One-pot enantioselective formation of eight-membered rings from alkenyl Fischer carbene complexes and ketone enolates

Eight-membered carbocycles with up to five new stereogenic centers are enantioselectively obtained following a one-pot procedure that involves the coupling of three components: an alkenyl Fischer carbene complex, a ketone enolate, and allyl lithium.     

Very-large-volume sampling of water in gas chromatography using the through oven transfer adsorption desorption (TOTAD) interface for pesticide-residue analysis

The Through Oven Transfer Adsorption Desorption (TOTAD) interface is used to directly introduce large volumes of water (1 mL or more) into a capillary gas chromatograph. The TOTAD interface is a greatly modified programmed temperature vaporizer injector incorporating changes that affect the pneumatics, sample introduction, solvent elimination, and operation mode. The system can easily be automated. The technique is applied to the analysis of pesticide residue in standard solutions and real water samples from the Ebro River (northeastern Spain). The speed of sample introduction was 1 mL/min, and the solvent elimination was almost complete. A nitrogen phosphorous detector is used, and the relative standard deviation varied from 5.7% to 11.7% for the absolute peak areas. The sensitivity achieved by introducing 1 mL of the sample is sufficient for most pesticide-residue analyses in water. The limits of detection ranged from 0.5 to 8.1 ng/L.     

Analysis of the Association Process Between a Series of Phenol Derivatives with Two Novel Fluorinated Stationary Phase Using the Cl− Anion as Retention Marker

Summary Lithium chloride (LiCl) effect on the retention process of a phenol derivative series was investigated on two types of fluorinated stationary phase (i.e. a silica grafted with fluorinated linear alkyl chain (L-FSP) and a silica grafted with fluorinated aromatic ring stationary phase (A-FSP)). The results showed that the solute retention is enhanced when the A-FSP was used instead of the L-FSP due to additional – interactions. For the two fluorinated stationary phases (FSPs), the phenol-FSP association process can be divided into two LiCl concentration domains demonstrated that it was important to take into account the adsorbtion of Cl^– anion on the FSPs. As well, enthalpy-entropy compensation revealed that the solute retention mechanism was independent of the solute molecular structure and confirmed a change on the solute retention mechanism at a critical LiCl concentration value around 0.02M.     

Assignment of Saharan dust sources to episodes in Hungarian atmosphere by PIXE and TOMS observations

Summary Thirty-seven episodes of dust intrusion were observed between February 12, 1991 and August 31, 2000 in the Hungarian atmosphere and found to be of Saharan origin. They have been assigned to typical source areas in Northern Africa selected by systematic investigations related to the Mediterranean Basin. Elemental concentrations and regional signatures deduced from PIXE analysis, total suspended particle mass, and black carbon mass have been measured on dust samples collected in Debrecen, Hungary. These data combined with Aerosol Index data, and dust plume axes obtained from TOMS data from NASA satellites were used for assigning the most probable source areas of the dust transported to the sampling site. Our data and conclusions are in accordance with other published investigations on the predominant role of Saharan dust emission in building up the aerosol load of the global atmosphere.     

On the biological importance of the hydrogen bond breaking potency of fluorocarbons

Fluorocarbons containing higher halogens have the potency of breaking certain hydrogen bonds in solutions. The relative strength of this potency varies in the series F < Cl < Br < I and the presence of hydrogen atoms in the fluorocarbon increases it. There is a striking parallelism between the hydrogen bond breaking and the anaesthetic potency of these molecules. It is suggested that the breaking of hydrogen bonds is an important step in the mechanism of anaesthesia.     

