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1.
Conversion of CO2 to organic compounds in hydrothermal systems is important in understanding prebiotic chemical evolution leading to the origin of life. However, organic compounds with carbon number of more than 3 have never been produced from dissolved CO2 in simulated hydrothermal experiments. In this paper, we report that not only CH4, C2H6 and C3H8, but also n-C4H10 and n-C5H12 could be produced from dissolved CO2 and H2 in the presence of cobalt-bearing magnetite at 300°C and 30 MPa. It is shown that unbranched alkanes in Anderson–Schulz–Flory distribution were the dominant hydrocarbon products produced from dissolved CO2 catalyzed by cobalt-bearing magnetite under certain hydrothermal conditions. It is proposed that magnetite with other transition metals may act potentially as effective mineral catalysts for abiotic formation of organic compounds from dissolved CO2 in hydrothermal systems.  相似文献   

2.
The thermodynamic potential for the abiotic synthesis of the five common nucleobases (adenine, cytosine, guanine, thymine, and uracil) and two monosaccharides (ribose and deoxyribose) from formaldehyde and hydrogen cyanide has been quantified under temperature, pressure, and bulk composition conditions that are representative of hydrothermal systems. The activities of the precursor molecules (formaldehyde and hydrogen cyanide) required to evaluate the thermodynamics of biomolecule synthesis were computed using the concentrations of aqueous N2, CO, CO2 and H2 reported in the modern Rainbow hydrothermal system. The concentrations of precursor molecules that can be synthesized are strongly dependent on temperature with larger concentrations prevailing at lower temperatures. Similarly, the thermodynamic drive to synthesize nucleobases, ribose and deoxyribose varies considerably as a function of temperature: all of the biomolecules considered in this study are thermodynamically favored to be synthesized throughout the temperature range from 0°C to between 150°C and 250°C, depending on the biomolecule. Furthermore, activity diagrams have been generated to illustrate that activities in the range of 10−2– 10−6 for nucleobases, ribose and deoxyribose can be in equilibrium with a range of precursor molecule activities at 150°C and 500 bars. The results presented here support the notion that hydrothermal systems could have played a fundamental role in the origin of life, and can be used to plan and constrain experimental investigation of the abiotic synthesis of nucleic-acid related biomolecules.  相似文献   

3.
Rogers KL  Schulte MD 《Geobiology》2012,10(4):320-332
Sulfur is central to the metabolisms of many organisms that inhabit extreme environments. While biotic and abiotic cycling of organic sulfur compounds has been well documented in low‐temperature anaerobic environments, cycling of organic sulfur in hydrothermal environments has received less attention. Recently published thermodynamic data have been used to estimate aqueous alkyl thiol and sulfide activities in deep‐sea hydrothermal systems. Here we use geochemical mixing models to predict fluid compositions that result from mixing end‐member hydrothermal fluid from the East Pacific Rise with bottom seawater. These fluid compositions are combined with estimates of methanethiol and dimethylsulfide activities to evaluate energy yields for potential organic sulfur‐based metabolisms under hydrothermal conditions. Aerobic respiration has the highest energy yields (over ?240 kJ/mol e?) at lower temperature; however, oxygen is unlikely to persist at high temperatures, restricting aerobic respiration to mesophilic communities. Nitrite reduction to N2 has the highest energy yields at higher temperatures (greater than ~40 °C). Nitrate and nitrite reduction to ammonium also yield significant energy (up to ?70 kJ/mol e?). Much lower, but still feasible energy yields are calculated for sulfate reduction, disproportionation, and reduction with H2. Organic compound family and the activity of methanethiol and dimethylsulfide were less important than metabolic strategy in determining overall energy yields. All metabolic strategies considered were exergonic within some portion of the mixing regime suggesting that organic sulfur‐based metabolisms may be prevalent within deep‐sea hydrothermal vent microbial communities.  相似文献   

