Nitric oxide-dependent bone marrow progenitor mobilization by carbon monoxide enhances endothelial repair after vascular injury

Carbon monoxide (CO) has emerged as a vascular homeostatic molecule that prevents balloon angioplasty-induced stenosis via antiproliferative effects on vascular smooth muscle cells. The effects of CO on reendothelialization have not been evaluated.

Catalytic systems based on carbon fiber materials for the low-temperature oxidation of carbon monoxide

New heterogenized catalytic systems for the low-temperature oxidation of CO were synthesized by supporting solutions of Pd, Cu, and Fe salts on carbon fibrous materials (carbopon and busofit). The carbon supports were studied by elemental analysis, SEM, TGA, and TPD. The effects of the nature of the support, the concentration and composition of the active component, and the conditions of preparation on the efficiency of the catalytic system were studied. It was ascertained that attenuation of hydrophilic properties of the support led to the decrease in system activity. The investigation of the catalysts by XPS showed that sample treatment in the reaction medium results in redistribution of the components of the active phase in the near-surface layer of the catalyst. The catalytic system based on carbon fibrous material carbopon prepared by supporting active components (Pd, Cu, and Fe salts) in three stages with intermediate activation in the reaction medium ensures 95% conversion of CO under respiratory conditions, and is promising for the design of the main element of breathing masks on its basis.

Carbon monoxide inhibits inward rectifier potassium channels in cardiomyocytes

Reperfusion-induced ventricular fibrillation (VF) severely threatens the lives of post-myocardial infarction patients. Carbon monoxide (CO) - produced by haem oxygenase in cardiomyocytes - has been reported to prevent VF through an unknown mechanism of action. Here, we report that CO prolongs action potential duration (APD) by inhibiting a subset of inward-rectifying potassium (Kir) channels. We show that CO blocks Kir2.2 and Kir2.3 but not Kir2.1 channels in both cardiomyocytes and HEK-293 cells transfected with Kir. CO directly inhibits Kir2.3 by interfering with its interaction with the second messenger phosphatidylinositol (4,5)-bisphosphate (PIP 2). As the inhibition of Kir2.2 and Kir2.3 by CO prolongs APD in myocytes, cardiac Kir2.2 and Kir2.3 are promising targets for the prevention of reperfusion-induced VF. © 2014 Macmillan Publishers Limited. All rights reserved.

Carbon monoxide inhibits sprouting angiogenesis and vascular endothelial growth factor receptor-2 phosphorylation

Carbon monoxide (CO) is a gaseous autacoid known to positively regulate vascular tone; however, its role in angiogenesis is unknown. The aim of this study was to investigate the effect of CO on angiogenesis and vascular endothelial growth factor (VEGF) receptor-2 phosphorylation. Human umbilical vein endothelial cells (HUVECs) were cultured on growth factor- reduced Matrigel and treated with a CO-releasing molecule (CORM-2) or exposed to CO gas (250 ppm). Here, we report the surprising finding that exposure to CO inhibits vascular endothelial growth factor (VEGF)-induced endothelial cell actin reorganisation, cell proliferation, migration and capillary-like tube formation. Similarly, CO suppressed VEGF-mediated phosphorylation of VEGFR-2 at tyrosine residue 1175 and 1214 and basic fibroblast growth factor- (FGF-2) and VEGF-mediated Akt phosphorylation. Consistent with these data, mice exposed to 250 ppm CO (1h/day for 14 days) exhibited a marked decrease in FGF-2-induced Matrigel plug angiogenesis (p<0.05). These data establish a new biological function for CO in angiogenesis and point to a potential therapeutic use for CO as an anti-angiogenic agent in tumour suppression.

