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1.
The influence of alkanolamine CO2 absorbents on the CO2 fixation in photoautotrophic culture of green alga Scenedesmus sp. was investigated using monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA) and triethanolamine (TEA). The dissolved inorganic carbon (DIC) contents increased when alkanolamine compounds existed in the medium. Utilizing the increased DIC for algal uptake, TEA exhibited a best enhancement in CO2 fixation performance compared to other absorbents, while primary ethanolamines displayed inhibition on cell growth due to the formation of relatively stable carbamate intermediate. By adding 5 mM TEA, the cell growth and CO2 fixation rate increased by 30.5% compared to the case with no TEA. TEA was supplemented when cell density was doubled, tripled and quadrupled to maintain the TEA to cells ratio constant pacing the increase of cell density. The repeated addition of TEA exhibited the enhancement of CO2 fixation rate by 39.3% and 18.5% from no-addition and one-time addition cases, respectively. 相似文献
2.
AbstractCarbonic anhydrase (CA) is the most effective CO2 hydratase catalyst, but the poor storage stability and repeatability of CA limit its development. Therefore, CA was immobilized on the epoxy magnetic composite microspheres to enhance the CO2 absorption into N-methyldiethanolamine (MDEA) aqueous solution in this work. In the presence of immobilized CA, the CO2 absorption rate of MDEA solution (10?wt%) (0.63?mmol·min?1) was greatly improved by almost 40%, and their reaction equilibrium time was shortened from 150?min to 90?min compared with that into MDEA solution. The results indicated that the absorption of CO2 into MDEA solution had been significantly enhanced by using CA. After the 7th reuse recycle, the activity of the immobilized CA was still closed to its initial value at 313.15?K. Moreover, enzyme catalytic kinetics of immobilized CA was investigated using the p-nitrophenyl acetate (p-NPA) as substrate. The values of Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of the immobilized CA were calculated to be 27.61?mmol/L and 20.14?×?10?3?mmol·min?1·mL?1, respectively. Besides, the kinetics of CO2 reaction into MDEA with or without CA were also compared. The results showed that CO2 absorption into CA/MDEA aqueous solution obeyed the pseudo first order regime and the second order kinetics rate constant (k2) was calculated to be 929?m3·kmol?1·s?1, which was twice higher than that of MDEA aqueous solution without immobilized CA (k2=414 m3·kmol?1·s?1) at 313.15?K. 相似文献
3.
Teruo Ogawa 《BBA》1982,681(1):103-109
Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO2 uptake and O2 evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O2. The minimum CO2 concentration required for the appearance of oscillations was 600 μl · l?1. The higher the CO2 concentration, the stronger the oscillations. The effect of CO2 concentration was saturated at 1000 μl CO2 · l?1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm?2 · s?1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm?2 · s?1. Oscillations could also be generated by increasing the CO2 concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C3 plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C4 plants, Zea mays and Amaranthus retroflexus L. 相似文献
4.
The unicellular green alga Chlamydomonas reinhardtii possesses a CO2-concentrating mechanism. In order to measure the CO2 permeability coefficients of the plasma membranes (PMs), carbonic anhydrase (CA) loaded vesicles were isolated from C. reinhardtii grown either in air enriched with 50 mL CO2 · L?1} (high-Ci cells) or in ambient air (350 μL CO2 · L?1}; low-Ci cells). Marker-enzyme measurements indicated less than 1% contamination with thylakoid and mitochondrial membranes, and that more than 90% of the PMs from high and low-Ci cells were orientated right-side-out. The PMs appeared to be sealed as judged from the ability of vesicles to accumulate [14C]acetate along a proton gradient for at least 10 min. Carbonic anhydrase-loaded PMs from high and low-Ci cells of C. reinhardtii were used to measure the exchange of 18O between doubly labelled CO2 (13C18O2) and H2O in stirred suspensions by mass spectrometry. Analysis of the kinetics of the 18O depletion from 13C18O2 in the external medium provides a powerful tool to study CO2 diffusion across the PM to the active site of CA which catalyses 18O exchange only inside the vesicles but not in the external medium (Silverman et al., 1976, J Biol Chem 251: 4428–4435). The activity of CA within loaded PM vesicles was sufficient to speed-up the 18O loss to H2O to 45360–128800 times the uncatalysed rate, depending on the efficiency of CA-loading and PM isolation. From the 18O-depletion kinetics performed at pH 7.3 and 7.8, CO2 permeability coefficients of 0.76 and 1.49·10?3} cm·s?1}, respectively, were calculated for high Ci cells. The corresponding values for low-Ci cells were 1.21 and 1.8·10?3} cm·s?1}. The implications of the similar and rather high CO2 permeability coefficients (low CO2 resistance) in high and low-Ci cells for the COi-concentrating mechanism of C. reinhardtii are discussed. 相似文献
5.
