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STEREOCHEMISTRY (Greek stereos firm, space + chemistry) — the section of chemistry devoted to studying of a spatial relationship of atoms in a molecule and its influences on physical properties and reactivity of substance. Biological, including and pharmacological, specificity of chemical groups in a molecule is defined by their spatial configuration. The ideas and methods C. are widely used in pharmacology, biological and medical chemistry and other medicobiological sciences. Except organic compounds, objects C. are also bioinorganic (intra complex) compounds.

It is necessary to distinguish L. Pasteur studying asymmetry of crystals wine to from the first researchers working in the area C. - you (1848), and A. M. Butlerov who created the theory of a structure of organic matters and by that S. as the independent section of chemistry which predetermined emergence (1863). According to Ja. Vant Hoff and Le Bel's representations (J. A. Le Bel, 1874), valent bonds of saturated carbon atom (C) meet to tops of a regular tetrahedron. This model well explained an equivalence of all four bonds of atom C and further received experimental confirmation. If atom C is connected with four various groups, then it is asymmetric, or, on new terminology, hiralen (Greek cheir a hand). Asymmetric substances can be either in right, or in the left form. Optical activity, opposite on a sign, is characteristic of them also equal in size. Molecules with two and more asymmetric centers (the molecule of threonine can be an example) form family of diastereomer. The majority of biomolecules are asymmetric; obviously, asymmetric systems have advantages before symmetric, selectively interacting with molecules of the environment. Cis-trance isomerism. molecules it is connected with position of deputies of rather double bond or the plane of a ring (see. Isomerism ).

An important role in S. is played by ideas of spatial configuration of molecules (see. Conformation ), the considering rotation of atoms or groups of atoms about single bonds and change of valence angles. For definition of interatomic distances, valence angles and a configuration of molecules use physical methods: X-ray crystallographic analysis (see), nuclear magnetic resonance (see), electronic paramagnetic resonance (see), submicroscopy (see), infrared spectroscopy (see), a polarimetry (see). S.'s problems include receiving pure stereoisomers, definition of their conformation and properties. The complex structure of biomolecules is a basis of «molecular recognition», the events at DNA replication, a transcription, biosynthesis of proteins, an enzyme catalysis, immunol. reactions, etc. Property of «molecular recognition» is used for the analysis and cleaning of biomolecules with method of affine chromatography (see). Data on S. of biomolecules allow to understand mechanisms biol. processes, napr, actions of antibiotics, antineoplastic activity of stereoisomers of platinoorganichesky connections, carrying out nervous impulse, etc. and to carry out the directed synthesis of pharmaceuticals on this basis.

Bibliography: Wolkenstein M. W. Biophysics, M., 1981; Potapov V. M. Stereochemistry, M., 1976; And 1 w about of t h W. L. Stereochemistry and its application in biochemistry, N. Y. a. o., 1972, bibliogr.

E. V. Ramensky.