Volumetric and Viscosity Properties for the Binary Mixtures of 1-Octyl-3-methylimidazolium Tetrafluoroborate with Butanone or Alkyl Acetates

In this work, densities and viscosities for the binary mixtures of 1-octyl-3-methylimidazolium tetrafluoroborate, [C₈mim][BF₄], with butanone, methyl acetate, ethyl acetate, propyl acetate and butyl acetate have been determined at 298.15?K. These data were used to calculate the excess molar volumes $ V_{m}^{\text{E}} $ and the viscosity deviations (ln??)^E for the mixtures. It is shown that values of $ V_{m}^{\text{E}} $ are negative, while those of (ln??)^E are positive in the whole concentration range. The $ V_{m}^{\text{E}} $ values show their minimum at the composition of x _IL ????0.3, and the (ln??)^E values exhibit a maximum at the same mole fraction. For the binary systems, the absolute values of $ V_{m}^{\text{E}} $ decrease in the order: butanone?>?methyl acetate?>?ethyl acetate?>?propyl acetate?>?butyl acetate, whereas those of (ln??)^E decrease in the order: methyl acetate?>?ethyl acetate?>?propyl acetate?>?butyl acetate?>?butanone. The results are discussed in terms of the ion?Cdipole interactions between cations of the ionic liquid and the organic molecules and hydrogen bonding interactions between anions of the ionic liquid and the organic compounds.     

Smart methanol sensor based on silver oxide-doped zinc oxide nanoparticles deposited on microchips

We have prepared calcined silver oxide-doped zinc oxide nanoparticles (NPs) by a hydrothermal method using reducing agents in alkaline medium. The doped NPs were characterized by UV/vis, FTIR, and X-ray photoelectron spectroscopy, and by X-ray powder diffraction and field-emission scanning electron microscopy. The NPs were deposited on microchips to result in a sensor that has a fast response to methanol in the liquid phase. Features include high sensitivity, low-sample volume, reliability, reproducibility, ease of integration, long-term stability, and enhanced electrochemical responses. The calibration plot is linear (r²?=?0.9981) over the 0.25 mmolL^?1 to 0.25 molL^?1 methanol concentration range. The sensitivity is ~7.917 μA cm^?2 mmolL^?2, and the detection limit is 71.0?±?0.5 μmolL^?1 at a signal-to-noise-ratio of 3.

PRIMARY INTERMEDIATES IN THE PULSED IRRADIATION OF RETINOIDS

Abstract Laser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol. For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 10⁴ dm³ mol^?1 cm^?1, decay constant 6.2 × 10⁵ s^?1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ～7 × 10⁴ dm³mol^?1 cm^?1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 10⁵ dm³mol^?1 cm^?1, appears to decay partially in methanol into another longer-lived neutral radical, wavelength maximum 420 nm, by loss of OH^?. For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 10⁴dm³mol^?1 cm^?1, decay constant 1.2 × 10⁶s^?1 is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH₃? in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ～ 2 × 10⁶ dm³ mol^?1 s^?1 and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ～ 1.0 × 10⁵ dm³mol¹ cm^?1. The long-lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 10⁵ dm³mol^?1 cm^?1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH₃? from this anion. These results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid.     

Semi‐micro reversed‐phase liquid chromatography for the separation of alkyl benzenes and proteins exploiting methacrylate‐ and polystyrene‐based monolithic columns

Monolithic columns were synthesized inside 1.02 mm internal diameter fused‐silica lined stainless‐steel tubing. Styrene and butyl, hexyl, lauryl, and glycidyl methacrylates were the functional monomers. Ethylene glycol dimethacrylate and divinylbenzene were the crosslinkers. The glycidyl methacrylate polymer was modified with gold nanoparticles and dodecanethiol (C₁₂). The separation of alkylbenzenes was investigated by isocratic elution in 60:40 v/v acetonitrile/water. The columns based on polystyrene‐co‐divinylbenzene and poly(glycidyl methacrylate)‐co‐ethylene glycol dimethacrylate modified with dodecanethiol did not provide any separation of alkyl benzenes. The poly(hexyl methacrylate)‐co‐ethylene glycol dimethacrylate and poly(lauryl methacrylate)‐co‐ethylene glycol dimethacrylate columns separated the alkyl benzenes with plate heights between 30 and 60 μm (50 μL min^?1 and 60°C). Similar efficiency was achieved in the poly(butyl methacrylate)‐co‐ethylene glycol dimethacrylate column, but only at 10 μL min^?1 (0.22 mm s^?1). Backpressures varied from 0.38 MPa in the hexyl methacrylate to 13.4 MPa in lauryl methacrylate columns (50 μL min^?1 and 60°C). Separation of proteins was achieved in all columns with different efficiencies. At 100 μL min^?1 and 60°C, the lauryl methacrylate columns provided the best separation, but their low permeability prevented high flow rates. Flow rates up to 500 μL min^?1 were possible in the styrene, butyl and hexyl methacrylate columns.     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