The reduction of spinach ferredoxin by the CO?2 radical and the hydrated electron (e?aq) has been studied by pulse radiolysis in the pH range between 5.05 and 9.67. The reduction of oxidized spinach ferredoxin by both CO?2 and e?aq was found to be essentially quantitative. The CO?2 radical reduces spinach ferredoxin by a single second-order process at a rate k5 = (6.2 ± 0.6) · 107 M?1 · s?1. Reduction by e?aq follows a biphasic pathway. The first phase obeys second-order kinetics for the reduction of the cluster, kapp = (9.4 ± 0.3) · 109 M?1 · s?1. The second phase follows an intramolecular first-order reaction kB = (8.3 ± 1.7) · 102 s?1 which is observed as a further reduction of the active site. Spectral changes accompanying the reduction of oxidized spinach ferredoxin in the ultraviolet and visible range are discussed. 相似文献
6.
CO2 flux in alpine wetland ecosystem on the Qinghai-Tibetan Plateau, China 总被引:3,自引:0,他引:3
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Using the CO2 flux data measured by the eddy covariance method in the northeast of Qinghai-Tibetan Plateau in 2005, we analyzed the carbon flux dynamics in relation to meteorological and biotic factors. The results showed that the alpine wetland ecosystem was the carbon source, and it emitted 316.02 gCO2 · m−2 to atmosphere in 2005 with 230.16 gCO2 · m−2 absorbed in the growing season from May to September and 546.18 gCO2 · m−2 released in the non-growing season from January to April and from October to December. The maximum of the averaged daily CO2 uptake rates and release rates was (0.45 ± 0.0012) mgCO2 · m−2 · s−1 (Mean ± SE) in July and (0.22 ± 0.0090) mgCO2 · m−2 · s−1 in August, respectively. The averaged diurnal variation showed a single-peaked pattern in the growing season, but exhibited very small fluctuation in the non-growing season. Net ecosystem exchange (NEE) and gross primary production (GPP) were all correlated with some meteorological factors, and they showed a negatively linear correlation with aboveground biomass, while a positive correlation existed between the ecosystem respiration (Res) and those factors. 相似文献
7.
《Free radical research》2013,47(5):255-263
Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained somc recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O2), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap. were eliminated by DHLA but not by TA. The sulhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O2-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O2x, suggesting the reduction of O2- by DHLA. Competition of O2- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O2- and DHLA, which was found to be a 3.3 × 105 M-1 s-1. On the other hand, the DMPO signal of hydroxyl radicals (HO ·) generated by Fenton's reagent were eliminated by both TA and DHLA. Inhibition of the Fenton reaction by TA was confirmed by a chemiluminescence measurement using luminol as a probe for HO ·. There was no electron transfer from Fe2+ to TA or from DHLA to Fe3 + detected by measuring the Fe2+ -phenanthroline complex. DHLA did not potentiate the DMPO signal of HO · indicating no prooxidant activity of DHLA. These results suggest that both TA and DHLA possess antioxidant properties. In particular. DHLA is very effective as shown by its dual capability by eliminating both O2-; and HO ·. 相似文献
8.
