Intrinsic CO Research Articles

Infrared studies of carbon monoxide binding to carbon monoxide dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica.

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzyme that catalyzes the reversible reduction of carbon dioxide into carbon monoxide and the coupled synthesis of acetyl-CoA from the carbon monoxide produced. Exposure of CODH/ACS from Moorella thermoacetica to carbon monoxide gives rise to several infrared bands in the 2100-1900 cm(-1) spectral region that are attributed to the formation of metal-coordinated carbon monoxide species. Infrared bands attributable to M-CO are not detected in the as-isolated enzyme, suggesting that the enzyme does not contain intrinsic metal-coordinated CO ligands. A band detected at 1996 cm(-1) in the CO-flushed enzyme is assigned as arising from CO binding to a metal center in cluster A of the ACS subunit. The frequency of this band is most consistent with it arising from a terminally coordinated Ni(I) carbonyl. Multiple infrared bands at 2078, 2044, 1970, 1959, and 1901 cm(-1) are attributed to CO binding at cluster C of the CODH subunit. All infrared bands attributed to metal carbonyls decay in a time-dependent fashion as CO(2) appears in the solution. These observations are consistent with the enzyme-catalyzed oxidation of carbon monoxide until it is completely depleted from solution during the course of the experiments.

Enhanced CO-Tolerance of Carbon-Supported Platinum and Molybdenum Oxide Anode Catalyst

The activity of carbon-supported toward oxidation of 100 ppm CO in was investigated using a rotating disk electrode in 0.5 M solution and by anodic polarization behavior in a single cell configuration. CO-stripping voltammetry of the catalyst showed a higher stripping peak potential compared to PtRu/C; however, the onset potential of the potentiodynamic oxidation of the mixture was somewhat smaller than that of PtRu/C. Anodic polarization of a anode in a mixture decreased with decreasing fuel flow rate and with decreasing thickness of the Nafion membrane, which indicated that part of the improved CO tolerance of the anode was due to that permeated from the cathode. This is supported by the anodic polarization of increasing and becoming independent of the fuel flow rate when the cathode gas was changed from to Analyses of CO concentration in the exhaust gas from the anode side showed that part of the CO in the fuel gas stream was oxidized by electrochemical and nonelectrochemical processes. The CO tolerance of the anode was attributed to the intrinsic CO tolerance of the catalyst and nonelectrochemical CO oxidation by the permeated © 2003 The Electrochemical Society. All rights reserved.

Effect of condensable impurity in CO 2/CH 4 gas feeds on performance of mixed matrix membranes using carbon molecular sieves

The permeation properties of a mixed matrix membrane film were investigated with 10% CO 2/90% CH 4 gas feeds containing a vapor impurity of toluene (70 ppm). The mixed matrix film was comprised of fine particles of high-selective carbon molecular sieves (CMS) dispersed within a glassy polyimide matrix (Matrimid ® 5218). In preceding publications, it was demonstrated that the carbon molecular sieve (CMS) particles produced a mixed matrix membrane having significantly enhanced effective permselectivities (CO 2/CH 4 and O 2/N 2) over the intrinsic properties of the neat polymer matrix phase alone. In this paper, a Matrimid ®-CMS mixed matrix flat film (19 vol.% CMS) was exposed to a 10% CO 2/90% CH 4/70 ppm toluene gas feed at 500 psia (34.5 bara) and 35 °C for a period of up to 60 h. The identical experiment was performed on a pure Matrimid ® polymer film for comparison. The results of this short-term study indicate that both the Matrimid ® mixed matrix film and the pure Matrimid ® film exhibit fairly stable properties in the presence of the low-concentration toluene impurity. The Matrimid ®-CMS mixed matrix film (19 vol.% CMS) sustains its CO 2/CH 4 selectivity enhancement (∼13%) over the intrinsic CO 2/CH 4 selectivity of the pure Matrimid ® polymer film. As speculated in a previous publication on CMS fibers, larger-sized impurities, such as toluene, may only be successful in blocking or occupying the larger, non-selective pores of the CMS particles and may not access the smaller, selective pores that are accessible to CO 2. In the presence of the binary mixture of 10% CO 2/90% CH 4, permeabilities approach a stable steady state within a few hours for both the pure Matrimid ® polymer film and the mixed matrix sample. For the pure Matrimid ® polymer film, the CO 2 permeability in the presence of the ternary mixture is slightly lower, but barely distinguishable beyond experimental uncertainty. On the other hand, the mixed matrix sample shows a more protracted approach to steady state in the presence of the toluene impurity, which ultimately stabilizes after roughly 60 h. We hypothesize that surface adsorption of the toluene molecules onto the CMS particles may induce a slow relaxation leading to better packing at the interface between the carbon and matrix reflected by the protracted changes seen.

