A colorimetric and fluorescent sensor for sequential detection of copper ion and cyanide

A simple cation sensor 1 ((E)-9-((2-hydroxynaphthalen-1-ylimino)methyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-8-ol) bearing both a julolidine moiety and a naphthol moiety was designed and synthesized as a colorimetric sensor for Cu²⁺. In methanol solution of 1, the presence of Cu²⁺ led to a distinct naked-eye color change from yellow to purple. The proposed sensing mechanism might be attributed to the decrease in internal charge transfer band. Moreover, the resulting 1–Cu²⁺ complex sensed cyanide in a fluorometric way via fluorescent changes. These results demonstrate a novel type of the sequential recognition of Cu²⁺ and CN⁻ using two different sensing methods, color change, and fluorescence.     

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.     

An efficient sensor for relay recognition of Zn and Cu through fluorescence ‘off–on–off’ functionality

A new bis(8-carboxamidoquinoline) dangled binaphthol derivatized fluorescent sensor (L) was designed and synthesized. L behaves ratiometric response to Zn²⁺ with high selectivity accompanied by remarkable emission enhancement and red shift. The resultant L–Zn²⁺ complex can act as a Cu²⁺ sensing probe with fluorescence quenching behavior through direct Zn²⁺ ion replacement. Furthermore, the binding modes of Zn²⁺ and Cu²⁺ with L are elucidated by X-ray crystallographic analysis, respectively.     

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.     

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⁺.     

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.     

A new colorimetric and fluorescent bifunctional probe for Cu and F ions based on perylene bisimide derivatives

A perylene bisimide derivative (PBI) based colorimetric and fluorescent bifunctional probe PAM-PBI was designed and synthesized. It was highly selective and sensitive for distinguishing both Cu²⁺ and F⁻ from other ions through a conspicuous change of UV–vis and fluorescence spectra. The recognition of Cu²⁺ by PAM-PBI showed an obvious color change from rose red to purple in aqueous solution, while the sensing of F⁻ gave a marked color change from rose red to light green in THF.     

Ratiometric fluorescent and colorimetric sensors for Cu based on 4,5-disubstituted-1,8-naphthalimide and sensing cyanide via Cu displacement approach

Two 4,5-disubstituted-1,8-naphthalimide derivatives 1 and 2 were synthesized as ratiometric fluorescent and colorimetric sensors for Cu²⁺, respectively. In 100% aqueous solutions of 1, the presence of Cu²⁺ induces a strong and increasing fluorescent emission centered at 478 nm at the expense of the fluorescent emission of 1 centered at 534 nm. Compound 2 senses Cu²⁺ by means of a colorimetric (primrose yellow to pink) method with a thorough quench in emission attributed to the deprotonation of the secondary amine conjugated to the naphthalimide fluorophore. 1-Cu²⁺ and 2-Cu²⁺ sense cyanide in ratiometric way via colorimetric and fluorescent changes.     

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⁺.     

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.     

Syntheses, spectroscopic and structural characterizations and metal ion binding properties of Schiff bases derived from 4′-aminobenzo-15-crown-5

A series of benzyloxybenzaldehyde derivatives (1-4) were synthesized by the reactions of 4-(bromomethyl)benzonitrile with 4-hydroxy-3-methoxybenzaldehyde (vanillin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin), 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde. Condensation reactions among the new benzyloxybenzaldehyde derivatives (1-4) with 4′-aminobenzo-15-crown-5 yielded the new Schiff base compounds (5-8). Sodium complexes (5a-8a) and potassium complexes (5b-8b) were prepared with NaClO₄ and KI, respectively. All of these synthesized compounds were characterized on the basis of FT-IR, ¹H and ¹³C NMR, mass spectrometry and elemental analyses data. The solid state structures of compounds 8 and 5a were determined by X-ray crystallography. The extraction abilities of compounds 5-8 were also evaluated in CH₂Cl₂ by using several main group and transition metal picrates, such as Na⁺, K⁺, Pb²⁺, Cr³⁺, Ni²⁺, Cu²⁺ and Zn²⁺.     

