A fluorescence "turn-on" probe for Cu (Ⅱ) based on flavonoid intermediates generated by copper-induced oxidative cyclization and its fluorescence imaging in living cells

A fluorescence "turn-on" probe for Cu (Ⅱ) ions was prepared based on the condensation reaction of coumaraldehyde and 1-hydroxy-2-acetylnaphthalene. A strong fluorescent flavonoid intermediate was formed and verified by the NMR and ESI-MS experiments. The water-soluble and pH dependence experiments were performed to confirm the optimal solvent condition (CH₃CN: HEPES = 1:1, v/v, pH = 7.2-7.4). The dynamic experiments indicated that the formation process of the intermediate catalyzed by Cu(Ⅱ) ions was probably pseudo-first-order reaction process. The probe showed good selectivity toward copper ions and almost no interference except Ag⁺ ions by the selectivity and competitive experiments. The HeLa cells were used in the cell fluorescence imaging tests and it was demonstrated that the probe could be used in the phycological condition and showed weak cytotoxicity by the MTT experiments.

Recent development in fluorescent probes for copper ion detection

Abstract:

Copper is the third most common heavy metal and an indispensable component of life. Variations of body copper levels, both structural and cellular, are related to a number of disorders; consequently, pathophysiological importance of copper ions demands the development of sensitivity and selective for detecting these organisms in biological systems. In recent years, the area of fluorescent sensors for detecting copper metal ions has seen revolutionary advances. Consequently, closely related fields have raised awareness of several diseases linked to copper fluctuations. Further developments in this field of analysis could pave the way for new and innovative treatments to combat these diseases. This review reports on recent progress in the advancement of three fields of fluorescent probes; chemodosimeters, near IR fluorescent probes, and ratiometric fluorescent probes. Methods used to develop these fluorescent probes and the mechanisms that govern their reaction to specific analytes and their applications in studying biological systems, are also given.

Design, synthesis and photophysical studies of BODIPY-o, m, p-phenylenediamine-based probes: Insights into their responsiveness under different pH conditions

In this paper, a series of novel phenylenediamine-fluoroboron pyrrole fluorescent derivatives were prepared which have distinct responsiveness under different hydrogen ion concentration (pH) conditions. It is noticed that the products showed excellent fluorescence properties in different solvents, especially in tetrahydrofuran and dichloromethane, with the most prominent fluorescence intensity, while the fluorescence in methanol, acetonitrile, and dimethyl sulfoxide was weaker. Responsiveness under different hydrogen ion concentration conditions in aqueous solutions were also observed, where the fluorescence intensity is quenching when the pH is 4.0. With regard to cells imaging investigation, the products showed the prominent fluorescence in HeLa cells. Further acidic cell imaging results showed that under acidic conditions made of formic acid or acetic acid, the intracellular fluorescence of the compounds was clustered around the cells and intensive enough different from without acidity control group. Especially, the compounds have unique fluorescence in acidic environment and has great potential and research value as acidic probes.

Dehydrogenation of amines in aryl-amine functionalized pincer-like nitrogen-donor redox non-innocent ligands via ligand reduction on a Ni(ii) template

We have synthesized a series of new redox non-innocent azo aromatic pincer-like ligands: 2-(phenylazo)-6-(arylaminomethyl)pyridine (HLa-c: HLa = 2-(phenylazo)-6-(2,6-diisopropylphenylaminomethyl)pyridine, HLb = 2-(phenylazo)-6-(2,6-dimethylphenylaminomethyl)pyridine, and HLc = 2-(phenylazo)-6-(phenylaminomethyl)pyridine), in which one side arm is an arylaminomethyl moiety and the other arm is a 2-phenylazo moiety. Nickel(ii) complexes, 1-3, of these ligands HLa-c were synthesized in good yield (approximately 70%) by the reaction of ligands : (NiCl2·6H2O) in a 1 : 1 molar ratio in methanol. The amine donor in each of the ligands HLa-c binds to the Ni(ii) centre without deprotonation. In the solid state, complex 3 is a dimer; in solution it exists as monomer 3a. The reduction of acetonitrile solutions of each of the complexes 1, 2 and 3a, separately, with cobaltocene (1 equivalent), followed by exposure of the solution to air, resulted in the formation of new complexes 7, 8 and 9, respectively. Novel free ligands Lx and Ly have also been isolated, in addition to complexes 7 and 8, from the reaction of complexes 1 and 2, respectively. Complexes 7-9 and free ligands Lx and Ly have been formed via a dehydrogenation reaction of the arylaminomethyl side arm. The mechanism of the reaction was thoroughly investigated using a series of studies, including cyclic voltammetry, EPR, and UV-Vis spectral studies and density functional theory (DFT) calculations. The results of these studies suggest a mechanism initiated by ligand reduction followed by dioxygen activation. A Cl-/I- scrambling experiment revealed that the dissociation of the chloride ligand(s) was associated with the one-electron reduction of the ligand (azo moiety) in each of the complexes 1, 2 and 3a. The dissociated chloride ligand(s) were reassociated with the metal following the dehydrogenation reaction to yield the final products. All of the newly synthesized compounds were fully characterized using a variety of physicochemical techniques. Single-crystal X-ray structures of the representative compounds were determined to confirm the identities of the synthesized molecules.

