Trifluoromethyl group containing C3 symmetric coumarin-triazole based fluorometric tripodal receptors for selective fluoride ion recognition: A theoretical and experimental approach

Fluorescent calix[4]triazole for selective fluoride anion sensing

Fluoride ions (F-) play an important role in preventing cavities and treating osteoporosis, but excessive exposure can lead to serious health problems such as fluorosis and kidney damage. These dual characteristics highlight the need for selective and sensitive methods to detect fluoride ions for health monitoring. Accordingly, in this study, we investigated the anion-binding ability of Py-CT4, a fluorescent chemosensor in which pyrene is linked to calix[4]triazole via an ester linker. Notably, Py-CT4 exhibited significant fluorescence quenching for F- compared to other anions, and its fluorescence intensity gradually decreased with increasing F- concentration. This phenomenon is driven by electron transfer from calix[4]triazole to pyrene, initiated by hydrogen bonding with F- and followed by F--induced deprotonation of calix[4]triazole. The selectivity of Py-CT4 for F- appears to stem from its relatively flexible structure and low acidity compared to the previously reported Py-CT4+. Py-CT4 thus represents the first macrocyclic receptor based on charge-neutral 1,2,3-triazole that selectively recognizes F- through fluorescence quenching. Compared to traditional detection methods, Py-CT4 utilizes the advantages of fluorescent detection, such as higher sensitivity, faster response times, and ease of use, for fluoride ion detection. Py-CT4 also demonstrates excellent selectivity for F- even in the presence of competing anions. These features make Py-CT4 a promising tool for monitoring fluoride ions in biological and environmental systems, providing valuable insights into public health and safety.

Highly Efficient, Tripodal Ion-Pair Receptors for Switching Selectivity between Acetates and Sulfates Using Solid-Liquid and Liquid-Liquid Extractions

A tripodal, squaramide-based ion-pair receptor 1 was synthesized in a modular fashion, and ¹H NMR and UV-vis studies revealed its ability to interact more efficiently with anions with the assistance of cations. The reference tripodal anion receptor 2, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by presence of cations. Besides the ability to bind anions in enhanced manner by the “single armed” ion-pair receptor 3, the lack of multiple and prearranged binding sites resulted in its much lower affinity towards anions than in the case of tripodal receptors. Unlike with receptors 2 or 3, the high affinity of 1 towards salts opens up the possibility of extracting extremely hydrophilic sulfate anions from aqueous to organic phase. The disparity in receptor 1 binding modes towards monovalent anions and divalent sulfates assures its selectivity towards sulfates over other lipophilic salts upon liquid–liquid extraction (LLE) and enables the Hofmeister bias to be overcome. By changing the extraction conditions from LLE to SLE (solid–liquid extraction), a switch of selectivity from sulfates to acetates was achieved. X-ray measurements support the ability of anion binding by cooperation of the arms of receptor 1 together with simultaneous binding of cations.

Antipyrine based Schiff's base as a reversible fluorescence turn "off-on-off" chemosensor for sequential recognition of Al3+ and F- ions: A theoretical and experimental perspective

A Schiff's base probe (L) based on antipyrine has been intended, synthesized and assessed as a turn "off-on-off" probe for successive recognition of Al³⁺ and F^-. The probe L act out as a turn "on" fluorescence probe towards Al³⁺ in methanol at pH 6 which turned "off" by F^- at 433 nm. The 1:1 binding stoichiometry of L + Al³⁺ complex was revealed by Job's plot and approved by ESI-HRMS data. The binding constant and limit of detection of probe L for Al³⁺ were found to be 2.951 × 10⁷ M^-1 and 0.61 × 10^-7 M respectively, which is lesser than the acceptable limit (0.74 × 10^-7 M) in drinking water. The proposed binding sites and the mode of interaction of probe L was studied and validated by ¹H NMR titration and ²⁷Al NMR spectroscopic studies. To get detailed vision into binding mechanism and optimized structure of receptor L and L + Al³⁺, L + Al³⁺ + F^- complex, theoretical calculations using DFT/DND and TDDFT method were performed. Furthermore, probe L can mimic INHIBIT logic function using Al³⁺ and F^- being logic inputs and examining the fluorescence maxima at 433 nm as output.

Traditional hydrogen bonding donors controlled colorimetric selective anion sensing in tripodal receptors: First-naked-eye detection of cyanide by a tripodal receptor via fluoride displacement assay

Here in we report tris (3-aminopropyl) amine based tripodal receptors L, L¹ and L² which were functionalized with 4-nitrophenyl moieties having thio-urea, amide and sulfonamide as hydrogen bonding moieties respectively, shows a strong selectivity towards cyanide. A competitive colorimetric assay with L in the presence of fluoride ion suggests that the cyanide ion is much capable of displacing the bound fluoride, showing a sharp distinguishable color change. To the best of our knowledge, this is the first example of a naked-eye detection of cyanide via fluoride displacement assay by a tripodal receptor and such a displacement phenomenon is not observes in the cases of L¹ and L², instead the receptor L¹ binds nitrate and cyanide; L² binds dihydrogen phosphate and cyanide. Using this assay, we have proposed an AND logic gate using L·F^- and CN^-.

Robust synthesis of sugar-coumarin based fluorescent 1,4-disubstituted-1,2,3-triazoles using highly efficient recyclable citrate grafted β-cyclodextrin@magnetite nano phase transfer catalyst in aqueous media

Green synthesis of 1,4-disubstituted-1,2,3-triazoles via click reaction using nano magnetic Fe₃O₄ core decorated with cyclodextrin-citric acid (Fe₃O₄@CD-CIT) acting as a phase transfer nanoreactor with low copper loading under ultrasonication at 40 °C, in aqueous media is described. Anchoring the surface of magnetite with cyclodextrin (CD) prevents its agglomeration and at the same time, CD provides a hydrophobic niche for lipophilic reactants while its outer hydrophilic core makes the reaction feasible in water yielding almost quantitative yield of desired products. Magnetic separation using an external magnet, recyclability and reuse (7 times), without appreciably affecting the %yield of the products are its other attractive attributes. Gram scale synthesis was also achieved with 93% yield.

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

A new sustainable green protocol for obtaining highly fluorogenic heterobioconjugates by a well-known copper-mediated azide-alkyne cycloaddition click reaction of nonfluorescent 3-azidocoumarins/benzyl azides (2a-f) and terminal alkynes (1a-e) using aqueous NaCl as a cheap and nontoxic salting-out agent under ultrasonication at ambient temperature is described. The presence of aqueous NaCl significantly influences the reaction by disturbing the water kosmotropes and augments the hydrophobic interaction of water-insoluble reactants, thus making the reaction feasible in water at neutral pH. The "beauty" of the presented ecofriendly approach is further boosted up by recycling the aqueous filtrate of the reaction mixture without further addition of NaCl, CuSO₄·5H₂O, and Na ascorbate up to seven cycles, resulting in effectively low copper loading (100 ppm) with excellent turn-over number (4850) and turn-over frequency (88.18 min^-1). A gram-scale synthesis was also successfully achieved with 92% yield, further elaborating the scope of this methodology.