A phenanthrene-based calix[4]arene as a fluorescent sensor for Cu2+ and F−

A review on polycyclic aromatic compounds based chemosensors for toxic ions detection - Present and future perspective

This comprehensive review delves into the current landscape and future outlook of chemosensors constructed from polycyclic aromatic compounds (PACs) for the detection of toxic ions. PACs, known for their unique molecular properties, have emerged as key building blocks for the development of chemosensors due to their sensitivity, selectivity, and versatility. The review begins by providing an overview of the existing literature on PAC-based chemosensors, detailing their design principles, structural modifications, and mechanisms of ion recognition. The discussion encompasses various toxic ions, including heavy metals, anions, and other environmental pollutants, showcasing the broad applicability of PAC-based chemosensors in diverse analytical contexts. The review also highlights recent advancements in the field, exploring novel strategies and materials for enhancing the performance of PAC-based chemosensors. Furthermore, the review critically evaluates the current challenges and limitations associated with PAC-based chemosensors, offering insights into potential avenues for future research and technological development.

Presenting a new fluorescent probe, methyl(10-phenylphenanthren-9-yl)sulfane sensitive to the polarity and rigidity of the microenvironment: applications toward microheterogeneous systems

A molecule, methyl(10-phenylphenanthren-9-yl)sulfane (MPPS), with a straightforward structure, has been synthesized, characterized, and explored as a new fluorescent probe for microheterogeneous systems. The photophysical properties of MPPS have been studied through experimental and theoretical calculations using the range-separated hybrid functional CAM-B3LYP in conjunction with a 6-311++g(d,p) basis set. Theoretical calculations show that the freely rotating phenyl ring forms a 94° dihedral angle with the phenanthrene ring in the ground state. Experimentally found two absorption bands correspond to the n → π* and π → π* transitions supported by the frontier molecular orbital calculations. Two excited singlet states, E-1 and E-2 (the former being more stable than the latter in the gas phase), exist with dihedral angles between the phenyl and phenanthrene rings as 142° and 133°, respectively, in the gas phase. Two emitting states in a condensed medium of varying polarities are supported by the steady-state fluorescence and fluorescence intensity decay data. Emission energies, fluorescence intensities, and excited singlet state lifetimes change with the polarity of the solvents. To support that the free rotation in the molecule is responsible for these changes, the fluorescence properties of another molecule, methyl(10-(o-tolyl)phenanthren-9-yl)sulfane (MTPS), with restricted rotation of the substituted benzene, i.e., o-tolyl ring have been studied. The fast-intensity decay component of MPPS is ascribed to the conformer in the E-1 state. The molecule has proved to be an excellent polarity probe explored to determine the critical micelle concentrations (cmc) values of different surfactants, which agree well with the literature reports. Different regions of binding isotherm (specific, non-cooperative, cooperative, and massive binding) of a gemini surfactant, 12-6-12,2Br- with bovine serum albumin (BSA) have been successfully demonstrated by the steady-state and time-resolved fluorescence and fluorescence anisotropic properties of MPPS. Docking results show that MPPS resides in the hydrophobic pocket of BSA. The fluorescence quenching of BSA by MPPS reveals the location of Trp residues of BSA. Thus, a polarity and molecular rigidity-sensitive fluorescent molecule, MPPS has been presented here that can potentially be used to monitor the changes in the microenvironment of biomolecules in different processes.

Progress in appended calix[4]arene-based receptors for selective recognition of copper ions

In the past two decades, there has been significant progress in the design and development of synthetic receptors for molecular recognition as they find application in the field of chemical, biological, medical, and environmental sciences. Synthetic receptors based on calix systems appended with fluorogenic and chromogenic groups have gained considerable attention for sensing and recognition of ions and molecules. Copper (Cu2+) is an essential element required in trace amounts in all living organisms to carry out various biological processes. The aim of this review is to summarize advancement in π-conjugated fluorogenic and chromogenic groups appended to calix[4]arene motifs for detection and quantitation of Cu2+ ion. The focus is to present a comprehensive account of extended calix[4]arene systems with different linkers and highlight the unique design and binding characteristics for the recognition and sensing of Cu2+ ions.

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.