New method for preparation of polyoxometalate-capped gold nanoparticles, and their assembly on an indium-doped tin oxide electrode

Functionalized gold nanoparticles capped with polyoxometalates were prepared by a simple photoreduction technique where phosphododecamolybdates serve as reducing reagents, photocatalysts, and as stabilizers. TEM images of the resulting gold nanoparticles show the particles to have a relative narrow size distribution. Monolayer and multilayer structures of the negatively charged capped gold nanoparticles were deposited on a poly(vinyl pyridine)-derivatized indium-doped tin oxide (ITO) electrode via the layer-by-layer technique. The surface plasmon resonance band of the gold nanoparticles displays a blue shift on the surface of the ITO electrode. This is due to the substrate-induced charge redistribution in the gold nanoparticles and a change in the electromagnetic coupling between the assembled nanoparticles. The modified electrode exhibits the characteristic electrochemical behavior of surface-confined phosphododecamolybdate and excellent electrocatalytic activity. The catalysis of the modified electrode towards the model compound iodate was systematically studied. The heterogeneous catalytic rate constant for the electrochemical reduction of iodate was determined by chronoamperometry to be ca. 1.34?×?10⁵ mol^?1·L·s^?1. The amperometric method gave a linear range from 2.5?×?10^?6 to 1.5?×?10^?3 M and a detection limit of 1.0?×?10^?6 M. We believe that the functionalized gold nanoparticles prepared by this photoreduction technique are advantageous in terms of fabrication of sensitive and stable redox electrodes.

Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether

Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10^?13 cm³ molecule^?1 s^?1 at 298 K. The primary products and molar yields for the OH reaction with ETBE in the presence of NO_x were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.     

Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon Electrodes

A new methodology, based on silver electrocatalytic deposition and designed to quantify gold deposited onto carbon paste electrode (CPE) and glassy carbon electrode (GCE), has been developed in this work. Silver (prepared in 1.0 M NH₃) electrodeposition at ?0.13 V occurs only when gold is previously deposited at an adequate potential on the electrode surface for a fixed period of time. When a CPE is used as working electrode, an adequate oxidation of gold is necessary. This oxidation is carried out in both 0.1 M NaOH and 0.1 M H₂SO₄ at oxidation potentials. When a GCE is used as working electrode, the oxidation steps are not necessary. Moreover, a cleaning step in KCN, which removes gold from electrode surface, is included. To obtain reproducibility in the analytical signal, the surface of the electrodes must be suitably pretreated; this electrodic pretreatment depends on the kind of electrode used as working electrode. Low detection limits (5.0×10^?10 M) for short gold deposition times (10 min for CPE and 5 min for GCE) were achieved with this novel methodology. Finally, sodium aurothiomalate can be quantified using silver electrocatalytic deposition and GCE as working electrode. Good linear relationship between silver anodic stripping peak and aurothiomalate concentration was found from 5.0×10^?10 M to 1.0×10^?8 M.     

Matrix‐assisted laser ablation production of gold cluster ions from Au‐coated photonic crystals

A new strategy was explored to generate pure gold cluster ions, Au_n^+/?, from gold films deposited on solid substrates via a matrix‐assisted laser ablation technique. The gold films deposited on SiO₂‐particle‐assembled photonic crystals were demonstrated to be the most ideal compared with the films deposited on various glass slides. Dropped with a matrix of 2‐(4‐hydroxyphenylazo) benzoic acid and bombarded by nitrogen pulse laser (355 nm), they could release a series of Au_n⁺ with n more than 110 or Au_n^? with n more than 60 according to the data obtained by inline time‐of‐flight mass spectrometry. The gold‐deposited photonic crystal substrates could be stored at room temperature for at least 6 months. The method is hence steady and convenient in use. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of derivatives and production of antiserum for class specific detection of pyrethroids by indirect ELISA

