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PubMed1982

Microbial methane oxidation in the River Saar.

In the River Saar, the distribution of methane-oxidizing bacteria and their metabolic activity were determined in vertical and longitudinal profiles. At the sediment surface about two orders of magnitude more methane oxidizers were detected than in the overlying water. In the river as well as in laboratory experiments, the rate of methane oxidation was closely related to the concentration of methane. Most of the methane produced by methanogenic bacteria in the the sediment escaped into the atmosphere. On the average only 1.2% of the produced methane was oxidized in the water phase.

Fresh Water↗

PubMed1982

Breath methane excretion in patients with unresected colorectal cancer.

The objective of our study was to verify or refute the observation that patients with unresected colorectal cancer are more likely to be breath methane excretors than the general population. Intracolonic heme had no effect on breath methane excretion of 11 normal volunteers given oral hemoglobin. Laxative-enema colonoscopy preparation had a profound effect on the subsequent measurement of breath methane. Three of 4 volunteer methane excretors became nonexcretors, and 2 remained nonexcretors for 21 days and 7 months, respectively. No significant difference was found in the frequency and the amount of breath methane excretion in 55 patients with unresected colorectal cancer and in 99 control subjects. However, 13 patients with unresected descending or sigmoid colon cancers were almost twice as likely to be breath methane excretors as 38 patients with colorectal cancer at other sites.

Adult↗

PubMedDate not supplied

Microbiological oxidation of methane in freshwater lakes of the Mari ASSR.

The quantity of methane-oxidizing microorganisms and intensity of microbiological methane oxidation in lakes of the Mari ASSR were studied. Maximum numbers of bacteria and highest intensity of methane oxidation were observed during summer stagnation in the thermocline, at the interface of aerobic and anaerobic zones. The intensity of oxidation was 4.6--28.1 x 10(-10) cm3 of methane per day per viable cell. During winter stagnation, the intensity of methane oxidation per cell was an order of magnitude lower. Over 69% of oxidized methane carbon was detected in extracellular metabolites, primarily CO2.

Bacteria↗

PubMed2002

Electronic state of small and large cavities for methane hydrate.

It is well known that methane hydrate is aggregates of small and large hydrogen bonded water cavities (composed of 12 pentagonal faces of 20 water molecules, and 12 pentagonal and two hexagonal faces of 24 water molecules, respectively) where one methane molecule is encaged. We calculated the methane molecule in vacuum, the small and large cavities by ab initio MO method to clarify the electronic state. The proton of methane in the cavities is shown to form the weak hydrogen bond (O...H[bond]C) between methane and four water molecules, and the H-bond lengths and energies in the small and large cavities were estimated as (0.293 nm, 6.8 kJ/mol) and (0.309 nm, 5.2 kJ/mol), respectively. The calculated values of symmetric C[bond]H stretching frequencies and (13)C-NMR chemical shieldings of the methane in the two cluster cavities show good agreement with the experimental ones observed by Sum et al. and Ripmeester and coworker, respectively.

Journal Article↗

PubMed2002

Grand canonical Monte Carlo simulation for determination of optimum parameters for adsorption of supercritical methane in pillared layered pores.

A grand canonical Monte Carlo (GCMC) method is carried out to determine optimum adsorptive storage pressures of supercritical methane in pillared layered pores. In the simulation, the pillared layered pore is modeled by a uniform distribution of pillars between two solid walls. Methane is described as a spherical Lennard-Jones molecule, and Steele's 10-4-3 potential is used for representing the interaction between the fluid and a layered wall. The site-site interaction is also used for calculating the interaction energy between methane molecules and pillars. An effective potential model that reflects the characteristics of a real pillared layered material is proposed here. In the model, a binary interaction parameter, k(fw), is introduced into the combining rule for the cross-energy parameter for the interaction between the fluid and a layered wall. Based on the experimental results for the Zr-pillared material synthesized and characterized by Boksh, Kikkinides, and Yang, the binary interaction parameter, k(fw), is determined by fitting the simulation results to the experimental adsorption data of nitrogen at 77 K. Then, by taking it as a model of pillared layered material, a series of GCMC simulations have been carried out. The excess adsorption isotherms of methane in a pillared layered pore with three different pore widths and porosities are obtained at three supercritical temperatures T=207.3, 237.0, and 266.6 K. Based on the simulation results at different porosities, various pore widths and different supercritical temperatures, the pillared layered pore with porosity psi=0.94 and pore width hsigma(p)=1.02 nm is recommended as adsorption storage material of supercritical methane. Moreover, the optimum adsorption pressure is determined at a given temperature and a fixed width of the pillared layered pore. For example, at temperature T=207.3 K, the optimum adsorption pressures are 3.1, 3.7, and 4.5 M Pa at H=1.02, 1.70, and 2.38 nm, respectively. In summary, the GCMC method is a useful tool for optimizing adsorption storage of supercritical methane in pillared layered material.

