A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates

A colorimetric sensor based on 2,3-bis(6-chloropyridin-2-yl)-6-fluoroquinoxaline for naked-eye detection of Iron (III) and its application in real sample analysis

Iron ions are crucial for numerous biological processes, and the levels of these ions have a significant impact on human well-being. Hence, it is essential to identify the level of Iron ions using a suitable technique. A new colorimetric sensor, namely "2,3-bis(6-chloropyridin-2-yl)-6-fluoroquinoxaline" (CF), has been introduced to detect Fe3+ through naked-eye observation. The sensor exhibits remarkable specificity towards Fe3+ compared to other metal ions in aqueous environments. Furthermore, it undergoes a substantial color change from colorless to yellow, which is visible without needing additional equipment. The complex formation was proposed to be in 1:1 ratio based on the Job's plot and molar ratio plot. The maximum sensitivity of CF towards Fe3+ was found at pH 6 to 8. Minimal or negligible interference was noticed from different metal ions in the detection of Fe3+. The binding constant using Benesi-Hildebrand was estimated at 1.434 × 104 M-1. Gibbs free energy was determined -23.728 kJ/Mol. The LOD and LOQ were calculated at 0.378 and 1.26 µM, respectively. The probe CF was utilized to recover Fe3+ in tap water, resulting in recovery percentages ranging from 99.44 to 103.61. This indicates that the CF has the ability to identify Fe3+ in environmental samples.

Nitroquinolone Fused Salicyl and Naphthyl Hydrazone Fluorescent Probes for the Detection of Fe3+and Pb2+ Ions

The application of quinolones stretches over a large umbrella of medicinal field as well as chemosensor due to the presence of privileged heterocyclic aromatic rig system. Salicyl and Naphthyl Hydrazide motifs are also established fluorophore groups. Therefore in this work, we have designed and synthesized Salicyl hydrazide (3a-c) and naphthyl hydrazide fused nitroquinolones (5a-c) investigated for their fluorescent behaviour. Preliminary UV- absorption studies were carried out and the metal selectivity were examined with various metal ion. Among them, it was found that compound 3a was selective towards Fe3+ ions (λex = 330 nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). 3a shows decrease emission intensity in presence of Fe3+ ions. Compound 5a shows enhancement in fluorescence intensity upon addition of Pb2+ ion (λex = 280 nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). Further, the concentration dependence, competitive binding and EDTA reversibility were studied for selected compounds towards the respective cations selectivity. Jobs plot analysis indicate that 1:1 binding of 3a with Fe3+ ion (Ka = 3.17 x104M-1 and Limit Of Detection (LOD) = 5.1 × 10-7 M) whereas 5a showed 1:2 binding mode with Pb2+ ions (Ka = 2.14 × 106 M-1 and Limit Of Detection (LOD) = 2.613 × 10-9 M). Density Function Theoretical studies were performed as support for the experimental results.

Naphthalene derived Schiff base as a reversible fluorogenic chemosensor for aluminium ions detection

Schiff base (HNPD) was achieved by reacting 2-hydroxy-1-naphthaldehyde with N-phenyl-o-phenylenediamine in enthanol medium. The spectroscopic analyses were done to establish the formation of Schiff base apparently. Further, synthesized Schiff base conjugate was successfully used as a fluorogenic chemosensor to detect aluminium ions (Al3+) with high fluorescence amplification among the other interfering various metal ions. The limit of detection of 0.0248 × 10-6 M and a binding constant of 6.19 × 103 M-1 were obtained by the receptor HNPD for Al3+ detection. A high influence of intramolecular charge transfer kinetics was established to realize the selective responsiveness towards Al3+ ions. Density functional theory approximation formulated the band energy modulation and localization and delocalization of electron density for the HNPD and Al3+ complexation. The developed sensor ultimately inspected on the real soil and water samples and ascertained the practical ability of Al3+ ions detection of HNPD chemosensor.

