An Asymmetric N-Rim Partially Substituted Calix[4]pyrrole: Its Affinity for Ag(I) and its Destruction by Hg(II)

A new partially substituted calix[4] pyrrole derivative obtained by the introduction of three thioamide functionalities in the N-rim has been synthesised and fully characterised by 1H, 13C, HSQC, ROESY NMR and mass spectroscopy. Computer modelling suggested an alternate conformation which was confirmed through ROESY 1H NMR. The receptor interacts only with the silver cation as shown by 1H NMR. The strength of interaction is quantitatively assessed by titration calorimetry. N-rim modification eliminates the possibility of interaction with anions. Unlike calix[4] pyrrole derivatives obtained by the introduction of functionalities through the meso-position, addition of Hg(NO3)2 leads to the degeneration of the receptor as demonstrated by 1H NMR, FTIR and XPS analyses. This is for the first time reported. Molecular simulation studies show significant strain in the mercury bound ligand in bonds, angles, torsions leading to the destruction of the receptor. Given the negative environmental impact produced by the availability of silver ions in aquatic organisms, the fundamental studies indicate that this receptor offers potential applications for monitoring silver (ion selective electrode) or indeed as a decontaminating material for removing silver ions from water.