Journal Article↗

PubMed2004

Methane production from steam-exploded bamboo.

To convert unutilized plant biomass into a useful energy source, methane production from bamboo was investigated using a steam explosion pretreatment. Methane could not be produced from raw bamboo but methane production was enhanced by steam explosion. The maximum amount of methane produced, i.e., about 215 ml, was obtained from 1 g of exploded bamboo at a steam pressure of 3.53 MPa and a steaming time of 5 min. A negative correlation between the amount of methane produced and the amount of Klason lignin was observed in the methane fermentation of steam-exploded bamboo.

Journal Article↗

PubMed2002

TpPtMe(H)(2): why is there H/D scrambling of the methyl group but not methane loss?

The reactivity of TpPtMe(H)(2) (Tp = hydrido-tris(pyrazolyl)borate) was investigated. This complex is remarkably resistant to methane loss; heating it in methanol at 55 degrees C does not lead to either methane or hydrogen loss. When CD(3)OD is used, reversible H/D scrambling of the hydrides and the methyl hydrogens occurs. This reactivity was investigated by density functional theory (DFT) methods at the mPW1k/LANL2DZ+P//mPW1k/LANL2DZ level. It was found that methane loss cannot occur due to the rigidity of the Tp ligand, which does not allow the trans geometry which would be required for the product of methane elimination, TpPtH. The resulting complex is very high in energy, and therefore the loss of methane is unfavorable. On the other hand, H/D scrambling of the methyl ligand is relatively facile. It proceeds through an eta(2-CH)-CH(4) complex, even though methane loss is not observed. The model system, [(NH(3))(3)PtMe(H)(2)](+) was examined to verify that the cause of the observations is the rigidity of the Tp system. The reaction was investigated at a number of levels of DFT. It was concluded that investigations of similar sized systems should be examined at the above level of theory or the mPW1k/SDB-cc-pVDZ//mPW1k/SDD level for improved accuracy of the energetic calculations.

Journal Article↗

PubMed2006

Kinetics and mechanism of methane, methanol, and dimethyl ether C-H activation with electrophilic platinum complexes.

