The structure of aqueous sodium hydroxide solutions: a combined solution x-ray diffraction and simulation study

To determine the structure of aqueous sodium hydroxide solutions, results obtained from x-ray diffraction and computer simulation (molecular dynamics and Car-Parrinello) have been compared. The capabilities and limitations of the methods in describing the solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in describing the hydration spheres of the sodium ion and yield structural information on the anion's hydration structure. Classical molecular dynamics simulations were not able to correctly describe the bulk structure of these solutions. However, Car-Parrinello simulation proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions and bulk structure of solutions. The results of Car-Parrinello simulations were compared with the findings of diffraction experiments.     

Multi-class determination of antimicrobials in meat by pressurized liquid extraction and liquid chromatography-tandem mass spectrometry

A multi-residue method using pressurized liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for determining trace levels of 31 antimicrobials, including beta-lactams, lincosamides, macrolides, quinolones, sulfonamides, tetracyclines, nitroimidazoles and trimethoprim. The extraction method required pre-homogeneization of the meat with EDTA-washed sand and subsequent one-static-cycle extraction for 10 min with 40 ml of water at 1500 psi and 70 degrees C. The effect of operation temperature, pressure, flush volume, and static cycles on PLE performance was studied. Average recoveries ranged from 75 to 99% with relative standard deviations <18%. The method was validated according to the European Union requirements (2002/657/EC). In addition to the quality parameters included in that decision, the limits of detection (LODs) and quantification (LOQs) were determined. The use of LC-MS/MS provided LODs (between 3 and 15 microg kg(-1)) and LOQs (between 10 and 50 microg kg(-1)), by far lower than half of their maximum residue limits (MRLs) (between 50 and 1200 microg kg(-1)). Confirmation of the presence of any of the studied compounds was accomplished in 1h after sample receipt. This methodology has been successfully applied to the analysis of cattle and pig tissue samples from local markets and slaughterhouses of the Valencian Community (Spain). The results showed the presence of some antimicrobials at different concentrations. Quinolones and tetracyclines were the antimicrobials most detected in cattle and pig samples, respectively. Sulfonamides were also frequently detected in both types of samples.     

Identification and structural characterization of biodegradation products of atenolol and glibenclamide by liquid chromatography coupled to hybrid quadrupole time-of-flight and quadrupole ion trap mass spectrometry

In this paper we report about the biodegradation of the beta-blocker atenolol and the hypoglycaemic agent glibenclamide. The biodegradation tests were performed in batch reactors under aerobic conditions, using as inocculums sewage sludge from a conventional activated sludge treatment and a laboratory-scale membrane bioreactor. Pharmaceuticals were used as sole carbon sources, spiked at 50ng/L and 10mg/L concentrations. Quadrupole time-of-flight mass spectrometry coupled to ultra-high-pressure liquid chromatograph was used for the screening and the structural elucidation of biodegradation products. A microbial metabolite of atenolol with [M+H](+) at 268 was detected in the positive electrospray ionization mode. This new compound was determined to be a product of microbial hydrolysis of the amide of the parent compound. Biodegradation of glibenclamide by activated sludge proceeded via bacterial hydroxylation of the cyclohexyl ring, which resulted in formation of metabolite with a protonated molecule, [M+H](+)=510. MS(3) experiments performed by hybrid quadrupole linear ion trap (QqLIT) mass spectrometry coupled to high-performance liquid chromatography enabled further structural elucidation of the identified metabolites. Moreover, the highly sensitive QqLIT instrument in the MRM mode enabled the detection of parent compounds and one of the microbial metabolites identified in real wastewater samples. The methodology used in this study permitted for the first time the identification and detection of biodegradation product of beta-blocker atenolol in real wastewater samples.     

High-throughput multiclass method for antibiotic residue analysis by liquid chromatography-tandem mass spectrometry

A simple and rapid method has been developed for the residue analysis of 39 antibiotics (tetracyclines, quinolones, penicillins, sulfonamides and macrolides) in foodstuffs of animal origin. The method combines an effective extraction technique, which uses water-methanol as extracting solvent, with ultra-high-pressure liquid chromatography-tandem mass spectrometry, allowing both confirmation and quantification in a single chromatographic run. The multiresidue method has been validated in chicken muscle matrix according to European Union Decision 2002/657/EC. It has been implemented as a routine method in a Public Health Laboratory, instead of the five plates test and LC methods previously used.     