Effects of incomplete combustion on atmospheric chemistry: Black carbon climate forcing and global carbon monoxide emissions

This thesis is actually the composition of two separate studies aimed at further understanding the role of incomplete combustion products on atmospheric chemistry. The first explores the sensitivity of black carbon (BC) forcing to aerosol vertical location since BC has an increased forcing per unit mass when it is located above reflective clouds. We used a column radiative transfer model to produce globally-averaged values of normalized direct radiative forcing (NDRF) for BC over and under different types of clouds. We developed a simple column-weighting scheme based on the mass fractions of BC that are over and under clouds in measured vertical profiles. The resulting NDRF is in good agreement with global 3-D model estimates, supporting the column-weighted model as a tool for exploring uncertainties due to diversity in vertical distribution. BC above low clouds accounts for about 20% of the global burden but 50% of the forcing. We estimate maximum-minimum spread in NDRF due to modeled profiles as about 40% and uncertainty as about 25%. Models overestimate BC in the upper troposphere compared with measurements; modeled NDRF might need to be reduced by about 15%. Redistributing BC within the lowest 4 km of the atmosphere affects modeled NDRF by only about 5% and cannot account for very high forcing estimates. The second study estimated global year 2000 carbon monoxide (CO) emissions using a traditional bottom-up inventory. We applied literature-derived emission factors to a variety of fuel and technology combinations. Combining these with regional fuel use and production data we produced CO emissions estimates that were separable by sector, fuel type, technology, and region. We estimated year 2000 stationary source emissions of 685.9 Tg/yr and 885 Tg/yr if we included adopted mobile sources from EDGAR v3.2FT2000. Open/biomass burning contributed most significantly to global CO burden, while the residential sector, primarily in Asia and Africa, were the largest contributors with respect to contained combustion sources. Industry production in Asia, including brick, cement, iron and steel-making, also contributed significantly to CO emissions. Our estimates of biofuel emissions are lower than most previously published bottom-up estimates while our other fuel emissions are generally in good agreement. Our values are also universally lower than recently estimated CO emissions from models using top-down methods.

Boreal forest fire impacts on lower troposphere carbon monoxide and ozone levels at the regional to hemispheric scales

Tropospheric ozone (O3) and carbon monoxide (CO) pollution in the Northern Hemisphere is commonly thought to be of anthropogenic origin. While this is true in most cases, copious quantities of pollutants are emitted by fires in boreal regions, and the impact of these fires on CO has been shown to significantly exceed the impact of urban and industrial sources during large fire years. The impact of boreal fires on ozone is still poorly quantified, and large uncertainties exist in the estimates of the fire-released nitrogen oxides (NO x ), a critical factor in ozone production. As boreal fire activity is predicted to increase in the future due to its strong dependence on weather conditions, it is necessary to understand how these fires affect atmospheric composition. To determine the scale of boreal fire impacts on ozone and its precursors, this work combined statistical analysis of ground-based measurements downwind of fires, satellite data analysis, transport modeling and the results of chemical model simulations. The first part of this work focused on determining boreal fire impact on ozone levels downwind of fires, using analysis of observations in several-days-old fire plumes intercepted at the Pico Mountain station (Azores). The results of this study revealed that fires significantly increase midlatitude summertime ozone background during high fire years, implying that predicted future increases in boreal wildfires may affect ozone levels over large regions in the Northern Hemisphere. To improve current estimates of NOx emissions from boreal fires, we further analyzed ΔNOy /ΔCO enhancement ratios in the observed fire plumes together with transport modeling of fire emission estimates. The results of this analysis revealed the presence of a considerable seasonal trend in the fire NOx /CO emission ratio due to the late-summer changes in burning properties. This finding implies that the constant NOx /CO emission ratio currently used in atmospheric modeling is unrealistic, and is likely to introduce a significant bias in the estimated ozone production. Finally, satellite observations were used to determine the impact of fires on atmospheric burdens of nitrogen dioxide (NO2 ) and formaldehyde (HCHO) in the North American boreal region. This analysis demonstrated that fires dominated the HCHO burden over the fires and in plumes up to two days old. This finding provides insights into the magnitude of secondary HCHO production and further enhances scientific understanding of the atmospheric impacts of boreal fires.

