Shailesh Upreti

Conformational morphosis in azocalix[4]arenes

The first example of cesium induced chemical morphosis of new azocalix[4]arene 2 is described. It has been observed that pyridylazocalix[4]arene 2a selectively reacts with cesium ion to yield a new polymorph 2b. The synthesized polymorphs (2a and 2b) have similar gross conformational structures which profoundly differ at supramolecular level to exhibit a ‘hand-shake’ arrangement with respect to pyridyl units or π–π interaction of phenolic units.

Synthesis and evaluation of neutral anion receptors based on acylhydrazide-appended calix[4]arenes

A new class of neutral receptors based upon acylhydrazide-appended calix[4]arenes was synthesised and evaluated for recognition of anions. Detailed NMR and single-crystal X-ray analyses of one of the synthesised compounds reveal that anion recognition in such derivatives is achieved through cooperative hydrogen bond interactions. The presence of three centred NH–O and two OH–O hydrogen bonds at the lower rim of the synthesised calixarene architecture apparently helps the molecular scaffold to retain cone conformation to enable deployment of intermolecular hydrogen bonds for selective recognition of HSO4 − ion in preference to F−, Cl−, Br−, I−, ClO4 −, AcO− and PF6 − ions.