Studies on the anesthetic mechanism of carbon dioxide by using Bombyx mori larvae.

The study of heartbeat variations of Bombyx mori larvae submitted to CO2 narcosis has provided new information on carbon dioxide anesthesia. Purely anoxiant action must be dismissed. Action at a nerve level is possible since CO2 produces the same effect as ether, which is a classical anesthetic.     

Metal-free carbon dioxide reduction and acidic C-H activations using a frustrated Lewis pair

Activation of CO₂ and acidic C-H bonds by the lutidine-tris(pentafluorophenyl)borane [Lut/B(C₆F₅)₃] frustrated Lewis pair (FLP) are described (lutidine = 2,6-dimethylpyridine). Lut/B(C₆F₅)₃ reacts with CO₂ and H₂ at ambient temperature and 4 atm of pressure to form the lutidinium boro-formate salt [LutH⁺][HC(O)OB(C₆F₅)₃⁻]. This salt has been fully characterized including an X-ray crystal structure and independent synthesis from formic acid and Lut/B(C₆F₅)₃. Attempts to activate a C-H bond in methane by Lut/B(C₆F₅)₃, analogous to its heterolytic cleavage of H₂, were unsuccessful, which are consistent with published calculations showing significant barriers to this reaction. Lut/B(C₆F₅)₃ does react with more acidic C-H bonds, including acetone and nitroalkanes. With nitromethane, the boro-nitrone anion H₂CNO₂B(C₆F₅)₃⁻ is formed, as indicated by NMR and mass spectral analyses.     

Separation of protein and fatty acids from tuna viscera using supercritical carbon dioxide

Supercritical carbon dioxide extraction was investigated as a method for removing lipids and bad flavor from tuna viscera. To find the optimum conditions, different experimental variables, such as pressure, temperature, flow rate of solvent and sample size, were evaluated for the effective removal of lipids and the undesirable smell. Ethanol was used as the entrainer, with a 3% by vol CO₂ flow rate. By increasing the pressure at constant temperature, the efficiency of the lipid removal was improved and the protein was concentrated without denaturalization. The main fatty acids extracted from the tuna viscera were palmitic acid (16∶0), heptadecanoic acid (17∶1), oleic acid (18∶1) and docosahexaenoic acid (22∶6). The major amino acids in the tuna viscera treated by supercritical carbon dioxide were glutamic acid, leucine and lysine, and the free amino acids werel-proline, taurine andl-α-aminoadipic acid.     

Control of the circadian rhythm of carbon dioxide assimilation in Bryophyllum leaves by exposure to darkness and high carbon dioxide concentrations

The circadian rhythm of CO₂ assimilation in detached leaves of Bryophyllum fedtschenkoi at 15° C in normal air and continuous illumination is inhibited both by exposure to darkness, and to an atmosphere enriched with 5% CO₂. During such exposures substantial fixation of CO₂ takes place, and the malate concentration in the cell sap increases from about 20 mM to a constant value of 40–50 mM after 16 h. On transferring the darkened leaves to light, and those exposed to 5% CO₂ to normal air, a circadian rhythm of CO₂ assimilation begins again. The phase of this rhythm is determined by the time the transfer is made since the first peak occurs about 24 h afterwards. This finding indicates that the circadian oscillator is driven to, and held at, an identical, fixed phase point in its cycle after 16 h exposure to darkness or to 5% CO₂, and it is from this phase point that oscillation begins after the inhibiting condition is removed. This fixed phase point is characterised by the leaves having acquired a high malate content. The rhythm therefore begins with a period of malate decarboxylation which lasts for about 8 h, during which time the malate content of the leaf cells must be reduced to a value that allows phosphoenolpyruvate carboxylase to become active. Inhibition of the rhythm in darkness, and on exposure to 5% CO₂ in continuous illumination, appears to be due to the presence of a high concentration of CO₂ within the leaf inhibiting malic enzyme which leads to the accumulation of high concentrations of malate in the leaf cells. The malate then allosterically inhibits phosphoenolpyruvate carboxylase upon which the rhythm depends. The results give support to the view that malate synthesis and breakdown form an integral part of the circadian oscillator in this tissue.Abbreviations B. Bryophyllum - PEPCase phosphoenolpyruvate carboxylase     

Improved method to detect trace amounts of gases in a carbon dioxide atmosphere

A method is described for concentrating and quantifying trace amounts of alkanes and alkenes, produced during phosphonate biodegradation, in a carbon dioxide atmosphere. The method is precise, repeatable, fast and cheap. Compared to direct headspace analysis, the variance in the quantification was reduced up to 50 times and the detection limit lowered 20 to 500 times. Quantification was independent of the pressure in the experimental tubes, the amount of dissolved gases in the medium, and the temperature.     

