A Review on Pyrazolines as Colorimetric Fluorescent Chemosensors for Cu2

The Pyrazoline derivatives display promising potential as sensitive and selective chemosensors for detecting Cu2+ ions. It has undergone screening for its sensing behavior with various metals using absorption, emission spectroscopic techniques. Their unique structure incorporates both donating and accepting sites, characterized by delocalized orbitals. These derivatives exhibit notable chromogenic and fluorogenic capabilities facilitated by intramolecular charge transfer. The sensors based on pyrazoline demonstrate exceptional selectivity, low detection limits, and precise detection of metal ions, particularly Cu2+. This review offers a comprehensive summary of recent discoveries concerning as pyrazoline-based "On-Off" chemosensors. The discussion places emphasis on exploring the design and photophysical properties of these chemosensors, with the primary objective of detecting Cu2+ metal ions. The unique features of pyrazoline derivatives make them promising candidates for practical applications in environmental and biological monitoring, showcasing their potential significance in advancing sensing technologies.

An efficient 2-aminothiazolesalicylaldehyde fluorescent chemosensor for Fe2+ ion detection and a potential inhibitor of NUDT5 signaling hormone for breast cancer cell and molecular keypad lock application

A novel thiazole phenol conjugate, 2-aminothiazolesalicylaldehyde (receptor1) was designed and synthesized for the first time through a single step process via Schiff base condensation reaction. The formation of receptor1 was confirmed by FTIR, ¹³C NMR, and ¹H NMR. The IR spectra confirmed the presence of the aldimine formation. It is further supported by the proton NMR, showing the disappearance of aldehyde peaks and the formation of a new imine peak. This is further corroborated by the ¹³C NMR. The receptor1 complexing with various metal ions were studied through fluorescence spectroscopy showed its selectivity toward Fe²⁺ ion following a reverse photoinduced electron transfer (PET) process compared to all other potentially competing ions. The receptor1 was applied as a sensor to sense Fe²⁺ ion in water samples. The detection limit for Fe²⁺ ion in drinking water was substantially lower (0.003 µM) than the EPA (environmental protection agency) recommendation (5.37 M). The capability of receptor1 in recovering Fe²⁺ ion in bore water, tap water, and drinking water was up to 99.5%. The receptor1 was also used as a chelating ligand (receptor1) in molecular docking and it was assessed as a potential inhibitor of NUDT5, a silence hormone signaling for breast cancer. The test compound (PDB: 5NWH) showed good affinity toward the target receptor1 with the binding energy of – 5.23 kcal mol⁻¹. Furthermore, the receptor1 showed excellent reversibility property on adding EDTA solution. Due to the marvelous reversible property, a molecular-scale sequential information processing circuit is designed for the multi-task behavior such as ‘Writing-Reading-Erasing-Reading’ in the form of binary logic gate. The consecutive addition of Fe²⁺ ion and EDTA solution to receptor1 paves a way for the construction of INHIBIT logic gate. Additionally, the receptor1 showed the mimicking behavior of molecular keypad lock.

A novel double target fluorescence probe for Al3+/Mg2+ detection with distinctively different responses and its applications in cell imaging

The metal cations, Al³⁺ and Mg²⁺, could affect human health and cell biological processes. Their fast and selective detection using one probe remains a challenge. A novel fluorescence probe, N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI), was developed for selectively monitoring Al³⁺ and Mg²⁺. The probe NHMI showed a distinctive "turn-on" fluorescence signal towards Al³⁺ and Mg²⁺ (cyan for Al³⁺ with 2556-folds enhancement and yellow for Mg²⁺ with 88-folds enhancement), which is quite distinct from other metal cations and allows for naked-eye detection. This interesting response was attributed to the influence of PET, ESIPT process and CHEF effect, when Al³⁺ or Mg²⁺ chelated with NHMI. Furthermore, the fluorescence titration experiments manifested that the detection limit of probe NHMI for Al³⁺/Mg²⁺ was as low as 1.20 × 10^-8 M and 7.69 × 10^-8 M, respectively. The formed complexes NHMI-Al³⁺ and NHMI-Mg²⁺ were analyzed by Job's plot, ESI-MS, ¹H NMR and FT-IR. The coordination pockets and fluorescence mechanisms of two metal complexes were explored by density functional theory calculation. Moreover, NHMI showed low cytotoxicity and good cell permeability. Fluorescence bioimaging of Al³⁺/Mg²⁺ in MCF-7 cells with NHMI indicated its potential application in biological diagnostic analysis.