Molecular Gas and Dust atz = 2.6 in SMM J14011+0252: A Strongly Lensed Ultraluminous Galaxy, Not a Huge Massive Disk

We used the IRAM interferometer to detect CO (3-2), CO (7-6), and 1.3 mm dust continuum emission from the submillimeter galaxy SMM J14011+0252 at z = 2.6. Contrary to a recent claim that the CO was extended over 66 (57 kpc), the new data yield a size of 2''× ≤ 05 for the CO and the dust. Although previous results placed the CO peak in a region with no visible counterpart, the new maps show that the CO and dust are centered on the J1 complex seen on K-band and optical images. We suggest that the CO is gravitationally lensed not only by the foreground cluster A1835 but also by an individual galaxy on the line of sight. Comparison of measured and intrinsic CO brightness temperatures indicates that the CO size is magnified by a factor of 25 ± 5. After correcting for lensing, we derive a true CO diameter of ~008 (700 pc), consistent with a compact circumnuclear disk of warm molecular gas similar to that in Arp 220. The high magnification means that the true size, far-IR luminosity, star formation rate, CO luminosity, and molecular gas mass are all comparable with those in present-epoch ultraluminous IR galaxies, not with a huge, massive, early-universe Galactic disk.

Mixed matrix membranes using carbon molecular sieves: I. Preparation and experimental results

Carbon molecular sieves (CMSs) have been incorporated into two different polymer matrices to form mixed matrix membrane films for gas separations. The CMSs were formed by pyrolysis of a polyimide (Matrimid ®) precursor to a final temperature of 800 °C. The CMS membrane films have an intrinsic CO 2/CH 4 selectivity of 200 with a CO 2 permeability of 44 Barrers and an O 2/N 2 selectivity of 13.3 with an O 2 permeability of 24 Barrers at 35 °C. The pyrolyzed CMS materials were ball-milled into fine particles, ranging in size from submicron to 2 μm, prior to dispersal in casting solvent. Mixed matrix films comprising high CMS particle loadings (up to 35 wt.%) dispersed within two polymer matrices (Matrimid ® 5218 and Ultem ® 1000) were successfully formed from flat-sheet solution casting. For Ultem ®–CMS mixed matrix membrane films, pure gas permeation tests show enhancements by as much as 40% in CO 2/CH 4 selectivity over the intrinsic CO 2/CH 4 selectivity of the pure Ultem ® polymer matrix. Likewise, for Matrimid ®–CMS mixed matrix films, enhancements by as much as 45% in CO 2/CH 4 selectivity were observed. Similar enhancements were observed when these mixed matrix membrane films were examined for the O 2/N 2 separation (8 and 20% for the Ultem ®–CMS and Matrimid ®–CMS mixed matrix films, respectively). Effective permeabilities of the fast-gas penetrants (O 2 and CO 2) through the mixed matrix membranes were also significantly enhanced over the intrinsic permeabilities of the Ultem ® and Matrimid ® polymer matrices. These encouraging selectivity and permeability enhancements confirm that mixed matrix membrane behavior is achievable with CMS particles.