Free Troposphere Ozone and Carbon Monoxide over the North Atlantic for 2001-2011

Carbon Monoxide (CO) and Ozone (O3) are considered to be one of the most important atmospheric pollutants in the troposphere with both having significant effects on human health. Both are included in the U.S. E.P.A list of criteria pollutants. CO is primarily emitted in the source region whereas O3 can be formed near the source, during transport of the pollution plumes containing O3 precursors or in a receptor region as the plumes subside. The long chemical lifetimes of both CO and O3 enable them to be transported over long distances. This transport is important on continental scales as well, commonly referred to as inter-continental transport and affects the concentrations of both CO and O3 in downwind receptor regions, thereby having significant implications for their air quality standards. Over the period 2001-2011, there have been decreases in the anthropogenic emissions of CO and NOx in North America and Europe whereas the emissions over Asia have increased. How these emission trends have affected concentrations at remote sites located downwind of these continents is an important question. The PICO-NARE observatory located on the Pico Mountain in Azores, Portugal is frequently impacted by North American pollution outflow (both anthropogenic and biomass burning) and is a unique site to investigate long range transport from North America. This study uses in-situ observations of CO and O3 for the period 2001-2011 at PICO-NARE coupled with output from the full chemistry (with normal and fixed anthropogenic emissions) and tagged CO simulations in GEOS-Chem, a global 3-D chemical transport model of atmospheric composition driven by meteorological input from the Goddard Earth Observing System (GEOS) of the NASA Global Modeling and Assimilation Office, to determine and interpret the trends in CO and O3 concentrations over the past decade. These trends would be useful in ascertaining the impacts emission reductions in the United States have had over Pico and in general over the North Atlantic. A regression model with sinusoidal functions and a linear trend term was fit to the in-situ observations and the GEOS-Chem output for CO and O3 at Pico respectively. The regression model yielded decreasing trends for CO and O3 with the observations (-0.314 ppbv/year & -0.208 ppbv/year respectively) and the full chemistry simulation with normal emissions (-0.343 ppbv/year & -0.526 ppbv/year respectively). Based on analysis of the results from the full chemistry simulation with fixed anthropogenic emissions and the tagged CO simulation it was concluded that the decreasing trends in CO were a consequence of the anthropogenic emission changes in regions such as USA and Asia. The emission reductions in USA are countered by Asian increases but the former have a greater impact resulting in decreasing trends for CO at PICO-NARE. For O3 however, it is the increase in water vapor content (which increases O3 destruction) along the pathways of transport from North America to PICO-NARE as well as around the site that has resulted in decreasing trends over this period. This decrease is offset by increase in O3 concentrations due to anthropogenic influence which could be due to increasing Asian emissions of O3 precursors as these emissions have decreased over the US. However, the anthropogenic influence does not change the final direction of the trend. It can thus be concluded that CO and O3 concentrations at PICO-NARE have decreased over 2001-2011.

Carbon dioxide reforming of methane to produce synthesis gas over metal-supported catalysts: State of the art

Carbon dioxide reforming of methane produces synthesis gas with a low hydrogen to carbon monoxide ratio, which is desirable for many industrial synthesis processes. This reaction also has very important environmental implications since both methane and carbon dioxide contribute to the greenhouse effect. Converting these gases into a valuable feedstock may significantly reduce the atmospheric emissions of CO2 and CH4. In this paper, we present a comprehensive review on the thermodynamics, catalyst selection and activity, reaction mechanism, and kinetics of this important reaction. Recently, research has centered on the development of catalysts and the feasible applications of this reaction in industry. Group VIII metals supported on oxides are found to be effective for this reason. However, carbon deposition causing catalyst deactivation is the major problem inhibiting the industrial application of the CO2/CH4 reaction. Ni-based catalysts impregnated on certain supports show carbon-free operation and thus attract much attention. To develop an effective catalyst for CO2 reforming of CH4 and accelerate the commercial application of the reaction, the following are identified to be the most important areas for future work: (1) selection of metal and support and studying the effect of their interaction on catalyst activity; (2) the effect of different promoter on catalyst activity; (3) the reaction mechanism and kinetics; and (4) pilot reactor performance and scale-up operation.

