DFT study of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O co-adsorption on carbon models of coal surface

The moisture content of coal affects the adsorption capacity of CO₂ on the coal surface. Since the hydrogen bonds are formed between H₂O and oxygen functional group, the H₂O cluster more easily adsorbs on the coal micropore than CO₂ molecule. The coal micropores are occupied by H₂O molecules that cannot provide extra space for CO₂ adsorption, which may leads to the reduction of CO₂ adsorption capacity. However, without considering factors of micropore and oxygen functional groups, the co-adsorption mechanisms of CO₂ and adsorbed H₂O molecule are not clear. Density functional theory (DFT) calculations were performed to elucidate the effect of adsorbed H₂O to CO₂ adsorption. This study reports some typical coal-H₂O···CO₂ complexes, along with a detailed analysis of the geometry, energy, electrostatic potential (ESP), atoms in molecules (AIM), reduced density gradient (RDG), and energy decomposition analysis (EDA). The results show that H₂O molecule can more stably adsorb on the aromatic ring surface than CO₂ molecule, and the absolute values of local ESP maximum and minimum of H₂O cluster are greater than CO₂. AIM analysis shows a detailed interaction path and strength between atoms in CO₂ and H₂O, and RDG analysis shows that the interactions among CO₂, H₂O, and coal model belong to weak van der Waals force. EDA indicates that electrostatic and long-range dispersion terms play a primary role in the co-adsorption of CO₂ and H₂O. According to the DFT calculated results without considering micropore structure and functional group, it is shown that the adsorbed H₂O can promote CO₂ adsorption on the coal surface. These results demonstrate that the micropore factor plays a dominant role in affecting CO₂ adsorption capacity, the attractive interaction of adsorbed H₂O to CO₂ makes little contribution.     

Study of Plasma Induced Chemistry by DC Discharges in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>/H<Subscript>2</Subscript>O Mixtures Above a Water Surface

The chemistry induced by atmospheric pressure DC discharges above a water surface in CO(2)/N(2)/H(2)O mixtures was investigated. The gaseous mixtures studied represent a model prebiotic atmosphere of the Earth. The most remarkable changes in the chemical composition of the treated gas were the decomposition of CO(2) and the production of CO. The concentration of CO increased logarithmically with the increasing input energy density and an increasing initial concentration of CO(2) in the gas. The highest achieved concentration of CO was 4.0 +/- 0.6 vol. %. The production of CO was crucial for the synthesis of organic species, since reactions of CO with some reactive species generated in the plasma, e. g. H* or N* radicals, were probably the starting point in this synthesis. The presence of organic species (including the tentative identification of some amino acids) was demonstrated by the analysis of solid and liquid samples by high-performance liquid chromatography, infrared absorption spectroscopy and proton-transfer-reaction mass spectrometry. Formation of organic species in a completely inorganic CO(2)/N(2)/H(2)O atmosphere is a significant finding for the theory of the origins of life.     

Photosynthetic CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O gas exchange and dynamics of carbohydrates content in maize leaves under drought

We studied the temporal sequence of changes in the photosynthetic CO₂/H₂O gas exchange intensity, as well as leaf water status, contents of soluble carbohydrates, starch, proline, pigments, and MDA, in maize seedlings (Zea mays L., cv. Luchistaya) under adaptation to increasing water deficit. The duration of drought was 2, 3, 5, and 6 days. Withholding water from maize plants caused gradual increase in the intensity of water deficit: from mild (2 or 3 days) to moderate (5 days) and nearly severe (6 days) water stress. After 6 days, relative leaf water content decreased by 19.8% as compared to the control. On the second day after the onset of drought, slight reduction in the photosynthetic CO₂/H₂O gas exchange intensity of the treated plants was observed. After 6 days, photosynthesis and transpiration of leaves synchronously reduced almost threefold due to stomatal closure. The progressive soil drought had substantial impact on the carbohydrate metabolism. After 2 days of water deficit, the content of reducing sugars and sucrose increased slightly, whereas after 6 days, it increased ten and four times, respectively. After 2, 3, and 5 days of drought, the starch content declined slightly; however, under severe drought (6 days), it increased by 30% as compared to the control. Simultaneously with the increase in the content of soluble sugars, proline content increased significantly and it was the highest on the sixth day of drought. At all stages of water deficit, the proline content increased more significantly than the content of reducing carbohydrates and sucrose. Under increasing water deficit (5 and 6 days), the content of MDA was found to rise. At the initial drought stage (2 or 3 days) and under severe water deficit (6 days), no significant changes in the pigment content were observed. Thus, at the initial stages of progressive drought, in the leaves of this maize cultivar, a decline in photosynthetic activity proceeded simultaneously with accumulation of reducing sugars, sucrose, and proline. The results obtained showed that, at the first stages of adaptation of maize seedlings to drought, the changes in carbohydrate and proline metabolism have been observed, which have increased upon further plant dehydration.     