BODIPY-Pyridylhydrazone Probe for Fluorescence Turn-On Detection of Fe3+ and Its Bioimaging Application

A novel pyridylhydrazone-tethered BODIPY (BODIPY-PH) was synthesized, fully characterized via nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopic (FTIR), and single-crystal X-ray diffraction (SC-XRD) techniques, and developed for the selective detection of Fe3+ through fluorescent enhancement process. This derivative showed 1:1 binding with Fe3+ in an acetonitrile-water mixture (1:9 v/v) with the binding constant (K) of 5.4 × 104 M−1 and the limit of detection of 0.58 µM. The Fe3+ complexation reaction has been proved to be a reversible process and could be effectively repeated up to three cycles. The electronic properties of BODIPY-PH and its Fe3+ complex modeled by the density functional theory (DFT) method suggested the presence of chelation-enhanced fluorescence (CHEF) effect in the Fe3+ binding reaction. The X-ray absorption spectroscopy (XAS) probed at Fe K-edge confirmed the complex formation between BODIPY-PH and the Fe3+ in an octahedral geometry. Finally, bioimaging against human embryonic kidney (Hek293) cell, through confocal fluorescence microscopic technique indicated that the BODIPY-PH displayed good permeability and low toxicity toward the tested cell lines and showed enhanced fluorescent signal in the cells incubated with Fe3+ proving its capability for Fe3+ analysis in cellular matrix.

Bis-BODIPY linked-triazole based on catechol core for selective dual detection of Ag+ and Hg2

Herein, we introduced a new chemosensor, bis-BODIPY linked-triazole based on catechol (BODIPY-OO) prepared by bridging two units of BODIPY fluorophore/triazole binding group with a catechol unit. A solution of this compound displayed 4- and 2-fold enhancements in fluorescence intensity after adding a mole equivalent amount of Ag⁺ and Hg²⁺ ions in methanol media, respectively. ¹H NMR titrations of BODIPY-OO with Ag⁺ and Hg²⁺ suggested that the triazole was involved in the recognition process. BODIPY-OO showed high sensitivity toward Ag⁺ and Hg²⁺ over other metal ions with detection limits of 0.45 μM and 1 μM, respectively. It can also distinguish Hg²⁺ from Ag⁺ by addition of an EDTA. This compound can therefore be employed as practical fluorescent probe for monitoring the presence of Ag⁺ and Hg²⁺ ions.

BODIPY–triazole–catechol combination serves as a “turn-on” fluorescent probe for dual detection and differentiation of Hg²⁺ and Ag⁺ ions.

Pyrene-phenylglycinol linked reversible ratiometric fluorescent chemosensor for the detection of aluminium in nanomolar range and its bio-imaging

Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al³⁺ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al³⁺ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al³⁺-ions demonstrated in living cells. The LOD of (R)-1 for Al³⁺ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO.

A novel coumarin-based fluorescence chemosensor for Al3+ and its application in cell imaging

As an efficient turn-on fluorescent chemosensor for Al³⁺, a new coumarin derivative (CND) has been designed and synthesized by the condensation of 8-formyl-7-hydroxycoumarin with niacin hydrazide. The spectroscopic studies revealed that the sensor CND exhibited a remarkable fluorescence enhancement towards Al³⁺ with high selectivity and sensitivity in EtOH-HEPES (95:5, v/v, pH = 7.40), which was attributed to the photoinduced electron transfer (PET) and CN isomerization mechanism. Fluorescence titration calculations data showed that the detection limit and the association constants of CND for Al³⁺ were found to be 2.51 × 10^-7 M and 9.64 × 10⁴ M^-1, respectively. The results of experiments, including Job's plot, ¹H NMR titration and ESI-MS, revealed that the stoichiometric binding between CND and Al³⁺ was 1:1. The investigations of the pH dependency of CND for Al³⁺ detection, and the cell imaging suggested the sensor CND could be promisingly applied for the recognition of Al³⁺ in biological cells.

Ratiometric red-emission fluorescence detection of Al3+ in pure aqueous solution and live cells by a fluorescent peptidyl probe using aggregation-induced emission

The development of a fluorescence method for the selective ratiometric detection of Al3+ ions in pure aqueous solutions and live cells is still a significant challenge. In the present study, we synthesized a new type of fluorescent probe using an Al3+-triggered self-assembly based on the dipeptide receptor and an aggregation-induced emission fluorophore. The fluorescent probe (1) bearing cyanostilbene with excitation by visible light detected Al3+ ions sensitively in pure aqueous buffered solution by ratiometric red-emission at 600 nm. 1 provided a highly selective ratiometric detection of Al3+ among 16 metal ions in aqueous solution. 1 exhibited sensitive ratiometric response to Al3+ in aqueous buffered solutions at pH ranging from 5 to 7.4. The detection limit (145 nM, R2 = 0.999) for Al3+ ions in pure aqueous solution was much lower than the maximum allowable level of Al3+ in drinking water demanded by the Environmental Protection Agency (EPA). The probe provided an efficient approach to detect low concentrations of Al3+ in ground water, tap water, and live cells by ratiometric red-emissions at 600 nm. The binding study using dynamic light scattering, NMR, IR, and TEM revealed that the complex between 1 and Al3+ self-assembled to form nanoparticles, resulting in the enhancement of the emission at 600 nm and a concomitant decrease in the emission at 535 nm.

