Mechanically interlocked molecules

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Mechanically interlocked molecules ( English Mechanically interlocked molecular architectures , mimas) are molecules which are linked to each other due to their topology. The connections behave like keys on a keyring. The keys are not in direct contact with the loop, but they cannot be separated without severing the loop. At the molecular level, this means that covalent bonds would have to be broken. Examples of mechanically interlocked molecules include catenanes , rotaxanes , molecular node ( knotanes ) and molecular Borromeo rings a. Work in this area was recognized with the 2016 Nobel Prize in Chemistry for Bernard L. Feringa , Jean-Pierre Sauvage , and J. Fraser Stoddart .

The synthesis of such mechanically interlocked architectures has been made possible through the combination of supramolecular chemistry with traditional synthesis, but they have properties that differ from supramolecular assemblers and from covalent molecules. The term “mechanical bond” describes the connection between the structures of a mechanically interlocked architecture. Although the research is concerned with the synthetically produced mechanically interlocked architectures, examples can also be found in biological systems: cytokine nodes, cyclotides , lasso peptides such as microin J25, which belong to the proteins, and other peptides.

Instead of mechanical bonding , the term topological bonding is also used and in this context we speak of topological isomerism and chemical topology , a term that goes back to Edel Wasserman (1961).

Mechanical bond and chemical reactivity

The introduction of the mechanical bond changes the chemistry of the substructures of the rotaxanes and catenanes. The steric hindrance of the reactive functional groups increases and the strength of the non-covalent interactions between the substructures changes.

Effects of mechanical bonding on non-covalent interactions

The strength of the non-covalent interactions in a mechanically interlocked architecture grows compared to the toothless analogues. The greater stability is evidenced by the harsher reaction conditions required to remove a metal template ion from catenanes compared to the reaction conditions required for the toothless analogues. This effect is counted among the "catenane effects". The increase in the strength of the non-covalent interactions is due to the loss of a degree of freedom due to the formation of the mechanical bond. The growing strength of the non-covalent interactions is more noticeable in small, interlocked systems, in which several (movement) degrees of freedom are lost, than in large ones, where the change in the degrees of freedom is less. Therefore, the strength of the non-covalent interactions increases as the ring of a rotaxane becomes smaller. The same effect can also be observed when the diameter of the molecular thread changes.

Effects of mechanical bonding on chemical reactivity

The mechanical bond can reduce the kinetic energy of the products. This is due to the greater steric hindrance . Because of this effect, the hydrogenation of an alkane that is interlocked with a rotaxane is slower compared to the reaction of the toothless compound. This effect also enables the isolation of otherwise reactive intermediate stages. The ability to change the reactivity without changing the covalent structure made MIMs interesting for technological applications.

Applications of mechanical bonding to control chemical reactivity

The ability of a mechanical bond to decrease reactivity and prevent unwanted chemical reactions has been explored in a number of areas. The first application was the protection of an organic dye from decomposition by environmental influences.

Examples

See also

Individual evidence

  1. ^ Wesley R. Browne, Ben L. Feringa: Making molecular machines work . In: Nature Nanotechnology . 1, No. 1, 2006, pp. 25-35. bibcode : 2006NatNa ... 1 ... 25B . doi : 10.1038 / nnano.2006.45 . PMID 18654138 .
  2. ^ JF Stoddart: The chemistry of the mechanical bond . In: Chem. Soc. Rev. . 38, No. 6, 2009, pp. 1802-1820. doi : 10.1039 / b819333a . PMID 19587969 .
  3. ^ A. Coskun, M. Banaszak, RD Astumian, JF Stoddart, BA Grzybowski: Great expectations: can artificial molecular machines deliver on their promise? . In: Chem. Soc. Rev. . 41, No. 1, 2012, pp. 19-30. doi : 10.1039 / C1CS15262A . PMID 22116531 .
  4. ↑ Fabien Durola, Valerie Heitz, Felipe Reviriego, Cecile Roche, Jean-Pierre Sauvage, Angelique Sour, Yann Trolez: Cyclic [4] Rotaxanes Containing Two parallel Porphyrinic Plates: Toward Switchable Molecular Receptors and Compressors . In: Accounts of Chemical Research . 47, No. 2, 2014, pp. 633-645. doi : 10.1021 / ar4002153 . PMID 24428574 .
  5. ^ Fritz Vögtle , Supramolekulare Chemie, Teubner 1992, p. 157
  6. ^ Edward A. Neal, Stephen M. Goldup: Chemical consequences of mechanical bonding in catenanes and rotaxanes: isomerism, modification, catalysis and molecular machines for synthesis . In: Chemical Communications . 50, No. 40, April 22, 2014, pp. 5128-42. doi : 10.1039 / c3cc47842d . PMID 24434901 .
  7. ^ Anne Marie Albrecht-Gary, Zeinab Saad, Christiane O. Dietrich-Buchecker, Jean Pierre Sauvage: Interlocked macrocyclic ligands: a kinetic catenand effect in copper (I) complexes . In: Journal of the American Chemical Society . 107, No. 11, May 1, 1985, pp. 3205-3209. doi : 10.1021 / ja00297a028 .
  8. ↑ J.Fraser Stoddart, Carson J Bruns: The Nature of the Mechanical Bond: From Molecules to Machines . Wiley, 2016, ISBN 978-1-119-04400-0 , p. 90.
  9. ↑ Hicham Lahlali, Kajally Jobe, Michael Watkinson, Stephen M. Goldup: Macrocycle Size Matters: "Small" Functionalized Rotaxanes in Excellent Yield Using the CuAAC Active Template Approach . In: Angewandte Chemie International Edition . 50, No. 18, April 26, 2011, pp. 4151-4155. doi : 10.1002 / anie.201100415 . PMID 21462287 .
  10. ↑ Parham, Amir Hossain and Windisch, Björna and Vögtle, Fritz: Chemical Reactions in the Axle of Rotaxanes - Steric Hindrance by the Wheel , 1999-05-01 in: European Journal of Organic Chemistry , (1999), 5, 1233-1238 , doi: 10.1002 / (SICI) 1099-0690 (199905) 1999: 53.0.CO; 2-Q .