The oxidative dehydrogenation of a coumarinyl scaffold with copper ion and metal ion detection in human liver cancer cells (HepG2)

An unsymmetrical o-phenylenediamine derivative, L (7-hydroxy-4-methyl-8-(1-(phenyl- (pyridin-2-yl)methyl)-1H-benzo[d]imidazol-2-yl)-2H-chromen-2-one), has been synthesized from (E)-N¹-(phenyl(pyridine-2-yl)methylene)benzene-1,2-diamine with 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde and characterized by X-ray, IR, ¹H NMR and ESI-MS spectral analyses. The X-ray structure shows L as a cyclic benzimidazole derivative, but it undergoes ring-opening upon reaction with transition metal ions. L is non-emissive in 9 : 1 (v/v) EtOH/H₂O (HEPES buffer, pH 7.4) but becomes highly fluorescent upon Zn²⁺ coordination, and the emissive Zn(ii) complex undergoes transmetallation in the presence of Cu²⁺ ions specifically, followed by amine to imine oxidation, i.e. an oxidative dehydrogenation (OD) reaction -(2e + 2H⁺) occurs. The transmetallation of Zn²⁺ from the complex by Cu²⁺ (CuCl₂) separated the non-emissive X-ray diffractable crystal of [Cu(L'')Cl] (L'' = amine oxidized form of L). A square pyramidal [Cu(L'')][ClO₄] complex was also isolated from the reaction of L with Cu(CH₃CN)₄(ClO₄) in the presence of air, and in this complex the amine is also oxidized to the imine. Here, copper ions in the presence of air play an important role in the OD reaction of L as determined by EPR and cyclic voltammetry studies. The ligand, L, is used for Zn²⁺ ion recovery from a municipally supplied water sample. A paper strip detection kit for Zn²⁺ and Cu²⁺ is designed using L. The ligand is also used for intracellular Zn²⁺ detection in a human liver cancer cell line (HepG2).

Near-infrared fluorescent probe for selective detection of Cu2+ in living cells and in Vivo

A NIR-rhodamine fluorescent probe was designed and successfully synthesized. The structure of the probe NRh-Cu was characterized by ¹H NMR, ¹³C NMR and HRMS. The probe was found to show high sensitivity and high selectivity. The detection limit was calculated to be as low as 0.95 ppb. The sensing mechanism was proposed and confirmed by HRMS spectra. Furthermore, it could be used for imaging Cu²⁺ in living cells and in vivo.

A quinoxaline-diaminomaleonitrile conjugate system for colorimetric detection of Cu2+ in 100% aqueous medium: observation of aldehyde to acid transformation

In this work, we have strategically incorporated a quinoxaline derivative and a diaminomaleonitrile moiety to construct a chemosensor, 2-amino-3-[(quinoxalin-2-ylmethylene)-amino]-but-2-enedinitrile (H2qm). The notable feature of this strategy is to generate a highly conjugated Schiff base platform with interesting binding properties. Remarkably, H2qm exhibited a visual sensing ability towards Cu2+ in 100% aqueous medium. The effectiveness of the chemosensor has been demonstrated by utilizing it to determine the Cu2+ concentration in real samples. Interestingly, the reaction between H2qm and Cu(ClO4)2·6H2O in DMSO yielded a quinoxaline-2-carboxylic acid based compound and single crystal X-ray diffraction analysis unveiled the resulting structure as [(qa)2Cu(H2O)2] (Hqa = quinoxaline-2-carboxylic acid).

