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1.
Jnos Szanyi Ja Hun Kwak Sarah Burton Jose A. Rodriguez Charles H.F. Peden 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):164-170
Adsorbed ionic NOx species formed upon the interaction of NO2 with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO2 disproportionates on both dehydrated catalyst materials forming NO+ and NO3− species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na+ and Ba2+), respectively. Although the nature of the adsorbed NOx species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO+ and H2O, and NO2 and H2O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO2 on these zeolite catalysts. 相似文献
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Two results on site percolation on thed-dimensional lattice,d1 arbitrary, are presented. In the first theorem, we show that for stationary underlying probability measures, each infinite cluster has a well-defined density with probability one. The second theorem states that if in addition, the probability measure satisfies the finite energy condition of Newman and Schulman, then there can be at most one infinite cluster with probability one. The simple arguments extend to a broad class of finite-dimensional models, including bond percolation and regular lattices. 相似文献
4.
D F Swaile D E Burton A T Balchunas M J Sepaniak 《Journal of chromatographic science》1988,26(8):406-409
The potential utility in pharmaceutical analysis of a capillary electrokinetic separation technique that employs a micellar "pseudo-stationary phase" is discussed and illustrated. Chromatograms of separations of vitamin metabolites and derivatized amino acids are presented to illustrate the high efficiency of the technique and the ability to simultaneously separate the charged and neutral components of pharmaceutical samples. The analytical characteristics of the technique and the importance of optimizing experimental parameters, such as surfactant concentration and capillary column diameter, are discussed and demonstrated with the aid of chromatograms. 相似文献
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It has been suggested from QSAR data (P. D. Edwards, D. J. Wolanin, D.A. Andisik and M. W. Davis, J. Med. Chem., 1995, 38, 76) that the inhibition of elastase by peptidyl alpha-ketoheterocyclic inhibitors can occur in two ways, the less potent inhibitors forming a non-bonded Michaelis complex and the more potent set a covalently bonded enzyme-substrate intermediate. We report QM/MM studies of both binding and reactivity that confirm these findings, showing that the activity of the least potent set of inhibitors correlates with the calculated binding energy, and that of the more potent set correlates with the stability of the intermediate. These calculations show that QM/MM methods can be successfully employed to understand complicated structure-activity relationships and might be employed in the design and assessment of new inhibitors. 相似文献
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Treatment of halo--methylphosphonium salts with potassium fluoride and halogen (I2, Br2, ICl, IBr) gives modest yields of halo--methanes. This method of preparation augments the classical Hunsdiecker approach to these materials. 相似文献
8.
Bonvin Y Callens E Larrosa I Henderson DA Oldham J Burton AJ Barrett AG 《Organic letters》2005,7(21):4549-4552
[reaction: see text] Oxidation of alkyl and cycloalkyl arenes with tert-butyl hydroperoxide catalyzed by bismuth and picolinic acid in pyridine and acetic acid gave the corresponding benzylic ketones (48-99%). Alternatively, oxidation of methyl arenes gave the corresponding substituted benzoic acids (50-95%). Preliminary mechanistic studies were consistent with a radical mechanism rather than a bismuth(III)-bismuth(V) cycle. 相似文献
9.
Summary The use ofp-methylaminophenol sulphate (metol) at 100 for the reduction of phosphomolybdic acid in the determination of phosphate in sea-water has a number of advantages over stannous chloride. The molybdenum blue colour once formed, is stable for several hours, and the calibration curve is not dependent upon the batches of reagent used; Beer's law is obeyed up to concentrations of at least 1 mg PO4-P/l. The salt error is very small and the method has approximately 30% greater sensitivity in sea-water than has the stannous chloride method. Arsenic does not interfere at concentrations five times greater than its sea-water concentration. Iron and copper in moderate amounts do not interfere.Evaporation to dryness with a mixture of concentrated nitric and perchloric acids, followed by colorimetric determination of inorganic phosphate, is employed for the determination of total phosphorus in sea-water and marine muds. The method shows a coefficient of variation of ca. 2% with sea-water containing 60g P/l.
Zusammenfassung Die Anwendung von p-Methylaminophenolsulfat (Metol) bei 100 für die Reduktion von PhosphomolybdÄnsÄure bei der Bestimmung der Phosphate in Meerwasser hat gegenüber Zinn(II)chlorid eine Reihe von Vorteilen. Das einmal gebildete MolybdÄnblau ist für einige Stunden stabil und die Eichkurve nicht von der angewendeten Menge Reagens abhÄngig; das Beersche Gesetz ist für Konzentrationen bis zu 1 mg Phosphat-Phosphor/l gültig. Der Salzfehler ist sehr klein und die Methode für Meerwasser etwa um 30% empfindlicher als die Zinn(II)chloridmethode. Arsen stört bei Konzentrationen, die fünfmal größer sind als in Meerwasser, nicht. Eisen und Kupfer in mÄßigen Mengen stören gleichfalls nicht.Für die Bestimmung des Gesamtphosphors in Meerwasser und Seeschlamm wird mit einer Mischung von konz. SalpetersÄure und PerchlorsÄure zur Trockne verdampft und das anorganische Phosphat kolorimetrisch gemessen. Die Methode zeigt eine Schwankungsbreite von etwa 2% für Meerwasser mit 60g P/l.
Résumé L'emploi du sulfate de p-méthylaminophenol (métol) à 100 pour la réduction de l'acide phosphomolybdique lors du dosage des phosphates contenus dans l'eau de mer présente de multiples avantages sur celui du chlorure stanneux. Après sa formation, le bleu de molybdène reste stable pendant plusieurs heures et la courbe d'étalonnage ne varie pas avec le lot de réactif employé; la loi deBeer est applicable jusqu'à des concentrations au moins égales à 1 mg de phosphore phosphorique par litre. L'erreur de sel est très faible et la sensibilité de la méthode appliquée à l'eau de mer est environ 30% plus élevée que la méthode au chlorure stanneux. L'arsenic ne gÊne pas mÊme pour des concentrations cinq fois supérieures à celle qu'il atteint dans l'eau de mer. Des teneurs modérées de fer et de cuivre n'apportent pas de perturbation. On évapore à siecité en présence d'un mélange d'acides nitrique et perchlorique concentrés puis on effectue une détermination colorimétrique des phosphates minéraux pour doser le phosphore total de l'eau de mer et des boues marines. La méthode est sujette à des variations d'environ 2% pour leau de mer contenant 60 g de phosphore par litre.相似文献
10.
Micellar electrokinetic capillary chromatography (MECC) involves the application of a high voltage (10 to 40 kV) across a capillary column (25 to 75 microns i.d.) that is filled with a solution containing micelles. The mobile phase in this work consists of sodium dodecyl sulfate in an aqueous phosphate/borate buffer system. Pyridoxine (vitamin B6) and five of its metabolites are separated, with efficiencies as high as 60,000 theoretical plates/meter. Pyridoxic acid, a metabolite of B6, is separated and quantitated in human urine using laser-excited fluorescence detection. Limits of detection are less than a picogram injected. 相似文献