Electrooxidation of formic acid at platinum nanoclusters electrodeposited on PEDOT coated carbon paper electrode

Nanoclusters of Pt were electrochemically deposited on a conducting polymer, namely, poly(3,4-ethylenedioxythiophene) (PEDOT), which was also electrochemically deposited on carbon paper current collector. PEDOT facilitated uniform distribution of Pt nanoclusters, when compared with Pt electrodeposition on bare carbon paper substrate. Spectroscopy data indicated absence of any interaction between PEDOT and Pt. The electrochemically active surface area as measured from carbon monoxide adsorption followed by its oxidation was several times greater for Pt-PEDOT/C electrode in comparison with Pt/C electrode. The catalytic activity of Pt-PEDOT/C electrode for electrooxidation of formic acid was significantly greater than that of Pt/C electrode. Amperometry data suggested that the electrodes were stable for continuous oxidation of HCOOH.

Ozone and carbon trioxide synthesis by low energy ion implantation onto solid carbon dioxide and implications to astrochemistry

Ion implantation experiments were carried out on amorphous (30 K) and crystalline (80 K) solid CO2 using both reactive (D+, H+) and non-reactive (He+) ions, simulating different irradiation environments on satellite and dust grain surfaces. Such ion irradiation synthesized several new species in the ice including ozone (O-3), carbon trioxide (CO3), and carbon monoxide (CO) the main dissociation product of carbon dioxide. The yield of these products was found to be strongly dependent upon the ion used for irradiation and the sample temperature. Ion implantation changes the chemical composition of the ice with recorded infrared spectra clearly showing the coexistence of D-3h and C-2v isomers of CO3, for the first time, in ion irradiated CO2 ice. (C) 2013 AIP Publishing LLC.

Carbon-carbon bond forming reactions from bis(carbene)-platinum(II) complexes and olefin polymerization and oligomerization using group 4 post-metallocene complexes

A long-standing challenge in transition metal catalysis is selective C–C bond coupling of simple feedstocks, such as carbon monoxide, ethylene or propylene, to yield value-added products. This work describes efforts toward selective C–C bond formation using early- and late-transition metals, which may have important implications for the production of fuels and plastics, as well as many other commodity chemicals.

The industrial Fischer-Tropsch (F-T) process converts synthesis gas (syngas, a mixture of CO + H₂) into a complex mixture of hydrocarbons and oxygenates. Well-defined homogeneous catalysts for F-T may provide greater product selectivity for fuel-range liquid hydrocarbons compared to traditional heterogeneous catalysts. The first part of this work involved the preparation of late-transition metal complexes for use in syngas conversion. We investigated C–C bond forming reactions via carbene coupling using bis(carbene)platinum(II) compounds, which are models for putative metal–carbene intermediates in F-T chemistry. It was found that C–C bond formation could be induced by either (1) chemical reduction of or (2) exogenous phosphine coordination to the platinum(II) starting complexes. These two mild methods afforded different products, constitutional isomers, suggesting that at least two different mechanisms are possible for C–C bond formation from carbene intermediates. These results are encouraging for the development of a multicomponent homogeneous catalysis system for the generation of higher hydrocarbons.

A second avenue of research focused on the design and synthesis of post-metallocene catalysts for olefin polymerization. The polymerization chemistry of a new class of group 4 complexes supported by asymmetric anilide(pyridine)phenolate (NNO) pincer ligands was explored. Unlike typical early transition metal polymerization catalysts, NNO-ligated catalysts produce nearly regiorandom polypropylene, with as many as 30-40 mol % of insertions being 2,1-inserted (versus 1,2-inserted), compared to <1 mol % in most metallocene systems. A survey of model Ti polymerization catalysts suggests that catalyst modification pathways that could affect regioselectivity, such as C–H activation of the anilide ring, cleavage of the amine R-group, or monomer insertion into metal–ligand bonds are unlikely. A parallel investigation of a Ti–amido(pyridine)phenolate polymerization catalyst, which features a five- rather than a six-membered Ti–N chelate ring, but maintained a dianionic NNO motif, revealed that simply maintaining this motif was not enough to produce regioirregular polypropylene; in fact, these experiments seem to indicate that only an intact anilide(pyridine)phenolate ligated-complex will lead to regioirregular polypropylene. As yet, the underlying causes for the unique regioselectivity of anilide(pyridine)phenolate polymerization catalysts remains unknown. Further exploration of NNO-ligated polymerization catalysts could lead to the controlled synthesis of new types of polymer architectures.

