Rotaxanes
Rotaxanes (lat. Rota , wheel; axis , axis) are substances that consist of at least one molecule with a linear unit, which is enclosed by at least one macrocycle (a cyclic molecule with a ring of sufficient diameter). The macrocycle is not held covalently in its position in the molecule, for example by bulky terminal groups on the linear unit, and / or by van der Waals, London, Coulomb and dipolar interactions between shaft and ring. Complex forms of isomerism occur.
The existence of rotaxanes was proven in 1967 as a small statistical fraction with simultaneous synthesis of a dumbbell-shaped and ring-shaped molecule. The first targeted synthesis was carried out by Gottfried Schill in 1967, who also suggested the name. Among other things, Fraser Stoddart received the Nobel Prize in Chemistry in 2016 for the synthesis of rotaxanes . Stoddart developed an efficient template-guided synthetic route.
Syntheses
There are basically three ways rotaxanes display .
- Threading
- The strategy of threading is based on the fact that the linear component (often referred to as thread) slides into the finished macrocycle and is then prevented from unthreading again by attaching voluminous end groups on both sides of the resulting pseudorotaxane.
- Slipping
- When slipping, both finished components are heated together. As a result, enough activation energy is applied so that the ring is placed over the end groups. When cooling down, the macrocycle remains on the thread because of the stabilizing non-covalent interactions.
- Clipping
- The third possibility is the so-called clipping (English: brackets). The macrocycle is first coordinated in several parts around the thread (again driven by non-covalent interactions) and then closed by a chemical reaction.
Pseudorotaxanes and semirotaxanes
As pseudorotaxanes such rotaxanes be referred to, in which the up threaded macrocycle is not prevented by terminal groups of the molecule from leaving its position, but on the macrocycle is threaded through interactions with the shaft.
As Semirotaxane such rotaxanes refer to operations where the macrocycle is prevented only by one of the terminal groups of the molecule on which it is threaded from leaving his position.
nomenclature
In 1971, Gottfried Schill made a proposal for the nomenclature of rotaxanes, in 2000 Fritz Vögtle and others proposed an expanded form of this nomenclature, but both proposals do not regulate the nomenclature completely clearly. An IUPAC recommendation on the clear nomenclature of rotaxanes was published in 2009.
application
Rotaxanes are of interest as possible switches and motors for nanotechnology .
See also
Web links
Individual evidence
- ↑ Ian Thomas Harrison, Shuyen Harrison, Synthesis of a stable complex of a macrocycle and a threaded chain , J. Am. Chem. Soc., Vol. 89, 1967, pp. 5723-5724
- ↑ Schill, Hubertus Zollenkopf, rotaxane compounds (1) , Liebigs Ann. Chemie, Volume 721, 1969, pp. 53-74. In the article on p. 53 it is pointed out that the content was presented in extracts at the West German Chemiedozententagung on April 13, 1967 in Saarbrücken (see also Nachr. Chemie Technik, Volume 15, 1967, p. 149).
- ↑ José A. Bravo, Francisco M. Raymo, J. Fraser Stoddart, Andrew J. White, David J. Williams, High Yielding Template-Directed Syntheses of [2] Rotaxanes , Eur. J. Org. Chem. 1998 (11) : 2565-2571
- ↑ Gottfried Schill: Nomenclature of Catenanes and Rotaxanes . In: Gottfried Schill, Catenanes, Rotaxanes, and Knots , Academic Press, 1971, ISBN 9781483275666 .
- ↑ Ida Schomburg: Nomenclature of Rotaxanes and Pseudorotaxanes. In: Angewandte Chemie , 2009, 121, 4719-4738. doi : 10.1002 / ange.200900665 .