Stereoselective conjugate addition reactions to phenylglycinol-derived, unsaturated oxazolopiperidone lactams

Phenylglycinol-derived, unsaturated oxazolopiperidone lactams are extremely useful building blocks that undergo stereoselective conjugate addition reactions with organocuprates, enolates, and sulfur-stabilized anions, allowing the stereocontrolled introduction of substituents at the piperidine 4-position. The factors governing the exo- or endo-facial selectivity are discussed. The methodology can be used for the preparation of a variety of enantiopure piperidines, including pharmaceuticals, alkaloids precursors, piperidine-fused derivatives, as well as complex piperidine-containing natural products.     

Influence of the Preparation Procedure on the Catalytic Activity of Gold Supported on Diamond Nanoparticles for Phenol Peroxidation

The catalytic activity of diamond‐supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L ^?1) and H₂O₂ excesses (100 g L ^?1) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O₂ evolved two different reactions of H₂O₂ decomposition (the Fenton reaction at acidic pH values and spurious O₂ evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol^?1). By using dimethylsulfoxide as a radical scavenger and N‐tert‐butyl‐α‐phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN? OCH₃ adduct was detected, supporting the generation of HO^., characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H₂O₂ decomposition at pH 4 (due to the barrierless attack of HO^. to phenol), but increases the activation energy gradually up to about 90 kJ mol^?1 at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol^?1).     

Determination of 40 currently used pesticides in airborne particulate matter (PM 10) by microwave-assisted extraction and gas chromatography coupled to triple quadrupole mass spectrometry

A confirmatory and sensitive procedure has been developed for the determination of 40 currently used pesticides (CUPs) in airborne particulate matter (PM 10) at trace level. The proposed method includes extraction of PM 10-bound pesticides by microwave-assisted extraction (MAE) followed by a gel permeation chromatography (GPC) clean-up and determination by GC-MS/MS. The injection mode and the main parameters in MS/MS were optimized. The matrix effect was also evaluated. Recoveries ranged from 70 to 120% except for pyrimethanil and pirimicarb. The limit of quantification (LOQ) ranged from 1.32 to 39.47 pg m(-3), when air volumes of 760 m(3) were collected. The method was applied to 38 samples collected from a rural station belonging to the atmospheric monitoring network of the Regional Valencia Government (Spain) during April-June 2010. Eighteen out of 40 pesticides investigated were found in at least one sample (bifenthrin, chlorothalonil, chlorpyriphos-e, chlorpyriphos-m, clorpropham, diazinon, dicofol, diphenylamine, fipronil, fludioxonil, folpet, malathion, metalaxyl, penconazole, quinoxyfen, triadimefon, trifluralin, and vinclozoline), with concentrations ranging from 1.32 to 625.80 pg m(-3).     

Design of fluorescent materials for chemical sensing

There is an enormous demand for chemical sensors for many areas and disciplines. High sensitivity and ease of operation are two main issues for sensor development. Fluorescence techniques can easily fulfill these requirements and therefore fluorescent-based sensors appear as one of the most promising candidates for chemical sensing. However, the development of sensors is not trivial; material science, molecular recognition and device implementation are some of the aspects that play a role in the design of sensors. The development of fluorescent sensing materials is increasingly captivating the attention of the scientists because its implementation as a truly sensory system is straightforward. This critical review shows the use of polymers, sol-gels, mesoporous materials, surfactant aggregates, quantum dots, and glass or gold surfaces, combined with different chemical approaches for the development of fluorescent sensing materials. Representative examples have been selected and they are commented here.     

Analysis of trace amounts of bovine beta-lactoglobulin in infant formulas by capillary electrophoresis with on-capillary derivatization and laser-induced fluorescence detection

Bovine beta-lactoglobulin (betaLG) has been described by several authors as the main allergen present in cow's milk. It can induce allergic reactions even at the low concentration existing in hypoallergenic formulas based on hydrolyzed cow's milk proteins (generally lower than microM). In this paper, the usefulness of a capillary electrophoresis method with on-capillary derivatization and laser-induced fluorescence detection for the analysis of trace amounts of betaLG in a commercial hypoallergenic formula has been demonstrated. To confirm the identity of the peak of betaLG based on migration time, an immunorecognition step employing an anti-betaLG antibody was performed. BetaLG was quantitated in the whey and casein fractions of the hypoallergenic formula. The concentration of betaLG in the whey fraction of the formula was about 3 orders of magnitude lower than the average value present in cow's milk. In the casein fraction of the formula, the concentration of betaLG was about 1 order of magnitude lower than in the whey fraction. The method developed was also used for the quality control of three cereal-based infant foods formulated without milk to test the presence or absence of betaLG as an indicator of milk contamination during the fabrication process. BetaLG in a concentration of 10(-7) M or higher was not observed in any of the cereal-based infant formulas analyzed.     