The reaction mechanisms involved in the scavenging of hydroxyl (OH·), methoxy (OCH3 ·), and nitrogen dioxide (NO2 ·) radicals by ellagic acid and its monomethyl and dimethyl derivatives were investigated using the transition state theory and density functional theory. The calculated Gibbs barrier energies associated with the abstraction of hydrogen from the hydroxyl groups of ellagic acid and its monomethyl and dimethyl derivatives by an OH· radical in aqueous media were all found to be negative. When NO2 · was the radical involved in hydrogen abstraction, the Gibbs barrier energies were much larger than those calculated when the OH· radical was involved. When OCH3 · was the hydrogen-abstracting radical, the Gibbs barrier energies lay between those obtained with OH· and NO2 · radicals. Therefore, the scavenging efficiencies of ellagic acid and its monomethyl and dimethyl derivatives towards the three radicals decrease in the order OH· >> OCH3 · > NO2 ·. Our calculated rate constants are broadly in agreement with those obtained experimentally for hydrogen abstraction reactions of ellagic acid with OH· and NO2· radicals. Figure
Reactant complex (RC), transition state (TS), and product complex (PC) for hydrogen abstraction from ellagic acid by an OH· radical 相似文献
9.
The reaction between ligninase and hydrogen peroxide yielding Compound I has been investigated using a stopped-flow rapid-scan spectrophotometer. The optical absorption spectrum of Compound I appears different to that reported by Andrawis, A. et al. (1987) and Renganathan, V. and Gold, M.H. (1986), in that the Soret-maximum is at 401 nm rather than 408 nm. The second-order rate constant (4.2·105 M−1·s−1) for the formation of Compound I was independent of pH (pH 3.0–6.0). In the absence of external electron donors, Compound I decayed to Compound II with a half-life of 5–10 s at pH 3.1. The rate of this reaction was not affected by the H2O2 concentration used. In the presence of either veratryl alcohol or ferrocyanide, Compound II was rapidly generated. With ferrocyanide, the second-order rate constant increased from 1.9·104 M−1·s−1 to 6.8·106 M−1·s−1 when the pH was lowered from 6.0 to 3.1. With veratryl alcohol as an electron donor, the second-order rate constant for the formation of Compound II increased from 7.0·103 M−1·s−1 at pH 6.0 to 1.0·105 M−1·s−1 at pH 4.5. At lower pH values the rate of Compound II formation no longer followed an exponential relationship and the steady-state spectral properties differed to those recorded in the presence of ferrocyanide. Our data support a model of enzyme catalysis in which veratryl alcohol is oxidized in one-electron steps and strengthen the view that veratryl alcohol oxidation involves a substrate-modified Compound II intermediate which is rapidly reduced to the native enzyme. 相似文献
10.
《Inorganica chimica acta》1987,133(2):347-352
When crystals of [Dy(OH2)7(OHMe)] [DyCl(OH2)2(18- crown-6)]2Cl7·2H2O [1] are allowed to warm from 5 °C to ambient temperature (22 °C) under the original solvent mixture (1:3 CH3OH: CH3CN), they redissolve and the title complex can be isolated by slow evaporation of the resulting solution. The crystal structure of this complex, [Dy(OH2)8]Cl3·18-crown-6·4H2O, has been determined. It crystallizes in the monoclinic space group, P21/c, with a = 10.395(1), b = 18.684(1), c = 16.259- (3) Å, β= 102.56(1)°, and Dcalc = 1.61 g cm−3 for Z = 4. A final conventional R value of 0.041 was obtained by least-squares refinement using 3453 independent observed [Fo⩾5σ(Fo)] reflections. The [Dy(OH2)8]3+ cations and crown ether molecules are hydrogen bonded in a polymeric chain with the crown molecules separating the cations and a total of seven DyOH2···O(crown ether) hydrogen bonds. The chains are connected by a hydrogen bonding network consisting of the cations, chloride ions, and uncoordinated water molecules. The geometry of the cation is best described as a bicapped trigonal prism with distortions on the reaction pathway toward dodecahedral symmetry. The two capping atoms average 2.41(1) Å from Dy, the remaining DyO distances average 2.38(2) Å. The 18-crown-6 molecule has the D3d conformation normally observed except for a distortion of one OCCO unit containing the oxygen atom accepting two hydrogen bonds. 相似文献
11.
