CO Precursor Research Articles

Collisional quenching of NCO () by some inorganic molecules

Collisional removal of the (0,00,0) level of the A2Σ+ state of the NCO radical has been studied at room temperature (298 K). NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of CH with N2O, then electronically excited with Nd:YAG laser pumped dye laser. The quenching rate coefficients kq and thermally averaged cross-sections σq were determined by the pressure dependence of the time-resolved fluorescence. Colliders investigated are Ar, N2, O2, CO, NO, N2O, CO2, SO2, H2O and photochemical precursor CHBr3. The quenching rates increase on the whole with the increasing of polarities of the colliders. By comparison with the formation cross-sections of complexes calculated by means of a collision complex model, it is believed that the attractive forces play main roles in the collision quenching processes of NCO (A2Σ+) by the quenchers studied in this work.

Novel Syntheses and Applications of [11C]CO Precursors in [11C]Chemistry

AbstractFor Abstract see ChemInform Abstract in Full Text.

Saccharin as a sole source of carbon and energy for Sphingomonas xenophaga SKN.

A bacterium, strain SKN, that was able to utilize saccharin as the sole source of carbon and energy for aerobic growth, was enriched and isolated from communal sewage. The isolate was identified as a strain of Sphingomonas xenophaga. Saccharin was quantitatively converted to cell material, sulfate, ammonium and, presumably, CO(2). The specific rate of saccharin-dependent oxygen uptake during growth reached a maximum before the culture entered the stationary phase and then fell to undetectable levels. Saccharin was degraded only in the presence of molecular oxygen. Catechol was detected as an intermediate during degradation of saccharin in whole cells and catechol 1,2-dioxygenase was expressed inducibly during growth with saccharin. There was an apparent requirement of 2 mol O(2)/mol saccharin to remove the substituents on the ring and to cleave the ring. We presume that S. xenophaga SKN synthesizes a multi-component saccharin dioxygenase that simultaneously cleaves off both vicinal substituents from the aromatic ring to yield catechol and the undefined precursor of CO(2) as well as sulfate and ammonium ions.

Comparative studies of the physical and hydrophobic properties of TEOS based silica aerogels using different co-precursors

In the present paper, the experimental results on the physical and hydrophobic properties of tetraethoxysilane (TEOS) based silica aerogels using six different organosilane co-precursors (C.P) of the type RnSiX4-n as synthesis components, are reported and discussed. The aerogels have been produced by sol-gel processing followed by supercritical drying using methanol solvent extraction. The molar ratio of TEOS, ethanol (EtOH), water (0.001M oxalic acid (H2C2O4) catalyst) was kept constant at 1:5:7, respectively, and the molar ratio of C.P/TEOS (A) was varied from 0.1 to 0.6 and compared the aerogel properties. The hydrophobicity of the aerogels has been tested by the contact angle measurements. The contact angle (θ) has been found to be the highest (θ =136˚) for the trimethylethoxysilane (TMES) co-precursor, while for the other co-precursors it is in between 12˚8 and 13˚8. The surface chemical modification of the hydrophobic aerogels has been studied using Fourier Transform Infrared Spectroscopy (FTIR). As the C.P/TEOS molar ratio increased, the intensity of the C–H and Si–C peaks in the FTIR spectra increased, clearly indicating the organic modification of the aerogels. The aerogels based on mono-alkyl (CH3) trialkoxysilane co-precursor have shown higher optical transmission (≈65%) compared to the phenyl, di or tri alkyl alkoxysilanes (5–50%). The trialkyl modified aerogels showed the lowest bulk density (118.3 kg/m3) and volume shrinkage (<2%). The alkyl alkoxy/chloro–silane modified aerogels have been found to be thermally stable up to a maximum temperature of 573 K, whereas the phenyl trialkoxysilane modified aerogels are stable up to a temperature as high as 823 K. The aerogels have been characterized by scanning electron microscopy, thermogravimetric and differential thermal analyses.