A highly selective and sensitive fluorescent probe for Cu2+ based on a novel naphthalimide-rhodamine platform and its application in live cell imaging

Copper plays important roles in a variety of fundamental physiological processes. At the cell organelle level, aberrant copper homeostasis in lysosomes can lead to various serious diseases. Herein, a bifluorophore-based, lysosome-targetable Cu²⁺-selective ratiometric fluorescent probe (V) has been synthesized by reasonable design. The probe V shows high selectivity toward Cu²⁺ ions over other cations and exhibits high sensitivity (1.45 nM) for the detection of Cu²⁺ ions. Meanwhile, the probe is cell permeable and suitable for ratiometric visualization of lysosomal Cu²⁺ in the living cell.

Encapsulation of Dual-Emitting Fluorescent Magnetic Nanoprobe in Metal-Organic Frameworks for Ultrasensitive Ratiometric Detection of Cu2

An effective dual-emission fluorescent metal-organic framework (MOF)-based nanoprobe has been established for ultrasensitive and rapid ratiometric detection of Cu²⁺ . Such a nanoprobe was prepared by encapsulating fluorescein isothiocyanate (FITC), and Eu(III) complex-functionalized Fe₃ O₄ into the zeolitic imidazolate framework material (ZIF-8). In this nanoprobe, FITC was used as a reference signal, thus improving the influence of external uncertainties. The Eu-complex signal could be quenched after adding an amount of Cu²⁺ . The ZIF-8 could enrich the target analytes, which can amplify the fluorescence signal due to the good adsorption properties of the ZIF-8. Based on above structural and compositional features, the detection limit of the nanoprobe is 0.1 nm for Cu²⁺ , almost 2×10⁴ times lower than the maximum allowable amount of Cu²⁺ in drinking water, which constructed a platform for effective detection of Cu²⁺ . Using the nanoprobe to detect Cu²⁺ in aqueous solution is rapid and the probe still remained stable. Additionally, this sensor for the ratiometric fluorescence imaging of copper ions was also certified in real samples and live cells.

A novel ferrocenyl–naphthalimide as a multichannel probe for the detection of Cu(ii) and Hg(ii) in aqueous media and living cells

The first reported probe that has been used for the bifunctional fluorescent monitoring Cu²⁺ and Hg²⁺ ions in living cells.

A novel glucosamine-linked fluorescent chemosensor for the detection of pyrophosphate in an aqueous medium and live cells

A glucosamine-linked Cu²⁺ ensemble has been successfully developed for detection of pyrophosphate (PPi) in aqueous medium and in live MD-AMB-231 cells.

Molecular visualizing and quantifying immune-associated peroxynitrite fluxes in phagocytes and mouse inflammation model

Reactions of peroxynitrite (ONOO^-) with biomolecules can lead to cytotoxic and cytoprotective events. Due to the difficulty of directly and unambiguously measuring its levels, most of the beneficial effects associated with ONOO^- in vivo remain controversial or poorly characterized. Recently, optical imaging has served as a powerful noninvasive approach to studying ONOO^- in living systems. However, ratiometric probes for ONOO^- are currently lacking. Herein, we report the design, synthesis, and biological evaluation of F₄₈₂, a novel fluorescence indicator that relies on ONOO^--induced diene oxidation. The remarkable sensitivity, selectivity, and photostability of F₄₈₂ enabled us to visualize basal ONOO^- in immune-stimulated phagocyte cells and quantify its generation in phagosomes by high-throughput flow cytometry analysis. With the aid of in vivo ONOO^- imaging in a mouse inflammation model assisted by F₄₈₂, we envision that F₄₈₂ will find widespread applications in the study of the ONOO^- biology associated with physiological and pathological processes in vitro and in vivo.

Naked eye instant reversible sensing of Cu(2+) and its in situ imaging in live brine shrimp Artemia

A Cu(2+)-specific colorimetric reversible fluorescent receptor was designed and synthesized which showed a naked eye observable colour change from colourless to pink on addition of an aqueous buffer (pH 7.4) solution of 30 ppb Cu(2+). Short response time (≤5 s) and low detection limit (nearly 3 ppb) make suitable as a reliable "dip-in" open eye sensor for Cu(2+). Bio-imaging application in live brine shrimp Artemia enabled to detect Cu(2+) at as low as 10 ppb exposure.