CO Hydrogenation on Ru-Promoted Co/MCM-41 Catalysts

A study of CO hydrogenation on MCM-41 and SiO 2-supported Ru-promoted Co catalysts has been performed using both global rate measurements and steady-state isotopic transient kinetic analysis (SSITKA). A significant increase in CO hydrogenation was observed when MCM-41 was used as the support in the order M1>M2>SiO 2 at methanation conditions, where M1 and M2 are small pore ( d p=3 nm) and larger pore ( d p=7 nm) MCM-41, respectively. TOF H based on H 2 chemisorption can be misleading since any suppression of hydrogen chemisorption, as probably occurred for CoRu/M1, results in larger values of TOF H being calculated. SSITKA results, on the other hand, provide a measure of the “true” intrinsic CO hydrogenation activity of the Co sites. SSITKA studies indicated that the higher CO hydrogenation rates for MCM-41-supported catalysts are due to their greater number of active sites, not to a change in the intrinsic site activity. N 2 physisorption and XRD results reveal that the structure of MCM-41 became less ordered and the surface area decreased after standard reduction and 24 h of FTS, probably due to an effect of water vapor produced during metal reduction and reaction. However, the Co surface was still accessible since there was no significant loss of activity with TOS. The extent of deactivation during the initial reaction period was similar for MCM-41- and SiO 2-supported CoRu catalysts. By providing high activity and unrestricted diffusion of FT reactants and products, CoRu/MCM-41 may be potentially useful for FTS as well as for other catalytic applications, although modified forms of MCM-41 will probably be required in order to increase its hydrothermal stability.

Disulfiram was effective in patients with cocaine abuse who were also methadone treated opioid addicts

Phox2b protein is a specific marker for neurons in the parafacial region of the ventral medulla, which are proposed to play a role in central chemoreception and postnatal survival. Mutations...

A parametric study of fuel cell system efficiency under full and part load operation

Fuel cell technology is an emerging, environmentally friendly energy conversion technology for use in mobile and stationary applications. A contribution to the understanding of fuel cell system efficiency and operation under full and part load is presented in this paper. An analytical, three-parameter model, independent of specific fuel cell system, is developed and important performance parameters defined and discussed. Three useful properties of fuel cells are documented: (i) their ability to produce electric energy with constant — or even increased — efficiency at reduced power (enhanced part power efficiency), (ii) their ability to respond instantaneously to changes in power delivery demands (instantaneous load-following properties), and (iii) their theoretical ability to deliver an exhaust gas consisting of almost pure CO 2 (intrinsic CO 2 separation).

CO 2-sensitive neurons in organotypic cultures of the fetal rat medulla

Medullary slices of the fetal rat at gestational day 16 were cultivated (organotypic culture) for up to 20 days and current clamp experiments were performed on outgrowing neurons. CO 2-sensitivity was tested by changing the P CO 2 in the bath solution (equilibrating CO 2 fraction from 0.02 to 0.09). Two groups of CO 2-sensitive neurons were found; one with and the other without intrinsic CO 2-chemosensitivity. Neurons with intrinsic CO 2-sensitivity maintained their spontaneous activity and chemosensitivity after blockade of synaptic transmission. These neurons exhibited action potentials that were preceeded by a spontaneous interspike depolarization and followed by an afterhyperpolarization (beating neurons). Increasing P CO 2 either decreased (inhibited neurons, n=55) or increased the spike frequency of these neurons (stimulated neurons, n=31). The reduced activity of CO 2-inhibited neurons was associated with membrane hyperpolarization and/or decreases in the slope of interspike depolarization. In contrast CO 2-stimulated neurons were depolarized and the slope of their interspike depolarization was augmented during acidosis. In addition, we demonstrated a strong voltage dependence of CO 2-induced effects on membrane potential and spike frequency. Neurons with non-beating activity did not show a spontaneous interspike depolarization and their spike generation and CO 2-sensitivity appeared to be entirely produced through synaptic inputs. The CO 2-mediated changes in electrical properties of these neurons closely resemble those of various CNS neurons, including respiratory neurons, in whole animal or neonatal brainstem-spinal cord preparations.

