Cyclic electron flow around photosystem I is essential for photosynthesis

Photosynthesis provides at least two routes through which light energy can be used to generate a proton gradient across the thylakoid membrane of chloroplasts, which is subsequently used to synthesize ATP. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP+ by way of photosystem I (PSI). This linear electron flow is driven by two photochemical reactions that function in series. The cytochrome b6f complex mediates electron transport between the two photosystems and generates the proton gradient (DeltapH). In the second route, driven solely by PSI, electrons can be recycled from either reduced ferredoxin or NADPH to plastoquinone, and subsequently to the cytochrome b6f complex. Such cyclic flow generates DeltapH and thus ATP without the accumulation of reduced species. Whereas linear flow from water to NADP+ is commonly used to explain the function of the light-dependent reactions of photosynthesis, the role of cyclic flow is less clear. In higher plants cyclic flow consists of two partially redundant pathways. Here we have constructed mutants in Arabidopsis thaliana in which both PSI cyclic pathways are impaired, and present evidence that cyclic flow is essential for efficient photosynthesis.     

Changes in the transthylakoid proton gradient are caused by the movement of phycobilisomes in the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> sp. strain PCC 6803

Phycobilisomes (PBSs) are the main accessory light-harvesting complexes in cyanobacteria and their movement between photosystems (PSs) affects cyclic and respiratory electron transport. However, it remains unclear whether the movement of PBSs between PSs also affects the transthylakoid proton gradient (ΔpH). We investigated the effect of PBS movement on ΔpH levels in a unicellular cyanobacterium Synechocystis sp. strain PCC 6803, using glycinebetaine to immobilize and couple PBSs to photosystem II (PSII) or photosystem I (PSI) by applying under far-red or green light, respectively. The immobilization of PBSs at PSII inhibited decreases in ΔpH, as reflected by the slow phase of millisecond-delayed light emission (ms-DLE) that occurs during the movement of PBSs from PSII to PSI. By contrast, the immobilization of PBSs at PSI inhibited the increase in ΔpH that occurs when PBSs move from PSI to PSII. Comparison of the changes in ΔpH and electron transport caused by the movement of PBSs between PSs indicated that the changes in ΔpH were most likely caused by respiratory electron transport. This will further improve our understanding of the physiological role of PBS movement in cyanobacteria.     

Phase analysis and thermal conductivity of in situ O′-sialon/β-Si3N4 composites

Typical O??-sialon-based ceramics, with a formula of Si_2?x Al _x O_1+x N_2?x , where x was set as 0.25, were fabricated by in-situ synthesis. Si₃N₄, Al₂O₃, and SiO₂ powders were used as raw materials, and MgO and Y₂O₃ were added as sintering additives. All the samples were sintered at different temperatures under a nitrogen pressure of 0.25?C0.30 MPa, and their microstructure, phase content, and thermal conductivity were evaluated. The effects of O??-sialon and ??-Si₃N₄ on the thermal conductivity were analyzed by numerical calculation in detail. In the case of the similar porosity, the thermal conductivity of O??-sialon-based ceramics decreased with the ratio of O??-sialon/??-Si₃N₄ increasing. When the ratio was 12, the thermal conductivity of O??-sialon ceramics sintered at 1360°C was 1.197 W·m^?1·K^?1.     

An atypical haem in the cytochrome b(6)f complex

Photosystems I and II (PSI and II) are reaction centres that capture light energy in order to drive oxygenic photosynthesis; however, they can only do so by interacting with the multisubunit cytochrome b(6)f complex. This complex receives electrons from PSII and passes them to PSI, pumping protons across the membrane and powering the Q-cycle. Unlike the mitochondrial and bacterial homologue cytochrome bc(1), cytochrome b(6)f can switch to a cyclic mode of electron transfer around PSI using an unknown pathway. Here we present the X-ray structure at 3.1 A of cytochrome b(6)f from the alga Chlamydomonas reinhardtii. The structure bears similarities to cytochrome bc(1) but also exhibits some unique features, such as binding chlorophyll, beta-carotene and an unexpected haem sharing a quinone site. This haem is atypical as it is covalently bound by one thioether linkage and has no axial amino acid ligand. This haem may be the missing link in oxygenic photosynthesis.     

