Redox-Switchable Copper(I) Metallogel: A Metal–Organic Material for Selective and Naked-Eye Sensing of Picric Acid

Abstract

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

A Gel-Based Approach To Design Hierarchical CuS Decorated Reduced Graphene Oxide Nanosheets for Enhanced Peroxidase-like Activity Leading to Colorimetric Detection of Dopamine

“…43,44 Our previous study has revealed that aqueous solution of Cu 2+ and thiourea (TU) proceeds through spontaneous one electron transfer protocol involving TU and Cu 2+ which results in Cu(I) species and oxidized form of TU. 39 The presence of Cl -and water molecules in the solution are very important as they participate in weak force interaction (i.e.…”

“…It is well known that TU reduces Cu 2+ to Cu + through one electron transfer process and itself transforms into α,α′-dithiobisformidinium dichloride. 39,[47][48][49] Related crystal structure study discloses the formation of 'CuS 4 ' unit where Cu + centre experiences tetrahedral geometry through sulfur donors of TU and the oxidized dithio product. 39,50 Here it is important to note that each 'CuS 4 ' motif held together through sharing dithio product and also with extended hydrogen bonding.…”

“…38 Another interesting study has been reported again from our group involving aqueous solution of CuCl 2 and thiourea to form copper(I)-thiourea supramolecular hydrogel (Cu-TU gel). 39 All these ideas motivate us to design a hierarchical porous CuS nanostructure on rGO nanosheets for improved peroxidase activity through a new supramolecular gel based synthetic strategy.…”

A Fluorescent 1,3‐Diaminonaphthalimide Conjugate of Calix[4]arene for Sensitive and Selective Detection of Trinitrophenol: Spectroscopy, Microscopy, and Computational Studies, and Its Applicability using Cellulose Strips

“…The fluorescence quenching of R by TNP is due to an adduct formed between these components through the interaction of the phenolate anion of TNP with the protonated amine center in R that prevents the ICT 20. 24, 54…”

Selective gelation of N-(4-pyridyl)nicotinamide by copper(ii) salts

“…The selectivity of copper(II) chloride salts over other copper(II) salts in metallogel formation have been reported 51 . Recently, the selectivity of copper(II) chloride and bromide over perchlorate, nitrate, sulphate, and acetate anions was reported 52 . These studies reveal the importance of metal salts specifically copper(II) salts in metallogel formation.…”