Complete suppression of the fluorophore fluorescence by combined effect of multiple fluorescence quenching groups: A fluorescent sensor for Cu with zero background signals

The reaction-based fluorescent sensors have attracted increasing attention in the past decades. However, the application of these sensors for accurate sensing was significantly retarded by the background fluorescence from the sensors themselves. In this work, we demonstrated a novel strategy that the background fluorescence of the sensor could be completely eliminated by the combined effect of multiple fluorescence quenching groups. Based on this new strategy, as proof-of-principle study, a fluorescent sensor (CuFS) for Cu²⁺ was judiciously developed. In CuFS, three types of fluorescence quenching groups were directly tethered to a commonly used coumarin fluorophore. The fluorescence of coumarin fluorophore in CuFS was completely suppressed by the combined effect of these fluorescence quenching groups. Upon treatment with 22 μM Cu²⁺, sensor CuFS achieved a dramatic fluorescence enhancement (fluorescence intensity enhanced up to 811-fold) centered at 469 nm. The detection limits was determined to be 12.3 nM. The fluorescence intensity enhancement also showed a good linearity with the Cu²⁺ concentration in the range of 12.3 nM to 2 μM. By fabricating test strips, sensor CuFS can be utilized as a simple tool to detect Cu²⁺ in water samples. Furthermore, the fluorescent sensor was successfully applied in detecting different concentration of Cu²⁺ in 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.     

A triphenylamine based multi-analyte chemosensor for Hg and Cu ions in MeCN/H2O

A novel triphenylamine based oxidative chemosensor TOC was synthesized. The chromogenic and fluorogenic behaviors of TOC towards Hg²⁺ and Cu²⁺ ions in a binary mixture of MeCN/H₂O (9/1) were dramatically different. TOC displays colorimetric ‘naked eye’ recognition of Hg²⁺ and fluorogenic ‘turn on’ response towards Cu²⁺ via a unique cyclization reaction using two different detection modes. Moreover, TOCAZOL obtained from the oxidative cyclization reaction of TOC with Cu(ClO₄)₂ can be used as a selective fluorescent sensor toward Hg²⁺ ion.     

FRET-derived ratiometric fluorescence sensor for Cu

New N-(pyrenylmethyl)naphtho-azacrown-5 (1) was synthesized as an ‘On-Off’ fluorescent chemosensor for Cu²⁺. Excited at 240 nm corresponding to the absorption of naphthalene unit (energy donor) of 1, emission at 380 nm from pyrene unit (energy acceptor) is observed, indicating that intramolecular fluorescence resonance energy transfer (FRET-On) occurs in 1. When Cu²⁺ is added to a solution of 1, however, the fluorescence of pyrene is strongly quenched (FRET-Off) whereas that of naphthalene group is revived. Such FRET ‘On-Off’ behavior of 1 is observed only in the case of Cu²⁺ binding, but not for other metal cations. The high selectivity of 1 toward Cu²⁺ can be potentially applied to a new kind of FRET-based chemosensor. The FRET On-Off behavior is supported by computational studies. The calculated molecular orbitals of HOMO and LUMOs suggest the excited-state interactions leading to FRET from naphthalene to pyrene in 1, but no electron density changes in 1·Cu²⁺ complex.     

Synthesis, characterization and electrochemical properties of two new calix[4]arene derivatives bearing two ferrocene imine or ferrocene amine units at the upper rim