The impact of nanoporous SiN x interlayer growth position on high-quality GaN epitaxial films

The impact of nanoporous SiN x interlayer growth position on high-quality GaN epitaxial film was elucidated from the behavior of dislocations. The best quality GaN film was achieved when a nanoporous SiN x interlayer was grown on a rough layer, with the high-resolution X-ray diffraction rocking curve full width at half maximum for ( 1102 ) reflection decreasing to 223 arcs, and the total dislocation density reduced to less than 1.0×10 8 cm 2 . GaN films were grown on sapphire substrates by metal organic chemical vapor deposition. The quality of these films was investigated with high-resolution X-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. A preference for the formation of half-loops to reduce threading dislocations was observed when an SiN x interlayer was grown on a rough layer. A growth mechanism is proposed to explain this preference.     

光声光谱技术在光合作用研究中的应用

当光照射密闭容器里的样品时,容器内能产生声波,这一现象称为光声效应,光声光谱是基于光声效应的一种光谱技术。由于光声光谱技术本身的特点,光合作用研究领域越来越多地应用该技术研究光合作用的机理,比如：光谱扫描、光声能量储存的性质、环式电子传递、状态转变与爱默生效应、光反应中心的原初光化学过程、光声瞬态研究、环境胁迫等。光声光谱技术在光合作用研究中的应用,开拓了视野,丰富了对光合作用机理的认识。     

Development of a propulsion system for a biomimetic thruster

We studied theoretically and experimentally a biomimetic propulsion system inspired by the motility mechanisms of bacteria such as E. coli. Our goal was to investigate the effect of the ??complex?? filament of Rhizobium Meliloti bacteria on thrust force. The complex filament is a helically perturbed filament, similar to a plain filament threaded through a small helix. The propulsive performance of this system was estimated by modeling the dynamics of helical wave motion in viscous fluid. The model consists of a helical filament which is axially rotated at angular velocity ??. Resistive force theory (RFT) was applied to this model to calculate the thrust force and required torque. The Buckingham PI theorem (non-dimensional analysis) was also used to analyze the theoretical results. The procedure for making a complex filament with various pitch angles ?? _s from a small helix and plain filament is explained in detail. To validate the theoretical results for helical wave propulsion and compare the characteristics of complex and plain filaments together, an experiment was performed to measure the thrust forces in silicone oil. The experimental results agreed with the theoretical values predicted by RFT. The thrust forces of complex filaments depended on the shape of small helix winding. The maximum thrust force was achieved at a small helix pitch angle of ?? _s = 45°. In addition, we found that the thrust force generated by a complex filament had a value about 10% higher than that of a plain filament with the same equivalent diameter d _e .     

Theoretical study on stereodynamics of H + NeH+ (v = 0, j = 0) → H2 + + Ne reaction

Stereodynamics of reaction H + NeH+(v = 0,j = 0) → H2+ + Ne is investigated by quasi-classical trajectory method using a new potential energy surface constructed by Lv et al.The distributions of P(r),P(r) and PDDCSs are calculated at four different collision energies.The rotational polarization of product H2+ presents different characters at different collision energies.The product rotational angular momentum vector j’ is not only aligned,but also oriented along the direction perpendicular to the scattering plane.With the increase of collision energy,the rotation of product molecule has a preference of changing from the "in-plane" mechanism to the "out-of-plane" mechanism.Although the title reaction is mainly dominated by the direct reaction mechanism,the indirect mechanism plays a role when the collision energies are low.     

铯对小麦叶片光合特性影响的研究

随着环境中铯(Cs)污染日益恶化,铯对生物毒害作用的研究受到越来越多的关注.为了探讨铯对植物光合作用的影响,在石英砂和Hoagland营养液培养体系下,从三叶期开始用浓度为0、0.5、1、5、10、20 mmol·L-1的133Cs+[CsCl]处理小麦(Triticum aestivum L.)幼苗.在处理后的第0、7、14、21、28 d时,检测小麦光合特性的改变.结果表明:用0.5 mmol·L-1和1 mmol·L-1低浓度133Cs+处理7 d后,小麦叶片的叶绿素含量、叶圆片放氧活性、类囊体膜电子传递活性均显著高于对照;但随133Cs+浓度的增加及处理时间的延长,这些参数的数值均显著下降.此外,光合系统II(PSII)活性的下降速率高于光合系统I(PSI)下降速率,说明PSII相对于PSI更容易受到133Cs+的胁迫伤害.这些结果表明133Cs+对小麦的毒害效应受时间和浓度的双重制约.低浓度133Cs+可以促进小麦光合作用,而高浓度133Cs+则显著抑制小麦光合作用.     

