Synthesis of an Ag–ZnO nanocomposite catalyst for visible light-assisted degradation of a textile dye in aqueous solution

The photocatalytic activity of silver-deposited ZnO in the photodegradation of methyl orange (MO) was investigated. The as-prepared photocatalysts were characterized by X-ray diffraction, UV–visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The results showed that the silver-deposited ZnO had a visible light plasmon absorption band. The photocatalytic degradation experiment revealed that the catalytic efficiency of the Ag–ZnO composite in the degradation of MO was greater than that of pure ZnO samples. This study shows that the degradation process is dominated by the Ag–ZnO photocatalytic system, complying with a pseudo-first-order rate law. Under the experimental conditions, approximately 65.0% dye removal was achieved within 100 min.     

Synthesis and light absorption of benzotellurazole crown ether cyanine dye

Various methods for synthesis of 2-methyl-5,6-(1,4,7,10,13-pentaoxatridecamethyl-ene)benzotellurazole (8) are described. Under different conditions, alkylation of compound 8 with methyl iodide gave telluronium salt 1,2-dimethyl-5,6-(1,4,7,10,13-pentaoxatridecamethylene)benzo-tellurazolium iodide (15) or quaternary ammonium salt 2,3-dimethyl-5,6-(1,4,7,10,13-pentaoxatri-decamethylene)benzotellurazolium iodide (14) in high yields, repectively. The cyanine dye 3,3'-dimethyl-5,6,5',6'-bis(1,4,7,10,13-pentaoxatridecamethylene)telluracarbocyanine iodide (16) is obtained by condensation of 14 with ethyl orthoformate in acetic anhydride. The visible absorption of the cyanine dye is also discussed.     

Aggregation behavior of hydrophobically modified β-cyclodextrins in aqueous solution

Three amphiphilic -cyclodextrins in aqueous solution were investigated upon their aggregation behavior. Surface methods, conductivity and scattering methods were used to determine the cmc and radius of gyration of the aggregates. Depending on the cotenside it was possible to shift the cmc to lower concentrations. Above the cmc small spherelike aggregates existed.     

The development of a cholesterol biosensor using a liquid crystal/aqueous interface in a SDS-included β-cyclodextrin aqueous solution

Sodium dodecyl sulphate (SDS) including β-cyclodextrin (β-CD) (β-CD_SDS) was used to detect cholesterol at the 4-cyano-4′-pentylbiphenyl (5CB)/aqueous interface in transmission electron microscopy (TEM) grid cells. The β-CD acts as a host for SDS (guest). The guest SDS enclosed within the β-CD cavity was replaced with cholesterol by injecting cholesterol solution into the TEM cell at concentrations greater than 3 μM. The replacement of SDS with cholesterol was confirmed by pH measurement and high performance liquid chromatography (HPLC). The SDS excluded from the β-CD altered the planar orientation of the 5CB confined within the TEM grid cell to a homeotropic orientation. This planar-to-homeotropic transition was observed using a polarized optical microscope under crossed polarizers. This convenient TEM grid cell provides a new method for the selective detection of cholesterol without immobilization of the detecting receptors (enzyme, antibody, or aptamer) or the use of sophisticated instruments.     

Supramolecular assembly of a new squaraine and β-cyclodextrin for detection of thiol-containing amino acids in water

A new unsymmetrical aniline-based squaraine (SQ2) bearing binding unit of Hg²⁺ ion was designed and synthesised. SQ2 can form 1:2 inclusion complex with β-cyclodextrin, and the resulting complex, which undergoes absorption and fluorescence bleaching upon binding Hg²⁺, can serve as a turn-on colorimetric or fluorescent chemosensor in organic solvent-free aqueous solution for thiol-containing amino acids with high selectivity and tunable measuring range.     

Complexation of β-cyclodextrin with carborane derivatives in aqueous solution

β-Cyclodextrin formed the most robust complexes with o-carboranols 1b and 1c in aqueous solution, and the association constants estimated from NMR titration studies indicated K_a >1 × 10⁶ M⁻¹ and K_a = 6 × 10⁵ M⁻¹, respectively.     

