Instantaneous and Selective Bare Eye Detection of Inorganic Fluoride Ion by Coumarin–Pyrazole‐Based Receptors

Abstract

A series of rationally designed coumarin–pyrazole‐based scaffolds, equipped with N―H and C―H hydrogen bond donors (R1–R5) and containing various electron‐withdrawing groups at key positions, are synthesized and characterized in order to investigate their inorganic fluoride binding properties in highly competitive media (1:1 DMSO–water). Only one, 3‐{4‐[(2,4‐dinitrophenyl)‐hydrazonomethyl]‐1‐phenyl‐1H‐pyrazol‐3‐yl}‐chromen‐2‐one (R1), of the five compounds synthesized, is found to be capable to selectively detect inorganic fluoride via naked eye amongst other anionic species in aqueous media. Qualitative and spectroscopic studies exhibit that receptor R1 has the potential of showing instantaneous change of color from yellow to pink upon addition of sodium fluoride (0.95 ppm) in aqueous media, at concentration lower than that recommended by World Health Organization (1 ppm). Intensity of color increases with increasing fluoride concentration till 5 ppm, beyond which intensity of color change becomes saturated. This has established the applicability of this receptor for assessment of the level of fluoride in water. Anion binding studies carried out by UV–visible titration portrayed substantial bathochromic peak shift from 410 to 495 nm, upon addition of varying concentrations of aqueous sodium fluoride solution, which has validated the color change. Jobs plot data confirmed 1:1 stoichiometry between R1 and fluoride ion. 1H‐NMR investigation reveals that the deprotonation of N―H hydrogen donor group of receptor R1 and its interaction with fluoride ion is responsible for the observed color change.

Chemical Waltz of Organic Molecules “On Water”: Saline-Assisted Sustainable Regioselective Synthesis of Fluorogenic Heterobioconjugates via Click Reaction

“…Inspired by recent reports on bio-orthogonal chemistry exploiting weakly or nonfluorescent reagents to produce highly fluorescent molecules, which could be exploited for tagging of biomolecules in living systems, especially in aqueous medium, − and in continuation to our previous work on fluorescent coumarin-based compounds, − herein, we describe a green protocol for the preparation of heterobioconjugate-based 1,4-disubsituted 1,2,3-traizoles through a 1,3-dipolar cycloaddition reaction using NaCl as a salting-out agent in water under ultrasonic irradiation at ambient temperature. Additional advantage of this protocol is recycling of the traditional Cu­(I) catalytic system up to seven cycles, which enhances the viability of this method by reducing the loading of toxic Cu.…”

Recent progress in chemosensors based on pyrazole derivatives

“…The probe was proposed as a simple and selective semi qualitative naked-eye chemosensor for uoride. 137 Fused-pyrazole derivatives have also been tested for uoride recognition, and an astonishing example was reported by Hu and his team in which a simple anthra [1,9-cd]pyrazol-6(2H)-one chemodosimeter 26 was designed for the highly selective and sensitive detection of F À ions (Fig. 13d).…”

3-[2-Oxo-2H-chromen-3(6)(8)-yl]-1-aryl/heteroaryl-1H-pyrazole-4-carbaldehydes: Synthesis, Reactions and Applications

“…Moreover, different biochemical and synthetic studies confirmed the hypothesis that the coumarinyl-pyrazole moiety is a basic structural motif for producing bioactive components in drug discovery. Coumarinyl-pyrazole compounds exhibited biologically properties such as anti-TB, 24 antioxidant, 25,26 anticancer, 27,28 antihyperglycemic agents, 25 antimicrobial, 29,30 antibacterial, 31 antiproliferative, 28,32 and PDE inhibitor. 33 With a part of our ongoing studies on biologically active relevant heterocycles, [34][35][36][37][38][39][40] we make a serious effort to present concise review focusing on the synthesis, reactions and applications of diverse 3-(2-oxo-2H-chromen-3(6)(8)-yl)-1-aryl/heteroaryl-1H-pyrazole-4carbaldehydes and related compounds.…”