Exploitation of a 1D coordination polymer as a portable kit for an eye-catching fluorometric response towards sensing of trivalent cations

The development and utilization of coordination polymers (CPs) have drawn interest for potential applications in different fields. Detection of metal ions in efficient and selective manners is an important field of research. It paves the way to protect human health by balancing toxic metal ions and biologically active metal ions in the atmosphere. In this regard, a new one-dimensional (1D) 4-(1-naphthylvinyl)pyridine (4-nvp) based CP [Cd(NCS)2(4-nvp)2]n (1) was synthesized and characterized structurally by single-crystal X-ray diffraction. Interestingly, this 1D CP underwent supramolecular aggregation via π⋯π stacking interactions, which specifically generated an environment for a potent "turn on" response in the presence of trivalent cations (Fe3+, Al3+, and Cr3+) in the nanomolar range but remained silent in the presence of other metal ions. Density functional theory (DFT) computations and X-ray photoelectron spectroscopy (XPS) were performed to establish the sensing phenomena. Fascinatingly, utilizing the sensitivity of 1 in an aqueous medium, a hands-on portable cotton swab kit was developed for instant identification of these three important trivalent metal cations.

Recent developments in the creation of a single molecular sensing tool for ternary iron (III), chromium (III), aluminium (III) ionic species: A review

Rational design of a molecular sensing tool is an important topic in molecular recognition, signalling, and optoelectronics that has piqued the interest of chemists, biologists, and environmental scientists. Approximately 150 years have passed since the beginning of the fluorescent chemosensor sector. Due to the paramagnetic properties of Cr3+ and Al3+ , it is tough to prepare a photoluminescence plug-in detector. Most dye-based Al3+ sensors must be utilized in organic or mixed solvents for robust hydration of Al3+ in water. The sophisticated molecular design of sensors, conversely, allows for the detection of these metal ions in aqueous medium. The design of chemosensors using various fluorophores and their mechanisms of action have been thoroughly discussed. A literature survey covering the design of chemosensors and their mechanisms of action have been thoroughly discussed covering the period 2010-2022 and that was carried out including innovative and exemplary activities from numerous groups throughout the world that have significantly contributed to this sector. The most important advantages of these probes are their aqueous solubility and quick response with outstanding selectivity and sensitivity for temporal distribution with high fidelity of metals in living cells.

Trivalent metal ion sensor enabled bioimaging and quantification of vaccine-deposited Al3+ in lysosomes

Extracellular metallic debris is deposited into the well-known 'recycle bins' of the cells named lysosomes. The accumulation of unwanted metal ions can cause dysfunction of hydrolyzing enzymes and membrane rupturing. Thus, herein, we synthesized rhodamine-acetophenone/benzaldehyde derivatives for the detection of trivalent metal ions in aqueous media. In solution, the synthesized probes exhibited a 'turn-on' colorimetric and fluorometric response upon complexation with trivalent metal ions (M³⁺). Mechanistically, M³⁺ chelation enables the appearance of a new emission band at approximately 550 nm, which verifies the disruption of the closed ring and the restoration of conjugation on the xanthene core in rhodamine 6G derivatives. Exclusive localization of the biocompatible probes at the lysosomal compartment favored the quantification of deposited Al³⁺. Moreover, the novelty of the work lies in the detection of Al³⁺ deposited in the lysosome that originated from hepatitis B vaccines, which shows their efficiency for near future in vivo applications.

Azo-hydrazone tautomerism in a simple coumarin azo dye and its contribution to the naked-eye detection of Cu2+ and other potential applications

A new tailor-made azo dye of coumarin connected to phenolic derivative is presented herein. Azo-hydrazone tautomerism in aqueous solution of the dye was observed and studied using spectroscopic assays such as ¹H NMR, absorption and emission assays, and theoretical studies. Tautomerism was attributed to the presence of a labile phenolic hydrogen in the ortho position to the azo functionality and the hydrazone was found to be the more dominant tautomer. Influence of metal ions on the azo-hydrazone chemical equilibrium and how the accompanying colour and spectroscopic changes can be exploited for various functions, especially the detection and quantification of Cu²⁺ in aqueous environments was explored. The presence of Cu²⁺ affects the azo-hydrazone equilibrium resulting in visual appearance and spectroscopic changes and the likely binding sites for Cu²⁺ were evaluated. Cu²⁺ pushes the azo-hydrazone equilibrium towards the more conjugated form and the presence of other metal ions does not have any perceivable impact on this mechanism. The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu²⁺ in domestic and environmental water samples, photo-imprinting and as a logic gate. The limits of detection (LOD) and quantification (LOQ) for Cu²⁺ were found to be 0.0779 mg/L and 0.236 mg/L, respectively, much lower than the World Health Organization (WHO) guideline limit for Cu²⁺ levels in drinking water.