4.
Original extracts from an unpublished 1958 experiment conducted by the late Stanley L. Miller were recently found and analyzed using modern state-of-the-art analytical methods. The extracts were produced by the action of an electric discharge on a mixture of methane (CH4), hydrogen sulfide (H2S), ammonia (NH3), and carbon dioxide (CO2). Racemic methionine was formed in significant yields, together with other sulfur-bearing organic compounds. The formation of methionine and other compounds from a model prebiotic atmosphere that contained H2S suggests that this type of synthesis is robust under reducing conditions, which may have existed either in the global primitive atmosphere or in localized volcanic environments on the early Earth. The presence of a wide array of sulfur-containing organic compounds produced by the decomposition of methionine and cysteine indicates that in addition to abiotic synthetic processes, degradation of organic compounds on the primordial Earth could have been important in diversifying the inventory of molecules of biochemical significance not readily formed from other abiotic reactions, or derived from extraterrestrial delivery.  相似文献   

5.
The parageneses physico-chemical analysis based on a method of thermodynamic potentials has been used to study the system of C-H-O organic compounds, which are, in particular, components of biomimetically built primordial cycles of carbon dioxide chemoautotrophic fixation. Thermodynamic data for aqueous organic compounds allowed one to construct the chemical potential diagrams and establish the areas of thermodynamic stability (facies) of components of CO2 fixation pathways in hydrothermal systems, in particular, a reductive citric cycle (RCC), 3-hydroxypropionate cycle (3-HPC) and acetyl-CoA pathway. An alternative deep source of carbon (hydrocarbons) proved by the data on endogenous emission of hydrocarbons in hydrothermal fields of oceanic ridges was suggested. The system was determined, which combines hydrocarbons, CO2 and components of RCC, 3-HPC and acetyl-CoA pathway with characteristic parageneses of methane and ethylene with acetate in two-component CH4-CO2 and C2H4-O2 subsystems, respectively. The thermodynamic analysis of a redox mode at various pressures and temperatures allowed one to uniquely determine hydrocarbon-organic system able to independently generate acetate and succinate at oxidation of deep hydrothermal hydrocarbon fluids emerging on sea surface. The limits for thermodynamic stability of CO2 archaic fixation (CAF) components responsible for generation and self-organization in hydrothermal environment was identified. The tentative integrated system of CAF was developed as a combined acetyl-CoA pathway, 3-HPC and RCC containing a succinate-fumarate core, capable of switching electron flow in forward or reverse direction depending on redox potential of geochemical environment that is governed by the (CH)2(COOH)2+H2(CH2)2(COOH)2 reaction. This core is a “redox switch”, which is sensitive to certain conditions of hydrothermal environment and defines electron flow direction. The redox geochemical mode caused by temperature, pressure, composition of a hydrothermal fluid and a mineralogical setting defines stability of CAF cycle components in paragenesis with hydrocarbons and possibility of cycle self-organization.  相似文献   

6.
The hydrothermal vent mussel Bathymodiolus sp. is demonstrated to incorporate inorganic CO2 from sea water. After ≈24 h incubation with H14CO2 the major part of the radioactivity is incorporated into macromolecules mostly in proteins but also in a notable lipidic fraction. 77 to 98% of this radioactivity is found in the gill and autoradiographs show that CO2 fixation is only observed in cells containing high concentrations of bacteria. The results endorse the hypothesis that the associated bacteria might provide a nutritional source for the mussel.The mussel is also able to absorb and incorporate dissolved amino acids. Heterotrophic processes involving dissolved organic matter may interfere with the autotrophic pathways. Beside its capability of feeding on particulate material, the mussel may be thus able to live on reduced carbon and nitrogen compounds synthesized by its associated bacteria as well as on dissolved organic compounds present in sea water. The effective participation of the different processes is probably related to the ecological conditions experienced by the mussel in vent areas.  相似文献   

7.
The molecular basis for the chemical evolution of low molecular compounds was studied using electric discharges on a higly oxidized atmosphere comprised of CO2, N2 and H2O. In the gas phase, O2 and CO were formed by the decomposition of CO2 and their yields were enhanced by the addition of N2 to the gas mixture. It was demonstrated that H2O suppressed the reduction of CO2 while H2O also had a role in producing organic compounds such as formic acid and formaldehyde. Infrared analysis of the water soluble products and the inner surface of the reaction vessel indicated the production of compounds more complex than formic acid and formaldehyde. These compounds contained the chemical bonds which were identified to be OH, CO, CN and/or CC.  相似文献   