A novel calix[4]arene derivative with two ferrocenyl Schiff-base groups at the upper rim 3 has been synthesized from 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxy calix[4]arene and 4-ferrocenylaniline via condensation reaction. Reduction of 3 with sodium borohydride led to calix[4]arene derivative 4 with two amino ferrocenyl groups at the upper rim. The ferrocenyl Schiff-base calix[4]arene and its corresponding reduced amine have been purified and characterized by elemental analysis,¹H NMR, FTIR, Mass and UV-vis spectral data. Electrochemical properties of compounds 3 and 4 have been investigated. Cyclic voltammograms of 3 and 4 show reversible redox couples of ferrocene/ferrocinium at E_1/2=0.401 V and 0.346 V, respectively. Electrochemical studies show these redox active compounds electrochemically recognize trivalent lanthanides La³⁺ and Ce³⁺ and divalent Pb²⁺ and Cu²⁺cations. With ferrocenyl Schiff-base calix[4]arene 3 an anodic shift as large as 130 mV is observed on addition of one equivalent of Ce³⁺ ion. Also extraction properties of compound 4 towards some metal cations have been described. It has been observed that compound 4 has a good selectivity for metal cations Fe³⁺, Cu²⁺, Pb²⁺ and Cd²⁺ against Ni²⁺ and Co²⁺.     

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.     

Catenar bimetallomesogens derived from quinoxaline–salicylaldimine conjugates

The preparation, characterization, and mesomorphic properties of two series of tridentate N-salicylidene-2-hydroxyanilines and their metal complexes were described. The crystal and molecular structure of bis[2-hydroxy-4-propyloxy-N-(2-hydroxy-3,4-dipropyloxybenzylidene) aniline]copper(II) were determined by means of X-ray analysis. It crystallizes in the monoclinic space group P2(1)/n and a Z=4. The geometry at Cu²⁺ ions is square pyramidal with a THF solvent molecule coordinated. The core structure was nearly flat, and the intramolecular Cu–Cu atoms were separated by ca. 3.0163(6) Å. All compounds 2a formed smectic C phases, and copper complexes 1a–Cu were not mesogenic. In contrast, compound 2e and complexes 1b–Cu, 1d–Cu, 1e–Cu, and 1e–Pd exhibited columnar phases. The lack of mesomorphism in 1e–Zn was attributed to a preferred tetrahedral over square planar geometry. A N_cell equal to 2.44–2.92, calculated from powder XRD data within a 9.0 Å thick indicated that an induced structure correlated by two catenar-shaped molecules was formed in Col_h phases.     

Assembly of cyano-bridged Cu(II)/Cu(II) and Cu(I)/Cu(II) compounds obtained by controlled ration of cyanide

One reaction system of Cu²⁺, dipn, and CN⁻ with two different molar ratio sets of 1:1:5, and 2:1:8 produced two compounds 1 [Cu^II(dipn)][Cu^II(CN)₄], and 2, respectively (dipn = dipropylenetriamine). Their structures were determined by X-ray crystallography. Compound 2 is built from Cu(I) and Cu(II) centers, which are bridged by cyanide groups and metal-metal bonds. The magnetic properties of 1 and 2 were investigated in 2-300 K. Compound 1 exhibits an antiferromagnetic exchange interaction between copper(II) ions mediated by cyano-bridges.     

Synthesis and photophysical properties of water-soluble sulfonato-Salen-type Schiff bases and their applications of fluorescence sensors for Cu in water and living cells

A series of water-soluble sulfonato-Salen-type ligands derived from different diamines including 1,2-ethylenediamine (Et-1–Et-4), 1,2-cyclohexanediamine (Cy-1 and Cy-2), 1,2-phenylenediamine (Ph-1–Ph-3 and PhMe-1–PhMe-4), and dicyano-1,2-ethenediamine (CN-1) has been designed and prepared. Sulfonate groups of ligands ensure good stability and solubility in water without affecting their excited state properties. These ligands exhibit strong UV/Vis-absorption and blue, green, or orange fluorescence. Time-dependent-density functional theory calculations have been undertaken to reveal the influence of ligand nature, especially sulfonate groups, on the frontier molecular orbitals. Since their fluorescence is selectively quenched by Cu²⁺, the sulfonato-Salen-type ligands can be used as highly selective and sensitive turn-off fluorescence sensors for the detection of Cu²⁺ in water and fluorescence imaging in living cells.