Dihydroindeno[1,2-b]pyrroles: new Al3+selective off–on chemosensors for bio-imaging in living HepG2 cells

An approach for the expeditious synthesis of a new Al³⁺-selective turn-on dihydroindeno[1,2-b]pyrrole probe under environmentally benevolent conditions and its bio-imaging studies on HepG2 cell.

Sensitive ratiometric detection of Al(iii) ions in a 100% aqueous buffered solution using a fluorescent probe based on a peptide receptor

The peptidyl bioprobe detected Al(iii) ions sensitively in a 100% aqueous buffered solution through ratiometric response.

Efficient two-step synthesis of water soluble BODIPY–TREN chemosensors for copper(ii) ions

Two promising, highly selective, water soluble, Cu(ii) sensors were synthesized in two reaction steps, using C–H functionalization reactions.

Highly sensitive and selective detection of Al(III) ions in aqueous buffered solution with fluorescent peptide-based sensor

A fluorescent sensor based on a tripeptide (SerGluGlu) with a dansyl fluorophore detected selectively Al(III) among 16 metal ions in aqueous buffered solutions without any organic cosolvent. The peptide-based sensor showed a highly sensitive turn on response to aluminium ion with high binding affinity (1.84×10(4)M(-1)) in aqueous buffered solutions. The detection limit (230nM, 5.98ppb) of the peptide-based sensor was much lower than the maximum allowable level (7.41μM) of aluminium ions in drinking water demanded by EPA. The binding mode of the peptide sensor with aluminium ions was characterized using ESI mass spectrometry, NMR titration, and pH titration experiments.

Preparation of Different Substitued Polypyridine Ligands, Ruthenium(II)-Bridged Complexes and Spectoscopıc Studies

Novel different substitued polypyridine ligands 4-((4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)phenoxy)methyl)benzaldehyde (BA-PPY), (E)-N-(4-((4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)phenoxy)methyl)benzylidene)-pyrene-4-amine (PR-PPY), (E)-N-(4-((4-(1H-imidazo[4,5-f][1,10] phenanthroline-2-yl)phenoxy)methyl)benzylidene)-1,10-phenanthroline-5amine (FN-PPY), 2-(4-(bromomethyl)phenyl)-1H-imidazo[4,5-f][1,10] phenanthroline (BR-PPY), 2-(4-(azidomethyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (N3-PPY) and triazole containing polypyridine ligand 3,4-bis[(4-(metoxy)-1,2,3-triazole)1-methylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline)] benzaldehyde (BA-DIPPY) and Ruthenium(II) complexes were synthesized and characterized. Their photopysical properties were investigated. The complexes RuP(PR-PPY), RuB(PR-PPY, RuP(FN-PPY) and RuB(FN-PPY) exhibited a broad absorption bands at 485, 475, 476, and 453 nm, respectively, assignable to the spin-allowed MLCT (dπ-π*) transition. The emission maxima of the pyrene-appended polypyridine ligand PR-PPY was observed at λems = 616 nm and the phenanthroline-appended polypyridine ligand FN-PPY was observed at λems = 668 nm. And the emission maxima of the complexes RuP(PR-PPY), RuB(PR-PPY), RuP(FN-PPY) and RuB(FN-PPY) were observed at λems = 646, 646, 685 and 685 nm, respectively. As seen in fluorescence spectra, the fluorescence intensities of the ligands are higher than their metal complexes. This is because of quenching effect of Ruthenium(II) metal on chromophore groups.

On-off Bodipy chemosensor for recognition of iron(III) ion based on the inner filter effect and its applications in cellular and bacterial imaging

One strong fluorescent Bodipy-containing derivative was synthesized and characterized using ¹ H NMR, electrospray ionization mass spectrometry and elemental analysis. Its electrochemical and photophysical properties were investigated. In addition, the Bodipy derivative could be used as an on-off fluorescent probe for the detection of Fe³⁺ ions based on the inner filter effect because the absorption band of the Fe³⁺ ion overlaps the excitation band of Bodipy very well upon irradiation with UV light. Furthermore, the Bodipy-based sensor has obvious advantages including simplicity, rapid response, high selectivity, sensitivity and a detection limit of 1.2 μmol/L, and has been demonstrated in real water samples including tap water, mineral water and water from Lake Tai. Moreover, the fluorescent probe could also be used as a probe for the determination of Fe³⁺ in cellular and bacterial imaging. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs

The unusual di-bromo product, 5b, confirmed by spectral analysis, showed the most potency with the lowest IC₅₀ and MIC values, with excellent activity comparable to the standard antibacterial drug, tetracycline.