Hydrothermal Stability of Adenine Under Controlled Fugacities of N<Subscript>2</Subscript>, CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>

An experimental study has been carried out on the stability of adenine (one of the five nucleic acid bases) under hydrothermal conditions. The experiments were performed in sealed autoclaves at 300 degrees C under fugacities of CO(2), N(2) and H(2) supposedly representative of those in marine hydrothermal systems on the early Earth. The composition of the gas phase was obtained from the degradation of oxalic acid, sodium nitrite and ammonium chloride, and the oxidation of metallic iron. The results of the experiments indicate that after 200 h, adenine is still present in detectable concentration in the aqueous phase. In fact, the concentration of adenine does not seem to be decreasing after approximately 24 h, which suggests that an equilibrium state may have been established with the inorganic constituents of the hydrothermal fluid. Such a conclusion is corroborated by independent thermodynamic calculations.     

Interaction of a Ti-doped semi-fullerene (TiC<Subscript>30</Subscript>) with molecules of CO and CO<Subscript>2</Subscript>

Using density functional theory (DFT) and molecular dynamics (MD), we studied the interaction of a titanium atom with a half of a C₆₀ fullerene (i.e., C₃₀), formed from the corannulene structure with a pentagonal base. We considered atmospheric pressure and 300 K. We found that the most stable adsorption of the titanium atom on C₃₀ occurs in the concave surface of the molecule. Afterward, we investigated the interaction of the system C₃₀-titanium with carbon monoxide and carbon dioxide molecules, respectively. We found that each of these molecules is chemisorbed, with no dissociation. The value of the adsorption energy for the carbon monoxide molecule varies from ?0.897 to ?1.673 eV, and for the carbon dioxide molecule, it is between ?1.065 and ?1.274 eV. These values depend on the initial orientation of these molecules with respect to TiC₃₀.

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Graphical Abstract The TiC₃₀ system chemisorbs CO or CO₂?with no dissociation at atmospheric pressure and 300K

     

The addition reactions of germylenoid H<Subscript>2</Subscript>GeAlCl<Subscript>3</Subscript> with ethylene: a theoretical investigation

Theoretical calculations using the M062X and QCISD methods were performed on the addition reactions of the aluminum germylenoid H₂GeAlCl₃ with ethylene. The most two stable structures of germylenoid H₂GeAlCl₃, i.e., the p-complex and three-membered ring structures, respectively, were employed as reactants. The calculated results indicate that, for the p-complex, H₂GeAlCl₃ there are two pathways, I and II, of which path I involves just one transition state, while path II involves two transition states between reactants and products. Comparing the reaction barrier heights of path I (44.6 kJ mol^?1) and II (37.6 kJ mol^?1), the two pathways are competitive, with similar barriers under the same conditions, while for the three-membered ring structure, another two pathways, III and IV, also exist. Path III has one transition state; however, in path IV, two transition states exist. By comparing their barrier heights, path III (barrier height 39.2 kJ mol^?1) could occur more easily than path IV (barrier height 92.8 kJ mol^?1). Considering solvent effects on these addition reactions, the PCM model and CH₂Cl₂ solvent were used in calculations, and the calculated results demonstrate that CH₂Cl₂ solvent is unfavorable for the reactions, except for path II. In CH₂Cl₂ solvent, paths II and III are more favorable than paths I and IV.     

Comparison of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O fluxes over grassland vegetations measured by the eddy-covariance technique and by open system chamber

Measurements of CO₂ and H₂O fluxes were carried out using two different techniques—eddy-covariance (EC) and open system gas exchange chamber (OC)—during two-years’ period (2003–2004) at three different grassland sites. OC measurements were made during fourteen measurement campaigns. We found good agreement between the OC and EC CO₂ flux values (n = 63, r ² = 0.5323, OC F_CO2 = −0.6408+0.9508 EC F_CO2). The OC F_H2O values were consistently lower than those measured by the EC technique, probably caused by the air stream difference inside and outside the chamber. Adjusting flow rate within the chamber to the natural conditions would be necessary in future OC measurements. In comparison with EC, the OC proved to be a good tool for gas exchange measurements in grassland ecosystems.     

