A thermodynamic analysis of electron production during syngas fermentation

Currently, syngas fermentation is being developed as one option towards the production of biofuels from biomass. This process utilizes the acetyl-CoA (Wood-Ljungdahl) metabolic pathway. Along the pathway, CO and CO₂ are used as carbon sources. Electrons required for the metabolic process are generated from H₂ and/or from CO. This study showed that electron production from CO is always more thermodynamically favorable compared to electron production from H₂ and this finding is independent of pH, ionic strength, gas partial pressure, and electron carrier pairs. Additionally, electron production from H₂ may be thermodynamically unfavorable in some experimental conditions. Thus, it is unlikely that H₂ can be utilized for electron production in favor of CO when both species are present. Therefore, CO conversion efficiency will be sacrificed during syngas fermentation since some of the CO will provide electrons at the expense of product and cell mass formation.     

Cofacial and antarafacial indenyl bimetallic isomers: a descriptive MO picture and implications for the indenyl effect on ligand substitution reactions

The hetero-bimetallic Ind complexes (Ind=indenyl anion) with the formula (CO)₃Cr(μ-Ind)RhL₂ (L=CO, ethylene; L₂=COD, COT, NBD) have two possible conformers, one with the metals at antipodal sides of the condensed bicyclic polyene (antarafacial, anti) and the other with both metals on the same side (cofacial, syn). These systems can be considered to contain 34 valence electrons by assuming that Ind is capable of donating all of its ten π electrons to the metals. A qualitative MO analysis, based on EHMO calculations, is presented. The anti conformer is compared to the homometallic 34e species, namely [CpRu(μ-Ind)RuCp]⁺. Here, the pseudo-symmetrical relationship between the two identical metal fragments strongly suggests that one Ind σ-bonding MO donates part of its electron density to each of the two metals, which thus become formally saturated (36e). This argument is extended to the anti Cr---Rh derivative in which a critical role is played by an empty FMO of the (CO)₂Rh(I) fragment with π symmetry (i.e. lying in the molecular mirror plane). The latter, in spit the large π_CO^* contributions, has good acceptor capabilities at the metal.The calculations suggest that the so-called indenyl effect, namely the increased rate of substitution of one CO ligand by another σ donor (e.g. a phosphine), although a structurally dynamic process, also depends on the electron density which accumulates on the aforementioned π FMO. In the series (η⁵-C₅H₅)Rh(CO)₂, (η⁵-C₇H₉Rh(CO)₂ and {η⁵-[(CO)₃CrC₇H₉]}-Rh(CO)₂ the progressively reduced donor capabilities of the cyclic polyene toward the (CO)₂Rh(I) fragment induce a larger electrophilicity in rhodium, in good agreement with the experimental data on substitution reactivity. Finally, the electronic features of the cofacial conformer (CO)₃Cr(μ-Ind)Rh(CO)₂ are examined. In spite of the long Cr---Rh separation (> 3 Å) the graphically illustrated MO analysis indicates a direct, heterodox, intermetallic linkage, which helps the metals to achieve a formal electronic saturation. In this case, the limited propensity of the complex toward any CO substitution reactions is likely attributable to the hindered mobility of the (CO)₂Rh(I) fragment.     

承德木本植物不同部位S及重金属含量特征的PCA分析

应用主分量分析(PCA)和排序技术(OA)对承德市10种木本植物的S及重金属含量进行了分析.结果表明,Z₁和Z₂主成份值基本代表了所有元素反应的信息,累积贡献率>98%.S对Z₁贡献最大(元素负荷量>0.96),Fe、Zn、Mn、Ph等对Z₂有较大的影响.表明承德市S污染是最主要的;重金属污染以Zn、Fe、Mn、Ph较显着,而Cu、Ni污染不明显.不同植物器官部位污染物含量的排序表明,城市木本植物的污染物以树皮为最高,其次是枝条,叶最低.     

