Carboxamide based gelator molecule used for the detection of iron by turning off the aggregate-induced emission and selective sensing anion by either switching off or switching on the emission property of the metallogel.

Two organogelators G2 and G3 with a carboxamide group have been synthesized and characterized with different spectroscopic tools. Dimethylformamide or dimethyl sulfoxide solutions of both the compounds upon the addition of a minute quantity of water show the tendency to form gels. Supramolecular self-assembly for gel formation paves the way for aggregation-induced emission enhancement (AIEE) phenomena for both the gelator molecules. Introduction of metal ions in organogels strengthens the gel property without much affecting the fluorescence behavior. However, the introduction of Ag, Fe, and Fe ions in the G2 organogel separately results in total quenching of AIEE, making it possible to sense that particular cation in the gel state. The G3 organogel shows a similar behavior with the Fe ion. Remarkably, other metallogels such as Ni(II)G2 and Co(II)G2 can sense sulfide ion and Cu(II)G2 can sense iodide ion by switching off the fluorescence even in multianalyte conditions. Furthermore, the copper-based metallogel Cu(II)G2 can be utilized as a catalyst and reaction medium for aerobic oxidation of catechol to quinone. To the best of our knowledge, this is the first attempt known so far to utilize a metallogel material for bioinspired catalysis such as catechol oxidation.

The development of metallogels widens the span of sensing activity as it opens new opportunities to develop chemosensors through metal–ligand interactions. Herein, a new nitrile-substituted 1,3,5-tricarboxamide-based gelator G4 has been fabricated and shows aggregate-induced enhanced emission (AIEE) after gelation in the presence of water. A dimethylformamide (DMF) solution of the gelator shows rapid crystallization, but addition of water to a DMF solution of gelator G4 leads to gelation at room temperature. In addition, gelator G4 was used for the formation of metallogels, and among them, the cobalt metallogel has been found to be effective for sensing l-tryptophan in the gel state through the quenching of AIEE. Interestingly, the gel is also effective in sensing bovine serum albumin protein at the nanomolar level, which contains an l-tryptophan residue. The limit of detection of Co­(II)­G4 for selective sensing of tryptophan has been found to be 2.4 × 10–8 M. To the best of our knowledge, there have been no reports to date of a metallogel being utilized to discriminate and selectively sense an amino acid and a protein. The gelation properties of the organic gelator molecule and metallogels have been explored through various spectroscopic tools and physicochemical experiments.

An ionic multifunctional gelator molecule triethylammonium 5-(3,5-bis­((1H-tetrazol-5-yl)­carbamoyl)­benzamido)­tetrazol-1-ide G7 is synthesized and characterized by spectroscopic tools and mass spectrometry. G7 tends to form a stable organogel in a mixture of N,N-dimethylformamide/dimethylsulfoxide (DMF/DMSO) and water. Introduction of different metal perchlorate salts in a DMSO solution of G7 furnished a series of metallogels M 1 G7, M 2 G7, M 3 G7, M 4 G7, M 5 G7, M 6 G7, and M 7 G7 [M1 = Fe­(III), M2 = Co­(II), M3 = Cu­(II), M4 = Zn­(II), M5 = Ag­(I), M6 = Ni, and M7 = Fe­(II)]. Among them, M 1 G7, M 3 G7, M 4 G7, M 6 G7, and M 7 G7 help individually in the synthesis and stabilization of bimetallic nanocomposites containing silver nanoparticles (AgNPs). Iron­(III)-containing nanocomposites M 1 G7AgNPs have been utilized in the form of catalysts in the reduction reaction of nitroaromatic compounds to corresponding amines with a quantitative yield. The organogel G7 has also shown the abilities to absorb different metal ions from aqueous solutions and allow selective transition of M 1 G7 from the gel state to the crystalline state. Fe­(III) formed dual metallogels with Zn­(II), which can be used for further applications. Furthermore, the nanocomposite M 1 G7AgNP powder, in the presence of the organogel G7, gets converted into a nanostructured metallogel, which shows exclusive self-healing properties. This is the first example where a nanocomposite powder contains the dual-metal system (Fe­(III) and Ag(0)) and shows a reduction catalytic property, and its nanostructured dual-metallogel form manifests the self-healing property in a fabricated metallogel.

Finding the most effective method for cancer treatment is one of the thought-provoking tasks. Drug delivery by collapsing of metallogel to the cancer cell is an appealing way out. Cancer cells have an acidic environment due to excessive accumulation of lactic acid. In this work, the novel G5 gelator with a strategically free carboxylic acid arm has been designed and fabricated and characterized by several spectroscopic and microscopic techniques. These experiments suggest the formation of an ordered supramolecular gel with clover-leaf-like morphology. Mechanical properties from rheological measurements suggest the viscoelastic nature of the gel. Furthermore, we have obtained crystals of G5 from the pure dimethyl sulfoxide solution, whereas gelation gets induced by addition of water. This G5 gelator loses its gelation capability once the carboxylate is esterified by layering with methanol, which furnished the crystals of Me-G5′ (G5′ = G5-H). Further, the G5 gelator is used for the formation of ruthenium metallogel. Interestingly, we obtained the monomeric species [Ru­(G5′)­(η6-p-cymene)­Cl] [Ru­(II)­G5] only in confined gel space upon addition of a [Ru2(η6-p-cymene)2Cl4] dimer to G5. The Ru­(II)­G5 metallogel has an inherent anticancer property with an IC50 value of 10.53 μM for the A549 cancer cell line. Treatment of the Ru­(II)­G5 metallogel by lactic acid for mimicking the acidic environment of the malignant cell results in collapsing of the gel by releasing the ruthenium metal ion. This released ruthenium ion binds with the lactic acid derivative making the gelator G5 free and producing a new compound Ru­(II)­L, which has also shown the anticancer property. The molecular docking study revealed that the released G5 could interact with a monocarboxylate transporter to disrupt the lactate transport chain, which might induce apoptosis.