Two series of haptens including 3-phenoxybenzoic acid (PBA) and 3-(2-chloro-3, 3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclo-propanecarboxylic acid (CF₃MPA) were used to prepare immunogens through attachment of 4-C or 6-C handles. Class selective antibodies were produced by immunising rabbits. Ab502 showed the highest reactivity towards tau-fluvalinate (IC₅₀ 1.3 ng mL^?1), λ-cyhalothrin (IC₅₀ 2.3 ng mL^?1), cyfluthrin (IC₅₀ 2.2 ng mL^?1) and fenpropathrin (IC₅₀ 18.5 ng mL^?1) among the antibodies in a competitive ELISA. The effects of methanol, pH and salt concentration were optimised for maximum efficiency of the ELISA (Enzyme-Linked ImmunoSorbent Assay). Ab502 (1:80000)/2-OVA-1(0.2 µg mL^?1) was chosen for ELISA optimisation. Finally, 0.05 M phosphate buffered saline (PBS) at pH 6.5 containing 30% methanol (v/v) was used to dilute the standards. Target analytes in honey samples were extracted with ethyl acetate by sonication. The samples were spiked with three different concentrations of each compound (tau-fluvalinate, 0.5 ng g^?1, 3 ng g^?1, 12 ng g^?1; λ-cyhalothrin and cyfluthrin 1 ng g^?1, 5 ng g^?1, 65 ng g^?1). The recoveries were 36–59% at the lowest spiking concentration and 61–81% at the higher concentration. This assay might be useful to screen pyrethroid residues in honey or other matrix.     

Temperature effects on positronium formation in solution of sodium acetate in methanol

The influence of the acetate ion (Ac^? in solutions of methanol on the Ps yield has been examined at 203, 248 and 294 K. Ac^? was found to be both a strong “limited” inhibitor through e⁺ scavenging and an enhancer through hole trapping. The temperature effects observed are interpreted by a change in the relative probabilities ofthe two processes.     

Electrocatalytic Reduction of Hydrogen Peroxide by Nanostructured Bimetallic Films of Metalloporphyrins

We report the sequential electrochemical deposition of bimetallic films of porphyrins onto gold nanoparticles, previously deposited by SAM on gold surface. SEM analysis of EAu/polyFeCuPP and EAu/cys/AuNp/polyFeCuPP showed a heterogeneous distribution of material aggregates in the former (ca. 0.1–1 μm), whereas the nanocomposite film exhibits a highly microporous structure in the micrometer diameter range. The sensitivity for H₂O₂ detection increased four times (609±6 mA M^?1 cm^?2 vs. 157±3 mA M^?1 cm^?2) with a linear relationship in the range of 1×10^?5–2×10^?3 M. The application of the particulate material to the first‐generation biosensor of glucose is described.     

Relative rates of nucleophilic reactions of benzyl carbocation formed in photolysis of benzyl chloride and benzyl acetate in aqueous solution

Benzyl chloride and benzyl acetate were photolyzed in 30% methanol–water mixtures (V/V) at 0°C. The photolysis produces benzyl carbocations that react with nucleophiles. The reaction products were analyzed by gas chromatography or liquid chromatography. From the amounts of products the relative values of rate constants of reactions of benzyl carbocation with nucleophiles N and water k(N)/k(H₂O) were calculated. Benzyl carbocation reacts with I^?, Br^?, Cl^?, and Ac^? ions with approximately diffusion-controlled rate. A value of 2.4 × 10⁷ dm³ mol^?1 s^?1 for the rate constant k(H₂O) and a lifetime of 0.7 ns were estimated for benzyl carbocation in the aqueous solution.     

Kinetics and mechanism of the atmospheric oxidation of tertiary amyl methyl ether

Tertiary-amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t-amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction. Values determined for the rate constants for the reaction with OH were 5.48 × 10^?12 (TAME), 1.75 × 10^?12 (t-amyl formate), and 3.85 × 10^?13 cm³ molec^?1 s^?1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t-amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t-amyl alcohol (0.026), 3-methyoxy-3-methyl-butanal (0.044, corrected), t-amyloxy methyl nitrate (0.029), 3-methyoxy-3-methyl-2-butyl nitrate (0.010), and 2-methoxy-2-methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc.     

Grain boundary diffusion coefficients in gold–nickel thin films

Polycrystalline gold–nickel thin films are deposited on silicon (111) wafers by evaporation in a vacuum of 2 × 10^?6 mbar. Concentration profiles of heat‐treated specimens are obtained by Auger electron depth profiling. The heat treatments are carried out in a vacuum furnace of 4 × 10^?6 mbar in the temperature interval 473–773 K. The grain boundary diffusion coefficient is determined, using a modified Wipple model, to be (3 × 10^?4 cm² s^?1) exp (?0.94 eV kT^?1). It is concluded that interdiffusion in the investigated system is characterized by type B kinetics, and that grain boundary diffusion plays a dominant role in the mass transport process of such films. Copyright © 2003 John Wiley & Sons, Ltd.     

