kiraalisuutta

Kiraalisuutta is the property of an object—most often a molecule—that makes it non-superimposable on its mirror image. When a molecule has this property, its mirror image is a distinct enantiomer, and the pair is known as enantiomers. If an object can be superimposed on its mirror image, it is achiral and lacks this property.

Chirality commonly arises from stereogenic centers, such as tetrahedral carbon atoms bonded to four different substituents. Enantiomers have identical physical properties in achiral environments but interact differently with chiral environments, including biological systems. They rotate plane-polarized light in opposite directions; this optical activity is described by the specific rotation, which depends on solvent, temperature, concentration, and wavelength. A mixture containing equal amounts of both enantiomers is racemic and, in general, is not optically active.

Importance: Chirality matters in biology and pharmacology because enantiomers can have different smells, tastes, or biological effects. Many drugs are enantiomerically specific in effect; in some cases a single enantiomer is therapeutic while its mirror image may be less active or harmful. Common biological examples include L-amino acids and D-sugars.

Measurement and separation: Polarimetry measures optical rotation; chiral chromatography and enantioselective synthesis or resolution separate enantiomers. Circular dichroism spectroscopy provides information about chiral conformations.

History: The concept emerged in 19th century chemistry; Louis Pasteur's separation of tartaric acid enantiomers laid foundations; later, van't Hoff and Le Bel described the stereochemical implications of chirality.