Formation of CO precursors during char gasification with O 2, CO 2 and H 2O

The nature of some of the carbon–oxygen complexes formed after chemisorption of O 2, CO 2 and H 2O on carbonaceous surfaces was determined. The analysis was done by means of density functional theories. Among the three reactions studied, CO 2 chemisorption is the less exothermic. The nature of carbon–oxygen complexes depends on the oxidant agents. However, surface transformations of those complexes produce common surface oxygen groups that can desorb CO. Therefore, new data are presented to get insight into an unified mechanism of uncatalyzed carbon gasification.

Endothelial cell–mediated type I collagen gel contraction is regulated by hemin

The contraction of three-dimensional type I collagen gels is regarded as a model of contraction during wound healing and tissue remodeling. Because such a process could contribute to vessel narrowing, we hypothesized that endothelial cells may be able to mediate gel contraction. To demonstrate this, type I collagen was extracted from rat tail tendon and used to prepare collagen gels. Bovine arterial endothelial cells (BAECs) or human pulmonary artery endothelial cells (HPAECs) were then plated on the top of the gels in serum-free Ham's F-12 medium or 2% fetal calf serum–endothelium growth medium-2 (FCS-EGM2), respectively. After 48 hours of attachment, gels were released and floated in 0.2% FCS-Ham's F-12 medium (BAECs) or 2% FCS-EGM2 (HPAECs). Gel size was measured with an image analyzer daily for 5 consecutive days. Gels were then digested with collagenase to quantify DNA and hydroxyproline. BAECs contracted the gels in a time-dependent manner over the 5 days. Contraction was dependent on cell density (gel size was 100% of initial size after 5 days with no cells vs 66.4% ± 0.5% with 0.9 × 104 cells/cm2 and 22.1% ± 0.3% with 7.5 × 104 cells/cm2) and was inversely related to collagen concentration (gel size was 22.3% ± 0.05%, 46.4% ± 0.9%, 72.3% ± 0.4%, and 87.4% ± 0.3% of initial size for gels prepared with 0.5 mg/mL, 0.75 mg/mL, 1 mg/mL, and 2 mg/mL of collagen, respectively). Hemin (a precursor for CO) and cytochalasin D inhibited collagen gel contraction mediated by both bovine and human endothelial cells without changing cell number or hydroxyproline content. In contrast, prostaglandin E2, an inhibitor, and transforming growth factor-β1, a stimulator of fibroblast-mediated gel contraction, had no effect on endothelial cell–mediated contraction. These findings demonstrate that endothelial cells are able to contract native type I collagen gels and that this process can be modulated by exogenous mediators. Such a capability may cause remodeling of subjacent matrix of endothelial cells and may contribute to vessel narrowing. (J Lab Clin Med 2000; 136:100-9)

SELECTIVE TOLUENE-METHANOL ALKYLATION OVER MODIFIED ZSM-5 ZEOLITE CATALYSTS

ABSTRACT H-ZSM-5 zeolite was modified with divalent elements of groups 11 and VIII of periodic system. The modifications were achieved by impregnating H-2SM-5, containing 35 wt% of alumina as a binder, with metal precursors of Mg, Sr, Ba, Co and Ni. Structure of the modified catalysts was characterized by means of XRD and FTIR techniques. The distribution and strength of different acid sites of zeolites were investigated using temperature-programmed desorption of ammonia. The active Bronsted acid sites were confirmed by measuring the rate constants for cracking of n-hexane, as a probe molecule. Changes resulted in reduction of pore opening size of the modified ZSM-5 were monitored by a standard test reaction of probe molecules of m-xylene and ethylbenzene. Selective alkylation of toluene with methanol to p-xylene was studied over modified ZSM-5 catalysts. The effect of reaction parameters such as temperature, weight hourly space velocity (WHSV), and methanol/toluene molar ratio has been also considered. It was found that the p-selectivity decreased according to the following order: Sr/ZSM-5 ≥ Mg/ZSM-5 > Ba /ZSM-5 > Ni/ZSM-5 ≥ Co/ZSM-5 >H-ZSM-5. Performance of the catalysts was correlated with alterations found in distribution and strength of different acidic sites, and regulation of pore opening size due to the adopted modifications. The p-selectivity of Sr/ZSM-5 and Mg/ZSM-5 catalysts is due to removal of stronger Bronsted acid sites located on the external surface and reduction of the pore opening size of zeolite. Sr/ZSM-5 catalyst exhibited higher conversion levels overall the studied range of the reaction temperatures. It was suggested that the better activity of Sr modified zeolite catalyst could be attributed to the presence of partially non-transformed Sr2+ ions as Sr (NO2 which promotes formation of carbonium ions as an intermediate complex of the alkylation. The deactivation of H-ZSM-5, and Sr/ZSM-5 zeolite catalysts, due to coke deposition during run, was also considered. The catalysts were slightly affected by coke deposition, in terms of toluene conversion, during the run of 2 h on stream. The stability and activity of Sr/ZSM-5 catalyst towards the selective toluenemethanol alkylation to produce p-xylene indicated that the modification with strontium is an effective and convenient route for modification of ZSM-5 zeolite type.