Investigation of the species-specific degradation behaviour of methylmercury and ethylmercury under microwave irradiation

The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh₄). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min. The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte loss was observed for EtHg after 2 minutes at 40 W of microwave power. Awarded a Poster Prize on the occasion of the European Winter Conference on Plasma Spectrochemistry, February 2005, Budapest, Hungary     

New polycyclic diamine scaffolds from dimerization of 3-alkyl-1,4-dihydropyridines in acidic medium

[reaction: see text] 3-Alkyl-1,4-dihydropyridines dimerize in acidic medium, at low temperature, to give polycyclic imminium salts derivatives that were reduced to afford new polycyclic diamine scaffolds. The reaction can be extended to enantiopure series starting from R-(+)- or S-(-)-1-phenylethylamine. Long exposure of the polycyclic imminium salt intermediates to air moisture at 20 degrees C resulted in formation of new amide derivatives. This is probably due to the addition of water followed by an intramolecular oxido-reduction process.     

Multiresidue method for simultaneous determination of ten quinolone antibacterial residues in multimatrix/multispecies animal tissues by liquid chromatography with fluorescence detection: single laboratory validation study

Quinolone antibacterials are veterinary drugs authorized for use in food animal production. The analysis of residual amounts of drugs in food from animal origin is important for quality control of products for consumers. For this purpose, Maximum Residue Limits (MRLs) have been set up by a European Union Council Regulation on Veterinary Drug Residues (No. 90/2377/EEC and subsequent), and 8 quinolones received MRLs at concentration levels depending on both the matrix and the animal species of interest. A method was developed for screening and confirming 10 quinolone residues (ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, oxolinic acid, sarafloxacin) in a wide variety of matrixes of different animal species. It involves extraction of the residues from the biological tissues/fluids by acidic aqueous solution, centrifugation and filtration prior to injection on a C18 narrow-bore column, and detection through a 3-step-mode fluorescence detector. The method was validated during a 2-week study for a set of 8 species-matrixes (i.e., bovine raw milk, bovine muscle, porcine muscle, porcine kidney, porcine liver, fish flesh and skin, poultry muscle, whole egg). Residues were quantified down to 15 microg/kg with limits of detection and quantitation ranging from 4 to 11 and 13 to 36 microg/kg, respectively, which are sufficient compared to the wide range of MRLs set for these substances (from 30 microg/kg for danofloxacin in milk to 1900 microg/kg for difloxacin in poultry liver). The limit of performance of the method in terms of CCalpha and CCbeta, the critical concentrations stated in the Decision No. 2002/657/EC and the ISO Standard No. 11843, has been calculated for the authorized (MRL) substances but only estimated in the case of the nonauthorized (non-MRL) substances.     

Implementation of the finite field perturbation method in the CRYSTAL program for calculating the dielectric constant of periodic systems

The finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results. The influence of the computational parameters is discussed. An alternative scheme has also been implemented, for inner check, that consists of applying a static electric field to a slab of increasing thickness in the direction orthogonal to the surface; the dielectric response at the center of the slab is shown to converge rapidly to the bulk value evaluated with the sawtooth field. The method is accurate and permits the determination of nonlinear corrections to the dielectric constant. When used in conjunction with the local density approximation (LDA) scheme, it provides for the dielectric constant of the three above-mentioned compounds values close to those recently obtained with a time-dependent density functional theory approach.     

Alkenyl selenols and selenocyanates: synthesis, spectroscopic characterization by photoelectron spectroscopy, and quantum chemical study

Vinyl, allyl, and homoallyl selenols were easily prepared by a chemoselective reduction of the corresponding selenocyanates with aluminum hydrides. Two stable vinyl and five stable allyl conformers of both series were predicted on the potential-energy surface. The interaction of SeH or SeCN groups with the vinyl group has been investigated with UV photoelectron spectroscopy and quantum chemical calculations, using the MP2/cc-pVTZ and B3LYP/cc-pVTZ levels. In the vinyl derivatives, a surprisingly strong direct conjugation of the selenium lone electron pair and the C=C double bond was observed. On the other hand, in allyl position the selenium lone pair is independent on the C=C double bond, and the hyperconjugation between the Se-C bond and the double bond is the ruling effect. Thus is clarified the type and extent of the interaction between the SeH or SeCN group and the unsaturated moiety.