菰和菖蒲对重金属的胁迫反应及其富集能力

通过盆栽实验研究了Cu—Zn—Ph-Cd复合污染条件下,菰和菖蒲的生长状况、生理特性及吸收和富集重金属的能力。结果表明,高浓度污染下菰和菖蒲不能存活;低、中浓度中菖蒲的生长受到抑制,菰各生长指标与对照相比差异不显著,表明菰对低、中浓度重金属的耐性强于菖蒲。随着污染浓度的增加,菰和菖蒲叶片叶绿索含量显著降低;菰叶绿素a／b值略有降低,菖蒲叶绿素a／b值显著降低;菰和菖蒲叶片脯氨酸含量、相对电导率显著升高,超氧化物歧化酶（SOD）、过氧化物酶（POD）活性在低浓度时升高,中浓度时降低。菰体内重金属含量为Zn〉Cu〉Pb〉Cd,菖蒲体内的含量为Cu〉Zn〉Pb〉Cd,且二者体内的重金属含量都随着污染浓度的增加而升高。菰和菖蒲对Cd的富集系数较大,地上部分（茎与叶）和地下部分（根与根状茎）均大于1;对Pb的富集系数较小,地上部分和地下部分均小于1。菰和菖蒲地下部分重金属含量均高于地上部分含量,二者根系对4种重金属都有较强的滞留效应,平均滞留率均大于50％。各处理中菰对重金属的吸收量均高于菖蒲。综合分析菰和菖蒲的生长、生理及富集重金属的能力,菰比菖蒲更适用于低、中浓度重金属污染水体的生态修复。     

Simulation of gas transport due to cardiogenic oscillations

We simulated gas transport due to cardiogenic oscillations (CO) using a model developed to quantify the gas mixing due to high-frequency ventilation (16). The basic components of the model are 1) gas mixing by augmented transport, 2) symmetrical lung morphometry, and 3) a Lagrangian (moving) reference frame. The theoretical predictions of the model are in general agreement with published experimental studies that have examined the effect of CO on the nitrogen concentration obtained by intrapulmonary gas sampling and the effect of CO on regional and total anatomical dead space. Further, the model predicts that augmentation of gas transport due to CO is less, nearer to the alveolar regions of the lung, and that the effect of CO during normal tidal breathing is negligible, but that CO may contribute up to approximately 10% of the alveolar ventilation in patients with severe hypoventilation. The agreement between experimental and theoretical results suggests that it may not be necessary to invoke gas transport mechanisms specific to an asymmetrical bronchial tree to explain the major proportion of gas transport due to CO.     

Insights into large-scale cell-culture reactors: II. Gas-phase mixing and CO₂ stripping

Most discussions about stirred tank bioreactors for cell cultures focus on liquid-phase motions and neglect the importance of the gas phase for mixing, power input and especially CO(2) stripping. Particularly in large production reactors, CO(2) removal from the culture is known to be a major problem. Here, we show that stripping is mainly affected by the change of the gas composition during the movement of the gas phase through the bioreactor from the sparger system towards the headspace. A mathematical model for CO(2)-stripping and O(2)-mass transfer is presented taking gas-residence times into account. The gas phase is not moving through the reactor in form of a plug flow as often assumed. The model is validated by measurement data. Further measurement results are presented that show how the gas is partly recirculated by the impellers, thus increasing the gas-residence time. The gas-residence times can be measured easily with stimulus-response techniques. The results offer further insights on the gas-residence time distributions in stirred tank reactors.     