In the present work, in order to investigate the electronic excited-state intermolecular hydrogen bonding between the chromophore coumarin 153 (C153) and the room-temperature ionic liquid N,N-dimethylethanolammonium formate (DAF), both the geometric structures and the infrared spectra of the hydrogen-bonded complex C153–DAF+ in the excited state were studied by a time-dependent density functional theory (TDDFT) method. We theoretically demonstrated that the intermolecular hydrogen bond C1?=?O1···H1–O3 in the hydrogen-bonded C153–DAF+ complex is significantly strengthened in the S1 state by monitoring the spectral shifts of the C=O group and O–H group involved in the hydrogen bond C1?=?O1···H1–O3. Moreover, the length of the hydrogen bond C1?=?O1···H1–O3 between the oxygen atom and hydrogen atom decreased from 1.693 Å to 1.633 Å upon photoexcitation. This was also confirmed by the increase in the hydrogen-bond binding energy from 69.92 kJ mol?1 in the ground state to 90.17 kJ mol?1 in the excited state. Thus, the excited-state hydrogen-bond strengthening of the coumarin chromophore in an ionic liquid has been demonstrated theoretically for the first time. 相似文献
12.
高寒矮嵩草草甸冬季CO2释放特征 总被引:1,自引:0,他引:1
冬季碳排放在高寒草地年内碳平衡中占有重要位置。为探讨高寒草地冬季碳排放特征及温度敏感性,于2003-2005年在中国科学院海北高寒草甸生态系统研究站,利用密闭箱-气相色谱法连续观测了高寒矮嵩草草甸2个冬季的生态系统、土壤呼吸通量特征。结果表明:1)高寒矮嵩草草甸冬季生态系统呼吸、土壤呼吸均具有明显的日变化和季节变化规律,温度是其主要的控制因子,能够解释44%以上的呼吸速率变异。2)冬季生态系统呼吸与土壤呼吸速率在统计上没有显著差异,土壤呼吸占生态系统呼吸的比例高达85%以上。3)2003-2004年冬季生态系统呼吸、土壤呼吸的Q10值分别为1.53,1.38;2004-2005年冬季生态系统呼吸与土壤呼吸的Q10值为1.86,1.68,2个冬季生态系统呼吸的Q10值均高于土壤呼吸。4)未发现高寒矮嵩草草甸冷冬年份的Q10值高于暖冬年份以及冬季的Q10值高于生长季。 相似文献
13.
13C‐nmr chemical shift tensor components are reported for a 13C‐labeled Gly1 amide carbonyl carbon of a glycylglycine (Gly1Gly2) single crystal, a GlyGly · HNO3 single crystal and a GlyGly · HCl · H2O single crystal, for which the three‐dimensional crystal structures have already been determined by x‐ray diffraction. The tensor components were measured by changing the angle between the crystal plane and the applied magnetic field by using a goniometer designed in this work for use in conventional 13C cross‐polarization/magic angle spinning nmr probe. From these experimental data, the principal values of the 13C chemical shift tensor and its directions for the Gly1 amide carbonyl carbon were determined. It was found that the 13C chemical shift tensor components (δ11, δ22, and δ33) for the Gly1 amide carbonyl carbon in GlyGly and GlyGly · HNO3 with a >NH · · · OC< type of hydrogen bond depend on the hydrogen‐bond length and the directions of the δ22 components of these peptides are along the hydrogen‐bonded >CO bond axis. In addition, the magnitude of the deviation from the bond axis depends on the hydrogen‐bond angle. Further, the experimental result for GlyGly · HCl · H2O with a O H · · ·OC< type of hydrogen bond was discussed. © 1999 John Wiley & Sons, Inc. Biopoly 50: 61–69, 1999 相似文献
14.
