperated.
Drugs can be synthesized in order to isolate a desired enantiomer. This enhances the efficiency of the drug and reduces or eradicates side effects. Such drugs are "enantiopure"
Why Chirality Actually Matters
Eszopiclone (Lunesta) vs Zopiclone (Imovane)
These are active enantiomers. In the synthesis of Lunesta, it was found that one stereoisomer ("S") was effective, while the other was inactive. Doses of eszopiclone are half that of zopiclone and are cheaper.
Ibuprofin (Advil/Motrin) vs Dexibuprofin (Seractil).
Ibuprofin is a racemic mixture. Dexibuprofin is a single enantiomer.
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