Development of a pressurized liquid extraction-solid-phase extraction followed by liquid chromatography-electrospray ionization tandem mass spectrometry method for the quantitative determination of benzoxazolinones and their degradation products in agricultural soil

A new analytical method for the quantitative determination of benzoxazolinones and their degradation products in agricultural soils based on the use of pressurized liquid extraction (PLE) followed by solid-phase extraction (SPE) and then instrumental determination using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS) is described. Using this method, the characterization, separation and quantitative detection of a mixture of two benzoxazolinones, benzoxazolin-2-one (BOA) and 6-methoxybenzoxazolin-2-one (MBOA) and their degradation products, 2-aminophenol (APH), N-(2-hydroxyphenyl)malonamic acid (HMPMA), 2-amino-3-H-phenoxazin-3-one (APO), 9-methoxy-2-amino-3-H-phenoxazin-3-one (AMPO), 2-acetylamino-3-H-phenoxazin-3-one (AAPO) and 2-acetylamino-9-methoxy-2-amino-3-H-phenoxazin-3-one (AAMPO) was achieved. The complete LC-ESI-MS-MS precursor-product ion fragmentation pathways for the degradation products of benzoxazolinones are described for the first time. Quantitative analysis was done in the multiple reaction mode using two specific combinations of precursor-product ion transitions for each compound. The optimized method was quality assessed by the measure of parameter as recovery, linearity, sensitivity, repeatability and reproducibility. Recoveries of the analytes ranged from 53 to 123%. The developed method offered improvements to the sensitivity as compared with our previously LC-MS method, with detection limits down to 2.4-21 ng/g of dry weight. This achievement allows us to identify and quantify for the first time degradation products of benzoxazolinones in real agricultural soil samples. Analytes were found in the range of 20.6-149 ng/g dry weight.     

Selective formal transesterification of fluorinated 2-(trimethylsilyl)ethyl alpha-imino esters mediated by TBAF

The scope of the transesterification reaction between beta-fluorinated alpha-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated alpha-imino esters.     

Site-selective catalysis of phenyl thionoformate transfer as a tool for regioselective deoxygenation of polyols

We report the application of peptide-embedded imidazoles as catalysts for the site-selective delivery of the phenyl thionoformate unit as a prelude to deoxygenation reactions of polyols. Methodology was developed that allows for the synthesis of thiocarbonyl derivatives based on a combination of additives that include N-alkylimidazoles and FeCl3 as co-catalysts. The use of this reagent combination leads to increased reaction rates and efficient yields relative to those of simple base-mediated reactions. In terms of controlling regioselectivity during the course of polyol modification, we found that histidine-containing peptides, in combination with FeCl3, could lead to modulation of the product distribution. Through screening of peptides and control of reaction conditions, products could be observed that reflected both the inherent preference of substrates and also reversal of inherent selectivity.     

Highly beta-(E)-selective hydrosilylation of terminal and internal alkynes catalyzed by a (IPr)Pt(diene) complex

The regioselective hydrosilylation of terminal and internal alkynes catalyzed by the novel (IPr)Pt(AE) ( 7) (IPr = bis(2,6-diisopropylphenyl)imidazo-2-ylidene, AE = allyl ether) complex is presented. The (IPr)Pt(AE) catalyst displays enhanced activity and regioselectivity for the hydrosilylation of terminal and internal alkynes with low catalyst loading (0.1 to 0.05 mol %) when compared to the parent (IPr)Pt(DVDS) complex ( 6) (DVDS = divinyltetramethyldisiloxane). The reaction leads to exquisite regioselectivity in favor of the cis-addition product on the less hindered terminus of terminal and internal alkynes. The solvent effects were examined for the difficult hydrosilylation of benzylpropargyl ether. In light of the observed product distribution and kinetic data, a mechanistic scheme is proposed involving two competing catalytic cycles. One cycle leads to high regioselectivities while the other, having lost the stereodirecting IPr carbene ligand, displays low regiocontrol and activities. The importance of this secondary catalytic cycle is either caused by the strong coordinating ability of the alkyne or by the low reactivity of the silane or both.     

Diastereoselective synthesis of allosecurinine and viroallosecurinine from menisdaurilide

A new and versatile synthetic route to Securinega alkaloids is reported. The first synthesis of allosecurinine has been accomplished in seven steps and 40% yield, starting from (+)-menisdaurilide, using a vinylogous Mannich reaction as the key transformation. Similarly, viroallosecurinine has been synthesized from (-)-menisdaurilide.     

Sensitive and stable monitoring of lead and cadmium in seawater using screen-printed electrode and electrochemical stripping analysis

Sensitive and stable monitoring of heavy metals in seawater using screen-printed electrodes (SPE) is presented. The analytical performance of SPE coupled with square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Pb and Cd in seawater samples, in the low μg L⁻¹ range, is evaluated. The stripping response for the heavy metals following 2 min deposition was linear over the concentration range examined (10-2000 μg L⁻¹) with detection limits of 1.8 and 2.9 μg L⁻¹ for Pb and Cd, respectively. The accuracy of the method was validated by analyzing metal contents in different spiked seawater samples and comparing these results to those obtained with the well-established anodic stripping voltammetry using the hanging mercury drop electrode. Moreover, a certified reference material was also used and the results obtained were satisfactory.