Isosteria

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In chemistry, isosteres are two molecules or ions that have the same number and arrangement of atoms (i.e. the same geometry), but not necessarily the same electron configuration. If the electron configuration is also identical, the particles are isoelectronic to one another . If only the number of valence electrons is the same, one speaks of isovalence electronic.

Isosteric compounds often have very similar physical properties, so one can often draw conclusions from known compounds about unknown isosteric compounds. This principle has also found its way into pharmaceutical chemistry in the search for new drugs . Here isosteria is also referred to as bioisosteria .

Examples

Examples are:

  1. Carbon monoxide (CO) and nitrogen (N 2 ): molecules each made up of two atoms and ten valence electrons each.
  2. Carbon dioxide (CO 2 ) and nitrous oxide (N 2 O).
  3. Diazomethane (H 2 CN 2 ) and ethenone ("ketene", H 2 C = C = O).
  4. Benzene (C 6 H 6 ) and borazine (B 3 N 3 H 6 ): molecules each made up of twelve atoms and 30 electrons.
  5. One CH group in benzene is isostere with one nitrogen atom in pyridine (azalogy).

Isosteric compounds can be found by replacing one of two atoms of any compound with an atom from a group x higher in the periodic table and the other with an atom from a group x lower in the periodic table. For example 1 this means: nitrogen is in group 15, carbon is in group 14 (15-1), oxygen in group 16 (15 + 1).

history

The term isosteria was coined by Irving Langmuir in 1919 and expanded to include biologically active substances by Hans Erlenmeyer .

Isosteria should not be confused with allostery or with the term " isosteres " from physical chemistry.

Individual evidence

  1. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 134.
  2. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon . Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , p. 1968.
  3. ↑ Heribert Offermanns : Azalogy principle: there and back. In: News from chemistry . Volume 59, 2011, pp. 1152-1153, doi: 10.1002 / nadc.201290011 .
  4. ↑ Hans Erlenmeyer, Ernst Willi: Relationship between constitution and effect in pyrazolone derivatives. In: Helvetica Chimica Acta . Volume 18, 1935, p. 740, doi: 10.1002 / hlca.193501801101 .
  5. ↑ Hans Erlenmeyer, Martin Leo: About pseudoatoms. In: Helvetica Chimica Acta . Volume 15, 1932, p. 1171, doi: 10.1002 / hlca.193201501132 .