Accumulation and distribution of heavy metals in a simulated mangrove system treated with sewage

Constructed tide tanks were used to examine the accumulation and distribution of heavy metals in various components of a simulated mangrove ecosystem. Young Kandelia candel plants grown in mangrove soils were irrigated with wastewater of various strengths twice a week for a period of one year. The amounts of heavy metals released via tidal water and leaf litter were monitored at regular time intervals. The quantities of heavy metals retained in mangrove soil and various plant parts were also determined. Results show that most heavy metals from wastewater were retained in soils with little being uptake by plants or released into tidal seawater. However, the amounts of metals retained in plants on a per unit dry weight base were higher than those in soils as the biomass production from the young mangrove plants was much smaller when compared to the vast quantity of soils used in this study. A significantly higher heavy metal content was found in roots than in the aerial parts of the mangrove plant,indicating that the roots act as a barrier for metal translocation and protect the sensitive parts of the plant from metal contamination. In both soil and plant, concentrations of Zn, Cd, Pb and Ni increased with the strengths of wastewater, although the bioaccumulation factors for these metals decreased when wastewater strengths increased. These results suggest that the mangrove soil component has a large capacity to retain heavy metals, and the role of mangrove plants in retaining metals will depend on plant age and their biomass production. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of dissolved CO(2) concentration and CO(2) production rate of mammalian cell suspension culture based on off-gas measurement

The determination of dissolved CO(2) and HCO(3)(-) concentrations as well as the carbon dioxide production rate in mammalian cell suspension culture is attracting more and more attention since the effects on major cell properties, such as cell growth rate, product quality/production rate, intracellular pH and apoptosis, have been revealed. But the determination of these parameters by gas analysis is complicated by the solution/dissolution of carbon dioxide in the culture medium. This means that the carbon dioxide transfer rate (CTR; which can easily be calculated from off-gas measurement) is not necessarily equal to carbon dioxide production rate (CPR). In this paper, a mathematical method to utilize off-gas measurement and culture pH for cell suspension culture is presented. The method takes pH changes, buffer and medium characteristics that effect CO(2) mass transfer into account. These calculations, based on a profound set of equations, allow the determination of the respiratory activity of the cells, as well as the determination of dissolved CO(2), HCO(3)(-) and total dissolved carbonate. The method is illustrated by application to experimental data. The calculated dissolved CO(2) concentrations are compared with measurements from an electrochemical CO(2) probe.     

CO-metal interaction: Vital signaling from a lethal gas

The past few years have witnessed intense research into the biological significance of carbon monoxide (CO) as an essential signaling mediator in cells and tissues. To transduce the signal properly, CO must react selectively with functional and structural proteins containing moieties that show preferred reactivity towards this gaseous molecule. This selectivity is exemplified by the interaction of CO with iron- and heme-dependent proteins, although systems containing other transition metals can potentially become a preferential target for CO. Notably, transition metal carbonyls, which carry and liberate CO, are also emerging as a pharmacological tool to mimic the bioactivity of endogenously generated CO. Thus, exploring how CO binding to metal complexes is translated into a cytoprotective function is a challenging task and might open up opportunities for therapeutic applications based on CO delivery.     

利用电化学活跃微生物协助电解发酵产氢

摘要：电解协助发酵产氢是在外源电解协助下,利用电化学活跃微生物在石墨阳极上生长达到彻底氧化因发酵产氢残存的有机酸,产生CO2、电子与质子,电子进入石墨阳极经导线传到铂阴极,而质子则穿过阳离子膜进入阴极池,在无氧环境下,通过外加电压和铂的催化下,电子与质子结合为氢。此过程电子回收率可达90%以上,产氢效率可达8-9mol H2/mol Glucose。这一战略从根本上克服发酵产氢的发酵障碍和代谢产物的反馈抑制,极大地提高了氢转化率,极有可能率先应用于能源作物原料的氢能转化、以及有机污水和有机废弃物处理。     

Effect of age and sex on the production of internal and external hydrocarbons and pheromones in the housefly, Musca domestica

