Positive allosteric systems designed on dynamic supramolecular scaffolds: toward switching and amplification of guest affinity and selectivity.

Positive homotropic allosterism appears in important information transduction processes where chemical and physical signals are efficiently amplified. The phenomena are ubiquitous in nature, but the general methodology for the design of such allosteric systems is not yet established in an artificial system. This account reviews such artificial receptors that can bind guest ions and molecules in a positive allosteric manner and discusses what kinds of factors are indispensable as scaffolds in the design of this novel class of allosteric systems and what common factors are needed to realize the cooperativity. It has been shown that the scaffolds are mostly dynamic and are skillfully combined with the molecular recognition systems so that the subsequent guest binding can occur more favorably than the first guest binding. In addition, it has been suggested that positive homotropic allosterism can be utilized as a new strategy to attain high guest selectivity and guest affinity which cannot be attained by conventional 1:1-type guest binding.