Electrochemical synthesis of urea at gas-diffusion electrodes

Abstract Simultaneous reduction of CO2 and nitrite ions was examined by using the gas-diffusion electrodes with Cu, Ag and Au catalysts. The formation of urea, CO, formic acid and ammonia was found in the simultaneous reduction. The maximum current efficiencies of urea formation at Cu, Ag and Au catalysts are 37%, 38% and 26% in the range of −0.75 to −3.0 V (SHE), respectively. Urea is supposed to be formed from both an ammonia precursor and CO precursor on the catalysts.

97/04544 Hydrodeoxygenation in low-rank coal liquefaction systems using novel organometallic catalyst precursors: Kirby, S. R. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 466–471

Oxygen functionalities, especially phenols, are undesirable components of coal derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these functionalities, or the prevention of their formation, during the liquefaction process. Organometallic precursors of Co, Ni and Mo have been studied as catalysts. To ascertain the hydrodeoxygenation properties of these catalysts under liquefaction conditions, model compounds were investigated. Anthrone, Dibutylmethyl phenol, dinaphthyl ether and xanthene were studied to provide a comparison of conversions of deoxygenated products. Studies of the deoxygenating abilities of these catalyst precursors in coal liquefaction systems have also been performed. Improvements in conversion and product quality are observed. Both these factors are dependent on the coal used.

Palladium(II)-Assisted Copolymerization of Ethylene and CO: Influence of the Chain End on the Regularity of the Polymer

A theoretical study based on nonlocal density functional theory has been carried out on the Pd(II)-assisted homogeneous catalytic copolymerization of olefin and carbon monoxide, where the catalytic center is modeled by Pd(II) coordinated to PH2CHCHPH2 and the olefin is modeled by C2H4. The investigation concentrated on the energetics of the chain propagation mechanism in the presence of a copolymer chain end with a carbonyl group coordinated to the metal center. With CO misinsertion ruled out in a previous work,1 the present investigation rules out ethylene misinsertion into a growing polyketone chain due to the lack of a thermodynamically stable ethylene π-complex and the high barrier (+78 kJ/mol) associated with insertion of ethylene into the Pd−C2H4COR bond. On the other hand, insertion of CO into a Pd−C2H4COR bond is favored by a rather stable CO precursor complex (−32 kJ/mol) and by a low activation barrier (+49 kJ/mol).

Non-Hydrolytic Decay of Formyl Chloride into CO and HCl in Aqueous Solution

Formyl chloride has been generated in aqueous solution (i) by stopped-flow ozonation of vinyl chloride and (ii) by reacting dichloromethyl radicals with OH radicals using the pulse radiolysis technique. Vinyl chloride reacts in water with ozone (k = 1.7 × 104 dm3 mol-1 s-1, as determined by stopped-flow) yielding as final products (mol per mol of ozone) chloride ions (1.05), CO (1.01), and formate ions (0.06). Hydroxymethyl hydroperoxide (formaldehyde plus H2O2; 1.08) is also formed. HCl and formic acid are formed in less than 2 ms (the detection limit of the stopped-flow setup). At high pH the CO yield decreases (at pH 13.6 by 50%). It is concluded that the precursor of CO, HCl, and formic acid is formyl chloride. It predominantly decays into CO and HCl, and only at very high pH can hydrolysis to formic acid and HCl compete successfully. Using the pulse radiolysis technique dichloromethyl radicals are generated in Ar-saturated solutions from chloroform by reacting it with the solvated electron (originati...