Formation of 8-RS-BODIPYs via direct substitution of 8-MeS-BODIPY by RSH (R = Et, Pr, Bu, tBu, n-C12H25, C6H5, p-MeC6H4, p-MeOC6H4, and 2,6-Me2C6H3)

Reactions between 8-RS-BODIPY (R = Me, 1) and alkyl and aryl thiols were readily accomplished in dichloromethane to provide a synthetic pathway to a range of new 8-organothio-BODIPYs in good yield. The new alkyl 8-RS-BODIPYs (R = Et, 2; Pr, 3; Bu, 4; tBu, 5; n-dodecyl, 6) exhibit absorption and emission properties essentially unchanged from those of 1 whereas the arylthio analogs (R = Ph, 7; 2,6-Me2C6H3, 8; p-MeC6H4, 9; p-MeOC6H4, 10) exhibit no fluorescence with the exception of 7, and then only in hexane. In common with other related 8-substituted BODIPYs, the new 8-alkylthio-BODIPY dyes show decreasing fluorescence intensity as solvent polarity increases. Compounds 2, 3, 7, and 8 were characterized via single-crystal X-ray analysis; the alkyl derivatives 2 and 3 exhibited planar BODIPY cores with co-planar organothio- substituents whereas the aryl derivatives exhibited both BODIPY core deformation and significant twisting about the S–C (8) bond removing co-planarity between the aryl group and the distorted BODIPY core. These deformations coincide with the significantly reduced emission properties.

A turn-on fluorescent chemodosimeter based on detelluration for detecting ferrous iron (Fe2+) in living cells

A turn-on fluorescent probe for the detection of Fe²⁺ is facilely synthesized via a nucleophile substitution reaction. The fluorescent probe, N-butyl-4-phenyltellanyl-1,8-naphthalimide (Naph-Te), shows excellent selectivity to Fe²⁺ in a mixed solution of acetonitrile and phosphate buffer under aerobic conditions. The coexistence of biological abundant metal ions such as Na⁺, K⁺, Ca²⁺ and Mg²⁺ has little effect on the fluorescence signal. This turn-on response is achieved via a redox-involved reaction triggered by Fe²⁺ at neutral pH and room temperature, which removes the heavy-atom effect of the tellurium atom on the naphthalimide fluorophore to afford a fluorescent product (N-butyl-4-hydroxyl-1,8-naphthalimide). The probe has excellent cell membrane permeability and is further applied successfully to monitor supplementary Fe²⁺ in live HL-7702 cells using a laser confocal fluorescence microscope.

A well-defined alternating copolymer based on a salicylaldimine Schiff base for highly sensitive zinc(ii) detection and pH sensing in aqueous solution

We report a new strategy to fabricate well-defined alternating Schiff base copolymers of poly(VBCDEG-alt-SaAEMI)s which display two distinguishable color fluorescence “OFF–ON” responses to zinc ions and pH in aqueous solution.

Synthesis of mono-(p-dimethylamino)styryl-containing BOPHY dye for a turn-on pH sensor

Mono-substitutional BOPHY 3a with a (p-dimethylamino)styryl group in the α-position was confirmed to be synthesized by the Knoevenagel-type condensation. Dimethylamino-containing BOPHY 3a can be used as a pH probe.

A new chromo-fluorogenic probe based on BODIPY for NO2 detection in air

A new fluorescent chemodosimeter for detecting NO₂ has been synthesized. The sensing mechanism is based on the regeneration of the carbonyl group induced by the target molecule. This reaction gives rise to both colorimetric and fluorescent changes. A LOD of 0.1 ppm has been determined.

The role of molecular oxygen in the iron(iii)-promoted oxidative dehydrogenation of amines

A mechanistic study is presented of the oxidative dehydrogenation of the iron(iii) complex [Fe^IIIL³]³⁺, 1, (L³ = 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanonane) in ethanol in the presence of molecular oxygen.

Computational design of a two-photon excited FRET-based ratiometric fluorescent Cu2+ probe for living cell imaging

A novel TP FRET ratiometric fluorescent probe 2a for Cu²⁺ is designed. 2a has a large TPA peak in the near-infrared light region and its energy transfer efficiency is nearly 100%.

