Bifunctional fluorescent thiacalix[4]arene based chemosensor for Cu and F ions

A new thiacalix[4]arene based fluorescent sensor bearing two dansyl groups has been synthesized in cone conformation. In CH₃CN:CH₂Cl₂ (1:1), the presence of Cu (II) induces the formation of a 1:1 metal:ligand complex, which exhibits increasing emission at 433 nm at the expense of the fluorescent emission of 1 centered at 504 nm. The detection limit of the sensor for Cu²⁺ is 2×10⁻⁷ mol L⁻¹. For anion sensing, 1 shows a high selectivity for fluoride ions over other anions tested.     

A new colorimetric and fluorescent chemosensor based on thiacalix[4]arene for fluoride ions

A new thiacalix[4]arene based fluorescent chemosensor thiacalix[4]arene-N-(quinolin-8-yl)acetamide (TCAN8QA) has been synthesized. TCAN8QA has been found to exhibit highly selective behavior for F⁻ ions among all other anions, that is, Cl⁻, Br⁻, I⁻, PO₄⁻³, OH⁻, H₂PO₄⁻, and CH₃COO⁻ in the absorption spectra as well as in the emission spectra. Red shift and quenching in emission spectra constituting the signature for fluoride detection are due to photoinduced charge transfer (PCT) which can be attributed to deprotonation of acidic NH proton in the presence of fluoride ions.     

Thiacalix[4]arene based fluorescent probe for sensing and imaging of Fe3+ ions

A thiacalix[4]arene based fluorescent chemosensor 3 in the cone conformation has been synthesized and its recognition behaviour is evaluated toward various metal ions in mixed aqueous media. The chemosensor 3 showed high selectivity towards Fe(3+) ions by fluorescence quenching of excimer emission. Further, evaluation of the 3·Fe(3+) complex prepared in situ demonstrated great promise for the detection of the Fe(3+) ion in the presence of amino acids, blood serum and bovine serum albumin (BSA) solution. The compound 3 has suitable permeability into the PC3 cells and can be utilized as a Fe(3+) selective sensor in living cells (PC3 cells).     

A novel rhodamine-based thiacalix[4]arene fluorescent sensor for Fe3+ and Cr3+

The novel fluorescent sensor 1, which is comprised of two rhodamine B lactams as fluorophores that are 1,3-alternately linked to a thiacalix[4]arene, behaves as a highly sensitive ion-induced fluorescent sensor for Fe³⁺ and Cr³⁺. This compound was synthesized, and its recognition of metal ions was evaluated by fluorescence and absorption spectroscopy. The possible mechanism of Fe³⁺- and Cr³⁺-induced spirocycle opening of 1 leads to fluorescent and colorimetric enhancement, and these properties were investigated by spectroscopy, ¹H NMR and IR. The stoichiometric ratios and association constants of the complexes between 1 and these ions have been measured and calculated, and showed that the presence of Fe³⁺ or Cr³⁺ induced sensor 1 to form a stable 1:1 complex.     

Comparative density functional theory study on thiacalix[4]arene binding modes for Zn2+ and Cu2+

A comparative study of the Zn(2+) and Cu(2+) complexation with thiacalix[4]arene is presented using density functional theory methods. The structures and energetics of the possible binding modes of both metal complexes are investigated in detail. Two types of patterns were found in the second deprotonated species, adjacent or opposite phenolate groups, which determine the stability of the different binding modes. The most stable structure for both metal ions was predicted to be a distorted square planar coordination at lower rim with opposite phenolate groups, which has never been referred to in the literature. The results show a higher complexation ability of Cu(2+) than Zn(2+) for all of the binding modes, which is in good agreement with the previous study on liquid-liquid extraction experiments. The analysis of the electrostatic potential surfaces of the metal complexes allows us to conclude that the different complexation features can also be explained by a bigger charge transfer from the metal to the coordinated atoms in the case of the Cu(2+) complex.     

Luminescent CdSe-ZnS quantum dots as selective Cu2+ probe

Luminescent CdSe-ZnS quantum dots (QDs) were modified with bovine serum albumin (BSA) and used as selective copper ion probe. The fluorescence of the water-soluble QDs can be quenched only by Cu²⁺ and Fe³⁺ in physiological buffer solution. Approximate concentrations of other physiologically important cations, such as Zn²⁺, Na⁺ and K⁺ etc. have no effect on the fluorescence. Adding F⁻ to form the colorless complex FeF₆³⁻ can eliminate the interference of Fe³⁺. The detection limit of Cu²⁺ ions was 10 nM. The results can be explained in terms of strong binding of Cu²⁺ onto the surface of CdSe resulting in a chemical displacement of Cd²⁺ ions and the formation of CuSe on the surface of the QDs.     