A large 13CO deficit in the lower Antarctic stratosphere due to “Ozone Hole” Chemistry: Part I, Observations

Isotope and concentration measurements are reported for CO and CH4 in air collected in the upper troposphere and lower stratosphere between New Zealand and Antarctica in October 1993. The 13C/12C ratio of CO for the stratospheric samples, which are identified using calculated potential vorticity and coherent isotope data, like the abundance of 14CO molecules, are much lower than all previously reported atmospheric values. The measurements manifest a very steep decrease in δ13C with declining CO, with one sample reaching a δ13C value relative to V‐PDB of −43‰ at 20 ppbv CO. This large isotope shift is caused by the local production of several ppbv of extremely depleted CO. Not only is C4 itself a 13C depleted precursor of CO, it is specifically the recently discovered large fractionation in Cl+CH4, and the availability of free Cl during ozone hole conditions, which causes the effect.

液相法により調製したＣｏ‐Ｐｒ系酸化亜鉛バリスタにおける添加元素の分布と電気特性

The precursor of Co and Pr added zinc oxide varistor was successfully obtained. by a wet chemical method using zinc acetate as a starting material with praseod ymium oxide and cobalt chloride as additives.Changes in crystalline size, compact density, additives distribution, and voltage-current curve were characterized with sintering temperatures from 1200 to 1300°C for the samples prepared by the wet chemical method with or without calcination, and by a ball-mill method for a comparison.The crystalline size of zinc oxide increased for each sample with the increase in sintering temperature.The distribution is narrower and the average crystalline size is smaller for a sample by a wet chemical method. Cobalt contributed to almost constant value of coefficient of variation for the samples prepared by the wet chemical method in this temperature range.Large value of coefficient of variation was obtained for praseodymium at high temperature, which resulted from segregation to grain boundaries with growth of crystalline. Decreasing tendency was observed of nonlinearity α and break-down voltage with the increase in sintering temperature. Smaller amount of addition of both Co and Pr in the samples prepared by the wet chemical method was effective for improving the varistor characteristics.

Convective transport over the central United States and its role in regional CO and ozone budgets

We have constructed a regional budget for boundary layer carbon monoxide over the central United States (32.5°–50°N, 90°–105°W), emphasizing a detailed evaluation of deep convective vertical fluxes appropriate for the month of June. Deep convective venting of the boundary layer (upward) dominates other components of the CO budget, e.g., downward convective transport, loss of CO by oxidation, anthropogenic emissions, and CO produced from oxidation of methane, isoprene, and anthropogenic nonmethane hydrocarbons (NMHCs). Calculations of deep convective venting are based on the method of Pickering et al. [1992a] which uses a satellite‐derived deep convective cloud climatology along with transport statistics from convective cloud model simulations of observed prototype squall line events. This study uses analyses of convective episodes in 1985 and 1989 and CO measurements taken during several midwestern field campaigns. Deep convective venting of the boundary layer over this moderately polluted region provides a net (upward minus downward) flux of 18.1×108kg CO month−1 to the free troposphere during early summer, assuming the June statistics are typical. Shallow cumulus and synoptic‐scale weather systems together make a comparable contribution (total net flux 16.2×108 kg CO month−1). Boundary layer venting of CO with other O3 precursors leads to efficient free tropospheric O3 formation. We estimate that deep convective transport of CO and other precursors over the central United States in early summer leads to a gross production of 0.66–1.1 Gmol O3 d−1 in good agreement with estimates of O3 production from boundary layer venting in a continental‐scale model [Jacob et al., 1993a, b]. In this respect the central U.S. region acts as a “chimney” for the country, and presumably this O3 contributes to high background levels of O3 in the eastern United States and O3 export to the North Atlantic.