Finally, we investigated the reactivity of a known Ti–phenoxy(imine) (Ti-FI) catalyst that has been shown to be very active for ethylene homotrimerization in an effort to upgrade simple feedstocks to liquid hydrocarbon fuels through co-oligomerization of heavy and light olefins. We demonstrated that the Ti-FI catalyst can homo-oligomerize 1-hexene to C₁₂ and C₁₈ alkenes through olefin dimerization and trimerization, respectively. Future work will include kinetic studies to determine monomer selectivity by investigating the relative rates of insertion of light olefins (e.g., ethylene) vs. higher α-olefins, as well as a more detailed mechanistic study of olefin trimerization. Our ultimate goal is to exploit this catalyst in a multi-catalyst system for conversion of simple alkenes into hydrocarbon fuels.

Investigations of group IVA transition metal mediated carbon-carbon bond forming reactions

Zirconocene aldehyde and ketone complexes were synthesized in high yield by treatment of zirconocene acyl complexes with trimethylaluminum or diisobutylaluminum hydride. These complexes, which are activated by dialkylaluminum chloride ligands, inserted unsaturated substrates such as alkynes, allenes, ethylene, nitriles, ketenes, aldehydes, ketones, lactones, and acid chlorides with moderate to high conversion. Insertion of aldehyde substrates yielded zirconocene diolate complexes with up to 20:1 (anti:syn) diastereoselectivity. The zirconocene diolates were hydrolyzed to afford unsymmetrical 1,2-diols in 40-80% isolated yield. Unsymmetrical ketones gave similar insertion yields with little or no diastereoselectivity. A high yielding one-pot method was developed that coupled carbonyl substrates with zirconocene aldehyde complexes that were derived from olefins by hydrozirconation and carbonylation. The zirconocene aldehyde complexes also inserted carbon monoxide and gave acyloins in 50% yield after hydrolysis.

The insertion reaction of aryl epoxides with the trimethylphoshine adduct of titanocene methylidene was examined. The resulting oxytitanacyclopentanes were carbonylated and oxidatively cleaved with dioxygen to afford y-lactones in moderate yields. Due to the instability and difficult isolation of titanocene methylidene trimethylphoshine adducts, a one-pot method involving the addition of catalytic amounts of trimethylphosphine to β,β-dimethyltitanacyclobutane was developed. A series of disubstituted aryl epoxides were examined which gave mixtures of diastereomeric insertion products. Based on these results, as well as earlier Hammett studies and labeling experiments, a biradical transition state intermediate is proposed. The method is limited to aryl substituted epoxide substrates with aliphatic examples showing no insertion reactivity.

The third study involved the use of magnesium chloride supported titanium catalysts for the Lewis acid catalyzed silyl group transfer condensation of enol silanes with aldehydes. The reaction resulted in silylated aldol products with as many as 140 catalytic turnovers before catalyst inactivation. Low diastereoselectivities favoring the anti-isomer were consistent with an open transition state involving a titanium atom bound to the catalyst surface. The catalysts were also used for the aldol group transfer polymerization of t-butyldimethylsilyloxy-1-ethene resulting in polymers with molecular weights of 5000-31,000 and molar mass dispersities of 1.5-2.8. Attempts to polymerize methylmethacrylate using GTP proved unsuccessful with these catalysts.

Black carbon measurements in the boundary layer over western and northern Europe

Europe is a densely populated region that is a significant global source of black carbon (BC) aerosol, but there is a lack of information regarding the physical properties and spatial/vertical distribution of rBC in the region. We present the first aircraft observations of sub-micron refractory BC (rBC) aerosol concentrations and physical properties measured by a single particle soot photometer (SP2) in the lower troposphere over Europe. The observations spanned a region roughly bounded by 50° to 60° N and from 15° W to 30° E. The measurements, made between April and September 2008, showed that average rBC mass concentrations ranged from about 300 ng m−3 near urban areas to approximately 50 ng m−3 in remote continental regions, lower than previous surface-based measurements. rBC represented between 0.5 and 3% of the sub-micron aerosol mass. Black carbon mass size distributions were log-normally distributed and peaked at approximately 180 nm, but shifted to smaller diameters (~160 nm) near source regions. rBC was correlated with carbon monoxide (CO) but had different ratios to CO depending on location and air mass. Light absorption coefficients were measured by particle soot absorption photometers on two separate aircraft and showed similar geographic patterns to rBC mass measured by the SP2. We summarize the rBC and light absorption measurements as a function of longitude and air mass age and also provide profiles of rBC mass concentrations and size distribution statistics. Our results will help evaluate model-predicted regional rBC concentrations and properties and determine regional and global climate impacts from rBC due to atmospheric heating and surface dimming.

