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In supramolecular chemistry, [1] host–guest chemistry describes complexes that are composed of two or more molecules or ions that are held together in unique structural relationships by forces other than those of full covalent bonds. Host–guest chemistry encompasses the idea of molecular recognition and interactions through non-covalent ...
Crystal structure of a nitrobenzene bound within a hemicarcerand reported by Cram and coworkers in Chem. Commun., 1997, 1303-1304.. In host–guest chemistry, a carcerand (from Latin carcer 'prison') is a host molecule that completely entraps its guest (which can be an ion, atom or other chemical species) so that it will not escape even at high temperatures. [1]
In chemistry, a cavitand is a container-shaped molecule. [2] The cavity of the cavitand allows it to engage in host–guest chemistry with guest molecules of a complementary shape and size. The original definition proposed by Cram includes many classes of molecules: cyclodextrins , calixarenes , pillararenes and cucurbiturils . [ 3 ]
Static molecular recognition is likened to the interaction between a key and a keyhole; it is a 1:1 type complexation reaction between a host molecule and a guest molecule to form a host–guest complex. To achieve advanced static molecular recognition, it is necessary to make recognition sites that are specific for guest molecules.
Coordination cages are used to study guest-guest and host–guest interactions and reactions. In some instance, planar aromatic molecules stack inside of metalloprisms, as can be observed by UV-visible spectroscopy. Metal-metal interactions can also be observed. [15] Mixed valence species have also been trapped inside of coordination cages. [15]
Computer models of CB[5], CB[6], and CB[7]. Top row is the view into the cavity and the bottom is the side view. In host–guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril (=C 4 H 2 N 4 O 2 =) monomers linked by methylene bridges (−CH 2 −).
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The three-dimensional interior cavity of a cryptand provides a binding site – or host – for "guest" ions. The complex between the cationic guest and the cryptand is called a cryptate. Cryptands form complexes with many "hard cations" including NH + 4, lanthanoids, alkali metals, and alkaline earth metals.