1. Dihydroxyacetone phosphate in concentrations ? 2.5 mM completely inhibits CO2-dependent O2 evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of Pi, but not by addition of 3-phosphoglycerate. In the absence of Pi, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the 14C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70–95%. Based on these results the mechanism of the inhibition of O2 evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts.2. Although O2 evolution is completely suppressed by dihydroxyacetone phosphate, CO2 fixation takes place in air with rates of up to 65μ mol · mg?1 chlorophyll · h?1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation.3. Under anaerobic conditions, the rates of CO2 fixation in presence of dihydroxyacetone phosphate are low (2.5–7 μmol · mg?1 chlorophyll · h?1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2 · 10?7 M) reaching values of up to 60 μmol · mg?1 chlorophyll · h?1. As under these conditions the ATP necessary for CO2 fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO2 fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded that only under anaerobic conditions an “overreduction” of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5 · 10?7 M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO2 fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO2 fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation.4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO2 fixation in presence of dihydroxyacetone phosphate by dibromothymoquinone under anaerobic conditions indicates that plastoquinone is an indispensible component of the endogenous cyclic electron pathway. 相似文献
15.
《Journal of experimental marine biology and ecology》1986,97(1):81-93
The benthic oxygen consumption and carbon dioxide production of undisturbed and sieved sediment cores with various values for the biomass of polychaetes collected from the intertidal mud-flat of Nanakita River estuary of Japan were measured simultaneously. The benthic oxygen consumption and carbon dioxide production increased in proportion to the biomass of a dominant polychaete species Neanthes japonica (Izuka). This increase was not explained by the respiration of the animals alone. The residual increase in benthic O2 and CO2 fluxes may be due to mineralization processes in the burrow wall and enhanced diffusion caused by the pumping activity of the worms. From the average biomass of polychaetes at the study site, total benthic O2 and CO2 fluxes were estimated to be 5.2 mmol·m−2·h−1 and 7.3 mmol·m−2·h−1, respectively, at 20 ° C. The worms were responsible for 79% of the total O2 flux and 73% of the total CO2 flux but the respiration of the worms accounted for only 53% of the total O2 flux and 36% of the total CO2 flux. The residual enhanced fluxes were 26% and 37% for the total O2 and CO2 fluxes, respectively. 相似文献
16.
Nicolas Soumis Marc Lucotte Catherine Larose François Veillette René Canuel 《Biogeochemistry》2007,86(2):123-135
In order to evaluate the role of photochemistry in the carbon dioxide (CO2) generation from a 10-year-old boreal reservoir, the photomineralization of dissolved organic matter (DOM) was assessed and
compared to a boreal river as well as to boreal and temperate lakes during July and August, 2003. Sterile water samples were
irradiated by sunlight over the whole photoperiod and subsequently analyzed for CO2. Mean energy-normalized apparent photochemical yield of CO2 (an index of DOM photoreactivity normalized for the energy absorbed by samples) was significantly higher in the reservoir
(27.7 ± 13.0 mg CO2·m−3·kJ−1) and the boreal river (35.8 ± 2.3 mg CO2·m−3·kJ−1) than in the boreal lakes (15.5 ± 5.1 mg CO2·m−3·kJ−1). The DOM photoreactivity of the temperate lakes (20.9 ± 8.1 mg CO2·m−3·kJ−1) was not statistically different from any type of boreal water bodies. There was no significant difference in either the
integrated photoproduction of CO2 (273–433 mg CO2·m−2·d−1) or the potential photochemical contribution to CO2 diffusive fluxes (56–92%) among these water bodies. DOM photoreactivity was significantly affected by the cumulative hydrological
residence time (CHRT) when considering the whole data set. However, when considering only the boreal water bodies, iron (Fe)
and manganese (Mn) also intervened. The fact that DOM photoreactivity was related to CHRT as well as to Fe and Mn concentrations,
which are respectively permanent and long-lasting features of the reservoir, suggests that the photoproduction of CO2 is not likely to decrease over time. This process may therefore play a substantial role in the long-term CO2 emissions from boreal reservoirs during the summer, its potential contribution to CO2 diffusive fluxes being estimated at 56 ± 29 %. 相似文献
17.
