共查询到20条相似文献,搜索用时 15 毫秒
1.
Atomic Na, K and Cs were codeposited with CO 2 in excess of matrix gas at the temperature of 12 K. The IR spectra revealed the presence of ionic aggregates corresponding to the molecules M(CO) 2 and M 2(CO 2) (M=Na, K, Cs). Both molecular species have C2v symmetry; M(CO 2) species have a planar ring structure while M 2(CO 2) have a W-shape structure. M 2(CO 2) molecules with Cs symmetry were also identified. The geometrical parameters of all the molecules were determined by 12C/ 13C and 16O/ 18O isotopic shifts. Raman spectra were also recorded and the results are reported in this study. The effect of photolysis on the structure of these molecules was examined. It was determined that photolysis promotes the formation of Na(CO 2) and transforms the M 2(CO 2) molecules with C2v symmetry into Cs symmetry isomers. 相似文献
2.
Reactions between the activated cluster [Os 3(CO) 10(NCMe) 2] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os 3H(CO) 10} 2(CO 2CH 2CO 2)] ( 1), [{Os 3H(CO) 10} 2(CO 2C 2H 4CO 2)] ( 2), and [{Os 3H(CO) 10} 2(C 4O 4)] ( 3) in good yield. Cluster 3 was subsequently treated with [Co 2(CO) 8] and this results in the addition of a “Co 2(CO) 6” group giving [{Os 3H(CO) 10} 2(C 2O 4){Co 2(CO) 6}] ( 4). The X-ray crystal structures are reported for 2– 4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms. 相似文献
3.
The new two-breath CO(2) method was employed to test the hypotheses that small alterations in arterial P(CO(2)) had an impact on the magnitude and dynamic response time of the CO(2) effect on cerebrovascular resistance (CVRi) and the dynamic autoregulatory response to fluctuations in arterial pressure. During a 10-min protocol, eight subjects inspired two breaths from a bag with elevated P(CO(2)), four different times, while end-tidal P(CO(2)) was maintained at three levels: hypocapnia (LoCO(2), 8 mmHg below resting values), normocapnia, and hypercapnia (HiCO(2), 8 mmHg above resting values). Continuous measurements were made of mean blood pressure corrected to the level of the middle cerebral artery (BP(MCA)), P(CO(2)) (estimated from expired CO(2)), and mean flow velocity (MFV, of the middle cerebral artery by Doppler ultrasound), with CVRi = BP(MCA)/MFV. Data were processed by a system identification technique (autoregressive moving average analysis) with gain and dynamic response time of adaptation estimated from the theoretical step responses. Consistent with our hypotheses, the magnitude of the P(CO(2))-CVRi response was reduced from LoCO(2) to HiCO(2) [from -0.04 (SD 0.02) to -0.01 (SD 0.01) (mmHg x cm(-1) x s) x mmHg Pco(2)(-1)] and the time to reach 95% of the step plateau increased from 12.0 +/- 4.9 to 20.5 +/- 10.6 s. Dynamic autoregulation was impaired with elevated P(CO(2)), as indicated by a reduction in gain from LoCO(2) to HiCO(2) [from 0.021 +/- 0.012 to 0.007 +/- 0.004 (mmHg x cm(-1) x s) x mmHg BP(MCA)(-1)], and time to reach 95% increased from 3.7 +/- 2.8 to 20.0 +/- 9.6 s. The two-breath technique detected dependence of the cerebrovascular CO(2) response on P(CO(2)) and changes in dynamic autoregulation with only small deviations in estimated arterial P(CO(2)). 相似文献
4.
A system has been developed for the study of photosynthetic CO 2 fixation by isolated spinach chloroplasts at air levels of CO 2. Rates of CO 2 fixation were typically 20 to 60 micromoles/milligrams chlorophyll per hour. The rate of fixation was linear for 10 minutes but then declined to less than 10% of the initial value by 40 minutes. Ribulose 1,5-bisphosphate (RuBP) levels remained unchanged during this period, indicating that they were not the cause for the decline. The initial activity of the RuBP carboxylase in the chloroplast was high for 8 to 10 minutes and then declined similar to the rate of CO 2 fixation, suggesting that the decline in CO 2 fixation may have been caused by deactivation of the enzyme. 相似文献
5.
A simple, inexpensive apparatus for making mixtures of accurately known amounts of CO 2 and CO 2-free atmospheric air is described. Calibration gases with CO 2 contents of 200 to 1500 microliters per liter produced with the apparatus had concentrations which were within 10 microliters per liter of the target concentration. 相似文献
6.
Yield increases observed among eight genotypes of tomato ( Lycopersicon esculentum Mill.) grown at ambient CO 2 (about 350) or 1000 microliters per liter CO 2 were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO 2 enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO 2. Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH 2PO 4. Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO 2-enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit. 相似文献
7.
Measurement of the internal CO(2) concentration (Ci) in tobacco leaves using a fast-response CO(2) exchange system showed that in the light, switching from 350 microLL(-1) to a low CO(2) concentration of 36.5 microLL(-1) (promoting high photorespiration) resulted in the Ci oscillating near the value of CO(2) compensation point (Gamma*). The oscillations are highly irregular, the range of Ci varying by 2-4 microLL(-1) in substomatal cavities with a period of a few seconds. The statistical properties of the time series became stationary after a transient of approximately 100s following transfer to low CO(2). Attractor reconstruction shows that the observed oscillations are not chaotic but exhibit stochastic behavior. The period of oscillations is consistent with the duration of photorespiratory post-illumination burst (PIB). We suggest that the observed oscillations may be due to a similar mechanism to that which leads to PIB, and may play a role in switching mitochondrial operation between oxidation of the photorespiratory glycine and of the tricarboxylic acid cycle substrates. 相似文献
8.
