Fluorescent chemosensor for Cu2+ ion based on iminoanthryl appended calix[4]arene

Calix[4]arene based podands 1a of cone conformation and 1b of 1,3-alternate conformation possessing imine units and bearing anthracene moieties have been synthesized by a 1 + 2 Schiff base condensation in good yields and examined for their cation recognition abilities towards cations such as lithium, sodium, potassium, nickel, cadmium, copper, zinc, lead, silver and mercury ions by UV–vis and fluorescence spectroscopy. The calix[4]arene derivative 1b shows a selective fluorescence enhancement in presence of Cu²⁺ ions among the various metal ions tested (Li⁺, Na⁺, K⁺, Ni²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Ag⁺ and Hg²⁺ ions). The colour of the solution changes from colourless to light yellow in the presence of Cu²⁺ ions. The stoichiometry of the complex formed between 1b and Cu²⁺ was found to be 1:1 as established by Job’s plot.     

A novel BF<Subscript>2</Subscript>–curcumin-based fluorescent chemosensor for detection of Cu<Superscript>2+</Superscript> in aqueous solution and living cells

A novel BF₂–curcumin-based chemosensor 1, namely monopicolinate of BF₂–curcumin complex, was designed, synthesized and applied for the detection of Cu²⁺ in aqueous buffer solution and living cells. Sensor 1 exhibited sensitive naked-eye color change toward Cu²⁺ from blue to pink in TBS solution and the detection limit was estimated to be 0.12 µM. The selectivity of sensor 1 for Cu²⁺ was high over competing metal ions (Ag⁺, Cu⁺, Hg²⁺, Mg²⁺, Ca²⁺, Co²⁺, Zn²⁺, Mn²⁺, Ni²⁺, Fe²⁺ and Fe³⁺). Based on the experimental results, the sensing mechanism was proposed for the Cu²⁺ triggered hydrolysis of 1 to BF₂–curcumin which has unique chromogenic and fluorogenic properties. Compared with other chemosensors with a similar mechanism, chemosensor 1 had a comparatively large Stokes shift and the emission wavelength was close to NIR. Moreover, cell imaging investigations indicated that sensor 1 has the potential to be applied for practical Cu²⁺ detection in biological systems.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

A highly selective turn-on fluorescent chemosensor for copper(II) ion

A new pyrene derivative (1) containing a diaminomaleonitrile moiety exhibits high selectivity for Cu²⁺ detection. Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence values for the system. The apparent association constant (K_a) of Cu²⁺ binding in chemosensor 1 was found to be 5.55×10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5-7.5.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

Ferrocene containing N-tosyl hydrazones as optical and electrochemical sensors for Hg2+, Cu2+ and F− ions

Ferrocene containing N-tosyl hydrazones as selective and sensitive optical and electrochemical chemosensors were synthesized and characterized by ¹H NMR, ¹³C NMR, ESI-MS and X-ray analysis. The cation and anion binding studies were carried out using various techniques including electrochemistry, UV–vis and ¹H NMR spectroscopy. Chemosensors 2a and 2b have shown excellent selective recognition toward Hg²⁺, Cu²⁺ and F^? through optical and electrochemical signals. The color of 2a and 2b in solution changed visibly from pale yellow to red upon addition of Hg²⁺ion, while the color of solution changed from pale yellow to yellow green upon addition of Cu²⁺, which can be easily detected by the naked eye.     

A dual-function chemosensor based on coumarin for fluorescent turn-on recognition of Hg2+ and colorimetric detection of Cu2+ in aqueous media

A novel coumarin derivative CTT was synthesized via the condensation of 7-(N,N-diethylamino) coumarin-3-aldehyde with 5-amino-1,3,4-thiadiazole-2-thiol and its structure was characterized using infrared spectroscopy (IR), ¹H NMR, mass spectrometry (MS) techniques, and elemental analysis. The recognition properties of CTT with metal ions were investigated in CH₃CN–H₂O (v/v = 1/1) solution using UV–vis absorption and fluorescence emission spectrum method. The results showed that CTT could monitor Cu²⁺ and Hg²⁺ simultaneously as a dual-function chemosensor in CH₃CN–H₂O (v/v = 1/1). CTT could be used to detect Cu²⁺ colorimetrically; when using CTT, a color change from yellowish-brown to yellowish-green could be readily observed by the naked eye. CTT showed turn-on fluorescent recognition of Hg²⁺, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of CTT. The recognition mechanism of CTT for Cu²⁺ and Hg²⁺ was studied by experiments and theoretical calculations, respectively. Therefore, CTT has the ability to be a “single chemosensor for dual targets.”     

A facile ratiometric and colorimetric azo-dye possessing chemosensor for Ni2+ and AcO− detection

A new tailor-made colorimetric chemosensor 1, containing pyridine and benzothiazole moieties connected through an azo (–N = N–) linkage has been synthesised. In 9:1 (v/v) aqueous THF (pH 7.0 HEPES buffer), it showed a conspicuous naked-eye colour change upon binding to Ni²⁺ (colourless to light green) and AcO^?  (colourless to orange) resulting in their ratiometric sensing. The cation and anion recognition property of the chemosensor 1 was monitored by UV–vis spectral analysis and ¹H NMR titrations.     