The relative rates of C-H activation of methane, methanol, and dimethyl ether by [(N-N)PtMe(TFE-d(3))](+) ((N-N) = ArN=C(Me)-C(Me)=NAr; Ar = 3,5-di-tert-butylphenyl, TFE-d(3) = CF(3)CD(2)OD) (2(TFE)) were determined. Methane activation kinetics were conducted by reacting 2(TFE)-(13)C with 300-1000 psi of methane in single-crystal sapphire NMR tubes; clean second-order behavior was obtained (k = 1.6 +/- 0.4 x 10(-3) M(-1) s(-1) at 330 K; k = 2.7 +/- 0.2 x 10(-4) M(-1) s(-1) at 313 K). Addition of methanol to solutions of 2(TFE) rapidly establishes equilibrium between methanol (2(MeOD)) and trifluoroethanol (2(TFE)) adducts, with methanol binding preferentially (K(eq) = 0.0042 +/- 0.0006). C-H activation gives [(N-N)Pt(CH(2)OD)(MeOD)](+) (4), which is unstable and reacts with [(RO)B(C(6)F(5))(3)](-) to generate a pentafluorophenyl platinum complex. Analysis of kinetics data for reaction of 2 with methanol yields k = 2.0 +/- 0.2 x 10(-3) M(-1) s(-1) at 330 K, with a small kinetic isotope effect (k(H)/k(D) = 1.4 +/- 0.1). Reaction of dimethyl ether with 2(TFE) proceeds similarly (K(eq) = 0.023 +/- 0.002, 313 K; k = 5.5 +/- 0.5 x 10(-4) M(-1) s(-1), k(H)/k(D) = 1.5 +/- 0.1); the product obtained is a novel bis(alkylidene)-bridged platinum dimer, [(diimine)Pt(mu-CH(2))(mu-(CH(OCH(3)))Pt(diimine)](2+) (5). Displacement of TFE by a C-H bond appears to be the rate-determining step for all three substrates; comparison of the second-order rate constants (k((methane))/k((methanol)) = 1/1.3, 330 K; k((methane))/k((dimethy)(l e)(ther)) = 1/2.0, 313 K) shows that this step is relatively unselective for the C-H bonds of methane, methanol, or dimethyl ether. This low selectivity agrees with previous estimates for oxidations with aqueous tetrachloroplatinate(II)/hexachloroplatinate(IV), suggesting a similar rate-determining step for those reactions.

Journal Article↗

PubMed2005

Activation energy of methyl radical decay in methane hydrate.

The thermal stability of gamma-ray-induced methyl radicals in methane hydrate was studied using the ESR method at atmospheric pressure and 210-260 K. The methyl radical decay proceeded with the second-order reaction, and ethane molecules were generated from the dimerization process. The methyl radical decay proceeds by two different temperature-dependent processes, that is, the respective activation energies of these processes are 20.0 +/- 1.6 kJ/mol for the lower temperature region of 210-230 K and 54.8 +/- 5.7 kJ/mol for the higher temperature region of 235-260 K. The former agrees well with the enthalpy change of methane hydrate dissociation into ice and gaseous methane, while the latter agrees well with the enthalpy change into liquid water and gaseous methane. The present findings reveal that methane hydrates dissociate into liquid (supercooled) water and gaseous methane in the temperature range of 235-260 K.

Journal Article↗

PubMed2006

Vibrational spectra of methane clathrate hydrates from molecular dynamics simulation.

Molecular dynamics simulations were performed on methane clathrate hydrates at ambient conditions. Thermal expansion results over the temperature range 60-300 K show that the unit cell volume increases with temperature in agreement with experiment. Power spectra were obtained at 273 K from velocity autocorrelation functions for selected atoms, and normal modes were assigned. The spectra were further classified according to individual atom types, allowing the assignment of contributions from methane molecules located in small and large cages within the structure I unit cell. The symmetric C-H stretch of methane in the small cages occurs at a higher frequency than for methane located in the large cages, with a peak separation of 14 cm(-1). Additionally, we determined that the symmetric C-H stretch in methane gas occurs at the same frequency as methane in the large cages. Results of molecular dynamics simulations indicate the use of power spectra obtained from the velocity autocorrelation function is a reliable method to investigate the vibrational behavior of guest molecules in clathrate hydrates.

Letter↗

PubMed2002

Decreased stability of methane hydrates in marine sediments owing to phase-boundary roughness.

Below water depths of about 300 metres, pressure and temperature conditions cause methane to form ice-like crystals of methane hydrate. Marine deposits of methane hydrate are estimated to be large, amassing about 10,000 gigatonnes of carbon, and are thought to be important to global change and seafloor stability, as well as representing a potentially exploitable energy resource. The extent of these deposits can usually be inferred from seismic imaging, in which the base of the methane hydrate stability zone is frequently identifiable as a smooth reflector that runs parallel to the sea floor. Here, using high-resolution seismic sections of seafloor sediments in the Cascadia margin off the coast of Vancouver Island, Canada, we observe lateral variations in the base of the hydrate stability zone, including gas-rich vertical intrusions into the hydrate stability zone. We suggest that these vertical intrusions are associated with upward flow of warmer fluids. Therefore, where seafloor fluid expulsion and methane hydrate deposits coincide, the base of the hydrate stability zone might exhibit significant roughness and increased surface area. Increased area implies that significantly more methane hydrate lies close to being unstable and hence closer to dissociation in the event of a lowering of pressure due to sea-level fall.

