Multivalent calix[4]arene-based fluorescent sensor for detecting silver ions in aqueous media and physiological environment

Abstract

A new derivative of dipodal 1,3-calix[4]arene-based chemosensor (R), which was containing several binding sites have been synthesized and characterized by NMR, IR and LC-MS spectroscopic methods. The selectivity of Rhas been investigated in aqueous methanol, resulting in fluorescence shift and selective recognition of Ag⁺ among 20 various alkali, alkaline earth and transition metal ions. Microstructural features of R and its complex with Ag⁺have been investigated by Atomic Force Microscopy (AFM). AFM images can clearly differentiate R from its complex of Ag⁺. Moreover; the complicated binding mode of metal-ligand complex has been explored by UV-Vis, LC-MS, FIR, Fluorescence titration, Job's plot method and theoretical approaches. Density functional theory (DFT) method at B3LYP/LANL2DZ level of theory was employed for computational studies. Theoretical calculations revealed that selectivity and specificity of R toward Ag⁺ could be attributed to structural conformation of 1,3-alternate-calix[4]arene scaffold and molecular electrostatic potential of its surface. Furthermore; the competitive experiments were carried out to test sensor's ability for practical uses. Finally, the efficiency of R in matrix of physiological cations was examined and showed gradual emission enhancement which makes R an ideal candidate for monitoring of Ag⁺ in physiological environment.

Keywords: Amino thiadiazole ligand; Calix[4]arene; Cation receptor; DFT studies; Fluorescent sensor; Physiological environment; Silver(I) recognition.