Mössbauer study of Sn(Fe)O2 prepared by mechanosynthesis

This work deals with first-principles investigation of the electronic structure of the BF₃??H₂O complex which is important in catalysis of organic reactions and polymerization. The dissociation energy of the BF₃??H₂O complex and the nuclear quadrupole interaction parameters for the excited nuclear state ¹⁹F* (I = 5/2) of the fluorine nuclei have been studied. Our investigation shows that the complexation bond BO between the BF₃ and H₂O units is strongly influenced by the larger electronegativity of Oxygen as compared to Nitrogen in BF₃??NH_3. The quadrupole coupling constants of ¹⁹F* and the asymmetry parameter are however quite close to those for BF₃??NH₃. The likely reasons for these features of these two important catalytic systems are suggested.     

Biomimetic synthesis of resorcylate natural products utilizing late stage aromatization: concise total syntheses of the marine antifungal agents 15G256iota and 15G256beta

Diketo-1,3-dioxin-2-ones underwent retro-Diels-Alder reaction on heating in toluene at 110 degrees C to generate alpha,gamma,-triketo-ketenes. These were trapped with alcohols to provide 2,4,6-triketocarboxylates, which were smoothly aromatized by sequential reaction with potassium carbonate and methanolic hydrogen chloride to give resorcylate esters. The reaction was applied in the total synthesis of the marine antifungal agents 15G256beta (1), 15G256iota (2), and 15G256pi (3) and the mycotoxin S-(-)-zearalenone (4).     

Electromembrane extraction (EME) and HPLC determination of non-steroidal anti-inflammatory drugs (NSAIDs) in wastewater samples

In this paper, an electromembrane extraction (EME) combined with a HPLC procedure using diode array (DAD) and fluorescence detection (FLD) has been developed for the determination of six widely used non-steroidal anti-inflammatory drugs (NSAIDs): salicylic acid (SAC), ketorolac (KTR), ketoprofen (KTP), naproxen (NAX), diclofenac (DIC) and ibuprofen (IBU). The drugs were extracted from basic aqueous sample solutions, through a supported liquid membrane (SLM) consisting of 1-octanol impregnated in the walls of a S6/2 Accurel^® polypropylene hollow fiber, and into a basic aqueous acceptor solution resent inside the lumen of the hollow fiber with a potential difference of 10 V applied over the SLM. Extractions that were carried out in 10 min using a potential of 10 V from pH 12 NaOH aqueous solutions shown concentration enrichments factors of 28-49 in a pH 12 NaOH aqueous acceptor solution. The proposed method was successfully applied to urban wastewaters. Excellent selectivity was demonstrated as no interfering peaks were detected. The procedure allows very low detection and quantitation limits of 0.0009-9.0 and 0.003-11.1 μg L⁻¹, respectively.     

Abatement of hydrocarbons by acid ZSM-5 and BETA zeolites under cold-start conditions

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.     

Continuous solid-phase extraction and preconcentration of bisphenol A in aqueous samples using molecularly imprinted columns

A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10–100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL^–1, respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL^–1); relative standard deviations (RSD) were lower than 5.0%.     

Experimental and theoretical vibrational study of 2,2,2-trifluoroethyl trifluoromethanesulfonate, CF3SO2OCH2CF3

The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).     

Phosphine and Thiophene Cyclopalladated Complexes: Hydrolysis Reactions in Strong Acidic Media

The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF₄ (R=P(OPh)₃, PPh₃, and SC₄H₈) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3–11.7 M range. In all cases, a biphasic behavior was observed with rate constants k_1obs, which corresponds to the initial step of the hydrolysis reaction, and k_2obs, where k_1obs>k_2obs. The plots of k_1obs and k_2obs versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k_1obs value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh₃, P(OPh)₃, and SC₄H₈, respectively. Regarding k_2obs, the change occurred in all cases at about 6.5 M H₂SO₄ and matched up with the results reported for the hydrolysis of the 2‐acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of k_i,_obs (i=1,2) versus ${c_{{\rm{H}}^ + } }$ . The rate‐determining constants, k_0,A‐1, k_0,A‐2, and k_0,A‐SE2 were evaluated in all cases. The R=P(OPh)₃ complex was most reactive due to its π‐acid character, which favors the rupture of the trans nitrogen–palladium bond in the A‐2 mechanism and also that of the pyridine nitrogen–palladium bond in the A‐1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent.     

A Flexible Pro‐porous Coordination Polymer: Non‐conventional Synthesis and Separation Properties Towards CO2/CH4 Mixtures

The novel coordination polymers [Cu(Hoxonic)(H₂O)]_n ( 1 ) and [Cu(Hoxonic)(bpy)_0.5]_n ? 1.5 n H₂O ( 2?H₂O ) (H₃oxonic: 4,6‐dihydroxy‐1,3,5‐triazine‐2‐carboxylic acid; bpy: 4,4′‐bipyridine) have been isolated and structurally characterised by ab initio X‐ray powder diffraction. The dense phase 1 contains 1D zig‐zag chains in which Hoxonic dianions bridge square‐pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary, 2?H₂O , prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridged by Hoxonic ligands, further pillared by bpy spacers. The resulting pro‐porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N₂ at 77 K nor CO₂ at 195 K are incorporated, and CH₄ is only minimally adsorbed at 273 K and high pressures (0.5 mmol g^?1 at 2500 kPa). By contrast, CO₂ is readily incorporated at 273 K (up to 2.5 mmol g^?1 at 2500 kPa). The selectivity of 2 towards CO₂ over CH₄ has been investigated by means of variable‐temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO₂/CH₄ mixtures. The results show the highly selective incorporation of CO₂ in 2 , which can be rationalised on the basis of the framework flexibility and polar nature of its voids.     

Hollow fiber-based liquid-phase microextraction (HF-LPME) of ibuprofen followed by FIA-chemiluminescence determination using the acidic permanganate-sulfite system

Hollow fiber-based liquid-phase microextraction (HF-LPME) is a relatively new technique employed in analytical chemistry for sample pretreatment which offers more selectivity and sensitivity than any traditional extraction technique. This paper describes a three-phase HF-LPME method for ibuprofen using a polypropylene membrane supporting dihexyl ether followed by a chemiluminescence (CL) determination using the CL enhancement on the acidic permanganate-sulfite system in a FIA configuration which is the first time that both techniques have been combined for analytical purposes. The CL intensity (peak area) was proportional to the log of ibuprofen concentration in the donor phase over the range 0.1-20 μg mL⁻¹. The detection limit was 0.03 μg mL⁻¹ of ibuprofen in the donor phase. The method was satisfactory reproducible and has been applied to the ibuprofen determination in pharmaceuticals and in real human urine samples.