柠檬酸盐稳定的水溶性CdSe量子点的合成及表征

以柠檬酸三钠为稳定剂在水溶液中合成了水溶性CdSe量子点,用X射线粉末衍射、透射电镜、紫外-可见吸收光谱和荧光发射光谱对CdSe量子点的结构、形貌及其荧光性质进行了表征.结果表明合成的CdSe量子点为立方闪锌矿结构,呈球形,分散性良好,平均尺寸约为2.6nm,具有窄且对称的荧光发射光谱,半峰宽为45nm.     

Magic sized ZnS quantum dots as a highly sensitive and selective fluorescence sensor probe for Ag+ ions

A green and simple chemical synthesis of magic sized water soluble blue-emitting ZnS quantum dots (QDs) has been accomplished by reacting anhydrous Zn acetate, sodium sulfide and thiolactic acid (TLA) at room temperature in aqueous solution. Refluxing of this mixture in open air yielded ZnS clusters of about 3.5 nm in diameter showing very strong and narrow photoluminescence properties with long stability. Refluxing did not cause any noticeable size increment of the clusters. As a result, the QDs obtained after different refluxing conditions showed similar absorption and photoluminescence (PL) features. Use of TLA as a capping agent effectively yielded such stable and magic sized QDs. The as-synthesized and 0.5 h refluxed ZnS QDs were used as a fluorescence sensor for Ag(+) ions. It has been observed that after addition of Ag(+) ions of concentration 0.5-1 μM the strong fluorescence of ZnS QDs was almost quenched. The quenched fluorescence can be recovered by adding ethylenediamine to form a complex with Ag(+) ions. The other metal ions (K(+), Ca(2+), Au(3+), Cu(2+), Fe(3+), Mn(2+), Mg(2+), Co(2+)) showed little or no effect on the fluorescence of ZnS QDs when tested individually or as a mixture. In the presence of all these ions, Ag(+) responded well and therefore ZnS QDs reported in this work can be used as a Ag(+) ion fluorescence sensor.     

Amphiphilic p-sulfonatocalix[4]arene-coated CdSe/ZnS quantum dots for the optical detection of the neurotransmitter acetylcholine

Water-soluble CdSe/ZnS (core-shell) semiconductor quantum dots surface-modified with tetrahexyl ether derivatives of p-sulfonatocalix[4]arene were synthesized for the optical detection of the neurotransmitter acetylcholine.     

Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu ions

Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu²⁺ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu²⁺ concentrations as low as 7.3 × 10⁻⁹ mol L⁻¹, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.     

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.     

Synthesis of a deep-cavity thiacalix[4]arene

A novel thiacalix[4]arene derivative bearing four phenyl groups on the upper rim was prepared by the direct condensation of biphenyl-4-ol with elemental sulphur. As revealed by X-ray diffraction analysis, this compound adopts the cone conformation in the solid state, thus creating a cavity with an extended π-aromatic system potentially applicable for solid-state inclusion of suitable molecules. Subsequent alkylation (RI/K₂CO₃/acetone, R=Me, Et, Pr) yielded tetraalkylated derivatives, which were studied for their conformational preferences using ¹H NMR spectroscopy. While the Me or Et derivatives are conformationally mobile and exhibit thermodynamic equilibria of several conformers in solution (CDCl₃ or CD₂Cl₂), the corresponding propoxy derivative is infinitely stable at room temperature.     

A phenanthrene-based calix[4]arene as a fluorescent sensor for Cu and F

A new phenanthrene-based fluorescent calix[4]arene (4) has been synthesized in cone conformation. This compound was examined for its fluorescent properties towards different metal ions (Na⁺, Li⁺, Mg²⁺, Ni²⁺, Ba²⁺, Ca²⁺, Cu²⁺, Pb²⁺) and anions (F⁻, Cl⁻, Br⁻, H₂₄PO⁻,${{\text{H}}_2{\text{PO}}_4}^{-}\text{,}$₃NO⁻,${{\text{NO}}_3}^{-}\text{,}$₄HSO⁻,${{\text{HSO}}_4}^{-}\text{,}$ CH₃COO⁻) by fluorescence spectroscopy. The properties of the compound were evaluated and show that it is a fluorescence sensor for Cu²⁺ and F⁻. With the addition of Cu²⁺ and F⁻, the fluorescence was severely quenched.     