Investigation of the Reaction of Gold(III) with 2‐[2‐(4‐Dimethylamino‐Phenyl)‐Vinyl]‐1,3,3‐Trimethyl‐3H‐Indolium. Application for Determination of Gold

A new, simple, rapid, sensitive, efficient and low‐cost spectrophotometric procedure for the determination of gold was developed. The method is based on the reaction of [AuCl₄]^? with 2‐[2‐(4‐dimethylaminophenyl)‐vinyl]‐1,3,3‐trimethyl‐3H‐indolium reagent to form a colored ion associate extractable by various organic solvents. The molar absorptivity of the ion associates is in the range (5.7–9.2) × 10⁴ L mol^?1 cm^?1 depending on the extractant. Butyl acetate was chosen as the extractant. The optimum reaction conditions were established: pH 2–4, concentration of the dye reagent (0.8–1.5) × 10^?4 mol L^?1. The determination of gold is not hindered even by a 1000‐fold concentration of Ni and Co; a 500‐fold concentration of Pb and Zn; a 100‐fold concentration of Bi, Cu, Cd, Pt, Rh and Ru; or a 20‐fold concentration of Ag. The established method was applied to the determination of gold in model samples and enriched polymetallic ores.     

Efficiency of Zn/TiO<Subscript>2</Subscript> catalyst operation in a microchannel reactor in methanol steam reforming

The activity of a Zn/TiO₂ catalyst deposited on metal microchannel plates in methanol steam reforming was studied. The catalyst exhibited maximum activity upon deposition on microchannel plates made of copper foam. In this case, the specific hydrogen production of a microreactor at 450°C was 78.6 l (g Cat)^?1 h^?1. The catalysts deposited on a microchannel plate of nickel foam and on corrugated brass foil exhibited lower activity because of the lower efficiency of heat transfer to the reaction zone. A correlation between the thermal conductivity of the microchannel plate material and the activity of the catalyst was observed in the following order: copper, brass, and nickel. The kinetic parameters of the process of methanol steam reforming in a microreactor were calculated with the use of a plug-flow reactor model. In this case, the calculated formal activation energy of 132 kJ/mol was independent of the microchannel plate material. A comparison of the equilibrium concentrations of reaction products at the reactor outlet, which were calculated from thermodynamic data, with the experimental data demonstrated that methanol steam reforming at a temperature higher than 400°C occurred in the nonequilibrium region. The concentration of carbon monoxide at the microreactor outlet was lower than 1 mol %, which is lower than the equilibrium concentration by one order of magnitude. This effect was attributed to the suppression of the reversed water gas shift reaction on the catalyst.     

High performance liquid chromatographic determination of butamyrate citrate in pharmaceutical preparation

An HPLC method was developed and validated for the determination of butamyrate citrate. The HPLC separation was achieved on a diol column (300 × 4.6 mm) packed with 5.0 μm particle size using a mobile phase of ammonium acetate buffer (pH = 6.5) and methanol (750:250, v/v) at a flow rate of 1.4 ml min^?1. The UV detector was operated at 225 nm. The method was validated for specificity, linearity, precision, accuracy and robustness. The retention time was 5.9 min. The proposed method provided linear responses within the concentration range 75–225 μg ml^?1 with LOD and LOQ values of 0.69 and 2.29 μg ml^?1, respectively. Correlation coefficient (r) of the regression equation was 0.9999. The method was found to be precise, accurate, and reproducible.     

Alloy formation at the deposition of palladium on gold at room temperature

Palladium is shown to be deposited underpotentially on gold electrodes in 1 M H₂OSO₄. The deposit forms an alloy according to a t^1/2 law. The rate of alloy formation is strongly dependent on the potential. The diffusion coefficient is about 10^?16 cm² s^?1. This value is discussed in comparison with earlier measurements on gold-palladium alloys at higher temperatures.     

Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes

The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N‐heterocyclic carbene‐based gold catalyst, [(NHC)AuX] (X=BARF^?, BF₄^?, OTf^?, OTs^?, TFA^?, or OAc^?) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs^? anion provides the best compromise to achieve efficient catalysis.