The Structure of Highly Dispersed SiO2-Supported Molybdenum Oxide Catalysts during Sulfidation

The structure of sulfided Mo-catalysts and their oxidic precursors has been abundantly studied, but the genesis of the active phase has remained much less investigated. The sulfidation (in H2S/H2 atmosphere) of a series of MoO3/SiO2 catalysts has been examined by means of temperature-programmed sulfidation, X-ray absorption fine structure, and transmission electron microscopy.The oxidic, oligomeric clusters in a 5.6 wt 5% MoO3/Si02 catalyst are transformed into partly sulfided particles (MOOS,,) by 0-S exchange at room temperature. A molybdenum sulfide species the structure of which resembles the MoS, structure is formed during sulfidation at 423 K. The MoS2 phase is formed at temperatures between 523 and 573 K, depending on the dispersion of the initial Moo3 phase. The transition of MoS3 into MoS2 can be monitored by the evolution of H2S from the catalyst with a simultaneous consumption of H2. The two-dimensional size of the MoS2 slabs can be derived from the EXAFS Mo-Mo coordination number by means of a theoretical model. TEM is required to elucidate the stacking height of the slabs. The application of supported molybdena-based catalysts in industrial processes, such as partial oxidation’-5 and hydrotreating,+lB has rendered supported molybdenum oxide catalysts a main subject of investigations. Many studies are dedicated to the preparation and the structure of Moo3 catalysts on different supports. The sulfded counterpart of the oxidic precursors of Co(Ni)/Mo(W) catalysts is one of the most thoroughly investigated catalyst systems. Conversion of the oxidic catalyst into the active sulfide occurs under reaction conditions, due to presulfiding or the presence of sulfur-containing feedstocks. It is industrial practice to “spike” the feedstock with agents, such as CS2, dimethyl sulfide (DMS), or dimethyl disulfide (DMDS), to accelerate the sulfidation of the catalyst.I9-20 As an alternative, thecatalyst can besulfided exsitu by impregnation with a sulfurcontaining liquid. In situ heating of the catalyst subsequently leads to sulfidation.2’ In most of the laboratory tests the catalyst is sulfided by a mixture of H2S/H2 at high temperat~re~~v~~ or in a temperature program. A number of models have been proposed to explain the activity of the Co(Ni)/Mo(W) catalysts. Consensus exists on the structure of the molybdenum sulfide phase: under typical hydrotreating conditions (i.e., p = 10-200 bar, T = 573-723 K, excess H2, and a sulfur-rich feedstock”) MoS2 is present, in which molybdenum is trigonal prismatically coordinated by sulfur However, the position and the role of the cobalt atoms in the catalysts are still debated. The earlier proposed models are based on the assumptionof a monolayer,34~ontactsynergy,’~J~ inter~alation,3S33~ and remote control.37 The most popular model is based on publications by Topsoe et al.30 and by Wive1 et a1.38 The latter reported a linear relationship between the activity in thiophene HDS and the concentration of Co present in the “Co-Mo-S” species. This phase had been designated as ‘COMOS”~~ because its Mbssbauer spectrum did not resemble any of the known cobalt sulfide or cobalt molybdenum sulfide spectra. The CoMoS species is envisioned as a MoS2 layer (slab), with cobalt atoms decorating the edges.30J9 Since the introduction of this model, some

Effects of tropical deforestation on global and regional atmospheric chemistry

A major portion of tropospheric photochemistry occurs in the tropics. Deforestation, colonization, and development of tropical rain forest areas could provoke significant changes in emissions of radiatively and photochemically active trace gases. A brief review of studies on trace-gas emissions in pristine and disturbed tropical habitats is followed by an effort to model regional tropospheric chemistry under undisturbed and polluted conditions. Model results suggest that changing emissions could stimulate photochemistry leading to enhanced ozone production and greater mineral acidity in rainfall in colonized agricultural regions. Model results agree with measurements made during the NASA ABLE missions. Under agricultural/pastoral development scenarios, tropical rain forest regions could export greater levels of N2O, CH4, CO, and photochemical precursors of NOy and O3 to the global atmosphere with implications for climatic warming.

