Adsorption and reactions of NO on clean and CO-precovered Ir(111)

Adsorption and reactions of NO on clean and CO-precovered Ir(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(111) surface at saturation coverage. NO adsorbed on hollow sites dissociated to Na and Oa at temperatures above 283 K. The dissociated Na desorbed to form N2 by recombination of Na at 574 K and by a disproportionation reaction between atop-NO and Na at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated Oa and desorbed as CO2 at 574 K.     

A novel scheme of heterogeneous polymerization of ethylene

The heterogeneous polymerization of ethylene initiated by radiation in tert-butyl alcohol was studied. The polymerization was carried out in a 100-ml reactor at 25–100°C and pressures of 200–300 kg/cm² in the presence of 50 ml of tert-butyl alcohol containing 7 wt-% water. The amounts of polymerized monomer, the average molecular weight of polymer formed, and the molecular weight distribution of polymer were measured at various stages of reaction and at various temperatures. The molecular weight distribution was found to be very much dependent on the reaction time and temperature. For the polymer formed at 50–60°C in the very early stages of reaction, the molecular weight distribution is unimodal, and in the intermediate stage a shoulder appears at a molecular weight higher than the first peak which increases as the polymerization proceeds; eventually a bimodal curve is formed. The bimodal distribution curves were analyzed to determine the fractions and average molecular weights of the each peak. On the basis of these data for the molecular weight distribution and kinetic behavior, a new scheme for the heterogeneous polymerization is proposed which indicates that the polymerization proceeds via propagating radicals in two different physical states, namely, loose and rigid states.     

Atomic absorption spectrometry of traces of tri- and hexavalent chromium

Summary Atomic absorption spectrometry combined with extraction is described for the determination of tri- and hexavalent chromium. The chromium diethyldithiocarbamate chelate was used for chromium (VI), whereas hydroxyquinolate or thenoyltrifluoroacetonate chelate for chromium(III). The method is rapid and precise.

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Zusammenfassung Extraktion und darauffolgende Messung der Atomarabsorption wurden zur Bestimmung von drei- und sechswertigem Chrom verwendet. Die Chelatverbindung mit Diäthyldithiocarbamat wurde für Chrom(VI), der Chelatkomplex mit Hydroxychinolin oder Thenoyltrifluoraceton für Chrom(III) verwendet. Das Verfahren ist rasch und genau.

     

High-performance liquid chromatographic determination of (S)-(-)-ofloxacin and its metabolites in serum and urine using a solid-phase clean-up

A sensitive and selective method for the simultaneous determination of (S)-(-)-ofloxacin [(S)-(-)-OFLX] and its metabolites in serum and urine was developed using isocratic high-performance liquid chromatography with a specific solid-phase extraction procedure. (S)-(-)-OFLX and its metabolites, desmethyl-(S)-(-)-OFLX and (S)-(-)-OFLX N-oxide, were eluted from a C8 solid-phase column with recoveries of more than 98%. These compounds were separated and determined by means of a reversed-phase column with fluorimetric detection. Validation studies showed that the results were linear for (S)-(-)-OFLX in serum over the range 10-1200 ng/ml and in urine over the range 1-200 micrograms/ml. Analysis for (S)-(-)-OFLX and its metabolites showed good precision and accuracy with a relative standard deviation of less than 6%.     

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al₂O₃ catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al₂O₃. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co₃O₄ serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species and then NO₂⁻ species react with the adsorbed NO species to form N₂ over the interface between the alkali metal and Co₃O₄.     

The catalytic Mannich reaction of 1,1-difluoro-2-trialkyl(aryl)silyl-2-trimethyl-silyloxyethenes: preparation of beta-amino acid derivatives

[reaction: see text] Catalytic Mannich reactions of 1,1-difluoro-2-trialkyl(aryl)silyl-2-trimethylsilyloxyethenes (3) with a variety of sulfonylimines were utilized for the preparation of alpha,alpha-difluoro-beta-amino acid derivatives (7). The influence of the Lewis acid on the reaction was examined. Methods for the conversion of alpha,alpha-difluoroacylsilanes to alpha,alpha-difluorocarboxylic acids were also explored.     