Unprecedented one-pot sequential thiolate substitutions under mild conditions leading to a red emissive BODIPY dye 3,5,8-tris(PhS)-BODIPY

Phenylthiol performs a thiol exchange with 8-MeS-BODIPY and activates/substitutes the 3,5 positions forming a tri-thiolated BODIPY.

Multichannel detection of Cu2+ based on a rhodamine–ethynylferrocene conjugate

A novel multichannel chemosensor DR3 juxtaposed with a rhodamine chromophore and the electrochemical characterization of an ethynylferrocene group was developed.

Europium(iii) β-diketone complex as portable luminescent chemosensor for naked eye Cu2+ detection and recyclable on–off–on vapor response

A novel Eu³⁺ complex coordinated by polymers with β-diketone pendant groups (Eu³⁺–PDKMA) has been synthesized for Cu²⁺ cation and acid–base vapor detections.

Heterogeneous Cu/OMS-2 as an efficient catalyst for the synthesis of tetrasubstituted 1,4-enediones and 4H-pyrido[1,2-a]-pyrimidin-4-ones

Copper supported on OMS-2: a heterogeneous catalyst Cu/OMS-2 was prepared for the synthesis of tetrasubstituted 1,4-enediones and 4H-pyrido[1,2-a]-pyrimidin-4-ones under the same conditions with air as the oxidant.

Europium(III) complex-functionalized magnetic nanoparticle as a chemosensor for ultrasensitive detection and removal of copper(II) from aqueous solution

Ultrasensitive, accurate detection and separation of heavy metal ions is very important in environmental monitoring and biological detection. In this paper, a highly sensitive and specific detection method for Cu(2+) based on the fluorescence quenching of a europium(III) hybrid magnetic nanoprobe is presented. This nanoprobe can detect Cu(2+) over a wide pH range (5.0-10.0) with a detection limit as low as 0.1 nM and it can be used for detecting Cu(2+) in living cells. After the magnetic separation, the Cu(2+) concentration decreased to 1.18 ppm, which is less than the US EPA drinking water standard (1.3 ppm), and more than 70% Cu(2+) could be removed when the amount of nanocomposite 1 reached 1 mg.

A naphthalimide-based bifunctional fluorescent probe for the differential detection of Hg²⁺ and Cu²⁺ in aqueous solution

A novel fluorescent probe NPM based on naphthalimide was designed and synthesized. Interestingly, NPM exhibited highly selective fluorescence turn-on for Hg(2+) and turn-off for Cu(2+) in aqueous solution (10 mM HEPES, pH 7.5). Its fluorescence intensity enhanced in a linear fashion with the concentration of Hg(2+) and decreased in a nearly linear fashion with the concentration of Cu(2+). Thus NPM could be potentially used for the quantification of Hg(2+) and Cu(2+) in aqueous solution. A series of model compounds were rationally designed and synthesized in order to explore the sensing mechanisms and binding modes of NPM with Hg(2+) and Cu(2+).

A styryl-containing aza-BODIPY as a near-infrared dye

A novel styryl-containing pyrrole was developed by the reaction of E-4-phenylbut-3-en-2-one with 3-phenyl-2H-azirine in the presence of LDA. Utilizing this pyrrole, asymmetric styryl-containing aza-BODIPYs have been prepared in the NIR region as a result of the extension of conjugation.

Oxidovanadium(iv), oxidomolybdenum(vi) and cobalt(iii) complexes of o-phenylenediamine derivatives: oxidative dehydrogenation and photoluminescence

Oxidovanadium(iv), cis-dioxidomolybdenum(vi) amide complexes and cobalt(iii) imine complex of an o-phenylenediamine derivatives are reported.

Rhodamine-based fluorescent off–on sensor for Fe3+ – in aqueous solution and in living cells: 8-aminoquinoline receptor and 2 : 1 binding

A rhodamine-based Fe³⁺ sensor of a rigid 8-aminoquinoline receptor shows a 2 : 1 binding according to 1D and 2D-¹HNMR experiments.

Off–on BODIPY-based chemosensors for selective detection of Al3+ and Cr3+versus Fe3+ in aqueous media

Off–on two channel BODIPY-based chemosensors, highly sensitive for trivalent cations. Selective sensing of Al³⁺ and Cr³⁺versus Fe³⁺ has been achieved.