Journal Article↗

PubMed2004

Microwave and ab initio studies of rare gas-methane van der Waals complexes.

Rotational spectra of the weakly bound Kr-methane van der Waals complex were recorded using a pulsed molecular beam Fourier transform microwave spectrometer in the range from 3.5 to 18 GHz. Spectra of 25 isotopomers of Kr-methane were assigned and analyzed. For isotopomers containing CH4, 13CH4, and CD4, two sets of transitions with K = 0 and one with K = 1 were recorded, correlating to the j = 0, 1, and 2 rotational levels of free methane, respectively (j is the rotational angular momentum quantum number of the methane monomer). For isotopomers containing CH3D and CHD3, two K = 0 components were recorded, correlating to the j(k) = 0(0) and 1(1) rotational levels of free methane (k corresponds to the projection of j onto the C3 axis of CH3D and CHD3). The obtained spectroscopic results were used to derive van der Waals bond distance R, van der Waals stretching frequency nu(s), and the corresponding stretching force constant k(s). Nuclear spin statistical weights of individual states were obtained from molecular symmetry group analyses and were compared with the observed relative transition intensities. The tentatively assigned j = 2 transitions were more intense than predicted from symmetry considerations. This is attributed to a relatively large effective dipole moment of this state, supported by ab initio dipole moment calculations. Ab initio potential energy calculations of Kr-CH4 and Ar-CH4 were done at the coupled cluster level of theory, with single and double excitations and perturbative inclusion of triple excitations, using the aug-cc-pVTZ basis set supplemented with bond functions. The theoretical results show that the angular dynamics of the dimer does not change significantly when the binding partner of methane changes from Ar to Kr. The dipole moment of Ar-CH4 was calculated at various configurations, providing a qualitative explanation for the unsuccessful spectral searches for rotational transitions of Ar-CH4.

Journal Article↗

PubMed2005

Molecular-dynamics simulations of methane hydrate dissociation.

Nonequilibrium molecular-dynamics simulations have been carried out at 276.65 K and 68 bar for the dissolution of spherical methane hydrate crystallites surrounded by a liquid phase. The liquid was composed of pure water or a water-methane mixture ranging in methane composition from 50% to 100% of the corresponding theoretical maximum for the hydrate and ranged in size from about 1600 to 2200 water molecules. Four different crystallites ranging in size from 115 to 230 water molecules were used in the two-phase systems; the nanocrystals were either empty or had a methane occupation from 80% to 100% of the theoretical maximum. The crystal-liquid systems were prepared in two distinct ways, involving constrained melting of a bulk hydrate system or implantation of the crystallite into a separate liquid phase. The breakup rates were very similar for the four different crystal sizes investigated. The method of system preparation was not found to affect the eventual dissociation rates, despite a lag time of approximately 70 ps associated with relaxation of the liquid interfacial layer in the constrained melting approach. The dissolution rates were not affected substantially by methane occupation of the hydrate phase in the 80%-100% range. In contrast, empty hydrate clusters were found to break up significantly more quickly. Our simulations indicate that the diffusion of methane molecules to the surrounding liquid layer from the crystal surface appears to be the rate-controlling step in hydrate breakup. Increasing the size of the liquid phase was found to reduce the initial delay in breakup. We have compared breakup rates computed using different long-range electrostatic methods. Use of the Ewald, minimum image, and spherical cut-off techniques led to more rapid dissociation relative to the Lekner method.

Journal Article↗

PubMed1989

Solubilisation of methane monooxygenase from Methylococcus capsulatus (Bath).

