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Limitations and Extensions of the Lock-and-Key Principle: Differences between Gas State, Solution and Solid State Structures

Universität des Saarlandes, FR Organische Chemie, D 66041 Saarbrücken, Germany
Academic Editor: John George Hardy
Int. J. Mol. Sci. 2015, 16(4), 6694-6717; https://doi.org/10.3390/ijms16046694
Received: 7 February 2015 / Accepted: 16 March 2015 / Published: 25 March 2015
(This article belongs to the Special Issue Supramolecular Interactions)
The lock-and-key concept is discussed with respect to necessary extensions. Formation of supramolecular complexes depends not only, and often not even primarily on an optimal geometric fit between host and guest. Induced fit and allosteric interactions have long been known as important modifications. Different binding mechanisms, the medium used and pH effects can exert a major influence on the affinity. Stereoelectronic effects due to lone pair orientation can lead to variation of binding constants by orders of magnitude. Hydrophobic interactions due to high-energy water inside cavities modify the mechanical lock-and-key picture. That optimal affinities are observed if the cavity is only partially filled by the ligand can be in conflict with the lock-and-key principle. In crystals other forces than those between host and guest often dominate, leading to differences between solid state and solution structures. This is exemplified in particular with calixarene complexes, which by X-ray analysis more often than other hosts show guest molecules outside their cavity. In view of this the particular problems with the identification of weak interactions in crystals is discussed. View Full-Text
Keywords: host and guest complexes; supramolecular chemistry; lock-and-key principle; solvent effects; stereoelectronic effects; binding mechanisms; non-covalent interactions; hydrophobic effects; high energy water; crystal structures; crown ethers; cyclophanes; calixarenes; cyclodextrins; cucurbiturils host and guest complexes; supramolecular chemistry; lock-and-key principle; solvent effects; stereoelectronic effects; binding mechanisms; non-covalent interactions; hydrophobic effects; high energy water; crystal structures; crown ethers; cyclophanes; calixarenes; cyclodextrins; cucurbiturils
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Schneider, H.-J. Limitations and Extensions of the Lock-and-Key Principle: Differences between Gas State, Solution and Solid State Structures. Int. J. Mol. Sci. 2015, 16, 6694-6717.

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