The epicuticular and internal waxes of male and female houseflies were examined by capillary gas chromatography-mass spectrometry at closely timed intervals from emergence until day-6 of adulthood. New components identified included tricosan-10-one, 9,10-epoxyheptacosane, heptacosen-12-one, a series of odd-carbon numbered dienes from C31 to C39, several positional isomers of monoenes including (Z)-9- and 7-pentacosene and a number of methyl- and dimethylalkanes. (Z)-9-tricosene appears in internal lipids prior to appearing on the surface of the insect, suggesting that it is transported in the hemolymph to its site of deposition on the epicuticle. The large increases in the amount of (Z)-9-tricosene in females from day-2 until day-6 is compensated for by a concomitant decrease in (Z)-9-heptacosene. The C23 epoxide and ketone only appear in females after the production of (Z)-9-tricosene is induced, and are only abundant in epicuticular waxes, suggesting they are formed after (Z)-9-tricosene is transported to the cells which are involved in taking them to the surface of the insect. Mathematical analysis indicated that the time shift between internal production and external accumulation in females is more than 24 h. The divergence between male and female lipid production occurs at an early stage, when insects are less than one day old.     

Low temperature catalytic gasification of pig compost to produce H2 rich gas

The low temperature catalytic gasification of pig compost before and after acid washing was carried out to produce H2 rich gas using a two-stage fixed-bed reactor. Little effect of the minerals on the manure pyrolysis is determined. Under the presence of Ni/Al2O3 catalyst nearly all the tarry matters were cracked into H2, CO, CO2 and residual carbon. High H2 and CO yields were obtained by low temperature catalytic steam gasification. Acid washing results in the decrease in the content of the ease-hydrolyzed organic components, which volatilize at low temperature. The change in the gas yields from the manure during catalytic decomposition is in accordance with its pyrolysis behavior.     

Partitioning of trace metals in sediments: Relationships with bioavailability

As a result of complex physical, chemical and biological processes, a major fraction of the trace metals introduced into the aquatic environment is found associated with the bottom sediments, distributed among a variety of physico-chemical forms. As these different metal forms will generally exhibit different chemical reactivities, the measurement of the total concentration of a particular metal provides little indication of potential interactions with the abiotic or biotic components present in the environment. In principle, the partitioning of sediment-bound metals could be determined both by thermodynamic calculations (provided equilibrium conditions prevail) and by experimental techniques. The modelling of sediment-bound metals is far less advanced than is that of dissolved species, primarily because the thermodynamic data needed for handling sediment-interstitial water systems are not yet available. The partitioning of a metal among various fractions obtained by experimental techniques (e.g., sequential extraction procedures) is necessarily operationally defined. These methods have, however, provided significant insight into the physico-chemical factors influencing the bioavailability of particulate trace metals; some of these factors are discussed.     

添加氧化铁对水稻土中H2、CO2和CH4形成的影响

水稻土是甲烷产生的重要源地．厌氧条件下甲烷的形成与有机质厌氧降解产生的乙酸、H2和CO2有关．氧化铁作为电子受体可有效地竞争有机质向甲烷的转化,其抑制作用机理可能与乙酸、H2和CO2的有效消耗有关．通过向水稻土泥浆中添加无定形氧化铁和纤铁矿．分别测定了25℃厌氧恒温培养105d过程中的H2、CO2和CH4的浓度变化．结果表明,添加无定形氧化铁及纤铁矿可导致H2浓度显著降低;无定形氧化铁对H2消耗的影响明显大于纤铁矿;添加不同氧化铁对CO2浓度的影响与H2浓度的变化有相同的趋势;添加氧化铁能显著抑制水稻土中甲烷形成,并导致有机碳的转移发生变化,使得CH4—C显著降低,气相中CO2—C量减少,而由土壤泥浆固定的CO3^2-—C量显著增加．     

An Ecological Risk Assessment of Air Emissions of Trace Metals from Copper and Zinc Production Facilities

