Methane aerobic oxidation

A metalimnion (the transitional layer between the epilimnion and the hypolim-nion) contains methanotrophic bacteria (bacteria that aerobically oxidize methane) at a cell concentration of 105 cells per milliliter. There is adequate oxygen available and the cells have a Vmax for CH4 of 10-19 mol/(cell sec) and a half saturation constant, Ks, of 10 4 mol/liter. At what rate, RCH<, is methane degraded if it is present at a concentration of 1.5 X 10-5 M ... 

Organisms which oxidize methane exclusively and use this substrate as a source of carbon and energy appear to be restricted to Methanomonas sp. The latter is a strict aerobe which presumably contains cytochromes (67). 

The aerobic oxidation of methane in water catalyzed by [Pt(Mebipym)Cl2] [PV2Mo1004o]5 (Mebipym = N-methy-2,2 -bipyrimidine) complex supported on Si02 was reported [149]. The conjugation of [PV2Mo1004o]5 to a known Pt2 + -bipyrimidine complex by electrostatic interaction could fadlitate the oxidation of the Pt2 + intermediate to a Pt4 + intermediate by 02, resulting in the catalytic aerobic oxidation of methane to methanol in water and then surprisingly further to acetaldehyde via a carbon-carbon coupling reaction. 

Direct oxidation of the lesser chlorinated ethenes, ethanes, polychlorinated benzenes, and chlorobenzene has been reported. Wiedemeier et al. [25] summarize a number of studies that report direct aerobic oxidation of vinyl chloride (VC), 1,2-dichloroethane, the three dichlorobenzene isomers, 1,2,4-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene. Bradley [33] reports that DCE has served as a primary substrate for energy production with oxygen as the electron acceptor, though use of DCE as a sole carbon source has not been demonstrated. Rittmann and McCarty [29] also report that the two least chlorinated methanes (dichloromethane and chloromethane) as well as chloroethane can be directly oxidized under aerobic conditions. Direct oxidation of the chlorinated compounds is typically modeled using either first-order or Monod kinetics [29,31]. 

Methane is subject to aerobic oxidation by methanotrophic bacteria when it diffuses across an anoxic-oxic interface before escaping to the atmosphere (King, 1992) ... 

The value for Kk, the saturation coefiicient or growth-limiting substrate concentration at which organism growth rate is one-half its maximum value, varies considerably with the reaction, the species mediating the reaction, and environmental conditions. In anaerobic methane fermentations, Kk tends to be much larger, at least with acetate and propionate, than for aerobic oxidations. Values of 10" moles/liter seem appropriate for the former and 10" for the latter. Kk also tends to increase with decrease in temperature. 

The aerobic oxidation of methane is carried out by bacteria called methanotrophs (1). These bacteria grow on methane as their sole carbon and energy source, oxidizing a portion of the methane to C02 and fixing a portion into cell material. They are obligate aerobes because the methane oxidation reaction requires molecular oxygen. 

In comparison to all other heterotrophs, the microorganisms oxidizing methane and other Cj compounds such as methanol, have a unique metabolic pathway which involves oxygenase enzymes and thus requires O. Only aerobic methane-oxidizing bacteria have been isolated and studied in laboratory culture, yet methane oxidation in marine sediments is known to take place mostly anaerobically at the transition to the sulfate zone. Microbial consortia that oxidize methane with sulfate have in particular been studied at methane seeps on the sea floor and the communities can now also be grown in the laboratory (Boetius et al. 2000 Orphan et al. 2001 Nauhaus et al. 2002) Anaerobic methane oxidation is catalyzed by archaea that use a key enzyme related to the coenzyme-M reductase of methanogens, to attack the methane molecule (Kruger et al. 2003 see Sect. 5.1). The best studied of these ANME (ANaerobic MEthane... 

Aerobic oxidation of alkanes requires dioxygen, hence it was originated only after plant photosynthesis thereby producing most part of the dioxygen on earth. Meanwhile methane is produced in anaerobic methanogenesis, therefore apparently this biological process existed before when life on earth was... 

Aerobic oxidation of methane catalyzed by [R(Mebipym)Cl2] [H4PV2Moio04o] /Si02... 

The supramolecular environment can not only protect an active species but also stabilize it through local constraints. Cu-ZSM-5, a Cu-loaded zeolite where Cu ions are incorporated into the walls, was proposed to generate a mono-(/z-oxo)-dicopper core upon activation at 723 K under an O2 flow, as evidenced by UV experiments. Aerobic oxidation of methane was carried out at 448 K and CH3OH was detected as the only product, trapped inside the host. The nature of the host (Al/Si and Cu/Al ratios)... 

Scheme 9.12 Consensus catalytic scheme for the oxidation of methane and the catalyst and reactions observed in the aerobic oxidation of methane in water.

A class of prokaryotes called methanotrophs (O Fig. 15.2) carry out the oxidative reactions leading from methane, the most reduced C-1 compound, to carbon dioxide, the most oxidized. Some C-1 oxidizing organisms (known as methylotrophs ) cannot oxidize methane to methanol but can carry out the next three oxidative reactions. Methane is a common natural product it is the main constituent of natural gas. Moreover, data suggests that a majority of the methane generated in lake sediments is oxidized in higher, aerobic levels of the lake by methanotrophs, and thus methane never enters the atmosphere. 

Zhou, Yin et al. disclosed an efficient CuCl-catalyzed synthesis of 2-hetarylquinazolin-4(3//)-ones through aerobic oxidative C(sp )-H amination of (2-azaaryl)methanes with 2-aminobenzamides using oxygen as the sole oxidant under mild conditions (Scheme 8.106). Three C(sp )-H and three N-H bonds are removed in one reaction to produce the highly valuable Af-heterocycles. This copper-catalyzed tandem oxidation-amination-cyclization transformation is easy to handle, and various prepared 2-hetaryl-substituted quinazolinones could be obtained in moderate to good yields [180]. 

The same authors developed an interesting system for aerobic oxidation of propene using the palladium(ii) catalysts with chelating bis(NHC) ligands and NaVOs as co-catalyst. The palladium(ii) catalyst was responsible for C-H functionalization, while the vanadium co-catalyst mediated the O2 activation. Both catalytic cycles were connected by a bromide-bromine redox pair, which mediated the C-H activation by oxygen. Unfortunately, a similar catalytic system for the oxidation of methane was extremely slow, probably due to decomposition of the catalyst. 

B) Methane aerobic oxidation and oxidative carbonyiation with Rh/Cu/02 oxidation system... 

The vast success found with Pd(0) and Cu(II) reoxidation led to Cu(II) being tested as an additive in other metal-catalyzed aerobic oxidations, including Rh(I)-catalyzed methane oxidation [27] and Mo(VI)-catalyzed alcohol oxidation [28] (Scheme 5.8). 

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