8.
Carbon dioxide can be incorporated into amino acids under conditions simulating the radiation environment of Mars. The mechanism apparently involves carboxyl exchange and may occur with other organic compounds as well. The reaction may play a role in maintaining CO2 equilibrium on the Martian surface.  相似文献   

9.
Most terrestrial ecosystems support a similar suite of biogeochemical processes largely dependent on the availability of water and labile carbon (C). Here, we explored the biogeochemical potential of soils from Earth’s driest ecosystem, the Atacama Desert, characterized by extremely low moisture and organic C. We sampled surface soil horizons from sites ranging from the Atacama’s hyper-arid core to less-arid locations at higher elevation that supported sparse vegetation. We performed laboratory incubations and measured fluxes of the greenhouse gases carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) as indices of potential biogeochemical activity across this gradient. We were able to stimulate trace gas production at all sites, and treatment responses often suggested the influence of microbial processes. Sites with extant vegetation had higher C concentrations (0.13–0.68%) and produced more CO2 under oxic than sub-oxic conditions, suggesting the presence of aerobic microbial decomposers. In contrast, abiotic CO2 production appeared to predominate in the most arid and C-poor (<0.08% C) sites without plants, with one notable exception. Soils were either a weak source or sink of CH4 under oxic conditions, whereas anoxia stimulated CH4 production across all sites. Several sites were rich in nitrate, and we stimulated N2O fluxes in all soils by headspace manipulation or dissolved organic matter addition. Peak N2O fluxes in the most C-poor soil (0.02% C) were very high, exceeding 3 ng nitrogen g?1 h?1 under anoxic conditions. These results provide evidence of resilience of at least some soil biogeochemical capacity to long-term water and C deprivation in the world’s driest ecosystem. Atacama soils appear capable of responding biogeochemically to moisture inputs, and could conceivably constitute a regionally-important source of N2O under altered rainfall regimes, analogous to other temperate deserts.  相似文献   

10.
The dependence of the CO2 concentration on the discharge conditions and the mixture composition in a CO laser is studied experimentally. The experimental data are compared with the calculated results. A scheme of the reactions that govern the concentration of CO2 molecules under the experimental conditions in question is constructed. It is shown that, in a gas-discharge plasma, an admixture of Xe in a mixture containing CO molecules gives rise to a new mechanism for the dissociation of CO2 molecules by metastable xenon atoms. Under conditions close to the operating conditions of sealed-off CO lasers, the dissociation of CO2 molecules in collisions with metastable. Xe(3P2) atoms becomes the dominant dissociation mechanism in a He: CO mixture because it proceeds at a fast rate. This explains the observed decrease in the CO2 concentration in a xenon-containing He: CO mixture.  相似文献   

11.
The reaction of iron sulfide (FeS) with H2S in water, in presence of CO2 under anaerobic conditions was found to yield H2 and a variety of organic sulfur compounds, mainly thiols and small amounts of CS2 and dimethyldisulfide. The same compounds were produced when H2S was replaced by HCl, in the H2S-generating system FeS/HCl/CO2. The identification of the products was confirmed by GC-MS analyses and the incorporation of H2 in the organic sulfur compounds was demonstrated by experiments in which all hydrogen compounds were replaced by deuterium compounds. Generation of H2 and the synthesis of thiols were both dependent upon the relative abundance of FeS and HCl or H2S, i.e. the FeS/HCl- or FeS/H2S-proportions. Whether thiols or CS2 were formed as the main products depended also on the FeS/HCl-ratio: All conditions which create a H2 deficiency were found to initiate a proportional increase in the amount of CS2. The quantities of H2 and thiols generated depended on temperature: the production of H2 was significantly accelerated from 50°C onward and thiol synthesis above 75°C. The yield of thiols increased with the amount of FeS and HCl (H2S), given a certain FeS/HCl-ratio and a surplus of CO2. A deficiency of CO2 results in lower thiol systhesis. The end product, pyrite (FeS2), was found to appear as a silvery granular layer floating on the aqueous surface. The identity of the thiols was confirmed by mass spectrometry, and the reduction of CO2 demonstrated by the determination of deuterium incorporation with DCl and D2O. The described reactions can principally proceed under the conditions comparable to those obtaining around submarine hydrothermal vents, or the global situation about 4 billion years ago, before the dawn of life, and could replace the need for a reducing atmosphere on the primitive earth.  相似文献   