Trace metals are components of releases to air emitted by copper and zinc production facilities in Canada. Six metals (copper, zinc, nickel, lead, cadmium, and arsenic) are examined as part of an overall environmental assessment of these releases. Estimates of metal deposition rates to soils and surface waters were derived from monitoring data in the vicinity of the production facilities and also through dispersion modelling studies. Fate and transport modelling of the metals deposited allowed an estimation of critical loads. Estimated annual deposition rates were compared with 25^th-percentile critical loads typically representative of effects on sensitive organisms under 25% of conditions in sandy soils or circumneutral to acidic lake waters. The results of the comparison suggest that there is a potential for adverse effects on aquatic and/or soil-dwelling organisms from exposure to steadystate concentrations of metals in the vicinity of copper and zinc production facilities. Approaches of particular significance in these assessments include probabilistic estimation of critical loads for metals, allowance for the speciation of metals defining the bioavailable fraction and limiting critical effect levels to the high end of natural background metal concentrations.     

Inhibitory effect of carbon dioxide on the fed-batch culture of Ralstonia eutropha: evaluation by CO2 pulse injection and autogenous CO2 methods

In order to see the effect of CO(2) inhibition resulting from the use of pure oxygen, we carried out a comparative fed-batch culture study of polyhydroxybutyric acid (PHB) production by Ralstonia eutropha using air and pure oxygen in 5-L, 30-L, and 300-L fermentors. The final PHB concentrations obtained with pure O(2) were 138.7 g/L in the 5-L fermentor and 131.3 g/L in the 30-L fermentor, which increased 2.9 and 6.2 times, respectively, as compared to those obtained with air. In the 300-L fermentor, the fed-batch culture with air yielded only 8.4 g/L PHB. However, the maximal CO(2) concentrations in the 5-L fermentor increased significantly from 4.1% (air) to 15.0% (pure O(2)), while it was only 1.6% in the 30-L fermentor with air, but reached 14.2% in the case of pure O(2). We used two different experimental methods for evaluating CO(2) inhibition: CO(2) pulse injection and autogenous CO(2) methods. A 10 or 22% (v/v) CO(2) pulse with a duration of 3 or 6 h was introduced in a pure-oxygen culture of R. eutropha to investigate how CO(2) affects the synthesis of biomass and PHB. CO(2) inhibited the cell growth and PHB synthesis significantly. The inhibitory effect became stronger with the increase of the CO(2) concentration and pulse duration. The new proposed autogenous CO(2) method makes it possible to place microbial cells under different CO(2) level environments by varying the gas flow rate. Introduction of O(2) gas at a low flow rate of 0.42 vvm resulted in an increase of CO(2) concentration to 30.2% in the exit gas. The final PHB of 97.2 g/L was obtained, which corresponded to 70% of the PHB production at 1.0 vvm O(2) flow rate. This new method measures the inhibitory effect of CO(2) produced autogenously by cells through the entire fermentation process and can avoid the overestimation of CO(2) inhibition without introducing artificial CO(2) into the fermentor.     

Energy generation from the CO oxidation-hydrogen production pathway in Rubrivivax gelatinosus

When incubated in the presence of CO gas, Rubrivivax gelatinosus CBS induces a CO oxidation-H2 production pathway according to the stoichiometry CO + H2O --> CO2 + H2. Once induced, this pathway proceeds equally well in both light and darkness. When light is not present, CO can serve as the sole carbon source, supporting cell growth anaerobically with a cell doubling time of nearly 2 days. This observation suggests that the CO oxidation reaction yields energy. Indeed, new ATP synthesis was detected in darkness following CO additions to the gas phase of the culture, in contrast to the case for a control that received an inert gas such as argon. When the CO-to-H2 activity was determined in the presence of the electron transport uncoupler carbonyl-cyanide m-chlorophenylhydrazone (CCCP), the rate of H2 production from CO oxidation was enhanced nearly 40% compared to that of the control. Upon the addition of the ATP synthase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD), we observed an inhibition of H2 production from CO oxidation which could be reversed upon the addition of CCCP. Collectively, these data strongly suggest that the CO-to-H2 reaction yields ATP driven by a transmembrane proton gradient, but the detailed mechanism of this reaction is not yet known. These findings encourage additional research aimed at long-term H2 production from gas streams containing CO.     