Synthesis, Characterization, and Electrocatalytic Activity toward Methanol Oxidation of Carbon-Supported Pt(x)-(RuO(2)-M)(1-x) Composite Ternary Catalysts (M = CeO(2), MoO(3), or PbO(x))

Carbon-supported platinum is commonly used as an anode electrocatalyst in low-temperature fuel cells fueled with methanol. The cost of Pt and the limited world supply are significant barriers for the widespread use of this type of fuel cell. Moreover, Pt used as anode material is readily poisoned by carbon monoxide produced as a byproduct of the alcohol oxidation. Although improvements in the catalytic performance for methanol oxidation were attained using Pt-Ru alloys, the state-of-the-art Pt-Ru catalyst needs further improvement because of relatively low catalytic activity and the high cost of noble Pt and Ru. For these reasons, the development of highly efficient ternary platinum-based catalysts is an important challenge. Thus, various compositions of ternary Pt(x)-(RuO(2)-M)(1-x)/C composites (M = CeO(2), MoO(3), or PbO(x)) were developed and further investigated as catalysts for the methanol electro-oxidation reaction. The characterization carried out by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry point out that the different metallic oxides were successfully deposited on the Pt/C, producing small and well-controlled nanoparticles in the range of 2.8-4.2 nm. Electrochemical experiments demonstrated that the Pt(0.50)(RuO(2)-CeO(2))(0.50)/C composite displays the higher catalytic activity toward the methanol oxidation reaction (lowest onset potential of 207 mV and current densities taken at 450 mV, which are 140 times higher than those at commercial Pt/C), followed by the Pt(0.75)(RuO(2)-MoO(3))(0.25)/C composite. In addition, both of these composites produced low quantities of formic acid and formaldehyde when compared to a commercially available Pt(0.75)-Ru(0.25)/C composite (from E-Tek, Inc.), suggesting that the oxidation of methanol occurs mainly by a pathway that produces CO(2) forming the intermediary CO(ads).

Highly stable external short-circuit-assisted oxygen ionic transport membrane reactor for carbon dioxide reduction coupled with methane partial oxidation

A membrane reactor allows for simultaneous separation and reaction, and thus, can play a good role to produce value-added chemicals. In this work, we demonstrated such a membrane reactor based on fluorite oxide samarium-doped ceria (SDC) using an external short-circuit concept for oxygen permeation. The fluorite phase was employed to impart its high structural stability, while its limited electronic conductivity was overcome by the application of an external short circuit to function the SDC membrane for oxygen transport. On one side of the membrane, i.e., feed side, carbon dioxide decomposition into carbon monoxide and oxygen was carried out with the aid of a Pt or Ag catalyst. The resultant oxygen was concurrently depleted on the membrane surface and transported to the other side of the membrane, favorably shifting this equilibrium-limited reaction to the product side. The transported oxygen on the permeate side with the aid of a GdNi/Al2O3 catalyst was then consumed by the reaction with methane to form syngas, i.e., carbon monoxide and hydrogen. As such, the required driving force for gas transport through the membrane can be sustained by coupling two different reactions in one membrane reactor, whose stability to withstand these different gases at high temperatures is attained in this paper. We also examined the effect of the membrane thickness, oxygen ionic transport rate, and CO2 and CH4 flow rates to the membrane reactor performance. More importantly, here, we proved the feasibility of a highly stable membrane reactor based on an external short circuit as evidenced by achieving the constant performance in CO selectivity, CH4 conversion, CO2 conversion, and O2 flux during 100 h of operation and unaltered membrane structure after this operation together with the coking resistance.