Aza-phenol Based Macrocyclic Probes Design for "CHEF-on" Multi Analytes Sensor: Crystal Structure Elucidation and Application in Biological Cell Imaging

Metal bound macrocyclic compounds found in biological systems inspired us to design and synthesize two Robson-type macrocyclic Schiff-base chemosensors, H ₂ L1 (H ₂ L1=1,11-dimethyl-6,16-dithia-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol) and H ₂ L2 (H ₂ L2=1,11-dimethyl-6,16-dioxa-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol). Both the chemosensors have been characterized with different spectroscopic techniques. They act as multianalyte sensor and exhibit "turn-on" fluorescence toward different metal ions in 1X PBS (Phosphate Buffered Saline) solution. In presence of Zn²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions, H ₂ L1 exhibits ∼6-fold enhancement of emission intensity, while H ₂ L2 shows ∼6-fold enhancement of emission intensity in the presence of Zn²⁺, Al³⁺ and Cr³⁺ ions. The interaction between the different metal ion and chemosensor have been examined by absorption, emission, and ¹H NMR spectroscopy as well as by ESI-MS⁺ analysis. We have successfully isolated and solved the crystal structure of the complex [Zn(H ₂ L1)(NO₃)]NO₃ (1) by X-ray crystallography. The crystal structure of 1 shows 1:1 metal:ligand stoichiometry and helps to understand the observed PET-Off-CHEF-On sensing mechanism. LOD values of H ₂ L1 and H ₂ L2 toward metal ions are found to be ∼10^-8 and ∼10^-7 M, respectively. Large Stokes shifts of the probes against analytes (∼100 nm) make them a suitable candidate for biological cell imaging studies. Robson type phenol based macrocyclic fluorescence sensors are very scarce in the literature. Therefore, the tuning of structural parameters as the number and nature of donor atoms, their relative locations and presence of rigid aromatic groups can lead to the design of new chemosensors, which can accommodate different charged/neutral guest(s) inside its cavity. The study of the spectroscopic properties of this type of macrocyclic ligands and their complexes might open a new avenue of chemosensors.

A Simple Schiff Base as Fluorescent Probe for Detection of Al3+ in Aqueous Media and its Application in Cells Imaging

A novel fluorescence probe for the detection of Al³⁺ was developed based on methionine protected gold nanoclusters (Met-AuNCs). A fluorescent Schiff base (an aldimine) is formed between the aldehyde group of salicylaldehyde (SA) and the amino groups of Met on the AuNCs, and developed for selective detection of Al³⁺ in aqueous solution. Al³⁺ can strongly bind with the Schiff base ligands, accompanied by the blue-shift and an obvious fluorescence emission enhancement at 455 nm. The limits of detection (LODs) of the probe are 2 pmol L^-1 for Al³⁺. Moreover, the probe can successfully be used in fluorescence imaging of Al³⁺ in living cells (SHSY5Y cells), suggesting that the simple fluorescent probe has great potential use in biological imaging.

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.

A novel dihydro phenylquinazolinone-based two-in-one colourimetric chemosensor for nickel(ii), copper(ii) and its copper complex for the fluorescent colourimetric nanomolar detection of the cyanide anion

Currently, considerable efforts have been devoted to the detection and quantification of hazardous multi-analytes using a single probe. Herein, we have developed a simple, environment-friendly colourimetric sensor for the sensitive, selective and rapid detection of Ni2+ and Cu2+ ions using a simple organic Schiff base ligand L in methanol-Tris-HCl buffer (1 : 1 v/v, 10 mM, pH = 7.2). The probe L exhibited a binding-induced colour change from colourless to yellow and fluorescence quenching in the presence of both Ni2+ and Cu2+ ions. The interactions between L and the respective metal ions were studied by Job's plot, electrospray ionisation-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FT-IR), density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The limit of detection (LOD) of L towards Ni2+ and Cu2+ was calculated to be 7.4 × 10-7 M and 4.9 × 10-7 M, respectively. Furthermore, the L-Cu2+ complex could be used as a new cascade fluorescent-colourimetric sensor to detect CN- ions with a very low level of detection (40 nM). Additionally, L could operate in a wide pH range, and thus was successfully applied for the detection and quantification of Ni2+ and Cu2+ in environmental samples, and for building OR- and IMPLICATION-type logic gates.

