Design, Synthesis and Characterization of Organic Receptors for the Selective Detection of Biologically and Environmentally Important Anions

Abstract

Nature in its fullest form is a reservoir of biochemical processes, regulated by various ionic species, which are primarily known to sustain the ecological balance in the living system. Among them, anions such as fluoride (F‒), dihydrogen phosphate (H2PO4‒), acetate (AcO ‒) and cyanide (CN‒) have profound impact on human health, both beneficial and detrimental, depending on the amount present in the living system. In this direction, design and synthesis of artificial organic receptors have garnered great attention to mimic molecular recognition at physiological level. Owing to the profound utility of the artificial receptors, the present work has been focused towards rational design of organic receptors which can aid the colorimetric detection of anions. Seven different series of receptors based on various backbones following binding site-signaling unit approach have been designed, synthesized and characterized by standard spectroscopic techniques. The anion binding ability of the receptors have been evaluated in appropriate solvent system and confirmed by UV-Vis titration, 1H-NMR titration, cyclic voltammetric and DFT studies. The binding constant and binding ratio have been evaluated using Benesi-Hildebrand (B-H) equation and B-H plot respectively. The lower detection limit values of the receptors achieved towards active anions signifies their efficacy in real life applications. Biological applications of the selected active receptors such as DNA binding studies; detection of F‒ in sea water and commercially available mouthwash; detection of H2PO4‒ in detergents; detection of AcO‒ ions in vinegar and bacterial culture and detection of CN‒ ions in sprouting potatoes prove their utility as chemosensors. The sol-gel transition of the organic receptors in the presence of anions highlights the utility of soft materials in the sensor applications. Based on the experimental findings, it could be concluded that artificial organic receptors are potent candidates to mimic molecular recognition at physiological level.