Molecular dynamics simulation in aqueous solution of N-methylazetidinone as a model of β-lactam antibiotics

In this article, we analyze the results of a molecular dynamics simulation in aqueous solution of the N-methylazetidinone molecule, often used to model β-lactam antibiotics. The radial distribution functions (RDFs) corresponding to the most interesting atoms, in terms of reactivity, are presented. We focus our study on the effect of a polar environment on the molecule. The solvent structure around the system is compared to the structure of β-lactam-water complexes, as obtained in a previous study of reaction mechanisms for the neutral and alkaline hydrolyses of N-methylazetidinone. Two types of complexes have been considered which are related to different hydrolysis mechanisms having similar energy barriers at the rate-limiting step of the reaction path. In the first type, the β-lactam-water interaction takes place through the oxygen carbonyl atom and there is agreement between the maxima of the RDFs obtained here and the ab initio structure of the complexes previously reported. In the second type, the interaction takes place through the nitrogen atom and we do not predict a coordination layer around the β-lactam nitrogen atom. The results suggest that in aqueous solution hydrolysis of the carbonyl group is the most probable starting point for the overall hydrolysis reaction. Some discussion on the use of cluster models to represent the solvent effect is included. Received: 29 July 1998 / Accepted: 13 October 1998 / Published online: 1 February 1999     

Deposition of gold nanoparticles on β-FeOOH nanorods for detecting melamine in aqueous solution

This study demonstrates a facile but efficient approach to deposit metallic (gold) nanoparticles on β-FeOOH nanorods to obtain Au/β-FeOOH nanocomposites without the assistance of any polymers or surfactants at ambient conditions. In this method, a strong reducing agent (NaBH(4)) can be used to extensively produce Au nanoparticles, converting β-FeOOH into Fe(3)O(4) and depositing gold particles onto magnetic Fe(3)O(4) simultaneously. The microstructure, composition, and chemical properties of the obtained nanocomposites are characterized by various advanced techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis spectroscopy. Moreover, the Au/β-FeOOH nanocomposite can be used to detect trace melamine using UV spectrum in the ultraviolet wavelength range (190-260 nm), in which the nanocomposites show a higher sensitivity toward melamine due to the promotion of symmetry-forbidden bands (n→π(*)) of melamine molecules and also avoid the disturbance of commercial products containing solid colloids or food colorings that distort visual spectrum during the detection of chemical sensing. The deposition mechanisms and their sensing detection toward melamine are discussed.     

The complexation of flurbiprofen with β-cyclodextrin: a NMR study in aqueous solution

The complexation process between racemic flurbiprofen and β-cyclodextrin in solution was investigated by 1D and 2D proton NMR spectroscopy. In the presence of β-cyclodextrin, the aromatic protons of flurbiprofen were the most affected, suggesting a strong involvement of the phenyl groups in the inclusion mechanism. The stoichiometry of the complex was determined by the method of continuous variation, using the chemical induced shifts of both host and guest protons. The association constant, K_a of the obtained complex was calculated and found to be 2483.8 M^?1. On the other hand, signals belonging to the protons associated with the carboxyl group are split in the presence of β-cyclodextrin indicating enantiomeric differentiation. Rotating frame NOE spectroscopy, (ROESY), was used to ascertain the solution geometry of the host–guest complex. The result suggested that the flurbiprofen molecule fully penetrates the β-cyclodextrin cavity with the carboxyl group protruding from the primary hydroxyl side and the phenyl group close to the secondary rim.     