The polythiophene molecular segment as a sensor model for H<Subscript>2</Subscript>O,HCN, NH<Subscript>3</Subscript>, SO<Subscript>3</Subscript>, and H<Subscript>2</Subscript>S: a density functional theory study

Studying the interaction of some atmospheric gases (H₂O, HCN, NH₃, SO₃ and H₂S) with 3PT oligomers is important in the development of polymeric sensors for gas detection. In the present study, we studied the relaxed geometries, interaction energies, charge analysis, HOMO–LUMO orbital analysis, and UV–vis spectra of all interacted systems using first-principles density functional theory (DFT). All these analyses indicated the potential of polythiophene as an inexpensive polymeric sensor for the analytes mentioned. Interaction energy values of ?19.90, ?19.66, ?14.01, ?8.70, and ?4.76 kJ mol^?1 were achieved for adsorption of SO₃, H₂O, NH₃, HCN, and H₂S on 3PT, respectively. Consequently, clarification of their physical parameters became the major focus of this study.     

Temporal Variability of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O Flux Spatial Patterns at a Mowed and a Grazed Grassland

Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO₂ and N₂O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N₂O flux, soil water content, and soil temperature during a 4-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80 × 60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N₂O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40–50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N₂O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p < 0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO₂ and N₂O fluxes.     

Decades-long effects of high CO<Subscript>2</Subscript> concentration on soil nitrogen dynamics at a natural CO<Subscript>2</Subscript> spring

The effects of high atmospheric CO₂ concentration ([CO₂]) on ecosystem processes have been explored using temporal facilities such as open-top-chambers and free-air CO₂ enrichment. However, the effects of high [CO₂] on soil properties takes decades and may not be captured by short-term experiments. Natural CO₂ springs provide a unique opportunity to study the long-term effects of high [CO₂]. In this study, we investigated soil properties at a natural CO₂ spring. We found that the amounts of total carbon (C) and nitrogen (N) stored in the soil at the high [CO₂] site exceeded those in the reference site by 60 and 30%, respectively. The effects of high [CO₂] were large in the upper slope position where the canopy openness was high and plants grew faster, but no effects were detected in the lowest position where the canopy openness was lower (half of that at the upper slope position). In contrast, effects of high [CO₂] on soil N dynamics, such as N mineralization and nitrification rates, did not exhibit a slope gradient. This suggests that effects of high [CO₂] differed among soil stoichiometric characteristics and N dynamics. These complicated effects of high [CO₂] imply that the future effects of high [CO₂] on ecosystems could vary widely in conjunction with environmental conditions such as light availability and/or topographic conditions.     

CO<Subscript>2</Subscript> bio-mitigation using microalgae

Microalgae are a group of unicellular or simple multicellular photosynthetic microorganisms that can fix CO(2) efficiently from different sources, including the atmosphere, industrial exhaust gases, and soluble carbonate salts. Combination of CO(2) fixation, biofuel production, and wastewater treatment may provide a very promising alternative to current CO(2) mitigation strategies.     

Foliar quality influences tree-herbivore-parasitoid interactions: effects of elevated CO<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and plant genotype

This study examined the effects of carbon dioxide (CO₂)-, ozone (O₃)-, and genotype-mediated changes in quaking aspen (Populus tremuloides) chemistry on performance of the forest tent caterpillar (Malacosoma disstria) and its dipteran parasitoid (Compsilura concinnata) at the Aspen Free-Air CO₂ Enrichment (FACE) site. Parasitized and non-parasitized forest tent caterpillars were reared on two aspen genotypes under elevated levels of CO₂ and O₃, alone and in combination. Foliage was collected for determination of the chemical composition of leaves fed upon by forest tent caterpillars during the period of endoparasitoid larval development. Elevated CO₂ decreased nitrogen levels but had no effect on concentrations of carbon-based compounds. In contrast, elevated O₃ decreased nitrogen and phenolic glycoside levels, but increased concentrations of starch and condensed tannins. Foliar chemistry also differed between aspen genotypes. CO₂, O₃, genotype, and their interactions altered forest tent caterpillar performance, and differentially so between sexes. In general, enriched CO₂ had little effect on forest tent caterpillar performance under ambient O₃, but reduced performance (for insects on one aspen genotype) under elevated O₃. Conversely, elevated O₃ improved forest tent caterpillar performance under ambient, but not elevated, CO₂. Parasitoid larval survivorship decreased under elevated O₃, depending upon levels of CO₂ and aspen genotype. Additionally, larval performance and masses of mature female parasitoids differed between aspen genotypes. These results suggest that host-parasitoid interactions in forest systems may be altered by atmospheric conditions anticipated for the future, and that the degree of change may be influenced by plant genotype.     

