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Rotaxane

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rotaxane [rō′tak‚sān]
(organic chemistry)
A compound with two or more independent portions not bonded to each other but linked by a linear portion threaded through a ring and maintained in this position by bulky end groups.

Rotaxane 

any of a group of chemical compounds composed of a linear molecular chain passing through a chainlike molecular ring. The compound is so arranged that the bulky end groups of the linear chain prevent the ring from slipping off.

Figure 1

The structural representation of a rotaxane molecule is shown in Figure 1, where R and R’ are radicals and the ring is a cyclic macromolecule.

The simplest type of rotaxane structure is shown in Figure 2, where η = 25–29. (This type of linear molecule will not fit within a smaller ring, that is, where η < 25; where n > 29, the stability of the rotaxane molecule is limited and the ring slips off the linear molecule.) The entities that form rotaxanes, that is, the linear and cyclic molecules, are bonded mechanically rather than chemically in what is called a topological bond.

Figure 2

Chemical compounds with topological bonding also include catenanes, wherein the cyclic macromolecules are joined in a fashion suggesting chain links. Figure 3 shows the structure of one of the synthesized catenanes. Rotaxanes and catenanes are obtained either by random formation in accordance with statistical laws (statistical synthesis) or by directed synthesis. The first statistical synthesis of rotaxanes was carried out by I. Harrison and S. Harrison (1967, United States); directed synthesis was first achieved by G. Schill and H. Zollenkopf (1969,

Figure 3

Federal Republic of Germany). Molecules of compounds constructed without chemical bonds occur in both organic and inorganic nature. Rotaxane and catenane forms of deoxyribonucleic acid (DNA) have been discovered.

REFERENCES

Schill, G., E. Logemann, and W. Vetter. “Ozonolytischer Abbau eines Catensins” Augewandte Chemie, 1972, vol. 84, no. 23, p. 1144.
Schill, G. Katenany, rotaksany i uzly. Moscow, 1973. (Translated from English.)
Kostianovskii, R. G. Katenany iklatraty. Moscow, 1966.

R. G. KOSTIANOVSKII



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Topics addressed include bioactive macrocyclic peptides and peptide mimics, macrocycles by ring-closure metathesis, supramolecular macrocycle synthesis by H-bonding assembly, cucurbiturils, tetra-urea calixarenes, shape-persistent macrocycles based on acetylenic scaffolding, supramolecular 3D architectures by metal-directed assembly of synthetic macrocycles, new properties and reactions in self-assembly M6L4 coordination cages, anion-binding macrocycles, and rotaxane and catenane synthesis.
The rings would still move mostly at random, but on average the gates would tend to push them in a specific direction, from one rotaxane to the next.
[1] The molecular switch, which is essentially a monolayer of rotaxane molecules sandwiched between 2 perpendicular electrodes, is still in its infancy, but it holds great promise for the next generation of CAENs patterned on miniscule tube wires and molecular switches.
 
 
 
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