chirality (rus. хиральность) — the geometrical property of an object (spatial structure) that makes it o to be identical to its mirror image in an ideally flat mirror.

Description

Chiral objects do not have Type II symmetry elements, such as a symmetry plane, symmetry centres and mirror-rotation axes. If at least one of those elements of symmetry is present, the object is achiral. Chiral objects can be molecules, crystals, nanostructures (for example, nanotubes).

Chiral molecules can exist as two optical isomers (enantiomers) that are mirror images of each other and differ in the ability to rotate the plane of light polarisation clockwise (D-isomers) or counterclockwise (L-isomers) (Fig.). Enantiomers have the same physical properties, as well as identical chemical properties when interacting with achiral substances. At the same time, the differences in the interaction of enantiomers of a particular substance with a specific optical isomer of another substance can serve as the basis for the separation of enantiomers, such as chiral chromatography. In chemistry, chirality is usually associated with the asymmetric carbon site, bearing four different substituents.

When molecules contain several asymmetric sites, they are referred to as the diastereoisomers. In this case, there may be several pairs of enantiomers (a pair of enantiomers should be described with a mutually antithetic configuration of asymmetric sites), and diastereoisomers of different enantiomeric pairs can have greatly varying properties.

Almost all biomolecules are chiral, including naturally occurring amino acids and sugars. In nature, most of those substances have a certain spatial configuration, for example, the majority of amino acids have the spatial configuration L, and sugar have D. In this regard, the enantiomeric purity is a prerequisite for biologically active agents.

Illustrations

Alanine is a chiral aminoacid.
Alanine is a chiral aminoacid.

Author

  • Eremin Vadim V.

Sources

  1. Chemical encyclopedia (in Russian) V. 5. — Moscow: Bol'shaja Rossijjskaja ehnciklopedija, 1998. P. 538.
  2. Compendium of Chemical Technology. IUPAC Recommendations. — Blackwell, 1997.

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