Carbon dioxide concentration at night affects translocation from soybean leaves

Studies have indicated that the concentration of carbon dioxide [CO2] during the dark period may influence plant dry matter accumulation. It is often suggested that these effects on growth result from effects of [CO2] on rates of respiration, but responses of respiration to [CO2] remain controversial, and connections between changes in respiration rate and altered growth rate have not always been clear. The present experiments tested whether translocation, a major consumer of energy from respiration in exporting leaves, was sensitive to [CO2]. Nineteen-day-old soybean plants grown initially at a constant [CO2] of 350 micromol mol(-1) were exposed to three consecutive nights with a [CO2] of 220-1400 micromol mol(-1), with a daytime [CO2] of 350 micromol mol(-1). Change in dry mass of the individual second, third and fourth trifoliate leaves over the 3-d period was determined, along with rates of respiration and photosynthesis of second leaves, measured by net CO2 exchange. Translocation was determined from mass balance for second leaves. Additional experiments were conducted where the [CO2] around individual leaves was controlled separately from that of the rest of the plant. Results indicated that low [CO2] at night increased both respiration and translocation and elevated [CO2] decreased both processes, to similar relative extents. The effect of [CO2] during the dark on the change in leaf mass over 3 d was largest in second leaves, where the change in mass was about 50% greater at 1400 micromol mol(-1) CO2 than at 220 micromol mol(-1) CO2. The response of translocation to [CO2] was localized in individual leaves. Results indicated that effects of [CO2] on net carbon dioxide exchange rate in the dark either caused or reflected a change in a physiologically important process which is known to depend on energy supplied by respiration. Thus, it is unlikely that the observed effects of [CO2] on respiration were artefacts of the measurement process in this case.     

Fluxes of carbon dioxide and water vapor above paddy fields

Atmospheric fluxes of carbon dioxide and water vapor were measured by the eddy correlation technique over a paddy field in 1989. The carbon dioxide was transported downward during daylight hours due to photosynthesis of the paddy crop. The downward flux of carbon dioxide increased with increasing net radiation. Maximum values of downward flux varied with the growing stage of the paddy crop: ca. 0.3 mg m^–2 s^–1 at early vegetative growth stage and ca. 1.3 mg m^–2 s^–1 at ear formation stage. The daytime totals of downward flux of carbon dioxide also showed seasonal variation reflecting the photosynthetic activity of the paddy crop: ca. 6 g m^–2 at early vegetative growth stage in June and 40 g m^–2 at ear formation stage in September. The seasonal variation of daily totals of carbon dioxide flux shows that carbon dioxide of about 28 t ha^–1 is fixed by the paddy crop from transplanting to harvesting. Taking into account the water use efficiency, the paddy crop requires water in amounts at least 100 times that of carbon dioxide fixed by photosynthesis. It is noted that the correlation coefficients between carbon dioxide, water vapor and vertical wind velocity have constant values under near neutral and free convective regimes.     

Effect of carbon dioxide on yeast growth and fermentation

Inhibition of yeast function by ethanol and by high substrate concentrations is well recognized and, to a limited extent, quantified. The role of carbon dioxide in affecting yeast metabolism (particularly growth processes) is not clear although inhibition is generally found at moderate to high concentrations of the dissolved gas. A similar situation exists with other microorganisms and with other fermentation systems. An understanding of the role of carbon dioxide, and particularly of its inhibitory effects on enzyme action and membrane function, is required if the observed global inhibition of yeasts and other fermentation systems is to be partitioned to its appropriate causes.     

Fluxes of dissolved carbon dioxide and inorganic carbon from an upland peat catchment: implications for soil respiration