The onset of photosynthetic acclimation to elevated CO2 partial pressure in field-grown Pinus radiata D. Don. after 4 years 总被引:4,自引:2,他引:2
K. L. Griffin D. T. Tissue M. H. Turnbull & D. Whitehead 《Plant, cell & environment》2000,23(10):1089-1098
The effects of CO2 enrichment on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1‐year‐old needles of the same branch of field‐grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open‐top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO2 partial pressures. Photosynthetic rates of the 1‐year‐old needles made at the growth CO2 partial pressure averaged 10·5 ± 0·5 μmol m?2 s?1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m?2 s?1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1‐year‐old needles was reduced by 25% from 23·0 ± 1·8 μmol m?2 s?1 in the 36 Pa CO2 grown trees to 17·3 ± 0·7 μmol m?2 s?1 in the 65 Pa grown trees. Growth in elevated CO2 also resulted in a 25% reduction in Vcmax (maximum carboxylation rate), a 23% reduction in Jmax (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non‐structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1‐year‐old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1‐year‐old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m?2. The current‐year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO2. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field‐grown trees and may be regulated by source‐sink balance, sugar feedback mechanisms and nitrogen allocation. 相似文献
18.
Mingkun Zhang Mingjie Tang Changcheng Shi Hong-liang Cui Chunlei Du 《Molecular simulation》2016,42(5):398-404
Terahertz absorption spectra of alanine polypeptides in water were simulated with classical molecular dynamics at 310 K. Vibrational modes and oscillator strengths were calculated based on a quasi-harmonic approximation. Absorption spectra of Alan (n = 5, 15, 30) with different chain lengths and Ala15 in coiled and helical conformations were studied in 10–40 cm? 1 bandwidth. Simulation results indicated both the chain length and the conformation have significant influences on THz spectra of alanine polypeptides. With the increase of chain length, the average THz absorption intensity increases. Compared with the helical Ala15 polypeptide, the THz spectra of coiled one shows stronger absorption peaks. These results were explained from different numbers of hydrogen bonds formed between polypeptides and the surrounding water molecules. 相似文献
19.
Satoru Taguchi 《Journal of experimental marine biology and ecology》1980,43(1):87-98
Maximum quantum yield (φmB) and maximum photosynthetic rate (PmB) of light-saturation curves of phytoplankton photosynthesis were determined for nannoplankton (< 20 μm) and netplankton (>20 μm) from the subsurface chlorophyll-maximum layer at 14 stations in the tropical North Pacific Ocean in the spring of 1976. The maximum quantum yield was significantly higher for nannoplankton (0.056 ± 0.006 moles CO2·Einstein?1 absorbed) than netplankton (0.039 ± 0.002 moles CO2·Einstein?1 absorbed). The importance of nannoplankton in the maximum photosynthetic rate (PmB) appears to be less consistent. At least 60% of the theoretical maximum quantum yield (0.12 moles CO2·Einstein?1 absorbed) was probably incorporated into the particulate fraction at the subsurface chlorophyll-maximum layer. 相似文献
20.
de Oliveira BG Araújo RC Chagas FF Carvalho AB Ramos MN 《Journal of molecular modeling》2008,14(10):949-955
The geometries of three isomers of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis
of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation
of infrared stretching modes, and Bader’s atoms in molecules (AIM) theory calculations was carried out in order to characterize
the hydrogen bonds in each isomer of the C2H4O···2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C2H4O and HF, (O···H), as well as in the hydrofluoric acid dimer, (HFD–R···HFD). However, the existence of a tertiary interaction (Fλ···Hα) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C2H4O was decisive in the identification of the preferred configuration of the C2H4O···2HF system.
Figure Geometries of three isomers of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex 相似文献