Thiacrownether and imidazolium receptor as sensor for cations and anions

Abstract

Acyclic thiacrown ether derivative containing imidazolium moieties and amide NH protons L was synthesized. Complexation studies of ligand L with various ions were carried out by [superscript 1]H-NMR, UV-Vis, and fluorescent spectroscopy. This receptor also forms 1:1 stoichiometry complexes with anion guest as confirmed by Job's plot. The maximum absorption band of ligand showed at 346 nm and in the presence of various anions, the absorption band shifted hypsochromically. For fluorescence technique, the appearance of the maximum emission band of free ligand showed at 532 nm. Upon the addition of anions the fluorescent intensity was decreased gradually. The stability constant of ligand L measured by fluorimetric titration in acetonitrile displayed the anions binding in order of CH[subscript 3]CO[subscript 2][superscript -] > F[superscript -] > H[subscript 2]PO[subscript 4][superscript -]. For cation complexation studies, ligand L was found to form a complex with copper ion selectively. Moreover, allosteric studies of transition metal induced anion complexation were carried out by fluorescence technique. Only silver ion showed the positive allosteric effect in term of the enhancement for action binding properties especially in the presence of F[superscript -] anion. In contrast, copper ion showed a negative allosteric effect because of ion-pairing.