Multi-site probe for selective turn-on fluorescent detection of Al(III) in aqueous solution: synthesis, cation binding, mode of coordination, logic gate and cell imaging

An easy to make organic probe (hereafter called as R) possessing multiple ligating sites have been synthesized and characterized using spectral techniques. The probe exhibits selective and sensitive turn-on fluorescence response with Al(III) in aqueous dimethylformamide (DMF) (1:1 v/v) solution. Fluorescence titration experiment shows that the probe binds with Al(III) with a 1:1 stoichiometry and a binding constant of 6.6 × 10⁴ M^-1.The mode of coordination of R with Al(III) has been established suing ²⁷Al and ¹H NMR studies and the results suggest formation of an octahedral complex been them. The suggested point of attachment of R with Al(III) corroborates well with Density Functional Theory (DFT) optimized structure and Mulliken charges computed. Chelation-enhanced fluorescence (CHEF) is proposed as the mechanism of enhancement of fluorescence upon addition of Al(III) to R. The probe detects Al(III) in aqueous solution with a detection limit of 0.2 μM, which is much lower than the permissible limit of Al(III) set by the World Health Organization (WHO).The probe works in a wide pH range (4-11) and thus makes it a suitable candidate for environmental and biological applications. The fluorescence signals of R were used to construct an INHIBIT molecular logic gate. The confocal fluorescence microscope experiments show that R could be employed as a fluorescent probe for detecting Al(III) in living cells.

Supramolecular assembly of a 4-(1-naphthylvinyl)pyridine-appended Zn(ii) coordination compound for the turn-on fluorescence sensing of trivalent metal ions (Fe3+, Al3+, and Cr3+) and cell imaging application

The as-synthesized Zn(ii) coordination compound exhibited turn-on fluorescence sensing of analytical group-IIIA metal ions (Fe³⁺, Al³⁺, and Cr³⁺) and applications in cell imaging.

Photophysical transformations induced by chemical substitution to salicylaldimines

The role of electron-acceptor strength and microenvironment polarity on the photophysical properties of salicylaldimines.

A rhodamine based biocompatible chemosensor for Al3+, Cr3+ and Fe3+ ions: extraordinary fluorescence enhancement and a precursor for future chemosensors

A rhodamine based chemosensor, 3-(((2-(3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)ethyl)imino)methyl)-2-hydroxy-5-methylbenzaldehyde (HL-CHO), has been developed for the detection of Al3+, Cr3+ and Fe3+ ions. The absorbance of HL-CHO at 528 nm increases significantly in HEPES buffer in methanol : water (9 : 1, v/v) (pH 7.4) in the presence of Al3+, Cr3+ and Fe3+ ions with the alteration of solution color from colorless to pink. The fluorescence intensity of the probe at 550 nm enhances by 1465, 588 and 800 fold in the presence of Al3+, Cr3+ and Fe3+ ions, respectively. To the best of our knowledge, this huge increase in fluorescence intensity with Al3+ and Cr3+ has not been observed for other rhodamine based chemosensing systems. The weak fluorescence and no coloration of the probe are due to the existence of a spirolactam ring. The trivalent cations induce the opening of the spirolactam ring and consequently change the color and the fluorescence intensity followed by the 1 : 1 complex formation with HL-CHO which are evident from Job's analysis, ESI mass spectral analysis and elemental analysis. The quantum yield and lifetime of HL-CHO have increased considerably in the presence of the trivalent cations. The high sensitivity of the probe towards all the cations is evident from the nM order of LOD values. This has been used in living cell imaging studies with the human neuroblastoma SH-SY5Y cell line. Having appended -CHO groups for Schiff-base condensation with other amines, HL-CHO could be a potential precursor for future chemosensors.