The membrane-bound (particulate) form of methane monooxygenase from Methylococcus capsulatus (Bath) has been solubilised using the non-ionic detergent dodecyl-beta-D-maltoside. A wide variety of detergents were tested and found to solubilise membrane proteins but did not yield methane monooxygenase in a form that could be subsequently activated. After solubilisation with dodecyl-beta-D-maltoside, enzyme activity was recovered using either egg or soya-bean lipids. Attempts to further purify the solubilized methane monooxygenaser protein into its component polypeptides were unsuccessful and resulted in complete loss of enzyme activity. The major polypeptides present in the solubilised enzyme had molecular masses of 49 kDa, 23 kDa and 22 kDa which were similar to those seen in crude extracts [Prior, S. D. & Dalton H. (1985) J. Gen. Microbiol. 131, 155-163]. Studies on substrate and inhibitor specificities indicated that the membrane-associated and solubilised forms of methane monooxygenase were quite similar to each other but differed substantially from the well-characterised soluble methane monooxygenase found in cells grown in a low copper regime and synthesised independently of the particulate methane monooxygenase.

Detergents↗

PubMed1980

Microbial Oxidation of Gaseous Hydrocarbons: Production of Secondary Alcohols from Corresponding n-Alkanes by Methane-Utilizing Bacteria.

Over 20 new strains of methane-utilizing bacteria were isolated from lake water and soil samples. Cell suspensions of these and of other known strains of methane-utilizing bacteria oxidized n-alkanes (propane, butane, pentane, hexane) to their corresponding secondary alcohols (2-propanol, 2-butanol, 2-pentanol, 2-hexanol). The product secondary alcohols accumulated extracellularly. The rate of production of secondary alcohols varied with the organism used for oxidation. The average rate of 2-propanol, 2-butanol, 2-pentanol, and 2-hexanol production was 1.5, 1.0, 0.15, and 0.08 mumol/h per 5.0 mg of protein in cell suspensions, respectively. Secondary alcohols were slowly oxidized further to the corresponding methylketones. Primary alcohols and aldehydes were also detected in low amounts (rate of production were 0.05 to 0.08 mumol/h per 5.0 mg of protein in cell suspensions) as products of n-alkane (propane and butane) oxidation. However, primary alcohols and aldehydes were rapidly metabolized further by cell suspensions. Methanol-grown cells of methane-utilizing bacteria did not oxidize n-alkanes to their corresponding secondary alcohols, indicating that the enzymatic system required for oxidation of n-alkanes was induced only during growth on methane. The optimal conditions for in vivo secondary alcohol formation from n-alkanes were investigated in Methylosinus sp. (CRL-15). The rate of 2-propanol and 2-butanol production was linear for the 40-min incubation period and increased directly with cell protein concentration up to 12 mg/ml. The optimal temperature and pH for the production of 2-propanol and 2-butanol were 40 degrees C and pH 7.0. Metalchelating agents inhibited the production of secondary alcohols. The activities for the hydroxylation of n-alkanes in various methylotrophic bacteria were localized in the cell-free particulate fractions precipitated by centrifugation between 10,000 and 40,000 x g. Both oxygen and reduced nicotinamide adenine dinucleotide were required for hydroxylation activity. The metal-chelating agents inhibited hydroxylation of n-alkanes by the particulate fraction, indicating the involvement of a metal-containing enzyme system in the oxidation of n-alkanes. The production of 2-propanol from the corresponding n-alkane by the particulate fraction was inhibited in the presence of methane, suggesting that the subterminal hydroxylation of n-alkanes may be catalyzed by methane monooxygenase.

Journal Article↗

PubMed1982

Methane production by fermentor cultures acclimated to waste from cattle fed monensin, lasalocid, salinomycin, or avoparcin.

