Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O,and15N) NMR study

A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by¹H ,¹³C,¹⁷O, and¹⁵N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995.     

Mass spectrometry of 3,4-dihydroquinazolin-4-ones of pharmaceutical interest. Part 3 . Electron ionization mass spectra of 2-substituted-3-(5′-pyrazolyl)-4(3H)-quinazolinones

The fragmentation reactions induced by electron impact of eighteen title compounds has been investigated with the aid of low beam energy spectra (14 eV, nom. value), metastable ion detection, high resolution measurements and labelling experiments. The loss of the 4-carbonyl oxygen together with the 3-substituent, which constitutes a characteristic fragmentation route of 3-aryl and 3-heteroaromatic substituted-4(3H)-quinazolinones, is again observed, but the presence of a carboxyethyl group at the 4′-position of the pyrazole ring is responsible of an anomalous loss of 47 daltons from the molecular ion. Lastly, a comparison with the previously described behaviour of 3-(5′-isoxazolyl) derivatives was carried out.     

Reaction of methyl 4-nitrobenzenesulfonate with Br- in water-formamide tetradecyltrimethylammonium bromide micellar solutions

Summary The reaction methyl 4-nitrobenzenesulfonate + Br^- was studied in water-formamide tetradecyltrimethylammonium bromide micellar solutions. A pseudophase kinetic model was used to quantitatively rationalize the kinetic micellar effects observed     

The exo-selectivity of the new non-natural chiral auxiliary (+)-(1R,endo)-2-benzonorbornenol in an asymmetric aza-Diels-Alder reaction

The recently reported compound (+)-(1R,endo)-2-benzonorbornenol (2) proved to be an efficient chiral auxiliary in the asymmetric aza-Diels-Alder reaction between cyclopentadiene and the N-benzyl imine of its glyoxylate, which afforded a virtually all-exo mixture of cycloaducts with a 1S:1R diastereomeric ratio of 63:37.     

An attempt on the VOC oxidation using mechanically activated catalyst

A catalytic action of the mechanochemical products of copper hydroxocarbonate with calcium carbonate was investigated in n-butyl alcohol oxidation tests. The solid products of high-energy milling were identified using thermogravimetry supplemented by X-ray diffraction method. It was shown that the mechanical activation induces more effective tested catalyst because it promotes the alcohol conversion at lower temperatures than that unmilled one. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical study on conformational conversion of 1,3-dioxane inside a capsular host

The conformational conversion of 1,3-dioxane guest encapsulated inside a cylindrical capsular host was investigated with PM3 method and single point energies were evaluated by B3LYP method. When entrapped in the capsule, the guest tumbles were slower than that in the free condition. The influences of the inner phase of the capsule on the guest conformational conversion were discussed in detail.     

Chiral comprehensive two-dimensional gas chromatography with electron-capture detection applied to the analysis of chiral polychlorinated biphenyls in food samples

The feasibility of comprehensive two-dimensional gas chromatography with electron-capture detection (GC x GC-ECD) for the enantioseparation of chiral PCBs from other possible interfering compounds has been evaluated. Three commercially available enantioselective beta-cyclodextrin-based capillary columns (Chirasil-Dex, BGB-172 and BGB-176SE) have been tested as first-dimension columns. Three non-enantioselective stationary phases (HT-8, BPX-50 and Supelcowax-10) were combined with the enantioselective columns to allow the unambiguous determination of the enantiomers of the target chiral PCBs. Each enantioselective first-dimension column tested was able to separate into enantiomers different PCB congeners, but in all cases, the use of Supelcowax-10 as second-dimension column provided the most satisfactory results. The Chirasil-Dex x Supelcowax-10 column combination allowed the determination of the enantiomeric fraction (EF) of PCBs 84, 91, 95, 132, 136, 149, 174 and 176 in the working standard solution, while that of congener 135 was hindered. The BGB-172 x Supelcowax-10 column set allowed a proper EF determination of congeners 45, 84, 131, 132, 135, 171, 174 and 183, while that of PCB 91 was interfered with co-elutants. The column combination BGB-176SE x Supelcowax-10 allowed the determination of all congeners that this enantioselective stationary phase was able to separate into enantiomers, i.e. PCBs 45, 91, 95, 136, 149 and 176. These column combinations have also been evaluated for the simultaneous determination of the 12 congeners with a toxic equivalency factor assigned by the WHO (PCBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, 189) and the seven indicator congeners (PCBs 28, 52, 101, 118, 138, 153 and 180), and evaluated for the analysis of food samples.     

Asymmetric silyl nitronate cycloadditions with bornane-10,2-sultam derivatives

Asymmetric silyl nitronate cycloadditions with N-acryloyl (2R)-bornane-10,2-sultam, N-acryloyl (2S)-bornane-10,2-sultam, and N-methacryloyl (2R)-bornane-10,2-sultam have been studied. The asymmetric silyl nitronate cycloaddidon/elimination methodology provides a general route for the asymmetric synthesis of 2-isoxazolines.     

A general and enantiodivergent method for the asymmetric synthesis of piperidine alkaloids: concise synthesis of (R)-pipecoline, (S)-coniine and other 2-alkylpiperidines

A simple and very efficient protocol for the preparation of highly enantioenriched 2-alkylpiperidines has been set up, which allows the preparation of the final heterocycles with any wanted configuration at the stereogenic center starting from the same starting material. The key step of the synthesis relies on a diastereodivergent aza-Michael reaction protocol using the readily available and cheap reagent (+)-(S,S)-pseudoephedrine as chiral auxiliary.     

Multicommutation as an environmentally friendly analytical tool in the hydride generation atomic fluorescence determination of tellurium in milk

The aim of this study is to show the advantages of the emerging multicommutation methodology based on the use of solenoid valves for Te determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS). The delivery of a series of alternating sequential insertions of small volumes of samples and reagents gives rise to new hydrodynamic processes and exciting analytical potentials by controlling the time of flow through the on/off-switched solenoid valves. This drastically reduces the reagent consumption by a factor of 4 and the generation of effluents (590 mL h^–1 instead of 750 mL h^–1 generated by the continuous-mode measurement) and also provides an improvement in the laboratory productivity by an increase of the sample throughput (85 h^–1 compared to 20 h^–1 found in the continuous mode). So, multicommutation is an environmentally and economically sustainable alternative to the methodology based on continuous measurements. The multicommutation-based method developed was applied to tellurium determination in commercially available milk samples; a calibration range of 0.0–0.5 ng mL^–1 and a detection limit of 0.20 ng L^–1 with average relative standard deviation of 2.1% were found. Comparable results were obtained for a series of samples using both continuous and multicommutation HG-AFS modes.