Emissions of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O from undisturbed,drained and mined peatlands in Estonia

The aim of this study is to estimate emissions of greenhouse gases CO₂, CH₄ and N₂O, and the effects of drainage and peat extraction on these processes, in Estonian transitional fens and ombrotrophic bogs. Closed-chamber-based sampling lasted from January to December 2009 in nine peatlands in Estonia, covering areas with different land-use practices: natural (four study sites), drained (six sites), abandoned peat mining (five sites) and active peat mining areas (five sites). Median values of soil CO₂ efflux were 1,509, 1,921, 2,845 and 1,741 kg CO₂-C ha^?1 year^?1 from natural, drained, abandoned and active mining areas, respectively. Emission of CH₄-C (median values) was 85.2, 23.7, 0.07 and 0.12 kg ha^?1 year^?1, and N₂O-N ?0.05, ?0.01, 0.18 and 0.19 kg ha^?1 year^?1, respectively. There were significantly higher emissions of CO₂ and N₂O from abandoned and active peat mining areas, whereas CH₄ emissions were significantly higher in natural and drained areas. Significant Spearman rank correlation was found between soil temperature and CO₂ flux at all sites, and CH₄ flux with high water level at natural and drained areas. Significant increase in CH₄ flux was detected for groundwater levels above 30 cm.     

Atlantic cod actively avoid CO<Subscript>2</Subscript> and predator odour,even after long-term CO<Subscript>2</Subscript> exposure

Introduction

The rising atmospheric CO₂ level is continuously driving the dissolution of more CO₂ into the oceans, and some emission scenarios project that the surface waters may reach 1000 μatm by the end of the century. It is not known if fish can detect moderately elevated CO₂ levels, and if they avoid areas with high CO₂. If so, avoidance behaviour to water with high CO₂ could affect movement patterns and migrations of fish in the future. It is also being increasingly recognized that fish behaviour can be altered by exposure to CO₂. Therefore this study investigated how long-term exposure to elevated pCO₂ affects predator avoidance and CO₂ avoidance in juvenile Atlantic cod (Gadus morhua). The fish were exposed to control water or CO₂-enriched water (1000 μatm) for six weeks before being subjected to tests of behaviour.

Results

Despite long term exposure to elevated pCO₂ the cod still strongly avoided the smell of a predator. These data are surprising because several coral reef fish have demonstrated reversal of olfactory responses after CO₂ exposure, turning avoidance of predator cues into preference for predator cues. Fish from both treatment groups also demonstrated strong avoidance of CO₂ when presented with the choice of control or CO₂-acidified water, indicating that habituation to the CO₂ sensory stimuli is negligible.

Conclusions

As Atlantic cod maintained normal behavioural responses to olfactory cues, they may be tolerant to CO₂-induced behavioural changes. The results also suggest that despite the long-term exposure to CO₂-acidified water, the fish still preferred the control water over CO₂-acidified water. Therefore, in the future, fish may alter their movements and migrations in search of waters with a lower CO₂ content.

     

Hydrolases in supercritical CO<Subscript>2</Subscript> and their use in a high-pressure membrane reactor

The thermal stability and activity of enzymes in supercritical carbon dioxide (SC CO(2)) and near-critical propane were studied at a pressure of 300 bar in the temperature range 20-90 degrees C. Proteinase from Carica papaya was incubated in microaqueous SC CO(2) at atmospheric pressure in a nonaqueous system. Lipase stability in an aqueous medium at atmospheric pressure and in SC CO(2) as well as near-critical propane at 100 bar and 40 degrees C was studied. In order to investigate the impact of solvent on lipases, these were chosen from different sources: Pseudomonas fluorescences, Rhizpous javanicus, Rhizopus niveus and porcine pancreas. On the basis of our previous study on lipase activities in dense gases, a high-pressure continuous flat-shape membrane reactor was designed. The hydrolysis of sunflower oil in SC CO(2) was performed as a model reaction in this reactor. The reaction was catalyzed by the lipase preparation Lipolase 100T and was performed at 50 degrees C and 200 bar.     