The ability of microorganisms to ferment waste from cattle fed monensin, lasalocid, or salinomycin to methane was determined. Continuously mixed anaerobic fermentors with 3-liter working volumes at 55 degrees C were used; fermentors were fed once per day. Initially, all fermentors were fed waste without antibiotics at 6% volatile solids (VSs, organic matter) and a 20-day retention time (RT) for 60 days. Waste from animals fed monensin, lasalocid, or salinomycin at 29, 20, and 16.5 mg per kg of feed, respectively, was added to duplicate fermentors at the above VSs, and RT. Avoparcin (5 to 45 mg/liter) was not fed to animals but was added directly to duplicate fermentors. Lasalocid and salinomycin had minimal effects on the rate of methane production at RTs of 20 days and later at 6.5 days. Avoparcin caused an increase in organic acids from 599 to 1,672 mg/liter (as acetate) after 4 weeks, but by 6 weeks, acid concentrations declined and the rate of methane production was similar to controls at a 6.5-day RT. The monensin fermentors stopped producing methane 3 weeks after antibiotic addition. However, after a 6-month acclimation period, the microorganisms apparently adapted, and methane production rates of 1.65 and 2.51 liters per liter of fermentor volume per day were obtained with 6% VSs, and RTs of 10 and 6.5 days, respectively. This compares with 1.78 and 2.62 liters/liter per day for controls (P > 0.05). All fermentors that were fed waste containing antibiotics had lower pH values and ammonia and alkalinity concentrations, suggesting less buffering capacity and protein catabolism than in controls. Acclimation results obtained with fermentors at 35 degrees C were similar to those for fermentors at 55 degrees C. These studies indicate that waste from cattle fed these selected growth-promoting antibiotics can be thermophilically fermented to methane at RTs of 6.5 days or longer and VS concentrations of 6%, at rates comparable to waste without antibiotics.

Journal Article↗

PubMed1984

Methane production in Minnesota peatlands.

Rates of methane production in Minnesota peats were studied. Surface (10- to 25-cm) peats produced an average of 228 nmol of CH(4) per g (dry weight) per h at 25 degrees C and ambient pH. Methanogenesis rates generally decreased with depth in ombrotrophic peats, but on occasion were observed to rise within deeper layers of certain fen peats. Methane production was temperature dependent, increasing with increasing temperature (4 to 30 degrees C), except in peats from deeper layers. Maximal methanogenesis from these deeper regions occurred at 12 degrees C. Methane production rates were also pH dependent. Two peats with pHs of 3.8 and 4.3 had an optimum rate of methane production at pH 6.0. The addition to peat of glucose and H(2)-CO(2) stimulated methanogenesis, whereas the addition of acetate inhibited methanogenesis. Cysteine-sulfide, nitrogen-phosphorus-trace metals, and vitamins-yeast extract affected methane production very little. Various gases were found to be trapped or dissolved (or both) within peatland waters. Dissolved methane increased linearly to a depth of 210 cm. The accumulation of metabolic end products produced within peat bogs appears to be an important mechanism limiting carbon turnover in peatland environments.

Journal Article↗

PubMed1987

Competitive mechanisms for inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments.

Mechanisms for inhibition of sulfate reduction and methane production in the zone of Fe(III) reduction in sediments were investigated. Addition of amorphic iron(III) oxyhydroxide to sediments in which sulfate reduction was the predominant terminal electron-accepting process inhibited sulfate reduction 86 to 100%. The decrease in electron flow to sulfate reduction was accompanied by a corresponding increase in electron flow to Fe(III) reduction. In a similar manner, Fe(III) additions also inhibited methane production in sulfate-depleted sediments. The inhibition of sulfate reduction and methane production was the result of substrate limitation, because the sediments retained the potential for sulfate reduction and methane production in the presence of excess hydrogen and acetate. Sediments in which Fe(III) reduction was the predominant terminal electron-accepting process had much lower concentrations of hydrogen and acetate than sediments in which sulfate reduction or methane production was the predominant terminal process. The low concentrations of hydrogen and acetate in the Fe(III)-reducing sediments were the result of metabolism by Fe(III)-reducing organisms of hydrogen and acetate at concentrations lower than sulfate reducers or methanogens could metabolize them. The results indicate that when Fe(III) is in a form that Fe(III)-reducing organisms can readily reduce, Fe(III)-reducing organisms can inhibit sulfate reduction and methane production by outcompeting sulfate reducers and methanogens for electron donors.

Journal Article↗