New Observations and a New Interpretation of CO(3–2) in IRAS F10214+4724

New observations with the IRAM interferometer of CO(3-2) from the highly luminous galaxy IRAS F10214+4724 show the source is 15 × ≤09; they display no evidence of any velocity gradient. This size, together with optical and IR data that show the galaxy is probably gravitationally lensed, lead to a new model for the CO distribution. In contrast to many lensed objects, we have a good estimate of the intrinsic CO and far-IR surface brightnesses, so we can derive the CO and far-IR/sub-mm magnifications. The CO is magnified 10 times and has a true radius of 400 pc, and the far-IR is magnified 13 times and has a radius of 250 pc. The true far-IR luminosity is 4-7 × 1012 L☉, and the molecular gas mass is 2 × 1010 M☉. This is nearly an order of magnitude less than previously estimated. Because the far-IR magnification is lower than the mid- and near-IR magnification, the intrinsic spectral energy distribution now peaks in the far-infrared. That is, nearly all the energy of this object is absorbed and reemitted in the far-infrared. In CO luminosity, molecular gas content, CO line width, and corrected far-IR luminosity, 10214+472 is a typical, warm, IR ultraluminous galaxy.

CO excitation and H2 masses of infrared-luminous galaxies

The CO(2-1) and CO(1-0) emission from four infrared-luminous galaxies, Arp 193, Arp 220, Mrk 231, and VII Zw 31, was mapped with the IRAM 30 m telescope. These maps show the molecular gas is concentrated in the central regions. The CO(2-1)/CO(1-0) brightness temperature ratio for these galaxies is low, 0.6-0.75, indicating the CO is subthermally excited in regions of moderate H2 density, roughly 400/cu cm. The intrinsic CO(1-0) brightness temperatures are inferred to be between 6 and 13 K, even if the gas kinetic temperatures are much higher. For these galaxies, the H2 mass-to-CO luminosity ratio is similar to that measured for giant molecular clouds in the Milky Way molecular ring. 20 refs.

The dissociation of carbon monoxide from the alpha and the beta subunits of human carbonmonoxy hemoglobin

We have measured the intrinsic CO dissociation rates from the subunits of the human hemoglobin tetramers (alpha CO beta NO)2 and (alpha NO beta CO)2 using microperoxidase and a stopped-flow spectrophotometer. The dissociation of NO is negligible. The rate constants for the and the subunits are similar (0.014 s-1 vs. 0.011 s-1, respectively, at pH 7, 20 C; and 0.016 s-1 for both in the presence of inositol hexaphosphate), indicating that they are equivalent in the first step of the CO dissociation. Therefore, the chain unequality observed in the third and fourth steps (Samaja, M., Rovida, E., Niggeler, M., Perrella, M., and Rossi-Bernardi, L. (1987). J. Biol. Chem.: 262, 4528-4533) are not due to the intrinsic properties of the subunits, but to the conformational state of the molecule.

Gasification reactivity of chars from low rank coal lithotypes

Intrinsic CO 2 gasification reactivities of fusain and vitrain chars from a subbituminous coal were measured. The vitrain char was significantly more reactive, especially at high burnout. The important differences between the gasification behaviour of the two lithotypes were due to differences in the amounts of naturally occurring ion-exchanged metals, predominantly Ca.