A rigid conjugated pyridinylthiazole derivative and its nanoparticles for divalent copper fluorescent sensing in aqueous media

A rigid conjugated pyridinylthiazole derivative (1) and two bithiazole derivatives with similar structures (2, 3) were synthesized and characterized. Their optical properties were investigated through spectral analysis. By applying the three compounds to Cu²⁺ ions detection, it was shown that compound 1 could be employed as a selective and sensitive Cu²⁺ ions fluorescent chemosensor. For aqueous assay, the nanoparticles of compound 1 were prepared in aqueous media. Compared to the monomer, 1 nanoparticles were more fluorescence sensitive to Cu²⁺ ions. Its binding mode with Cu²⁺ ions was correlated well with Langmuir equation. Compound 1 nanoparticles exhibit a dynamic working range for Cu²⁺ ions from 0.02 to 0.50 μM with a detection limit of 10 nM. The proposed chemosensor has been used for the direct measurement of Cu²⁺ content in drinking water samples with satisfying results.     

Synthesis and complexation properties towards metal ions of new tri-substituted thiacalix[4]arenes

New thiacalix[4]arenes appended with three amide functions have been prepared. Their conformations have been solved thanks to ¹H NMR 2D correlation spectroscopy (COSY) and nuclear overhauser and exchange spectroscopy (NOESY). The complexation ability of these ligands towards various metal ions (Cd^2 + , Pb^2 + , Pd^2 + , Ni^2 + , Hg^2 + , Hg⁺, Ag⁺, Zn^2 +  and Cu^2 + ) has been investigated by the UV–vis absorption and the stoichiometry of the metal–ligand complexes was determined.     

Sulfonamide and Morpholine‐Based Dual Chemosensor for Cu2+ and Ag+ in Different Solvent Media

The detection of cations has attracted considerable interest because of their importance in various physiological processes. In this study, compound 1 bearing sulfonamide and morpholine functionalities was synthesized. Its structure was well characterized by NMR spectroscopy and mass spectrometry. UV/vis absorption spectra and fluorescence spectra indicated that it displayed high sensitivity and selectivity for Cu²⁺ and Ag⁺ by switching solvent media. It means that: (1) it showed selective response to Cu²⁺ in acetonitrile, (2) whereas it exhibited high selectivity for Ag⁺ in water. The density functional theory calculations were used to clearly explain the different recognition behaviors in different solvent media. This research suggests that compound 1 bearing sulfonamide and morpholine functionalities could act as a multifunctional chemosensor for monitoring multiple cations by changing solvent media and provides an alternative approach to design novel dual cations chemosensors.     

Novel azo-dye quinazolinones as colorimetric chemosensors for detection of cobalt and ferrous ions in aqueous medium

Highly efficient azo-day quinazolinone derivatives carrying a π bond and OH electron donor groups have been designed, synthesized, and evaluated as colorimetric chemosensors for detecting metal ions in biological and environmental samples, which was further supported by the DFT studies and UV–vis titration experiment. The 3-amino-2-styrylquinazolin-4(3H)-one (1) was directed to react with phenols during a diazotization type reaction to form a series of azo-day 3-(diazenyl)-2-(styryl)quinazolin-4(3H)-one (4a-e), which could not only have been confirmed by FTIR, H¹NMR, C¹³NMR, Ms and elemental analysis but could also be easily used for the detection of metal ions. Compound 4c exhibited a rapid qualitative and quantitative method for the detection of Co^II at λ max (582 nm) and Fe^II at λ max (566 nm) in an aqueous solution. The current study introduces a facile, low cost, more specific and selective chemosensor for detecting trace amounts of cobalt and ferrous ions.     

Benzothiazole-based heterodipodal chemosensor for Cu2+ and CN– ions in aqueous media

A simple and selective chemosensor, A, was developed for recognizing Cu²⁺. The emission spectra of receptor A showed a fluorescence quenching response upon addition of Cu²⁺ with a low detection limit of 4.51 nM, significantly less than the WHO recommended guideline for drinking water. In addition, the formed A?Cu²⁺ complex was examined for secondary sensing of anions. The A?Cu²⁺ complex showed selectivity for CN^– via a recovering emission profile of A.     

