Design, Synthesis and Characterization of Colorimetric Receptors for the Detection of Biologically and Environmentally Important Anions and its Applications

Abstract

Nature in its fullest form is a reservoir of biochemical processes regulated by various ionic species, which are primarily known to sustain ecological balance in the living system. Among them, anions such as fluoride (Fˉ), acetate (AcOˉ), dihydrogen phosphate (H2PO4ˉ), carbonate (CO32ˉ), arsenite (AsO2ˉ), arsenate (AsO42 ),־and dicarboxylates have a profound impact on human health, which are both beneficial and detrimental, depending on the amount present in the living system. Apart from the above anions detection, the detection of sodium fluoride and acetate ions in aqueous medium is important due its importance in household usage in the form of food, medicine, and cosmetics. Beyond an optimum amount, anions can lead to health issues. In this direction, the design and synthesis of artificial organic receptors has garnered great attention due to its ability to mimic molecular recognition at the physiological level. Owing to the profound utility of artificial receptors, this work focuses on the rational design of organic receptors, which can aid the colorimetric detection of anions. Seven different series of receptors based on various backbones, following binding sitesignalling unit approach, has been designed, synthesized, and characterized by standard spectroscopic techniques. The anion binding ability of the receptors is evaluated in appropriate solvent systems and confirmed by UV-Vis titration, 1H-NMR titration, Cyclic voltammetric, and DFT studies. The binding constant for the receptor-anion complex is calculated using the Benesi–Hildebrand equation. The binding mechanism is proposed based on UV-Vis titration and the same is confirmed by 1H NMR titration. The lower detection limit valves of the receptors achieved towards active anions signifies their efficacy in real- life application. Based on the experimental results, it is concluded that simple organic molecules can act as very good colorimetric receptors for biologically important anions such as Fˉ, AcOˉ, H2PO4ˉ, dicarboxylate, and CO32ˉ. Along with colorimetric detection, these receptors exhibited practical application such as detection of Fˉ ion in sea water, commercially available mouthwash and toothpaste, detection of AcOˉ ion in vinegar solution and test strip application.