Contribution of continuing gas exchange to phase III exhaled PCO2 and PO2 profiles

Changes in PCO2 and PO2 during expiration have been ascribed to simultaneous gas exchange, but other factors such as ventilation-perfusion inhomogeneity in combination with sequential emptying may also contribute. An experimental and model approach was used to study the relationship between gas exchange and changes in expired PCO2 and PO2 in anesthetized dogs during prolonged high tidal volume expirations. Changes in PCO2 and PO2 were quantified by taking the area bounded by the sloping exhalation curve and a line drawn horizontally from a point where the Fowler dead space plus 250 ml had been expired. This procedure is similar to using the slope of the exhalation curve but it circumvents problems caused by nonlinearity of the PCO2 and PO2 curves. The gas exchange components of the CO2 and O2 areas were calculated using a single-alveolus lung model whose input parameters were measured in connection with each prolonged expiration. The relationship between changes in experimental CO2 areas caused by sudden reductions in mixed venous PCO2 (produced by right atrial infusions of NaOH) and those calculated by the model was also studied. In seven dogs, calculated CO2 and O2 areas were 13% higher and 25% lower than the respective experimental areas, but interindividual variations were large. Changes in experimental CO2 areas caused by step changes in mixed venous PCO2 were almost identical to changes in the calculated areas. We conclude that the changes in PCO2 and PO2 during expiration cannot be explained solely by gas exchange. However, the single-alveolus lung model accurately predicts changes in the CO2 exhalation curve caused by alterations in the alveolar CO2 flow.     

Uptake of atmospheric carbon dioxide into silk fiber by silkworms

The relation between the uptake of atmospheric CO(2) and insect's production of silk fiber has not yet been reported. Here, we provide the first quantitative demonstrations that four species of silkworms (Bombyx mori, Samia cynthia ricini, Antheraea pernyi, and Antheraea yamamai) and a silk-producing spider (Nephila clavata) incorporate atmospheric CO(2) into their silk fibers. The abundance of (13)C incorporated from the environment was determined by mass spectrometry and (13)C NMR measurements. Atmospheric CO(2) was incorporated into the silk fibers in the carbonyl groups of alanine, aspartic acid, serine, and glycine and the C(gamma) of aspartic acid. We show a simple model for the uptake of atmospheric CO(2) by silkworms. These results will demonstrate that silkworm has incorporated atmospheric CO(2) into silk fiber via the TCA cycle; however, the magnitude of uptake into the silk fibers is smaller than that consumed by the photosynthesis in trees and coral reefs.     

Molybdenum nitrogenase catalyzes the reduction and coupling of CO to form hydrocarbons

The molybdenum-dependent nitrogenase catalyzes the multi-electron reduction of protons and N(2) to yield H(2) and 2NH(3). It also catalyzes the reduction of a number of non-physiological doubly and triply bonded small molecules (e.g. C(2)H(2), N(2)O). Carbon monoxide (CO) is not reduced by the wild-type molybdenum nitrogenase but instead inhibits the reduction of all substrates catalyzed by nitrogenase except protons. Here, we report that when the nitrogenase MoFe protein α-Val(70) residue is substituted by alanine or glycine, the resulting variant proteins will catalyze the reduction and coupling of CO to form methane (CH(4)), ethane (C(2)H(6)), ethylene (C(2)H(4)), propene (C(3)H(6)), and propane (C(3)H(8)). The rates and ratios of hydrocarbon production from CO can be adjusted by changing the flux of electrons through nitrogenase, by substitution of other amino acids located near the FeMo-cofactor, or by changing the partial pressure of CO. Increasing the partial pressure of CO shifted the product ratio in favor of the longer chain alkanes and alkenes. The implications of these findings in understanding the nitrogenase mechanism and the relationship to Fischer-Tropsch production of hydrocarbons from CO are discussed.