Enhancement of dissolved inorganic carbon and carbon fixation by green alga Scenedesmus sp. in the presence of alkanolamine CO2 absorbents

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.     

Absorption characteristics and kinetics of CO2 capture into N-methyldiethanolamine aqueous solution catalyzed by the immobilized carbonic anhydrase

Abstract

Carbonic 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 (K_m) and the maximum velocity (V_max) 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.     

Simple oscillations in photosynthesis of higher plants

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.     

The CO2 permeability of the plasma membrane of Chlamydomonas reinhardtii: mass-spectrometric 18O-exchange measurements from 13C18O2 in suspensions of carbonic anhydrase-loaded plasma-membrane vesicles

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-C_i cells) or in ambient air (350 μL CO₂ · L?1}; low-C_i 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-C_i 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-C_i 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 C_i cells. The corresponding values for low-C_i 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-C_i cells for the CO_i-concentrating mechanism of C. reinhardtii are discussed.     

Kinetics of some electron-transfer reactions in biological photosystems. I. Pulse radiolysis study of spinach ferredoxin reduction by the hydrated electron and CO−2 radical

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, k_app = (9.4 ± 0.3) · 10⁹ M^?1 · s^?1. The second phase follows an intramolecular first-order reaction k_B = (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.     

CO2 flux in alpine wetland ecosystem on the Qinghai-Tibetan Plateau, China

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 (R_es) and those factors.     

Thioctic Acid and Dihydrolipoic Acid are Novel Antioxidants Which Interact With Reactive Oxygen Species

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 Fe^{3 +} 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 ·.     

Modeling the scavenging activity of ellagic acid and its methyl derivatives towards hydroxyl, methoxy, and nitrogen dioxide radicals

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.

Pre-steady-state kinetic study on the formation of Compound I and II of ligninase

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.     

f-Element/crown ether complexes. 16. Synthesis,crystallization and crystal structure of [Dy(OH2)8]Cl3·18-crown-6·4H2O

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 D_calc = 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 [F_o⩾5σ(F_o)] 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 DyOH₂···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 DyO distances average 2.38(2) Å. The 18-crown-6 molecule has the D_3d conformation normally observed except for a distortion of one OCCO unit containing the oxygen atom accepting two hydrogen bonds.     

Time-dependent density functional theory study on the electronic excited-state hydrogen bonding of the chromophore coumarin 153 in a room-temperature ionic liquid

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.     

高寒矮嵩草草甸冬季CO2释放特征

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。     

13C‐NMR chemical shift tensor and hydrogen‐bonded structure of glycine‐containing peptides in a single crystal

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 · · · OC< 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 >CO 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 · · ·OC< type of hydrogen bond was discussed. © 1999 John Wiley & Sons, Inc. Biopoly 50: 61–69, 1999     

Rates and properties of endogenous cyclic photophosphorylation of isolated intact chloroplasts measured by CO2 fixation in the presence of dihydroxyacetone phosphate

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 P_i, but not by addition of 3-phosphoglycerate. In the absence of P_i, 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.     

Contribution of the polychaete,Neanthes japonica (Izuka), to the oxygen uptake and carbon dioxide production of an intertidal mud-flat of the Nanakita River estuary,Japan

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.     

Photomineralization in a boreal hydroelectric reservoir: a comparison with natural aquatic ecosystems

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 %.     

The onset of photosynthetic acclimation to elevated CO2 partial pressure in field-grown Pinus radiata D. Don. after 4 years

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 V_cmax (maximum carboxylation rate), a 23% reduction in J_max (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.     

Molecular dynamics simulations of conformation and chain length dependent terahertz spectra of alanine polypeptides

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 Ala_n (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.     

Phytoplankton photosynthesis in the subsurface chlorophyll-maximum layer of the tropical North Pacific Ocean

Maximum quantum yield (φ_m^B) and maximum photosynthetic rate (P_m^B) 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 $\text{(φ}{}_{\mathrm{m}}{}^{\mathrm{B}}\text{±}\text{s.e.}\text{)}$ 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 (P_m^B) 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.     

The electronic structure of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex: a theoretical study

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, (HF^D–R···HF^D). However, the existence of a tertiary interaction (F^λ···H^α) 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