This study uses long-term water chemistry records for a circum-neutral peat stream to reconstruct a 7-year record of dissolved CO₂ and DIC flux from the catchment. Combining catchment flux with a knowledge of in-stream metabolism and gas evasion from the stream surface enables an estimate of the dissolved CO₂ content of water emerging from the peat profile to be made; furthermore, these can be used to estimate soil CO₂ respiration. In this way multi-annual records of CO₂ production can be reconstructed, and therefore inter-annual controls on production examined. The results suggest that:(i) Stream evasion of CO₂ within the catchment varied between 80 and 220 g C/m of stream/yr, while in-stream metabolism produces between 1.0 and 2.9 g C/m of stream/yr;Export of dissolved CO₂ emerging from the soil profile, above that expected at equilibrium with the atmosphere, varies between 9.6 and 25.6 tonnes,C/km²/yr; andThe export of dissolved CO₂ implies a soil respiration rate of between 64.2 and 94.9 tonnes C/km²/yr.The inter-annual variation in both dissolved CO₂ flux and soil CO₂ respiration suggests that severe drought has no long-term effect on CO₂ production and that temperature-based models of soil CO₂ respiration will be adequate in all but the severest of summer droughts. The inter-annual variation in CO₂ flux shows that CO₂ production is decoupled from dissolved organic carbon (DOC) production. The decoupling of DOC and dissolved CO₂ production shows that enzymatic-latch production of DOC is an anaerobic process and will not increase soil CO₂ respiration.     

Behavioural responses of rats to gradual-fill carbon dioxide euthanasia and reduced oxygen concentrations

Carbon dioxide (CO₂) is widely used for euthanasia of laboratory rats, but little is known about the pain and distress caused by this procedure. Physiological and human self-report data suggest that CO₂ may cause pain and dyspnea, a sensation of breathlessness and increased respiratory effort, at the concentrations used for gradual-fill euthanasia. However, previous studies examining the behavioural responses of rats have reported conflicting results. In this study, detailed behavioural responses of rats were examined during gradual-fill CO₂ euthanasia and during gradual-fill with argon to produce a similar reduction in oxygen concentration. Animals were randomly allocated to the CO₂ or reduced oxygen treatment groups (n = 8 for both), and were first tested with air exposure and then with treatment gas exposure on the following day. Observations were taken for 105 s before and after gas flow began (baseline and exposure periods), as animals had ceased purposeful movement within 105 s of CO₂ flow starting. Behavioural changes from baseline during gas exposure were compared to changes during air exposure on control days. In comparison to air exposure, CO₂ resulted in increased activity, rearing, touching the nose to the chamber lid, escape behaviours and vocalizations. A small increase in touching the nose to the chamber lid was observed when oxygen concentrations were reduced with argon, but no other behavioural changes were observed. These results suggest that gradual-fill CO₂ euthanasia causes distress in rats, and that hypoxia alone is not a major cause of this distress.     

Biomass production and carbon dioxide fixation by Aphanothece microscopica Nägeli in a bubble column photobioreactor

The objective of the present study was to evaluate the growth kinetics of Aphanothece microscopica Nägeli under different conditions of temperature, light intensity and CO₂ concentration. The growth kinetics of the microorganism and carbon biofixation were evaluated using a central composite design, considering five different temperature levels (21.5, 25, 30, 35 and 38.5 °C), light intensities (0.96, 3, 6, 9 and 11 klux) and carbon dioxide concentrations (3, 15, 25, 50 and 62%). The results obtained showed the effects of temperature, light intensity and CO₂ concentration (p < 0.05) on the photosynthetic metabolism of the microorganism. Response surface methodology was adequate for process optimisation, providing a carbon fixation rate to the order of 109.2 mg L⁻¹ h⁻¹ under conditions of 11 klux, 35 °C and 15% carbon dioxide, representing an increase of 58.1% as compared to the conditions tested initially.     

Expansion of mesenchymal stem cells under atmospheric carbon dioxide

Stem cells are needed for an increasing number of scientific applications, including both fundamental research and clinical disease treatment. To meet this rising demand, improved expansion methods to generate high quantities of high quality stem cells must be developed. Unfortunately, the bicarbonate buffering system – which relies upon an elevated CO₂ environment – typically used to maintain pH in stem cell cultures introduces several unnecessary limitations in bioreactor systems. In addition to artificially high dissolved CO₂ levels negatively affecting cell growth, but more importantly, the need to sparge CO₂ into the system complicates the ability to control culture parameters. This control is especially important for stem cells, whose behavior and phenotype is highly sensitive to changes in culture conditions such as dissolved oxygen and pH. As a first step, this study developed a buffer to support expansion of mesenchymal stem cells (MSC) under an atmospheric CO₂ environment in static cultures. MSC expanded under atmospheric CO₂ with this buffer achieved equivalent growth rates without adaptation compared to those grown in standard conditions and also maintained a stem cell phenotype, self‐renewal properties, and the ability to differentiate into multiple lineages after expansion. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1298–1306, 2013     

The influence of plant carbon dioxide and nutrient supply on susceptibility to insect herbivores

