Thiacalix[4]arene-tetra-(quinoline-8- sulfonate): a Sensitive and Selective Fluorescent Sensor for Co (II)

Selective detection of Fe3+ via fluorescent in real sample using aminoanthraquinone resorcin[4]arene-based receptors with logic gate application

Resorcin[4]arene based fluorescent sensors RES-AAQ containing eight anthraquinone groups as binding sites, were developed for very accurate and sensitive detection of Fe3+ metal ion. The motivation for this study lies in the need for advanced sensing techniques for precisely identifying Fe3+ ions. Due to its unique redox properties, Fe3+ plays a crucial role in biological processes, environmental remediation, medical diagnostics, and advanced detection methods. The sensors were extensively characterized using FT-IR, 1H NMR, 13C NMR, and ESI-MS techniques. The absorption spectra revealed significant interactions between RES-AAQ and Fe3+ ions. Fluorescence quenching was observed due to Photoinduced electron transfer (PET). The quenching process was systematically analyzed using Stern-Volmer analysis. Each sensor (L1, L2, L3, L4) demonstrated remarkable detection limits for Fe3+ ions (10.51 nM, 10.48 nM, 10.49 nM, 10.47 nM, respectively) along with substantial binding affinities (binding constants: 9.07x109 M-1, 1.19x109 M-1, 1.49x109 M-1 and 1.03x109 M-1 for L1, L2, L3, and L4, respectively). Traditional, Fe3+ detection methods often suffer from limitations such as complexity, lack of sensitivity, or interference from other metal ions. This research offers highly sensitive fluorescent sensors for Fe3+ detection with potential applications in human blood serum and tap water. Molecular docking, DFT studies, and ESI-MS investigation have been employed to gain insights into the binding interactions between the molecules. The low detection limits, high binding affinity, and real-world applicability highlight the significant advantages of developed sensors compared to existing methods. Additionally, a combinatorial logic gate was constructed to facilitate a proper understanding of the working principle of RES-AAQ.

Benzene Sulfonyl Linked Tetrasubstituted Thiacalix[4]arene for Selective and Sensitive Fluorometric Sensing of Sulfosulfuron along with Theoretical Studies

Herein, we designed two fluorescent tetrasubstituted benzene sulfonyl appended Thiacalix[4]arene receptors named L1 and L2, which sensitively and selectively detect Sulfosulfuron among other herbicides and pesticides. The detection limit (LOD) was found to be 0.21 ppm and 0.35 ppm, and the enhancement constant (Ks) was determined to be 7.07 X 104 M-1 and 5.55 X 104 M-1 for L1 and L2, respectively. Using the non-linear regression method, the association constant was obtained as 2.1 X 104 M-1 and 2.23 X 104 M-1 whereas, the binding ratio was found to be 1:1 for both L1 and L2, respectively. Additionally, the interference studies show the selective nature of receptors for Sulfosulfuron among its sulfonylurea family. To further confirm the interaction mechanism, 1H-NMR spectroscopy, and a computational investigation were carried out, which validates the 1:1 binding ratio. The receptors were found to be recyclable in nature with simple acid-base treatment. This new approach of using supramolecules as fluorescent probes for sensitive and selective detection of herbicides is rare in the literature.

Tailored calix[4]arene-gold nanoconjugate as a ultra-sensitive immunosensing nanolabel

The construction of highly sensitive and specific immunosensing nanolabels have attracted tremendous attention in the development of reliable point-of-care disease diagnostics. However, there are still challenges with traditional immunoassays, such as complicated and time-consuming procedure, the use of enzyme label, non-specificity, and require readers for detection. Therefore, we have designed and developed site-directed antibody-immobilized calix[4]arene-gold nanoconjugate based colorimetric immunosensing nanolabel to offer high sensitivity. The prepared nanolabel enabled oriented binding of the antibodies by providing full accessibility of Fab domain for antigen binding. The improved sensitivity of the developed nanolabel was evaluated using vertical flow immunoassay (VFIA) for detecting C-reactive protein (CRP) with a lower detection limit up to 1 ng/ml. Our developed nanolabel was found to be highly specific, easy, quick, and appropriate for onsite detection. The nanolabel is validated with spiked blood samples which exhibited ~90% recovery having a relative error of ~2%. Furthermore, the nanolabel was also used for screening of human blood real samples which showed relative error of ~0.6%. The developed nanolabel can be utilized as a potential nanolabel for the quantitative detection of various biomolecules in clinical samples.

