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In chemistry, a molecular recognition event is one in which a host molecule is able to form a complex with a second molecule, the guest. This process occurs through non-covalent chemical bonds including hydrogen bonding, hydrophobic interactions, ionic interaction, or other interactions between the two molecules.
The knowledge of molecular recognition is a relatively new field dating to 1967, when C. J. Pedersen discovered crown ether. Molecular recognition chemistry is also referred to as host-guest chemistry, and it is usually categorized as supramolecular chemistry. Specific examples of molecular recognition include systems in which hydrophobic molecules are included in cyclodextrins as well as the interaction between a crown ether or calixarene and alkali metals.
Molecular recognition can be subdivided into static molecular recognition and dynamic molecular recognition.
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 achieve advanced static molecular recognition, it is necessary to make recognition sites that are specific for guest molecules.
Dynamic molecular recognition is a molecular recognition reaction that dynamically changes the equilibrium to an n:m type host-guest complex by a recognition guest molecule (see figure). There are some equivalents by the combination of host molecules. Both static molecular recognition and dynamic molecular recognition by metal ions are observed in the case of molecular recognition between crown ether complex and alkali metal ion.
Dynamic molecular recognition appearing in supermolecules is essential for designing highly functional chemical sensors and molecular devices. The quest for understanding this principle and its functions is now an important issue.