A lysosome-targetable fluorescent probe for imaging trivalent cations Fe3+, Al3+ and Cr3+ in living cells

An effective morpholine-type naphthalimide chemsensor, N-p-chlorophenyl-4-(2-aminoethyl)morpholine-1,8-naphthalimide (CMN) has been developed as a lysosome-targeted fluorometric sensor for trivalent metal ions (Fe³⁺, Al³⁺ and Cr³⁺). Upon the addition of Fe³⁺, Al³⁺ or Cr³⁺ ions, the probe CMN showed an evident naked-eye color changes which pale yellow solution of CMN turned deepened and it displayed turn-on fluorescence response in methanol. CMN showed a significant selective and sensitive toward Fe³⁺, Al³⁺ or Cr³⁺ ions, while there was no obvious behavior to other monovalent or divalent metal ions from the UV-vis and fluorescence spectrum. Based on the Job's plot analyses the 1:1 coordination mode of CMN with Fe³⁺, Al³⁺ or Cr³⁺ was proposed. The limit of detection (LOD) observed were 0.65, 0.69 and 0.68 μM for Fe³⁺, Al³⁺ and Cr³⁺ ions, respectively. The N-atom of morpholine directly involved in complex formation, CMN emitted fluorescence through inhibition of photoinduced electron transfer (PET). This probe exhibited excellent imaging ability for Fe³⁺, Al³⁺and Cr³⁺ ions in living cells with low cytotoxicity. Significantly, the cellular confocal microscopic research indicated that the lysosome-targeted group of morpholine moiety was introduced which realized the capability of imaging lysosomal trivalent metal ions in living cells for the first time.

Rhodamine functionalized mesoporous silica as a chemosensor for the efficient sensing of Al3+, Cr3+ and Fe3+ ions and their removal from aqueous media

Rhodamine incorporated mesoporous silica acts as a selective chemosensor for Al³⁺, Cr³⁺ and Fe³⁺ ions and it is used for their separation from an aqueous medium.

A novel hydrazide-based selective and sensitive optical chemosensor for the detection of Ni2+ ions: applications in live cell imaging, molecular logic gates and smart phone-based analysis

A novel hydrazide-based optical sensor for Ni²⁺ ions was designed, which can be applied for recovery of contaminated water samples, smart phone-based analysis and live cell imaging.

Triazole-based novel bis Schiff base colorimetric and fluorescent turn-on dual chemosensor for Cu2+ and Pb2+: application to living cell imaging and molecular logic gates

A triazole-based novel bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized by elemental analysis, ¹H-NMR, ESI-MS, FTIR spectra and DFT studies. The receptor L showed selective and sensitive colorimetric sensing ability for Cu²⁺ and Pb²⁺ ions by changing color from colorless to yellow and light yellow respectively in CH₃OH–tris-buffer (1 : 1, v/v). However, it displayed strong fluorescence enhancement upon the addition of both Cu²⁺ and Pb²⁺ ions, attributed to the blocking of PET. The fluorometric detection limits for Cu²⁺ and Pb²⁺ were found to be 12 × 10⁻⁷ M and 9 × 10⁻⁷ M and the colorimetric detection limits were 3.7 × 10⁻⁶ M and 1.2 × 10⁻⁶ M respectively; which are far below the permissible concentration in drinking water determined by WHO. Moreover, it was found that chemosensor L worked as a reversible fluorescence probe towards Cu²⁺ and Pb²⁺ ions by the accumulation of S²⁻ and EDTA respectively. Based on the physicochemical and analytical methods like ESI-mass spectrometry, Job plot, FT-IR, ¹H-NMR spectra and DFT studies the detection mechanism may be explained as metal coordination, photoinduced electron transfer (PET) as well as an internal charge transfer (ICT) process. The sensor could work in a pH span of 4.0–12.0. The chemosensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in real samples, living cells and building of molecular logic gate.

A novel triazole-based bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized. The chemo-sensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in living cells and building molecular logic gate.