12.
13.
Concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the water column and their exchange at the water/air interface were studied during the open water period in two freshwater ponds with different catchment characteristics in the northern boreal zone in Finland; either peatlands or coniferous upland forests dominated the catchment of the ponds. Both ponds were supersaturated with dissolved CO2 and CH4 with respect to the equilibrium with the atmosphere, but were close to the equilibrium with N2O. The mean CO2 efflux from the pond was higher in the peatland-dominated catchment (22 mg m–2 h–1) than in the forested catchment (0.7 mg m–2 h–1), whereas the mean CH4 emissions were similar (7.6 and 3.5 mg m–2 d–1, respectively). The fluxes of N2O were generally negligible. The higher CO2 concentrations and efflux in the pond with the peatland-dominated catchment were attributed to a greater input of allochthonous carbon to that pond from its catchment due to its higher water colour and higher total organic carbon (TOC) concentration. The water pH, which also differed between the ponds, could additionally affect the CO2 dynamics. Since the catchment characteristics can regulate aquatic carbon cycles, catchment-scale studies are needed to attain a deeper understanding of the aquatic greenhouse gas dynamics.  相似文献   

14.
15.
Ground water beneath the U.S. Department of Energy (USDOE) Pantex Plant is contaminated with the high explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine). The authors evaluated biodegradation as a remedial option by measuring RDX mineralization in Pantex aquifer microcosms spiked with 14C-labeled RDX (75 g soil, 15 ml of 5 mg RDX/L). Under anaerobic conditions and constant temperature (16°C), cumulative 14CO2 production ranged between 52% and 70% after 49 days, with nutrient-amended (C, N, P) microcosms yielding the greatest mineralization (70%). The authors also evaluated biodegradation as a secondary treatment for removing RDX degradates following oxidation by permanganate (KMnO4) or reduction by dithionite-reduced aquifer solids (i.e., redox barriers). Under this coupled abiotic/biotic scenario, we found that although unconsumed permanganate initially inhibited biodegradation, > 48% of the initial 14C-RDX was recovered as 14CO2 within 77 days. Following exposure to dithionite-reduced solids, RDX transformation products were also readily mineralized (> 47% in 98 days). When we seeded Pantex aquifer material into Ottawa Sand that had no prior exposure to RDX, mineralization increased 100%, indicating that the Pantex aquifer may have an adapted microbial community that could be exploited for remediation purposes. These results indicate that biodegradation effectively transformed and mineralized RDX in Pantex aquifer microcosms. Additionally, biodegradation may be an excellent secondary treatment for RDX degradates produced from in situ treatment with permanganate or redox barriers.  相似文献   

16.
A closed pyrolysis system has been developed as a tool for studying the reactions of organic compounds under extreme hydrothermal conditions. Small high pressure stainless steel vessels in which the ratio of sediment or sample to water has been adjusted to eliminate the headspace at peak experimental conditions confines the organic components to the bulk solid matrix and eliminates the partitioning of the organic compounds away from the inorganic components during the experiment. Confined pyrolysis experiments were performed to simulate thermally driven catagenetic changes in sedimentary organic matter using a solids to water ratio of 3.4 to 1. The extent of alteration was measured by monitoring the steroid and triterpenoid biomarkers and polycyclic aromatic hydrocarbon distributions. These pyrolysis experiments duplicated the hydrothermal transformations observed in nature. Molecular probe experiments using alkadienes, alkenes and alkanes in H2O and D2O elucidated the isomerization and hydrogenation reactions of aliphatic compounds and the competing oxidative reactions occurring under hydrothermal conditions. This confined pyrolysis technique is being applied to test experiments on organic synthesis of relevance to chemical evolution for the origin of life.  相似文献   