Biosilicated CdSe/ZnS quantum dots as photoluminescent transducers for acetylcholinesterase-based biosensors

CdSe/ZnS core/shell quantum dots (QDs) are functionalized with mercaptoundecanoic acid (MUA) and subsequently covered with poly-L-lysine (PLL) as the template for the formation of the silica outer shell. This nanocomposite is used as a transduction and stabilization system for optical biosensor development. The covalent immobilization of the enzyme acetylcholinesterase from Drosophila melanogaster (AChE) during the formation of the biomimetically synthesized silica is used here as a model, relatively unstable enzyme, as a proof of principle. The enzyme is successfully immobilized onto the QDs and then stabilized by the PLL capping and the subsequent formation of the outer nanoporous silica thin shell, giving rise to the QD/AChE/PLL/silica biosensor. It is shown that the poly-L-lysine templated silica outer shell does not modify the optical properties of the quantum dots, while it protects the enzyme from unfolding and denaturation. The small pores of the silica shell allow for the free diffusion of the analyte to the active center of the enzyme, while it does not allow for the proteases to reach the enzyme. The response of the QD/AChE/PLL/silica nano-biosensor to its substrate, acetylcholine chloride, is evaluated by monitoring the changes in the QDs' photoluminescence which are related to the changes in pH. These pH changes of the surrounding environment of the QDs are induced by the enzymatic reaction, and are associated with the analyte concentration in the solution. The biodetection system proposed is shown to be stable with a storage lifetime of more than 2 months. The data presented provides the grounds for the application of this nanostructured biosensor for the detection of AChE inhibitors.     

Pyridinyl hydrazone derivatives of thiacalix[4]arene as selective extractants of transition metal ions

The recognition ability of pyridinyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards transition and alkali metals has been investigated by picrate extraction method. The stoichiometry of complexes and the extraction constants have been determined. It has been found that hydrazones do not extract alkali metal ions but show an excellent affinity towards transition and heavy metal cations. The removal of tert-butyl groups from calix[4]arene platform in the case of cone and 1,3-alternate isomers leads to an increase of d-ion extraction selectivity or efficiency.     

A pyrenyl-appended triazole-based calix[4]arene as a fluorescent sensor for Cd2+ and Zn2+

The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.     

La掺杂ZnS量子点的制备及其表征

ZnS量子点的发光强度较弱,用水相合成技术掺杂一定浓度的La3+可以增强其发光性能。本文以实验用N-乙酰-L-半胱氨酸作保护剂,Zn(Ac)2作锌源,Na2S作硫源、La(Ac)3作镧源合成La掺杂的ZnS量子点,并通过透射电镜(TEM)和X-射线粉末衍射(XRD)对其物相进行了表征。紫外-可见(UV-Vis)及荧光(PL)光谱性质亦进行了表征。     

(1+1) or (2+2) Coupling for bis(tosyloxyethoxy)benzenes with calix[4]arene and thiacalix[4]arene

As bifunctional reagents, bis(tosyloxyethoxy)benzenes can react with p-tert-butylcalix[4]arene or p-tert-butylthiacalix[4]arene to afford intramolecularly bridged (1+1) or intermolecularly bridged (2+2) products. It was found that the bridging pattern strongly depended on the structure of bis(tosyloxyethoxy)benzene and the kind of calixarene. For the ortho-isomer of bis(tosyloxyethoxy)benzene, intramolecularly bridged calix[4]arene and thiacalix[4]arene were the main products. For the para-isomer, the bridging reaction was in a (2+2) fashion. As for the meta-isomer, double thiacalix[4]arene and intramolecularly bridged calix[4]crown were synthesized.     

A highly efficient capillary electrophoresis-based method for size determination of water-soluble CdSe/ZnS core-shell quantum dots

This paper describes a highly efficient method for size determination of water-soluble CdSe/ZnS core-shell quantum dots (QDs) by capillary electrophoresis (CE) using polymer additive as sieving medium. The influence of some factors, such as kinds and concentrations of the sieving medium, pH, concentrations of the background electrolyte (BGE) and applied voltage, on the separation of QDs was investigated. Under the optimal separation conditions, four different sized QDs were successfully separated, and the relative standard deviation (RSD) of the migration times for these QDs was below 1.013%. In addition, an equation was fit by taking into account the correlation existing between the electrophoretic mobilities and the sizes of a set of QDs. The feasibility of this equation to measure the sizes of other QDs was confirmed by comparison with the sizes obtained by transmission electron microscopy (TEM) experiment. This work offers a novel method for size determination of QDs, and provides an important reference on the study of QDs based on CE.     

Macrocyclic anthracene-anchored calix[4]arene as a sensitive and selective fluorescent chemosensor for ytterbium ions

ABSTRACT

A novel anthracene anchored cone calix[4]arene pyridine amide receptor C4PA was synthesized and characterized by combination of spectroscopic and spectrophotometric techniques. Ion binding properties of C4PA towards a series of metal cations were investigated by UV and fluorescence spectra. A remarkable increase for receptor C4PA in fluorescence intensity in the presence of trace amounts of Yb³⁺ was observed. C4PA showed “turn on” type fluorescence response toward Yb³⁺ with high selectivity and C4PA also retained its selectivity toward Yb³⁺ in the presence of most competing metal ions.