Selective effects of H<Subscript>2</Subscript>O<Subscript>2</Subscript> on cyanobacterial photosynthesis

The sensitivity of phytoplankton species for hydrogen peroxide (H₂O₂) was analyzed by pulse amplitude modulated (PAM) fluorometry. The inhibition of photosynthesis was more severe in five tested cyanobacterial species than in three green algal species and one diatom species. Hence the inhibitory effect of H₂O₂ is especially pronounced for cyanobacteria. A specific damage of the photosynthetic apparatus was demonstrated by changes in 77 K fluorescence emission spectra. Different handling of oxidative stress and different cell structure are responsible for the different susceptibility to H₂O₂ between cyanobacteria and other phytoplankton species. This principle may be potentially employed in the development of new agents to combat cyanobacterial bloom formation in water reservoirs.     

Putrescine protects hulless barley from damage due to UV-B stress via H<Subscript>2</Subscript>S- and H<Subscript>2</Subscript>O<Subscript>2</Subscript>-mediated signaling pathways

Key message

In hulless barley, H ₂ S mediated increases in H ₂ O ₂ induced by putrescine, and their interaction enhanced tolerance to UV-B by maintaining redox homeostasis and promoting the accumulation of UV-absorbing compounds.

Abstract

This study investigated the possible relationship between putrescence (Put), hydrogen sulfide (H₂S) and hydrogen peroxide (H₂O₂) as well as the underlying mechanism of their interaction in reducing UV-B induced damage. UV-B radiation increased electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and UV-absorbing compounds but reduced antioxidant enzyme activities and glutathione (GSH) and ascorbic acid (AsA) contents. Exogenous application of Put, H₂S or H₂O₂ reduced some of the above-mentioned negative effects, but were enhanced by the addition of Put, H₂S and H₂O₂ inhibitors. Moreover, the protective effect of Put against UV-B radiation-induced damage to hulless barley was diminished by dl-propargylglycine (PAG, a H₂S biosynthesis inhibitor), hydroxylamine (HT, a H₂S scavenger), diphenylene iodonium (DPI, a PM-NADPH oxidase inhibitor) and dimethylthiourea (DMTU, a ROS scavenger), and the effect of Put on H₂O₂ accumulation was abolished by HT. Taken together, as the downstream component of the Put signaling pathway, H₂S mediated H₂O₂ accumulation, and H₂O₂ induced the accumulation of UV-absorbing compounds and maintained redox homeostasis under UV-B stress, thereby increasing the tolerance of hulless barley seedlings to UV-B stress.

     

Pre-treatment with H<Subscript>2</Subscript>O<Subscript>2</Subscript> induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 μM H₂O₂ for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H₂O₂ alone had no effect on the proline, malondialdehyde (MDA) and H₂O₂ contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 μM H₂O₂ treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H₂O₂ pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of ¹⁴CO₂ fixation was higher and MDA, H₂O₂ and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl⁻ content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H₂O₂ metabolism is involved as a signal in the processes of barley salt tolerance.     

Root-derived CO<Subscript>2</Subscript> flux from a tropical peatland

Tropical peatlands release significant quantities of greenhouse gases to the atmosphere, yet the relative contributions of heterotrophic and autotrophic respiration to net CO₂ fluxes remains sparsely quantified. We used a combination of in situ trenching and vegetation removal in ex situ pots to quantify root-derived CO₂ under two plant functional types within a mixed species forest. Trenching significantly reduced surface CO₂ flux, indicating that approximately two-thirds of the released CO₂ was derived from roots. In contrast, ex situ vegetation removal in pots indicated that root-derived CO₂ accounted for 27% of the total CO₂ flux for Campnosperma panamensis, a broadleaved evergreen tree, and 49% for Raphia taedigera, a canopy palm. The results show that root-derived CO₂ is a major contribution to net CO₂ emissions in tropical peatlands, and that the magnitude of the emissions is affected by plant species composition. This is important in the context of land use change driving alterations in vegetation cover.