The carbon/nutrient ratio of plants has been hypothesized to be a significant regulator of plant susceptibility of leaf-eating insects. As rising atmospheric carbon dioxide stimulates photosynthesis, host plant carbon supply is increased and the accompanying higher levels of carbohydrates, especially starch, apparently dilute the protein content of the leaf. When host plant nitrogen supply is limited, plant responses include increased carbohydrate accumulation, reduced leaf protein content, but also increased carbon-based defensive chemicals. No change, however, has been observed in the concentration of leaf defensive allelochemicals with elevated carbon dioxide during host plant growth. Insect responses to carbon-fertilized leaves include increased consumption with little change in growth, or alternatively, little change in consumption with decreased growth, as well as enhanced leaf digestibility, reduced nitrogen use efficiency, and reduced fecundity. The effects of plant carbon and nutrient supply on herbivores appear to result, at least in part, from independent processes affecting secondary metabolism.     

Ventilatory responses to exercise and carbon dioxide in elderly and younger humans

The present investigation examined the relationship between CO₂ sensitivity [at rest (S _R) and during exercise (S _E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO₂ production ( _E/ CO₂) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S _R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min^–1 · kPa^–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min^–1 · mmHg^–1; P<0.05], but S _E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min^–1 · kPa^–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min^–1 · mmHg^–1]. There were significant correlations between both S _R and S _E, and _E/ CO₂ (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that _E/ CO₂ is not an appropriate index of the ventilatory response to exercise for elderly humans.     

Varietal differences of carbohydrates in defatted soybean flour and soy protein isolate by-products

Soy protein isolates (SPI) were prepared from 12 soybean lines grown in Harrow, Ontario and by-products (fibers and wheys) from SPI making were saved. The identification and quantification of soluble sugars in defatted flours, fibers and wheys were carried out using high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) and with a colorimetric method for uronic acids. Defatted flours and fibers were acid hydrolyzed, then analyzed by HPAEC-PAD for monosaccharide composition. The results showed varietal differences in the carbohydrate composition suggesting different applications for these defatted flours and their SPI by-products.     

Longevity and temperature response of pollen as affected by elevated growth temperature and carbon dioxide in peanut and grain sorghum

It is important to understand the effects of environmental conditions during plant growth on longevity and temperature response of pollen. Objectives of this study were to determine the influence of growth temperature and/or carbon dioxide (CO₂) concentration on pollen longevity and temperature response of peanut and grain sorghum pollen. Plants were grown at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/34 °C at ambient (350 μmol mol⁻¹) and at elevated (700 μmol mol⁻¹) CO₂ from emergence to maturity. At flowering, pollen longevity was estimated by measuring in vitro pollen germination at different time intervals after anther dehiscence. Temperature response of pollen was measured by germinating pollen on artificial growth medium at temperatures ranging from 12 to 48 °C in incubators at 4 °C intervals. Elevated growth temperature decreased pollen germination percentage in both crop species. Sorghum pollen had shorter longevity than peanut pollen. There was no influence of CO₂ on pollen longevity. Pollen longevity of sorghum at 36/26 °C was about 2 h shorter than at 32/22 °C. There was no effect of growth temperature or CO₂ on cardinal temperatures (T_min, T_opt, and T_max) of pollen in both crop species. The T_min, T_opt, and T_max identified at different growth temperatures and CO₂ levels were similar at 14.9, 30.1, and 45.6 °C, respectively for peanut pollen. The corresponding values for sorghum pollen were 17.2, 29.4, and 41.7 °C. In conclusion, pollen longevity and pollen germination percentage was decreased by growth at elevated temperature, and pollen developed at elevated temperature and/or elevated CO₂ did not have greater temperature tolerance.     

Activity and stability of immobilised soybean lipoxygenase-1 in aqueous and supercritical carbon dioxide media

The activity of immobilised soybean lipoxygenase-1 (LOX-1) was studied in aqueous and supercritical carbon dioxide (SCCO₂) media for the production of 13S-hydroperoxyoctadecadenoic acid (13S-HPODE). In SCCO₂, it was optimal at 33 °C and 25 MPa. A higher space-time yield of 5.7×10^–3 Ms^–1 mg^–1 LOX-1 for 13S-HPODE was obtained in SCCO₂ compared to only 5×10^–5 Ms^–1 mg^–1 LOX-1 in aqueous medium. The stability of immobilised LOX-1 was only significantly affected by the pressurisation and depressurisation steps during reactions in SCCO₂.