The ‘pocket’ porphyrins: Hemoprotein models with lowered CO affinities

A new series of hemoprotein models, the iron(II) ‘pocket’ porphyrins [1], have been synthesized (Fig.1). This series of congruent models has been designed so as to incorporate varying degrees of steric encumbrance at the gaseous ligand binding site. Throughout the series, the pockets are expected to accommodate the formation of unhindered, bent FeO 2 units, while providing, in differing degrees, steric hindrance sufficient to interfere with the binding of CO in a normal linear fashion. Dilute solutions of several iron(II) ‘pocket’ porphyrin complexes in toluene are five-coordinate in the presence of excess axial ligands (1-methylimidazole and 1,2-dimethylimidazole) and are sufficiently stable with respect to oxidation so as to allow determination of ▪ and ▪ at room temperature under equilibrium conditions. Whereas the oxygenaffinities of the ferrous ‘pocket’ systems are comparable to those of the ‘picket fence’ [2] compounds, the carbon monoxide affinities are significantly lowered and approach that of myoglobin (Table I). Kinetic data indicate that the lowered CO affinities in the ‘pocket’ complexes are primarily reflected in decreased association rates. By contrast, the ‘pocket’ models show both decreased O 2 dissociation and association rates as compared to the ‘picket fence’ analogues, FeTpivP(1,2-Me 2Im), I, and FePiv 35CIm, II. These results indicate that steric hindrance can selectively discriminate against CO binding in model compounds and support the hypothesis that the intrinsic CO affinities of hemes may be reduced by steric interaction with the binding pocket in hemoproteins [3]. A full account of this work is to be published elsewhere [1]. ▪ t001 O 2 and CO Binding to Iron Porphyrins and Hemoproteins a,b . k CO B ( M −1 s −1) P CO 1 2 (torr) k O 2 B ( M −1 s −1) P O 2 1 2 (torr) Mb c [0.1 M KPi] 3–5 × 10 5 0.014 –0.025 1–2 × 10 7 0.37–1 HbA, R state c [0.05–0.1 M KPi] 4.6 × 10 6 0.0014 3.3 × 10 7 0.22 d , 0.36 e 2.9 × 10 6 d HbA, T state c [0.1 M KPi] 2.2 × 10 5 0.30 1.2 × 10 7 e 40 d , 140 e FePiv 35Clm( II) f 3.6 × 10 7 2.2 × 10 −5 4.3 × 10 8 0.58 FeMedPoc(1-Melm) ( IVa) f 1.5 × 10 6 6.5 × 10 −4 1.7 × 10 7 0.36 g FePocPiv(1-MeIm) ( IIIa) f 5.8 × 10 5 1.5 × 10 −3 2.2 × 10 6 0.36 FeTpivP(1,2-Me 2Im) ( I) f 1.4 × 10 6 8.9 × 10 −3 1.1 × 10 8 38 FeTalPoc(1,2-Me 2Im) ( V) f 1.1 × 10 −3 7.4 × 10 8 4 FeMedPoc(1,2-Me 2Im) ( IVb) f 2.1 × 10 5 0.026 5.2 × 10 6 12.4 FePocPiv(1,2-Me 2Im) ( IIIb) f 9.8 × 10 4 0.067 1.9 × 10 6 12.6 a Errors ⩽ 15%, unless otherwise indicated. b For original literature citations see references 1a and 1c. c Aqueous, pH 7.0–7.4, 20°C. d Value for α chain. e Value of β chain. f Toluene, 25°C. g −+20% error.

Cooperative ligand binding to hemoglobin. Effects of temperature and pH on a hemoglobin with spectrophotometrically distinct chains (Tunnus thynnus).

Binding of CO to the hemoglobin of Tunnus thynnus has been studied by kinetic and static methods in the range pH 6.75-8.0 and at temperatures between 1.5-40 degrees C. The results may be described in terms of the two-state model of cooperativity (Monod. J., Wyman, J., and Changeux, J. P. (1965) J. Mol. Biol. 12, 88-118) extended to include chain differences. The rate constants for CO binding to alpha and beta chains in the R state, at 20 degrees C, were 8.4 and 1.9 microM-1 s-1 with associated apparent activation energies of 3.5 and 10.5 kcal mol-1. Dissociation from the R state was monophasic with a rate constant, at 20 degrees C, of 0.016 s-1 and Ea of 26.4 kcal mol-1. The difference spectrum for binding of CO to the alpha chain in the T state is displaced 2 nm to the red as compared to the spectra associated with CO binding to the beta chain in the T state and to both chains in the R state. The proportion of T state hemoglobin present at different fractional saturations can thus be measured and compared with the results predicted from the model. When the temperature is raised, the value of L decreases greatly with an enthalpy of +80 kcal mol-1. The effects of the change in L override the decrease in intrinsic CO affinity of T. thynnus hemoglobin in the R and T states and result in a reverse temperature dependence of CO equilibria compared to mammalian hemoglobins.