Synthesis of optically pure 1,2-diaryl- and 1,2-alkylaryl-1,2-amino sulfides

[reaction: see text] The reactions of the lithium (S)-alpha-(methylthio)-2-(p-toluenesulfinyl)benzyl carbanion with (S)-N-p-tolylsulfinyl aldimines evolve in a completely stereoselective manner providing a one-step synthesis of enantiomerically pure anti-1,2-disubstituted 1,2-amino sulfide derivatives.     

Pressurized liquid extraction and microwave-assisted extraction in the determination of organochlorine pesticides in fish muscle samples

This paper describes a comparative study of 2 extraction methods, pressurized liquid extraction (PLE) and microwave-assisted extraction (MAE), for the determination of organochlorine pesticides (OCPs) in fish muscle samples. In both cases, samples were extracted with hexane-acetone (50 + 50), and the extracts were purified by solid-phase extraction using a carbon cartridge as the adsorbent. Pesticides were eluted with hexane-ethyl acetate (80 + 20) and determined by gas chromatography with electron-capture detection. Both methods demonstrated good linearity over the range studied (0.005-0.100 microg/mL). Detection limits ranged from 0.029 to 0.295 mg/kg for PLE and from 0.003 to 0.054 mg/kg for MAE. For most of the pesticides, analytical recoveries with both methods were between 80 and 120%, and the relative standard deviations were < 10%. The proposed methods were shown to be powerful techniques for the extraction of OCPs from fish muscle samples. Although good recovery rates were obtained with both extraction methods, MAE provided advantages with regard to sample handling, cost, analysis time, and solvent consumption. Acceptable validation parameters were obtained although MAE was shown to be more sensitive than PLE.     

Advanced MCMC methods for sampling on diffusion pathspace

The need to calibrate increasingly complex statistical models requires a persistent effort for further advances on available, computationally intensive Monte-Carlo methods. We study here an advanced version of familiar Markov-chain Monte-Carlo (MCMC) algorithms that sample from target distributions defined as change of measures from Gaussian laws on general Hilbert spaces. Such a model structure arises in several contexts: we focus here at the important class of statistical models driven by diffusion paths whence the Wiener process constitutes the reference Gaussian law. Particular emphasis is given on advanced Hybrid Monte-Carlo (HMC) which makes large, derivative-driven steps in the state space (in contrast with local-move Random-walk-type algorithms) with analytical and experimental results. We illustrate its computational advantages in various diffusion processes and observation regimes; examples include stochastic volatility and latent survival models. In contrast with their standard MCMC counterparts, the advanced versions have mesh-free mixing times, as these will not deteriorate upon refinement of the approximation of the inherently infinite-dimensional diffusion paths by finite-dimensional ones used in practice when applying the algorithms on a computer.     

Rapid determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in water samples by using solid-phase microextraction followed by gas chromatography with tandem mass spectrometry

A rapid and simple method of using solid-phase microextraction was developed for determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in water samples. In this method, the target analyte is extracted from the sample into the polymeric coating of the fused-silica fiber. After exposure, the fiber is thermally desorbed in the heated injection port of the gas chromatograph, and a chromatographic analysis is performed by using low-resolution tandem mass spectrometry. Parameters that may affect the extension of the microextraction process, such as sampling mode, sample volume, temperature, agitation, and sampling time, were studied. Extraction efficiencies for 3 coating fibers were investigated: 100 microm poly(dimethylsiloxane) (PDMS), 65 microm PDMS-divinylbenzene, and 75 microm carboxen-PDMS. Linearity was evaluated (R = 0.999) for a 250-fold concentration range from the fg/mL to the pg/mL level. The 2,3,7,8-TCDD was detected at the fg/mL level when the headspace over the water sample was sampled for 60 min; the limit of detection obtained was better than that of Method 8280B of the U.S. Environmental Protection Agency. The proposed method performed well when applied to the analysis of tap water, lake water, and seawater samples.