The photochemical oxidation reaction of W(CO) 6 to [W(CO) 4Cl 2] 2 with CCl 4 was applied in the synthesis of [WCl 2(CO) 3(PPh 3) 2] and [WCl 2(CO) 2−- (dppe)]. 相似文献
9.
Some physiological characteristics of a mutant (E 1) of Anacystis nidulans R 2, incapable of growing at air level of CO 2, are described. E 1 is capable of accumulating inorganic carbon (C i) internally as efficiently as the wild type (R 2). The apparent photosynthetic affinity for C i in E 1, however, is some 1000 times lower than that of R 2. The kinetic parameters of ribulose 1,5-bisphosphate carboxylase/oxygenase from E 1 are similar to those observed in R 2. The mutant appears to be defective in its ability to utilize the intracellular C i pool for photosynthesis and depends on extracellular supply of Ci in the form of CO 2. The very high apparent photosynthetic Km (CO 2) of the mutant indicate a large diffusion resistance for CO 2. Data obtained here are used to calculate the permeability coefficient for CO 2 between the bulk medium and the carboxylation site of cyanobacteria. 相似文献
10.
A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O 2 evolution or CO 2 uptake was observed, O 2 evolution was normal but completely compensated by O 2 uptake. Similarly, when CO 2 uptake was totally or partially inhibited, O 2 evolution proceeded at a high (near maximal) rate. Under all conditions, O 2 uptake balanced that fraction of the O 2 evolution which could not be accounted for by CO 2 uptake. 相似文献
12.
Nonautotrophic CO 2 metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of 14CO 2 and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the 14C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The 14CO 2 assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species. The rates of O2 and CO2 exchange and estimated CO2 fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found. The products of 14CO2 fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity. A rapid turnover of the fixed 14CO2 was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10−3 min−1 with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids. 相似文献
13.
The mechanical extensibilities of stage IVb Phycomyces were measured before and after a humidified wind stimulus. We find that when the humidity of the wind is greater than that of the ambient air, there is an increase in the mechanical extensibility of the cell wall. We also find that a step decrease in wind humidity results in a decrease in the mechanical extensibility of the cell wall. 相似文献
15.
The mutant E 1 of Anacystis nidulans R 2 requires high CO 2 concentration for growth but was able to adapt to low CO 2 concentration. This was exhibited by the increased ability to accumulate inorganic carbon within the cells and the large increase in the amount of a 42-kilodalton polypeptide located in the cytoplasmic membrane. The adaptation occurred in E 1 cells at an extracellular CO 2 concentration as high as 0.3%, which was 8 times the concentration for maximal adaptation in R 2 cells. The ability of E 1 cells to exhibit low CO 2 characteristics at a higher CO 2 concentration was attributed to lower intracellular CO 2 concentration. 相似文献
16.
A field application of the radiocarbon ((14)C) method was developed to determine the ratio of biogenic vs. fossil CO(2) emissions from waste-to-energy plants (WTE). This methodology can be used to assign the Kyoto relevant share of fossil CO(2) emissions, which is highly relevant for emission budgets and emission trading. Furthermore, heat and electricity produced by waste incinerators might be labelled depending on the fossil or biogenic nature of the primary energy source. The method development includes representative on-site CO(2) absorption and subsequent release in the laboratory. Furthermore, a reference value for the (14)C content of pure biogenic waste (f(M,bio)) was determined as 1.130+/-0.038. Gas samples for (14)CO(2) analysis were taken at three WTEs during one month each. Results were compared to an alternative approach based on mass and energy balances. Both methods were in excellent agreement and indicated a fraction of biogenic CO(2) slightly above 50%. 相似文献
17.
In order to measure CO 2 exchange reactions by leaves using isotopes of CO 2, it is necessary to know precisely the discrimination against 14CO 2 by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO 2 in light, and so provide suitable material for this measurement. Discrimination against 14CO 2 in photosynthesis by maize leaves is almost precisely the same as in CO 2 absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of 12CO 2 and 14CO 2, calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against 14CO 2 in photosynthesis. 相似文献
18.
The quantum yields of C 3 and C 4 plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O 2 and in 2% O 2. At 30 C, the quantum yields of C 3 plants averaged 0.0524 ± 0.0014 mol CO 2/absorbed einstein and 0.0733 ± 0.0008 mol CO 2/absorbed einstein under 21 and 2% O 2. At 30 C, the quantum yields of C 4 plants averaged 0.0534 ± 0.0009 mol CO 2/absorbed einstein and 0.0538 ± 0.0011 mol CO 2/absorbed einstein under 21 and 2% O 2. At 21% O 2, the quantum yield of a C 3 plant is shown to be strongly dependent on both the intercellular CO 2 concentration and leaf temperature. The quantum yield of a C 4 plant, which is independent of the intercellular CO 2 concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C 3 plants are due to changes in the O 2 inhibition. The evolutionary significance of the CO 2 dependence of the quantum yield in C 3 plants and the ecological significance of the temperature effects on the quantum yields of C 3 and C 4 plants are discussed. 相似文献
19.
The postillumination transient of CO 2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco ( Nicotiana tabacum) and maize ( Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O 2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO 2 exchange equivalents ( i.e. nanomoles CO 2) versus time were derived from the analyzer responses of individual transients. In tobacco (C 3), subtraction of the time course of cumulative CO 2 exchange under photorespiratory conditions (21 or 43% O 2) from that obtained under nonphotorespiratory conditions (1% O 2) revealed the presence of an O 2-dependent and CO 2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C 4) and at low external O 2:CO 2 ratios ( i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O 2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO 2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration. 相似文献
|