Novel versatile imine—enamine chemosensor based on 6-nitro-4-oxo-4H-chromene for ion detection in solution, solid and gas-phase: synthesis, emission, computational and MALDI-TOF-MS studies

A new versatile emissive molecular probe (3) derived from 1,5-bis(2-aminophenoxy)-3-oxopenthane bearing two units of 6-nitro-4-oxo-4H-chromene- has been prepared by a Schiff-base condensation method using conventional and green, ultrasound-aided, methods. The dry yellow powder was characterized as the imine species (3). These imine species, however, where found to rapidly convert to their enamine form (4) in solution, under the presence of water traces. This reaction was computationally studied through Density Functional Theory (DFT) in order to investigate the relative stability of the molecular pair 3/4. The sensing properties of the enamine (4) towards various metal ions were investigated via absorption and fluorometric titrations in solution in dichloromethane, acetonitrile and DMSO. The compound shows a fluorescent turn-off response in the presence of Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Ag⁺ over the other metal ions studied, such as Li⁺, Na⁺, K⁺, Ca²⁺, Co²⁺ and Ni²⁺, being stronger for Cu²⁺ and Hg²⁺. The gas phase chemosensing abilities of (3) were also explored suggesting (3) as new active MALDI-TOF-MS matrix by two dry methods showing a strong selectivity towards Cu²⁺ and Ag⁺. Our preliminary results show promising uses of (3) supported in PPMA films as metal ion solid chemosensor.     

Photoactive chemosensors 4: a Cu protein cavity mimicking fluorescent chemosensor for selective Cu recognition

Fluorescent chemosensor 3 can sense Cu²⁺ ions (1-8 μM) even in the presence of elevated levels of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Ag⁺ and Pb²⁺ (5000 μM). 3 can also analyze for Ag⁺ ions (50-500 μM) in the presence of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺ (5000 μM) but Cu²⁺ strongly interferes.     

A highly selective colorimetric and fluorescent chemosensor for Cr2+ in aqueous solutions

A new rhodamine-based chemosensor was synthetized through a modified copper-catalyzed [3+2]-cycloaddition of an azidocoumarin with an alkynyl-rhodamine. Its sensing properties toward various metal cations in aqueous solutions were investigated by colorimetric changes, UV–vis and fluorescence spectroscopies. The sensor exhibited a high selectivity for Cr²⁺ over Cr³⁺ and other divalent cations such as Cu²⁺, Mg²⁺, Zn²⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺ and Ni²⁺. The linear range of detection by fluorescence spectroscopy is 0.07–3.5 mM, with a detection limit of ca. 64 μM. The binding mode of Cr²⁺ with the sensor was rationalized through experimental evidences.     

A ratiometric chemosensor for fluorescent determination of Hg based on a new porphyrin-quinoline dyad

Quinolin-8-ol p-[10′,15′,20′-triphenyl-5′-porphyrinyl]benzoate (1) was synthesized for the first time and developed as a ratiometric fluorescent chemosensor for recognition of Hg²⁺ ions in aqueous ethanol with high selectivity. The 1–Hg²⁺ complexation quenches the fluorescence of porphyrin at 646 nm and induces a new fluorescent enhancement at 603 nm. The fluorescent response of 1 towards Hg²⁺ seems to be caused by the binding of Hg²⁺ ion with the quinoline moiety, which was confirmed by the absorption spectra and ¹H NMR spectrum. The fluorescence response fits a Hill coefficient of 1 (1.0308), indicating the formation of a 1:1 stoichiometry for the 1–Hg²⁺ complex. The analytical performance characteristics of the chemosensor were investigated. The sensor shows a linear response toward Hg²⁺ in the concentration range of 3 × 10⁻⁷ to 2 × 10⁻⁵ M with a limit of detection of 2.2 × 10⁻⁸ M. Chemosensor 1 shows excellent selectivity to Hg²⁺ over transition metal cations except Cu²⁺, which quenches the fluorescence of 1 to some extent when it exists at equal molar concentration. Moreover, the chemosensor are pH-independent in 5.0–9.0 and show excellent selectivity for Hg²⁺ over transition metal cations.     

New fluorescent sensor for antimony and transition metal cations based on rhodamine amide-arm homotrioxacalix[3]arene

A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb³⁺, Fe³⁺, Ni²⁺), a significant fluorescent enhancement in the range of 500–600 nm and colorimetric change was observed.     

Terphenyl based fluorescent chemosensor for Cu and F ions employing excited state intramolecular proton transfer

A new terphenyl based bifunctional fluorescent chemosensor 3a has been synthesized, which demonstrates selective optical recognition of Cu²⁺ and F⁻ ions in two contrasting modes. The compound shows highly selective ‘On-Off’ switchable behavior toward Cu²⁺ ions and ‘On-Off-On’ behavior toward F⁻ ions among various cations and anions tested. The detection limits of chemosensor for Cu²⁺ and F⁻ ions are found to be 100 nM and 10 nM, respectively.     

A New Fluorescent Chemosensor for Cu2+ Based on 1,2,3,4,5,6,7,8,9,10‐Decahydroacridine‐1,8‐dione Fluorophore

A new chemosensor for Cu²⁺ was synthesized based on 1,2,3,4,5,6,7,8,9,10‐decahydroacridine‐1,8‐dione dyes, which exhibited an obvious fluorescent selectivity to the sensing of Cu²⁺ ions over other cations, such as Na⁺, K⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺, Ag⁺ and Pb²⁺. Moreover, it presented a fluorescent switch function when EDTA was added to the compound‐Cu²⁺ complex in examined systems.