Pyrene functionalized oxacalix[4]arene architecture as dual readout sensor for expeditious recognition of cyanide anion

A pyrene functionalized oxacalix[4]arene architecture (DPOC) was utilized as a fluorescence probe for selective recognition of cyanide ions. The receptor DPOC shows excellent selectivity towards cyanide ion with a red shift of 108 nm in absorption band along with a significant change in colour from light yellow to pink. The fluorescence titration experiments further confirm the lower limit of detection as 1.7µM with no significant influences of competing anions. ¹ H-NMR titration experiments support the deprotonation phenomena, as the -NH proton disappears upon successive addition of cyanide ions. The DFT calculation also indicates a certain increment of -NH bond length upon interaction with cyanide ions. The spectral properties as well as colour of DPOC-CN^- system may be reversed upon the addition of Ag⁺/ Cu²⁺ ions up to 5 consecutive cycles. Moreover, DPOC coated "test strips" were prepared for visual detection of cyanide ions.

A New Benzothiazin-functionalized Calix[4]arene-based Fluorescent Chemosensor for the Selective Detection of Co2+ Ion

Calixarenes, which have a great place in supramolecular chemistry, have become the most prominent macrocyclic compounds in synthetic organic chemistry due to their easy synthesis and functionalization. In this study, p-tert-butyl calix[4]arene dihydrazide derivative was synthesized and then reacted with 3-oxo-3,4-dihydro-2 H-benzo[b][1,4] thiazin-2-ylideneacetyl chloride to prepare new calixarene based chromophore compound 4. The structure of the synthesized compound was elucidated by spectroscopic methods such as 1H NMR 13C NMR and FT-IR spectroscopy. Chromogenic and fluorescence properties of compound 4 were evaluated. It was observed from both studies that compound 4 was Co2+ selective and shows fluorescence Switched-off behavior. Stoichiometry, binding constant and the detection limit were calculated. The stoichiometry between compound 4 and Co2+ was found to be 1:1. The binding constant value (K) was calculated as 666.67 M- 1 using Benesi-Hildebrand equation, while the detection limit for Co2+ ion was calculated as 0.0465 µM.

Synthesis of new anthracene-substituted calix[4]triazacrown-5 as highly sensitive fluorescent chemosensor and extractant against hazardous dichromate anion

A new fluorogenic anthracene functionalized calix[4]triazacrown-5 (Ant-AzClx) was successfully synthesized using a simple Schiff's base reaction. The ¹ H-NMR, ¹³ C-NMR, ESI-MS, and elemental analysis techniques were performed to characterize its structure. Excited at 370 nm, Ant-AzClx reveals excimer emission at 418 nm. Therefore, its anion binding properties were investigated against F^- , HCO₃ ^- , H₂ PO₄ ^- , NO₃ ^- , Cr₂ O₇ ^2- , and SO₄ ^2- ions. When hazardous dichromate anion was introduced into medium, the fluorescence intensity of Ant-AzClx was markedly quenched. The binding constant, stoichiometry, the detection limits and Stern-Volmer equation for the complex formed between Ant-AzClx and Cr₂ O₇ ^2- ion were determined. Furthermore, the ¹ H-NMR technique was also performed to assess the mechanism of the complex (Ant-AzClx@Cr₂ O₇ ^2- ). Apart from its excellent fluorescent chemosensor properties for selective and sensitive recognition of Cr₂ O₇ ^2- ion, Ant-AzClx was used as an efficient extractant towards dichromate anion. The extraction results indicated that Ant-AzClx exhibited high extraction capability, leading to it being a promising extractant for the removal of dichromate anions from water.

Synthesis of New Quinoline-Conjugated Calixarene as a Fluorescent Sensor for Selective Determination of Cu2+ Ion

A novel quinoline-functionalized calix [4] arene derivative (Quin-Calix) has been successfully synthesized at partial cone conformation and duly characterized by using FTIR, ¹H-NMR, ¹³C-NMR, ESI-MS and elemental analysis techniques. Moreover, the cation-binding property of the calix [4] arene derivative (Quin-Calix) has been investigated towards Cu²⁺, Ba²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Fe³⁺ ions, and the recognition event monitored by UV-Vis absorption and fluorescence studies. The results indicated that Quin-Calix displays a remarkable affinity and selectivity only for Cu²⁺ ion. The binding constant and stoichiometry of the complex formed between Quin-Calix and Cu²⁺ ion have been also calculated from the fluorescence data. In addition, Stern-Vohmer equation has been used to elucidate the mechanism of quenching.