Photocatalytic performance of combustion synthesized β-Ga2O3 for the degradation of tri-n-butyl phosphate in aqueous solution

Nanostructures of β-Ga₂O₃ were prepared by solution combustion route using urea as the fuel. Transmission electron microscopic measurements and powder X-ray diffraction measurements confirmed the crystalline nature of β-Ga₂O₃ with particle size in the range of 10–15 nm. Surface area measurements indicated that the synthesized semiconductor catalyst had a specific surface area of 30 m²/g. In this work, photocatalytic degradation studies of tri-n-butyl phosphate using nano sized β-Ga₂O₃ is presented. A cylindrical photoreactor was used for the degradation studies and gas chromatographic estimation was adopted to follow the extent of degradation. Complete degradation of tributyl phosphate could be achieved in less than 40 min using 10 mg of photocatalyst and 0.5 mL of H₂O₂ for 1000 mL of 400 ppm TBP. Degradation of TBP was found to follow pseudo first order kinetics and the rate of TBP degradation was found to be superior for β-Ga₂O₃ photocatalyst compared to P-25 TiO₂.     

Characterization of the inclusion complex of β-cyclodextrin with sorbic acid in the solid state and in aqueous solution

Crystal structure of β-cyclodextrin (β-CD) complexes with sorbic acid, usually as food preservative, has been determined by single-crystal X-ray diffraction at 113 K. The space group of β-cyclodextrin-sorbic acid complex is P1 with unit cell dimensions of a = 15.284(3) Å, b = 15.402(3) Å, c = 17.981(4) Å, α = 99.67(3)°, β = 112.83(3)°, γ = 102.48(3)° and Z = 1. The result indicates that the β-CD molecules form head-to-head dimers which pack in the intermediate mode. Each dimer contains two guest molecules whose methyl groups are located at the dimer interface while the carboxyl groups protrude from the β-CD primary faces. Water molecules (25.5) are distributed outside the cyclodextrin cavity over 31 sites. Furthermore, nuclear magnetic resonance spectroscopy (¹H NMR) has been employed to investigate the inclusion behavior between the host β-CD and guest sorbic acid in aqueous solution. The results obtained enabled us to structurally characterize the β-CD inclusion complex with sorbic acid.     

Synthesis of a β-cyclodextrin-modified Ag film by the galvanic displacement on copper foil for SERS detection of PCBs

A mono-6-thio-β-cyclodextrin-modified silver film was synthesized via galvanic displacement on copper foil. The prepared silver films could enrich non-polar polychlorinated biphenyls (PCBs) molecules from hydrophilic phase using thiolate β-cyclodextrins (SH-β-CDs) as receptors. The components of as-prepared Ag-coated-Cu (Ag-Cu) film were confirmed by powder X-ray diffraction (XRD). Both surface-enhanced Raman spectroscopy (SERS) and energy dispersive X-ray spectroscopy (EDS) measurements gave strong evidences that the thiolated β-cyclodextrins (SH-β-CDs) had been immobilized on the surface of silver film. Compared to the substrates prepared in the absence of SH-β-CD, the surface morphology of the CD-modified Ag films was obviously changed. The interfacial enrichment and the capability of substrates to form inclusion complexes with PCBs molecules were tested by using PCB-15 (4,4'-dichlorobiphenyl) as the probe molecules via SERS technique. The measured SERS spectra could distinguish the PCB-15 molecules at micro-molar level according to the most intense CCC bending in-plane mode of PCBs. The enhancement factor (EF) of the SERS substrates for PCB-15 was 1.2×10(5), which was comparable with a number of previous reports.     

Solubilization of cholesterol in aqueous solution by two β-cyclodextrin dimers and a negatively charged β-cyclodextrin derivative

Two βCD dimers (linked by succinic acid, 2, or ethylenediaminetetraacetic acid, EDTA, 3, bridges) and a negatively charged monomer derivative of βCD, 1, have been synthesized and their ability to solubilize cholesterol in aqueous solution was studied. The three compounds exhibit a great capacity in solubilizing cholesterol as, for instance, concentrations up to 6 mM of cholesterol were measured in the presence of 25 mM of 3. The phase-solubility diagrams of the two dimers exhibit A _L type profiles while the monomer 1 follows an A _P isotherm. The cholesterol/dimer complexes have 1:1 stoicheiometries while monomer 1 forms two complexes with molar ratios of 1:1 and 1:2 (cholesterol/1). The equilibrium constants are K _1:1 = (5.9 ± 0.3) × 10⁴ M^?1 and K _1:1 = (8.8 ± 0.2) × 10⁴ M^?1 for 2 and 3, respectively, and K _1:1 = 73 ± 19 M^?1 and K _1:2 = 204 ± 65 M^?1 for 1. The comparison of K _1:1(3) with the product K _1:1 × K _1:2 (1) reveals that a chelate effect in binding the cholesterol by 3 exists. The structure of the cholesterol/3 complex was studied by ROESY experiments and by molecular dynamics simulations.     