A Cr(VI) selective probe based on a quinoline-amide calix[4]arene

A new quinoline-amide calix[4]arene 3-receptor for detection of hazardous anions and cations have been synthesized. The 3-receptor was examined for its sensing properties towards several different anions (Cr₂O₇^2-, SCN^-, F^-, Cl^-, NO₃^-) and metal ions (Hg²⁺, Cd²⁺, Ag⁺) by UV-vis and fluorescence spectroscopies. It was detected that the 3-receptor has only sensing ability for Cr₂O₇^2- and Hg²⁺ ions, resulting in the association constants higher for Cr₂O₇^2- than to the Hg²⁺ ions. High selectivity towards Cr₂O₇^2- were also observed by fluorescence measurement among other ions (F^-, Cl^-_, SCN^-, Hg²⁺, Cd²⁺, Ag⁺) with a low limit of detection (7.36×10^-6moldm^-3). Proton NMR anion-binding investigations revealed a strong interaction of Cr₂O₇^2- anion with NH and CH groups of the receptor, showing that the combination with hydrogen-bonds donor groups strengthened the anion receptor association. Furthermore, remarkable association constants for dichromate anion obtained by all techniques strongly suggest the 3-receptor as a selective Cr(VI) sensor.

Fluorescence in complexes based on quinolines-derivatives: a search for better fluorescent probes

Quinoline-derived fluorescent complexes were designed; synthesized by the reaction of 5-nitro-8-hydroxyquinoline and 5-chloro-8-hydroxyquinoline with Al(3+), Mg(2+), Zn(2+), and Cd(2+) salts (1-8); and characterized. The (1)H NMR spectra of complexes 1 and 5, containing Al(3+), were consistent with an octahedral structure having approximate D3 symmetry, and the results supported the favored facial isomer (fac). Data for complexes 2-4 and 6-8 supported the formation of tetrahedral structures. Intense luminescence was detected for complexes 5-8, even with the naked eye, as indicated by quantum yield values of 0.087, 0.094, 0.051, and 0.021, respectively. Furthermore, in contrast to 5-nitro-8-hydroxyquinoline, the 5-chloro-8-hydroxyquinoline ligand exhibited bands at different energies depending on the coordinated metal, which supported its potential application in ionic and biological probes, as well as in cell imaging.

A novel tripodal colorimetric and fluorescence "turn on" chemosensor for AcO(-) and F(-) anions in CH3CN

A novel chemosensor, 3',3‴,3‴″-(((nitrilotris(ethane-2,1-diyl))tris(azanylylidene))tris(methanylylidene))tris(4-hydroxy-4'-biphenylcarbonitrile) (L) was synthesized and characterized by the combination of (1)H,(13)C, APT, COSY NMR, FT-IR, and elemental analysis. The behavior of the receptor (L) toward different anions was investigated using UV-visible and fluorescence spectroscopy. The receptor (L) indicated an efficient colorimetric "naked-eye" and "turn on" fluorescent response for fluoride and acetate in CH3CN, respectively.

Salicylyl Fluorene Derivatives as Fluorescent Sensors for Cu(II) Ions

Two derivatives of fluorene containing salicylic acid groups are successfully synthesized by palladium-catalyzed coupling reactions and subsequent hydrolysis of salicylate esters. The compounds are characterized by various spectroscopic methods. In phosphate buffer (pH 8.0) solutions, these compounds are well soluble. They show maximum absorption wavelengths in the range of 304-330 nm and exhibit maximum emission wavelength around 420 and 430 nm with the quantum yields of 2.7 and 4.4 %, respectively. The compound with alkynyl salicylate groups (2) exhibits a selective fluorescence quenching towards Cu(II) and Fe(II) with a relatively similar sensitivity. The selectivity favoring Cu(II) over Fe(II) and other metal ions can be achieved upon the addition of 30 μM Triton X-100. The Cu(II) detection limit in solution phase is 1.47 ppb. The fluorescence signal recovery upon the addition of EDTA indicate a reversible complexation between 2 and Cu(II) ion. Fabrication of 2 on filter paper using a 50 μM solution in THF affords a naked-eye detection for Cu(II) and Fe(II) in aqueous media at picomole level.

Selective chromo-fluorogenic molecular sensor for dual channel recognition of Cu2+and F−: effect of functional group on selectivity

The amido-Schiff base (3-hydroxy-naphthalene-2-carboxylic acid(4-cyano-benzylidene)-hydrazide) shows dual mode sensibility towards Cu²⁺and F⁻. It can detect Cu²⁺in HEK 293 cells and F⁻in tooth paste and in solid state.

Dual mode selective chemosensor for copper and fluoride ions: a fluorometric, colorimetric and theoretical investigation

Sensor1can detect both copper and fluoride ions selectively in dual sensing mode. Moreover, it has been found to exhibit good membrane permeability for the detection of Cu²⁺in HEK 293 cells.