Selective Detection of Cu2+ Ions by Immobilizing Thiacalix[4]arene on Graphene Field-Effect Transistors

Highly accurate quantitative detection of heavy metals is essential for environmental pollution monitoring and health safety. Here, for selective detection of Cu2+ ions with high sensitivity, thiacalix[4]arene (TCA) immobilized on graphene field-effect transistors (G-FETs) are developed. Our proposed TCA-immobilized G-FETs are successfully used to detect Cu2+ ions at concentrations ranging from 1 μM to 1 mM via changes in their transfer characteristics. Moreover, the measured transfer characteristics clearly shift only when Cu2+ ions are introduced in the buffer solution despite it containing other metal ions, including those of Na+, Mg2+, Ni2+, and Cd2+; this selective detection of Cu2+ ions is attributed to the planar arrangement of TCA on graphene. Therefore, TCA-immobilized G-FETs selectively detect Cu2+ with high sensitivity.

Selectivity for La3+ ion by synthesized 4-((5-methylfuran-2-yl)methylene)hydrazono)methyl)phenol receptor and its spectral analysis

The functionalized molecules with specific molecular sites appear to be a promising approach for detection of cation in UV-visible and fluorescence spectroscopy. The synthesized receptor 4-((5-methylfuran-2-yl)methylene)hydrazono)methyl)phenol MFMHMP was found selective for La³⁺ among Ag⁺, K⁺, Na⁺, Be²⁺, Mg²⁺, Ca²⁺, Eu³⁺, Al³⁺, La³⁺, Zr⁴⁺, Th⁴⁺, UO₂²⁺, Fe³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺ metal ions used as their nitrates by UV-visible spectroscopy and fluorescence spectroscopy. The binding nature of MFMHMP with La³⁺ ion was analyzed by UV-visible, fluorescence, IR, mass spectroscopy and cyclic voltammetric studies. The stoichiometry was established to be 1:1 by Benesi-Hildebrand, mole-ratio method and method of continuous variation (Job's method) with good association affinity K = 6.245 × 10⁴ M^-1. Computational studies and Density functional theory (DFT) calculation gives the proof of electron transfer during excitation and emission. Binding energy of complex through Density Function Theory -62.387 kcal/mol has also indication of strong binding. The electron transfer energy of Higher occupied molecular orbital (HOMO) to Lower unoccupied molecular orbital (LUMO) is about 4.662 eV for MFMHMP+La³⁺ Complex. Among that all transitions HOMO → LUMO + 8 and HOMO → LUMO + 9 play a key role for the blue shift transition during complexation.

Ameliorative effects of quercetin against bisphenol A-caused oxidative stress in human erythrocytes: an in vitro and in silico study

Bisphenol A (BPA) is an endocrine disruptor of xenobiotic type, mainly used for the production of polycarbonate plastic, epoxy resins and non-polymer additives. Because of its wide usages in the environment, the toxic effects of BPA have proved to be harmful to human health. However, its effects on human haemoglobin remain unclear. The affinity between BPA and haemoglobin, as well as erythrocytes, is an important factor in understanding the mechanism of the toxicity of BPA. Flavonoids are strong antioxidants that prevent oxidative stress and Quercetin is a flavonoid found in numerous vegetables and fruits. Therefore, the present investigation was undertaken to investigate whether Quercetin can be used to alleviate the toxic effects of BPA in vitro in human red blood cells (RBC). Venous blood samples were collected from healthy, well-nourished adult volunteers (25-30 years old) by phlebotomy. In a RBC suspension with a cell density of 2 × 104 cell per mL, the concentration of BPA (25-150 µg mL-1) was found to cause an increase in the lipid peroxidation (LPO) and a decrease in the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in human RBC. However, the concurrent addition of BPA (150 µg mL-1) and quercetin (10-50 µg mL-1) lead to significant amelioration. In silico studies gave structural insight into BPA and quercetin to decipher the plausible binding mechanism and molecular level recognition.

Pharmacophore-based virtual screening of catechol-o-methyltransferase (COMT) inhibitors to combat Alzheimer's disease

Alzheimer's disease (AD) is one of the most significant neurodegenerative disorders and its symptoms mostly appear in aged people. Catechol-o-methyltransferase (COMT) is one of the known target enzymes responsible for AD. With the use of 23 known inhibitors of COMT, a query has been generated and validated by screening against the database of 1500 decoys to obtain the GH score and enrichment value. The crucial features of the known inhibitors were evaluated by the online ZINC Pharmer to identify new leads from a ZINC database. Five hundred hits were retrieved from ZINC Pharmer and by ADMET (absorption, distribution, metabolism, excretion, and toxicity) filtering by using FAF-Drug-3 and 36 molecules were considered for molecular docking. From the COMT inhibitors, opicapone, fenoldopam, and quercetin were selected, while ZINC63625100_413 ZINC39411941_412, ZINC63234426_254, ZINC63637968_451, and ZINC64019452_303 were chosen for the molecular dynamics simulation analysis having high binding affinity and structural recognition. This study identified the potential COMT inhibitors through pharmacophore-based inhibitor screening leading to a more complete understanding of molecular-level interactions.