Cytological composition of lymph during the febrile reaction

In the present work the effect of the precursor of Co a D-bis (N- pantothenyl-beta-aminoethyl) disulfide--pantethine on post heparin lipolytic activity and the intensity of lipid peroxidation has been investigated. Pantethine in doses of 5 mg/kg enhanced post heparin lipolytic activity (60.6%) and lipoprotein lipase activity (39.9%) in plasma and reduced the amount of NEFA (35.1%) and content of MDA (57.4%) in the mitochondria.

Sticking probability of CO on an oxygen covered Pd(110) surface under reaction conditions

The adsorption of carbon monoxide into an oxygen overlayer on a Pd(110) surface and its conversion to CO 2 was studied by quantitative mass spectrometric methods and video recorded LEED. For temperatures with negligible desorption of CO ( T ≤420 K) the sticking probability of CO into the oxygen adsorbate is reduced by approximately 1/2 compared to a CO adsorbate on a clean Pd(110) surface of the same coverage. The evaluation reveals that each oxygen adatom effectively blocks more than ten sites for CO adsorption, which is explained by the influence of adsorbed oxygen on the transition probability of the CO precursor to the chemisorbed state. Initially due to a locally higher sticking probability CO is adsorbed at defects of the c(2×4) oxygen overlayer. After consumption of less ordered oxygen regions further reaction is restricted to the domain boundaries of the reactands and propagates preferably in an unidirectional fashion along the surface troughs with a constant turnover number until whole domains of oxygen have been consumed by the reaction.

Measurement of sulfur dioxide in the post-combustion environment

Tunable Atomic Line Molecular Spectroscopy (TALMS) has been used to measure sulfur dioxide in the post flame region of an atmospheric pressure stoichiometric methane/air flame. The technique is sensitive and highly selective and thus is useful for research and commercial applications. Response is linear to 20,000 ppM in a 7 cm path length, with a limit of detection of approx. 2000 ppM at 1500 K and approx. 40 ppM at 300 K. Ultraviolet absorption spectra of SO/sub 2/ were recorded in the 205 to 220 nm range at various temperatures, and reveal significant broadening due to rotational redistribution at the higher temperatures, and no interference from other combustion products. TALMS signal dependence on magnetic field strength confirms that the same transition is observed in the flame as at room temperature. Fluorescent quenching of SO/sub 2/ by combustion products were measured in a Thermo Electron model 40 analyzer. Plots of S/sub 0//S-1 are linear and yield relative quenching coefficients which increase in the order: Ar, CO/sub 2/, O/sub 2/, H/sub 2/, CH/sub 4/, CO, and C/sub 6/H/sub 6/. Significant quenching corrections are needed to accurately determine SO/sub 2/ concentrations in combustion mixtures, especially for the case of rich combustion, where largemore » concentrations of CO, unburned hydrocarbons, and aromatic soot precursors may be present. 28 references, 6 figures, 1 table.« less

A Compact in-House Multi-Particle Cyclotron for Production of Radionuclides and Labeled Compounds for Medical Use

The Sloan-Kettering cyclotron located with covered access to two large hospitals, Memorial Hospital for Cancer and the New York Hospital, can accelerate deuterons to 8 MeV, protons and He-4 ions to 15 MeV and He-3 iohs to 23 MeV. A large number of radionuclides can be produced with these four particles and many compounds of physiological significance may be labeled. Methods will be described for the production of 15O as O2, CO and CO2 11C as CO, CO2, HCN, and other precursors for organic synthesis; 13N as N2, NO3-, NH4+ and 13N-labeled L-amino acids; 18F as NaF; 52Fe as ferrous citrate; 38K as KC1. Yields will be discussed, as well as the uses to which these radio indicators are put. The use of radioisotopes carbon-11, nitrogen-13 and fluorine-18 enables one to label compounds of true physiological or biochemical significance, and the concurrent development of instrumentation to quantitatively detect the localization of such compounds in the human body offers the opportunity to study phenomena heretofore impossible in the intact human, in a safe, non-invasive way. Examples of compounds which can be studied in this way are hormones, e.g. estradiol, for detection of breast cancer, amino acids for the detection of protein synthesis in tumors and the pancreas, precursors of DNA and RNA for the detection of abnormal cell growth, drugs related to neural disorders, e.g. haloperidol in schizophrenia.