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Paper Details

Calix[4]pyrroles as Sensors:A Review

Aparna Sharma1*, Sangeeta Obrai2 and Rakesh Kumar2

Journal Title:Journal of Chemical, Biological and physical sciences

Molecules with specific binding sites serve as sensors. Calix[4]pyrrole is one such class, which holds a great promise in the fields of sensors, and their unique behaviour as sensors owe to its structural flexibility. Anion binding ability of calix[4]pyrrole has been modified in a variety of ways. Introduction of electron-releasing and electron-withdrawing groups at the meso- position or at ?-pyrrolic positions lead to calix[4]pyrrole with deep cavities and fixed walls which shows increased selectivity and modified binding effects. Strapping of calix[4]pyrrole is another way to modify its structural behaviour which is responsible for its binding behaviour. Choice of strap could play a profound role not only in increasing the intrinsic anion binding affinity of calix[4]pyrrole, but also in modulating the receptor anion stoichiometry, thereby modifying potentially the inherent anion binding selectivity. Calix[n]pyrroles with extended cavities have also been synthesized. Such as Calix[3]bipyrrole binds bromide substantially with high affinity than calix[4]pyrrole. Calix[4]pyrrole has also been used to produce anion sensors that can report the presence of anion by means of a colour change. The medium effect on the complexation of calix[4]pyrrole and anion has been investigated in various solvents. Calix[4]pyrrole has also been used to increase the ionic conductivity of solid polymer electrolyte by anion complexation of the metal salt. Calix[4]pyrrole has been used to obtain optical sensors using surface plasmon resonance technique. Composite films of cellulose acetate containing calix[4]pyrrole has also been reported which has potential usage in packaging, storage and preservation. In nut shell, cailx[4]pyrrole can be modified in a variety of ways to form versatile sensors which can be used in variety of ways in various areas.