Ionic-conductivity switching of vinyl malachite green leuconitrile copolymers based on photoinduced carrier generation

Copolymers of bis[4-(N,N-dimethylamino)phenyl]-4-vinylphenylmethanenitrile (vinyl Malachite Green leuconitrile) with methyl methacrylate or ω-methoxyoligo(oxyethylene) methacrylate have been synthesized, aiming at designing one-component-type organic polymers for photoswitchable ion-conducting films. The triphenylmethanenitrile copolymers with ω-methoxyoligo(oxyethylene) methacrylate were found to undergo ionic-conductivity switching by turning on and off UV light at ambient temperature, owing to their low glass transition temperature. © 1993 John Wiley & Sons, Inc.     

Time-dependent fluctuations in infrared vsCH2 frequencies in acyl chain membranes of Acholeplasma laidlawii cells

We measured FT-IR spectra of intact Acholeplasma laidlawii cells grown at 37 °C on palmitic acid (C16:0) or on binary palmitic acid-d31/oleic acid (C16:0-d31/C18:1(9)) at an initial mole ratio of 2:3, which have been previously reported to produce significant fluctuations in CH₂ symmetric stretching (ν_sCH₂) and CD₂ asymmetric stretching (ν_aCD₂) frequencies (Biochim. Biophys. Acta 1279 (1996) 49). Time courses for acyl chain ν_sCH₂ and ν_aCD₂ frequencies determined from fourth derivative spectra are presented. Fluctuations were detected with the C16:0 enriched cells at temperatures above 40 °C as well as with the cells enriched in 2:3 C16:0-d₃₁/C18:1(9). These observations at temperatures above 40 °C for the C16:0 enriched cells were not in agreement with the conclusion in the previous work by Moore et al. Our results have suggested that the 2850 cm⁻¹ ν_sCH₂ band comprises two components arising from trans and gauche conformations, and that the fluctuations in ν_sCH₂ frequency are caused by random temporal changes in the relative intensities of these two components.     

A study of molecular vibrational relaxation mechanism in condensed phase based upon mixed quantum-classical molecular dynamics. II. Noncollisional mechanism for the relaxation of a polar solute in supercritical water

Mixed quantum-classical molecular dynamics method has been applied to vibrational relaxation of a hydrophilic model NO in supercritical water at various densities along an isotherm above the critical temperature. The relaxation rate was determined based on Fermi's golden rule at each state point and showed an inverse S-shaped curve as a function of bulk density. The hydration number was also calculated as a function of bulk density based on the calculated radial distribution function, which showed a good correlation with the relaxation rate. Change of the survival probability of the solute vibrational state was analyzed as a function of time together with the trajectory of the solvent water and the interaction with it. We will show that the solvent molecule resides near the solute molecule for a while and the solvent contributes to the relaxation by the random-noiselike Coulombic interaction only when it stays near the solute. After the solvent leaves the solute, it shows no contribution to the relaxation. The relaxation mechanism for this system is significantly different from the collisional one found for a nonpolar solute in nonpolar solvent in Paper I. Then, the relaxation rate is determined, on average, by the hydration number or local density of the solvent. Thus, the density dependence of the relaxation rate for the polar solute in supercritical water is apparently similar to that found for the nonpolar solute in nonpolar solvent, although the molecular process is quite different from each other.     

Spectroscopic study of atomization processes and inter-element effects on the flame emission of chromium and iron in an air—acetylene flame

Emission spectroscopy is applied for characterization of reactions occurring in air—acetylene flames normally used for atomic absorption spectrometry. Inter-element effects on the emissions of chromium and iron are discussed. Two atomic emission lines with different upper energies and a molecular emission line of the diatomic oxide MO are compared for determination of the excitation temperature and the degree of atomization in fuel-rich and lean flames. The reductive power of the fuel-rich flame is essential for atomization of chromium salts. Inter-element effects by iron can be attributed to the formation of refractory oxides, and to mutual catalytic oxidation.