New cavitand derivatives bearing four coumarin groups as fluorescent chemosensors for Cu and recognition of dicarboxylates utilizing Cu complex

New cavitand derivatives (1, 2) bearing four coumarin groups were synthesized, and the binding properties of these cavitands towards metal ions were examined through their fluorescent changes. Cavitand 1 effectively recognized the Cu²⁺ ions among the metal ions examined. The recognition of cavitand 1-Cu²⁺ with dicarboxlyates is also described.     

Azobenzene coupled chromogenic receptors for the selective detection of copper(II) and its application as a chemosensor kit

Azobenzene-based receptors 1-4 as colorimetric sensing materials were synthesized and their sensing properties were examined. In solution, the proposed sensing materials give rise to a large cation-induced hypochromic shift for Cu²⁺ resulting in a change from red to pale-yellow, whereas no significant color change was observed upon addition of other selected metal ions. The use of the silica gel plate modified with immobilization of receptor 4 to detect Cu²⁺ was also reported.     

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.     

A chemosensor showing discriminating fluorescent response for highly selective and nanomolar detection of Cu and Zn and its application in molecular logic gate

A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu²⁺ and Zn²⁺ in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn²⁺ and Cu²⁺ ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu²⁺ and Zn²⁺ ions, respectively. Further, we have effectively utilized the two metal ions (Cu²⁺ and Zn²⁺) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm.     

Coumarine–imino–C2-glucosyl conjugate as receptor for Cu in blood serum milieu,on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition

A coumarine–imino–C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu²⁺ in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7–10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on–off behavior has been clearly demonstrated on the basis of the binding variability of Cu²⁺ to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and ¹H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu²⁺ by L. The structural features of [CuL]₂ complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu²⁺ on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu²⁺ even in blood serum and exhibits appropriate fluorescence responses in living cells.     

Epoxy-based polymer bearing 1-naphthylamine units: highly selective fluorescent chemosensor for ferric ion

A simple epoxy-based polymer 1 bearing 1-naphthylamine units has been synthesized and its recognition behaviors toward various metal ions have been investigated in THF-water (8:2, v/v) solution. The designed polymer 1 was found to exhibit selective ON-OFF-type fluorosensing behavior toward Fe³⁺ ions over other representative metal ions such as Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, and Hg²⁺ ions.     

Regulation of metal ion recognition by allosteric effects in thiacalix[4]crown based receptors

Three new ditopic receptors 3a-c based on thiacalix[4]arene of 1,3 alternate conformation possessing two different complexation sites have been designed and synthesized for both soft and hard metal ions. The imino nitrogens bind soft metal ion (Ag⁺/Pb²⁺/Cu²⁺) and the crown moiety binds K⁺ ion. The preliminary investigations show that 3a-c behave as ditopic receptors for Ag⁺/K⁺, Pb²⁺/K⁺, and Cu²⁺/K⁺ ions, respectively. In all the three receptors it was observed that the formation of 3a·Ag⁺/3b·Pb²⁺/3c·Cu²⁺ complex triggers the decomplexation of K⁺ ion from crown moiety and acts as a gateway, which regulates the binding of alkali metal to crown moiety. Thus, allosteric binding between metal ions ‘switch off’ the recognition ability of crown ether ring.     

Highly selective colorimetric fluorescence sensor for Cu: cation-induced ‘switching on’ of fluorescence due to excited state internal charge transfer in the red/near-infrared region of emission spectra

A 1,8-naphthalimide-based colorimetric fluorescence perinone dye, receptor 1 is reported herein for the selective detection of Cu²⁺ over the other heavy and transition metal ions. Receptor 1 shows a strong colorimetric change from orange to purple and a dramatic enhancement of fluorescence intensity due to cation-induced excited state internal charge transfer during the sensing event, that is, a dual optical response that would facilitate naked-eye detection of Cu²⁺.     

Synthesis of a sugar-aza-crown ether-based cavitand as a selective fluorescent chemosensor for Cu ion

A chemosensor based upon the sugar-aza-crown ether 7 with one anthracenetriazolymethyl moiety was prepared and its fluoroionophoric properties toward transition metal ions were investigated. Chemosensor 7 exhibits highly selective recognition toward Cu²⁺ ion among a series of tested metal ions in MeOH solution. The association constant for 7∗Cu²⁺ in MeOH solution was calculated to be 2.5 × 10⁴ M⁻¹.     

