Synthesis and anion recognition studies of novel bis (4-hydroxycoumarin) methane azo dyes

Unlocking the Molecular Behavior of Natural Amine-Targeted Carbon Quantum Dots for the Synthesis of Diverse Pharmacophore Scaffolds via an Unusual Nanoaminocatalytic Route

Despite the fact that carbon quantum dots (CQDs) have significant catalytic potential, only emblematic applications that rely on simple acid-base or hydrogen-bonding activation pathways have been reported. In this study, natural amine-targeted CQDs (NAT-CQDs) have been successfully fabricated using a sustainable technique that harnesses a renewable green source. Based on a holistic sustainable assessment, the present approach for the synthesis of NAT-CQDs surpasses previously reported methods in terms of estimated circular and good-manufacturing-practice metrics. A set of spectroscopic and analytical techniques, including FTIR, XPS, conductometric assay, pH titration, 19FNMR, and 13CNMR confirms the presence of the assessable amino-rich groups (0.0083N) at the surface of NAT-CQDs. The occurrence of surface amine groups unlocked the molecular behavior of as-prepared NAT-CQDs and makes them an unprecedented nanoaminocatalytic platform for the synthesis of diverse pharmacophore scaffolds (>40 examples) via a one-pot Knoevenagel/(aza) Michael addition reaction in water at room temperature. The assessable amine group can covalently activate carbonyl groups through nucleophilic iminium activation modes in water and facilitate the ability to build valuable and therapeutic scaffolds on a gram scale. By transferring significant molecular primacy at the frontier of nanoscale materials, NAT-CQDs can thus bridge the gap between the nanoscale and molecular domains. This protocol can also be applied for the preparation of therapeutic anticoagulant drugs, warfarin, and coumachlor. All the reactions exhibited a high atom economy, low E-factor, low process mass intensity (PMI), high reaction mass efficiency (RME), high carbon efficiency (CE), and high catalyst reusability with overall high sustainable values. NAT-CQDs show high recyclability, and the spectral data of reused catalysts indicate that the NAT-CQDs maintained their surface chemistry and electronic properties, suggesting their stability under the tested conditions. This study presents a remarkable instance of NAT-CQDs showcasing covalent catalysis. Expanding on the aforementioned design concept, the utilization of NAT-CQDs' "potential" as distinct colloidal organocatalysts in aqueous environments at the molecular level introduces valuable prospects for aminocatalytic pathways.

(E)-3-(2-(4-methylthiazol-2-yl)hydrazineylidene)chromane-2,4-dione

(E)-3-(2-(4-methylthiazol-2-yl)hydrazineylidene)chromane-2,4-dione was synthesized for the first time and the compound was characterized by 1H and 13C spectroscopy, IR spectroscopy, and UV-Vis. The chemical structure and isomeric configuration of the molecule were confirmed by single-crystal X-ray diffraction.

Synthesis, characterization and biological investigations of potentially bioactive heterocyclic compounds containing 4-hydroxy coumarin

In this paper, we have reported the synthesis of a series of heterocyclic azo dyes containing 4-hydroxy coumarin by diazo-coupling reaction. The structural aspect of the newly synthesized compounds was accomplished by various physico-chemical techniques like UV-Visible, FT-IR, NMR, and mass spectrometry. The computational calculations and geometrical optimization of the newly synthesized azo dyes were investigated by using Gaussian software with the help of Density functional theory (DFT)/B3LYP method using 6-31G(d,p) basis set at gaseous phase. Also, the quantum chemical parameters were evaluated to understand the structural activity concept of the dyes. The pharmacological efficacy of the azo dyes was investigated by antimicrobial, antitubercular, DNA cleavage and in silico molecular docking studies. All the newly synthesized compounds were able to exhibit significant inhibitory activity against tested microbes. Further, the in silico molecular docking showed effective binding properties of the compounds against RpsA target receptor.

Triazole derived azo-azomethine dye as a new colorimetric anion chemosensor

In the pursue of developing anion sensors, an efficient triazole derived azo-azomethine dye chemosensor (S) that differentially senses F‾ and AcO‾ ions has been reported. The ions recognition ability of S was investigated by colorimetric and UV-visible spectroscopic methods. Interestingly, this chemosensor molecule is virtually inactive in presence of other anions such as Cl‾, Br‾ and I‾ and HSO₄‾. We have further presented a ratiometric approach to differentiate F‾ and AcO‾ ions. The reversibility of F‾ ion binding with S was established by the addition of Ca(NO₃)₂ to the fluoride bound S, which led to the regeneration of S. The quantum chemical calculation of energies of unbound and bound S has been employed using Density Functional Theory (DFT) to understand the interaction between chemosensor and anions. Evidence in support of fluoride-induced deprotonation of a O-H bond during the detection of F⁻ ion has been demonstrated by employing ¹H NMR titration experiments.

Chromogenic hydrazide Schiff base reagent: Spectrophotometric determination of CN- ion

A Schiff base reagent, Picolinohydrazide-naphthol (HL), is used for trace level detection of toxic CN^- selectively in presence of eighteen other anions (SCN^-, OCN^-, S₂O₃^2-, HPO₄^2-, H₂PO₄^-, I^-, ClO₄^-, HSO₄^-, SO₄^2-, AsO₄^3-, NO₂^-, AsO₂^-, Cl^-, F^-, HF₂^-, NO₃^-, Br^-, N₃^-) by visual color change, colorless to yellow, in DMSO/H₂O (9:1, v/v) at pH, 7.2 (HEPES buffer) medium. The sensitivity of the probe shows that the limit of detection (LOD) is 7.08 μM. The probable mechanism for the sensing behavior involves the deprotonation of naphthol-OH by CN^- that has been authenticated by ¹H NMR titration and Mass spectra. The composition (1:1 mol ratio) is supported by Job's plot and binding constant (K_a, 1.5 × 10⁴ M^-1) is reported by Benesi-Hildebrand plot. Furthermore, a simple paper strip device is fabricated for the determination of CN^- ion in water. DFT computation is carried out to explain the electronic spectral feature of the sensor.

Visual detection of cyanide ion in aqueous medium by a new chromogenic azo-azomethine chemosensor

A simple and new chromogenic azo-azomethine chemosensor N'-(5-((2,4-dichloro- phenyl) diazenyl)-2-hydroxylbenzylidene) picolinohydrazide (L) has been synthesized as an effective colorimetric sensor for cyanide ion. The sensing behavior of the probe L towards CN^- over other anions was examined by naked-eye, UV-vis spectroscopy and NMR studies. L exhibited a selective sensing ability to CN^- in DMSO/H₂O(6:4, v:v) binary solution and DMSO/Tris(10 mM, pH = 7.1, 6:4, v:v) buffer solution by changing color from colorless to yellow. The detection limit was calculated to be 6.4 μM. The recognition mechanism was attributed to deprotonation process according to ¹H NMR titration method. Moreover, test strips coated with L were easily fabricated with low cost and could be used to detect CN^- in aqueous solution conveniently.

‘Naked-eye’ colorimetric/fluorimetric detection of F− ions by biologically active 3-((1H-indol-3-yl)methyl)-4-hydroxy-2H-chromen-2-one derivatives

An improved synthetic protocol has been developed to construct highly functionalized heterologous alkyl and benzyl indolyl-coumarin derivatives using a rapid, catalyst-free and solvent-free one-pot three-component reaction of indole, aldehyde and 4-hydroxy-coumarin.