Crown Ethers and Related Hosts The First Class of Artificial Host

Crown Ethers and Related Hosts - The First Class of Artificial Host 

Crown ethers were the first artificial host molecules discovered. They were accidentally found as a byproduct of an organic reaction. When Pedersen synthesized bisphenol, contaminations from impurities led to the production of a small amount of a cyclic hexaether (Fig. 2.1). This cychc compound increased the solubihty of potassium permanganate in benzene or chloroform. The solubility of this cyclic compound in methanol was enhanced in the presence of sodiiun ion. Based on the observed phenomena, Pedersen proposed that a complex structure was formed where the metal ion was trapped in a cavity created by the cychc ether. At that time, it was already known that naturally occurring ionophores such as valinomycin incorporated specific metal ions to form stable complexes because of this, compounds able to selectively include metal ions were the source of much attention from researchers. Pedersen called the cychc compound a crown ether, because the cychc host wears the ion guest like a crown. 

Because the rings of the crown ethers are rather flexible, there is some degree of structural freedom during complexation. When the metal ion is larger than the crown ether, 2 1 complex formation is possible through a sandwich-type 

Signal Input/Output in Crown Ether Systems 

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Crown Ethers and Related Hosts - The First Class of Artificial Hosts Crown ethers are macrocyclic polyethers with crown-like shapes. Various cations are selectively bound to the crown ether, depending on the size of the macrocyclic ring. More precise recognition can be accomphshed using modified crown ethers such as lariat ethers and cryptands. 

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