Synthesis of new binary porphyrin–cyanine conjugates and their self-aggregation in organic-aqueous media

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Electrochemically active–inactive switching molecular beacon for direct detection of DNA in homogenous solution

We report a new kind of electrochemical molecular beacon, termed “electrochemically active–inactive switching molecular beacon”, for direct detection of DNA in homogenous solution. The electrochemical molecular beacon consists of a stable stem-loop oligonucleotide carrying two carminic acid moieties (acting as electrochemical reporter) attached at its termini. In a close form, the electrochemical signal is quenched because two carminic acid moieties are close enough to associate into dimer. In the presence of the complementary DNA target, the electrochemical molecular beacon undergoes a conformational transformation from closed (hairpin) to open (linear) structure, which is associated with an increase in electrochemical signal. We found that the electrochemical molecular beacon is as effective as conventional molecular beacon in signaling the presence of complementary target and discriminating targets that differ by a single nucleotide. The proposed electrochemical molecular beacon has a great potential for investigating the interactions of DNA-protein and developing electrochemical real-time polymerase chain reaction.     

Synthesis of a new class of β-iodo N-alkenyl 2-pyridones

A new method for the synthesis of β-iodo N-alkenyl 2-pyridones from substituted 2-propargyloxypyridines has been discovered . These compounds present a unique complement of orthogonal functionality and structural characteristics that are unavailable via other routes. The ready access to these compounds renders them an important entry point for the preparation of more complex N-alkyl pyridone-containing targets.     

Synergistic enhancement of the fluorescence intensity of 4,5-benzopiaselenol by surfactants and β-cyclodextrin in aqueous solution

The synergistic enhancement of the fluorescence intensity of 4,5-benzopiaselenol (I _F ^Se-DAN ) by surfactants (Sf) and -cyclodextrin (-CD) has been studied. The (I _F ^Se-DAN ) in sodium dodecyl sulfate (SDS)//gb-CD was approximately 30 times greater than that in water, and 5–6 times greater than that in either SDS or -CD solutions alone, and a blue-shift of the emission wavelength was observed.¹H-NMR experiments and determination of CMC values of Se-DAN/-CD, Se-DAN/SDS, and Se-DAN/SDS/-CD systems reveal that the synergistic fluorescence enhancement was produced by the SDS monomer/-CD inclusion complex. In essence, the synergistic enhancement is due to the altered microenvironment experienced by Se-DAN upon its transfer from water to the hydrophobic cavity upon complexation.     

Synthesis of β-fluoroenones and their reductive rearrangement in aqueous media

In this paper, a simple and efficient preparation of β-fluoroenones, as a mixture of E/Z isomers with the E-isomer as the main product, from 1,2-allenic ketones by using TBAF·3H₂O in water as a nucleophilic fluorination agent has been developed. Moreover, in exploring the synthetic applications of β-fluoroenones, an unprecedented reductive defluorination rearrangement of β-fluoroenones toward enones under mild conditions in aqueous media was also discovered.     

Polyurethane Molecular Stamps for the in situ Synthesis of DNA Microarray

Fabrication of polyurethane molecular stamps (PU stamps) based on polypropylene glycol (PPG) and toluene dissocyanate (TDI), using 3,3′-dichloro-4,4′-methylenedianiline (MOCA) as the crosslinker ,is reported. It was shown from the contact angle measurement that PU stamps surface has good affinity with acetonitrile,guaranteeing the well distribution of DNA monomers on patterned stamps. Laser confocal fluorescence microscopy images of oligonucleotide arrays after hybridization confirmed polyurethane is an excellent material for molecular stamps when ransferring polar chemicals and conducting rections on interfaces by stamping.