Metallomesogens derived from benzoxazoles-salicylaldimine conjugates

The synthesis, characterization, and mesomorphic properties of a new series of Schiff bases 2a-h and metal complexes 1a-h-M are prepared and their mesomorphic properties studied. Two single crystallographic structures of 2d (n=12, m=1) and 1g-Pd (n=m=12) were determined by X-ray analysis. Both compounds crystallize in a triclinic space group P−1. A dimeric structure formed by intermolecular H-bonds in 2d was observed, giving nematic phase due to a better aspect ratio. The central geometry at Pd²⁺ ion is nearly perfect square plane. All Schiff bases 2a-h formed N or/and SmC phases. The formation of mesophases of complexes 1a-h-M was strongly dependent on metal ions incorporated. All Cu²⁺, Ni²⁺ and Pd²⁺ complexes exhibited N or/and SmC phase, respectively. However, Zn²⁺ and Co²⁺ complexes were not mesogenic. The lack of mesomorphism was probably attributed to a preferred tetrahedral geometry at Zn²⁺ and Co²⁺ over a square-planar geometry at Cu²⁺ and Pd²⁺.     

Azo 8-hydroxyquinoline benzoate as selective chromogenic chemosensor for Hg and Cu

Azo 8-hydroxyquinoline benzoate (2) was synthesized and studied to detect metal ions. Distinct color change was found for compound 2 in the presence of transition metal ions Hg²⁺ or Cu²⁺ in CH₃CN, respectively, which makes it possible for distinguishing Hg²⁺ and Cu²⁺ from other metal ions by the ‘naked eye’.     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

Squaraine-based colorimetric and fluorescent sensors for Cu-specific detection and fluorescence imaging in living cells

New squaraine-based chemosensors SQ1 and SQ2 functionalized with 2-picolyl units were first synthesized and used as highly selective and sensitive colorimetric and fluorometric dual-channel sensors for Cu²⁺-specific recognition in aqueous systems. Among a series of individual metal ions, only Cu²⁺ could result in dramatic color changes. We also evaluated their capability of biological applications and found that SQ2 could be successfully employed as a Cu²⁺-selective probe in the fluorescence imaging of living cells.     

A novel chromatism switcher with double receptors selectively for Ag in neutral aqueous solution: 4,5-diaminoalkeneamino-N-alkyl-l,8-naphthalimides

Two novel fluorosensors of 4,5-disubstituted-N-alkyl-l,8-naphthalimide derivatives (H1, H2, H3) with double ethylenediamino receptors, double propylenediamino receptors, or one methylpiperazine receptor were synthesized, respectively. Their fluorescence and absorption in the presence or absence of nine metal ions were studied. In the presence of Ag⁺, H1's absorption moved to long wavelength with color change from yellow-green to red, its quenching and red shift in fluorescence were also remarkable. Similarly, H1's fluorescence was also strongly quenched in the presence of Cu²⁺. In addition, H1 and H2 show high pH sensitively. There was 139-folds fluorescence enhancement for H1, 22-folds for H2, and 4-folds for H3 when pH was changed from 8 to 3, respectively.     

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.     

Three different fluorescent responses to transition metal ions using receptors based on 1,2-bis- and 1,2,4,5-tetrakis-(8-hydroxyquinolinoxymethyl)benzene

The dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (3) and tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl)benzene (5) have been synthesized through nucleophilic substitution of respective 1,2-bis(bromomethyl)benzene (2) and 1,2,4,5-tetra(bromomethyl)benzene (4) with 8-hydroxyquinoline (1). For comparison, 1,3,5-tris(8-hydroxyquinolinoxymethyl)benzene derivatives (7a and 7b) have been obtained. The complexation behavior of these podands towards Ag⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ metal ions has been investigated in acetonitrile by fluorescence spectroscopy. The sterically crowded 1,2,4,5-tetrapod 5 displays unique fluorescence ‘ON-OFF-ON’ switching through fluorescence quenching (λ_max 395 nm, switch OFF) with <1.0 equiv of Ag⁺ and fluorescence enhancement (λ_max 495 nm, switch ON) with >3 equiv Ag⁺ and can be used for estimation of two different concentrations of Ag⁺ at two different wavelengths. The addition of Cu²⁺, Ni²⁺, and Co²⁺ metal ions to tetrapod 5 causes fluorescence quenching, i.e., ‘ON-OFF’ phenomena at λ_max 395 nm for <10 μM (1 equiv) of these ions but addition of Zn²⁺ and Cd²⁺ to tetrapod 5 results in fluorescence enhancement with a gradual shift of λ_em from 395 to 432 and 418 nm, respectively. Similarly, dipod 3 behaves as an ‘ON-OFF-ON’ switch with Ag⁺, an ‘ON-OFF’ switch with Cu²⁺, and an ‘OFF-ON’ switch with Zn²⁺. The placement of quinolinoxymethyl groups at the 1,3,5-positions of benzene ring in tripod 7a-b leads to simultaneous fluorescence quenching at λ_max 380 nm and enhancement at λ_max 490 nm with both Ag⁺ and Cu²⁺. This behavior is in parallel with 8-methoxyquinoline 8. The rationalization of these results in terms of metal ion coordination and protonation of podands shows that 1,2 placement of quinoline units in tetrapod 5 and dipod 3 causes three different fluorescent responses, i.e., ‘ON-OFF-ON’, ‘ON-OFF’, and ‘OFF-ON’ due to metal ion coordination of different transition metal ions and 1, 3, and 5 placement of three quinolines in tripod 7, the protonation of quinolines is preferred over metal ion coordination. In general, the greater number of quinoline units coordinated per metal ion in 5 compared with the other podands points to organization of the four quinoline moieties around metal ions in the case of 5.     

Solvent-dependent chromogenic sensing for Cu and fluorogenic sensing for Zn and Al: a multifunctional chemosensor with dual-mode

A new multifunctional chemosensor 1 was synthesized and characterized by spectroscopic tools along with a single crystal X-ray crystallography. It can exhibit selective recognition responses toward Cu²⁺, Zn²⁺ and Al³⁺ in different solvent systems with bimodal methods (colorimetric and fluorescence). This sensor 1 detected Cu²⁺ ions through a distinct color change from colorless to yellow in aqueous solution. Interestingly, the receptor 1 was found to be reversible by EDTA. The detection limit (11 μM) of 1 for Cu²⁺ is much lower than WHO guideline (30 μM) in drinking water. In addition, the sensor 1 showed significant fluorescence enhancements in the presence of Zn²⁺ ion and Al³⁺ ion in two different organic solvents (DMF and MeCN), respectively. The binding modes of the three complexes were determined to be a 1:1 complexation stoichiometry through Job plot, ESI-mass spectrometry analysis, and ¹H NMR titration.     

Bisnitronyl nitroxides bridged by tetra(ethyleneoxy) sensing metal ions spectroscopically and electrochemically

Compound 1 containing two nitronyl nitroxide units bridged by tetra(ethyleneoxy) was designed and synthesized for sensing metal ions, by taking the features of nitronyl nitroxides: a chromophore showing absorption in visible range, reversible oxidation/reduction and coordination to metal ions. The absorption spectrum of 1 was altered markedly upon mixing with a few rare earth metal ions and some transition metal ions. Moreover, the oxidation potential of 1 was shifted to more positive range in the presence of metal ions including Pb²⁺, Ba²⁺, and Ca²⁺. Thus, compound 1 can sense metal ions both spectroscopically and electrochemically.     

Fluorescence sensing of Cu within a pseudo 18-crown-6 cavity

We report herein a pseudo-crown based fluorescent receptor (1) for the selective detection of Cu²⁺ cation. Receptor 1 can detect Cu²⁺ even in 5 μM level in acetonitrile-water (9:1 v/v). Compound 1 is very effective for the detection of Cu²⁺ amongst the series of metal ions studied (Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Pb²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Mn²⁺).     

Metal ion-induced FRET modulation in a bifluorophore system

A new fluorogenic sensor 1 capable of illustrating metal ion-triggered FRET changes has been synthesized. Based on the FRET changes, 1, bearing coumarin-fluorescein moieties, provides a selective sensor for Cu²⁺ and Hg²⁺ ions for experiments implemented in aqueous media with a chloride counter anion.