17.
Organic soils are an important source of N2O, but global estimates of these fluxes remain uncertain because measurements are sparse. We tested the hypothesis that N2O fluxes can be predicted from estimates of mineral nitrogen input, calculated from readily-available measurements of CO2 flux and soil C/N ratio. From studies of organic soils throughout the world, we compiled a data set of annual CO2 and N2O fluxes which were measured concurrently. The input of soil mineral nitrogen in these studies was estimated from applied fertilizer nitrogen and organic nitrogen mineralization. The latter was calculated by dividing the rate of soil heterotrophic respiration by soil C/N ratio. This index of mineral nitrogen input explained up to 69% of the overall variability of N2O fluxes, whereas CO2 flux or soil C/N ratio alone explained only 49% and 36% of the variability, respectively. Including water table level in the model, along with mineral nitrogen input, further improved the model with the explanatory proportion of variability in N2O flux increasing to 75%. Unlike grassland or cropland soils, forest soils were evidently nitrogen-limited, so water table level had no significant effect on N2O flux. Our proposed approach, which uses the product of soil-derived CO2 flux and the inverse of soil C/N ratio as a proxy for nitrogen mineralization, shows promise for estimating regional or global N2O fluxes from organic soils, although some further enhancements may be warranted.  相似文献   

18.
Detached roots and nodules of the N2-fixing species, Albus glutinosa (European black alder), actively assimilate CO2. The maximum rates of dark CO2 fixation observed for detached nodules and roots were 15 and 3 micromoles CO2 fixed per gram dry weight per hour, respectively. The net incorporation of CO2 in these tissues was catalyzed by phosphoenolpyruvate carboxylase which produces organic acids, some of which are used in the synthesis of the amino acids, aspartate, glutamate, and citrulline and by carbamyl phosphate synthetase. The latter accounts for approximately 30 to 40% of the CO2 fixed and provides carbamyl phosphate for the synthesis of citrulline. Results of labeling studies suggest that there are multiple pools of malate present in nodules. The major pool is apparently metabolically inactive and of unknown function while the smaller pool is rapidly utilized in the synthesis of amino acids. Dark CO2 fixation and N2 fixation in nodules decreased after treatment of nodulated plants with nitrate while the percentage of the total 14C incorporated into organic acids increased. Phosphoenolpyruvate carboxylase and carbamyl phosphate synthetase play key roles in the synthesis of amino acids including citrulline and in the metabolism of N2-fixing nodules and roots of alder.  相似文献   

19.
Modelling of soil emissions of nitrous oxide (N2O) and carbon dioxide (CO2) is complicated by complex interactions between processes and factors influencing their production, consumption and transport. In this study N2O emissions and heterotrophic CO2 respiration were simulated from soils under winter wheat grown in three different organic and one inorganic fertilizer-based cropping system using two different models, i.e., MoBiLE-DNDC and FASSET. The two models were generally capable of simulating most seasonal trends of measured soil heterotrophic CO2 respiration and N2O emissions. Annual soil heterotrophic CO2 respiration was underestimated by both models in all systems (about 10?C30% by FASSET and 10?C40% by MoBiLE-DNDC). Both models overestimated annual N2O emissions in all systems (about 10?C580% by FASSET and 20?C50% by MoBiLE-DNDC). In addition, both models had some problems in simulating soil mineral nitrogen, which seemed to originate from deficiencies in simulating degradation of soil organic matter, incorporated residues of catch crops and organic fertilizers. To improve the performance of the models, organic matter decomposition parameters need to be revised.  相似文献   

20.
We investigated the effects of spring barley growth on nitrogen (N) transformations and rhizosphere microbial processes in a controlled system under elevated carbon dioxide (CO2) at two levels of N fertilization (applied with 15N labelling). After 25 d, elevated CO2 (twice ambient) increased plant growth (dry weight, DW) by 141% at low‐N fertilization and by 60% at high‐N fertilization, but its positive effect on the root‐to‐shoot ratio was only significant at low‐N input. As a result of this plant response, elevated CO2 caused a greater soil CO2 efflux, rhizosphere soil DW, and soil microbial biomass under N‐limiting conditions than under high N availability. Elevated CO2 also caused a significant (P < 0.001) increase in the N recovered by the plant from both the labelled (Nf) and unlabelled (Ns + Nuf) N pools. The dynamics of N in the system as affected by elevated CO2 were driven principally by mineralization–immobilization turnover, with little loss by denitrification. Under N‐limiting conditions, there is evidence to suggest enhanced nutrient release from soil organic matter (SOM) pools—a process which could be defined as priming. The results of our experiment did not indicate a direct plant‐mediated effect of elevated CO2 on nitrous oxide (N2O) fluxes or denitrification activity.  相似文献   

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