Potential red-emitting phosphor GdNbO4:Eu3+,Bi3+ for near-UV white light emitting diodes

A red-emitting phosphor GdNbO₄:Eu³⁺,Bi³⁺ was prepared by a high temperature solid-state reaction technique. The phosphor was characterized by X-ray diffraction (XRD), particle size analyzer and fluorescence spectrometer. The single phase of GdNbO₄:Eu³⁺,Bi³⁺ was obtained at 1150°C and the average particle diameter was about 2.30 ??m. Excitation and emission spectra reveal that the phosphor can be efficiently excited by ultraviolet (UV) light (394 nm) and emit the strong red light of 612 nm due to the Eu³⁺ transition of ⁵D₀??⁷F₂. The optimum content of Eu³⁺ doped in the phosphor GdNbO₄:Eu³⁺ is 20mol%. The phosphor Gd_0.80NbO₄:0.20Eu³⁺,0.03Bi³⁺ shows much stronger photoluminescence intensity and better chromaticity coordinates (x=0.642, 0.352) than GdNbO₄:Eu³⁺. It is confirmed that Gd_0.80NbO₄:0.20Eu³⁺,0.03Bi³⁺ is a potential candidate for near-UV chip-based white light emitting diodes.     

Synthesis of Mg2B2O5 whiskers via coprecipitation and sintering process

Mg₂B₂O₅ whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl₂·6H₂O, H₃BO₃, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microcopy (SEM). It is found that the products synthesized at 832°C are monoclinic Mg₂B₂O₅ whiskers with a diameter of 200?C400 nm and a length of 50?C80 ??m. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analyses show that the whiskers obtained at 832°C are single crystalline and grow along with the [010] direction. The growth mechanism of Mg₂B₂O₅ whiskers was also presented.     

Addition of IrO2 to RuO2+TiO2 coated anodes and its effect on electrochemical performance of anodes in acid media

Ternary mixed metal oxide coatings with the nominal composition IrxRu(0.6-x)Ti0.4O2(x=0, 0.1, 0.2, 0.3) on the titanium substrate were prepared by thermal decomposition of a chloride precursor mixture. Surface morphology and microstructure of the coatings were investigated by Scanning electron microscopy(SEM), Field emission scanning electron microscopy(FE-SEM) and X-ray diffraction(XRD) analysis. Systematic study of electrochemical properties of these coatings was performed by cyclic voltammetry(CV) and polarization measurements. The corrosion behavior of the coatings was evaluated under accelerated conditions(j=2 A cm-2) in acidic electrolyte. The role of iridium oxide admixture in the change of electrocatalytic activity and stability of Ru0.6Ti0.4O2coating was discussed. Small addition of IrO2can improve the stability of the RuO2+TiO2mixed oxide, while the electrocatalytic activity for oxygen evolution reaction(OER) is decreased. The shift of redox potentials for Ru0.6Ti0.4O2electrode that is slightly activated with IrO2and improvement in the stability can be attributed to the synergetic effect of mixed oxide formation.     

计时电量法测定4,5-二氮芴-9-酮的扩散系数和反应速率常数

运用循环伏安法测定4,5-二氮芴-9-酮（DAFO）在DMF溶液中不同扫描速率时的循环伏安图,出现2对峰形良好的氧化还原峰;采用计时电量法通过控制阶跃电位,测得不同温度下DAFO在DMF溶液中的扩散系数和反应速率常数,293K时扩散系数为5.39×10-6cm2·s-1;当选择阶跃电位使电极过程处于扩散和电化学混合控制时,测得不同电位的反应速率常数k_f. 根据不同温度下的标准速率常数k₀,得到表观活化能E_a为10.5kJ·mol-1.      

Improved electrochemica l properties by lithium insertion into Co3O4 in aqueous LiOH solution

Co₃O₄ microspheres were synthesized by a simple hydrothermal treatment.The first-cycle charge-discharge tests were carried out between-0.6 and 0.6 V vs.SCE.The pristine,discharged and recharged specimens were characterized by X-ray power diffraction and scanning electron microscopy.Cyclic voltammetry（CV） curves of Co₃O₄ at various concentrations in LiOH solution were investigated.The appearance of the two pairs of redox peaks indicated that two sets of faradaic reactions were involved in the redox reactions of Co₃O₄ to LiCoO₂ and LiHCoO₂.     

Cyclic peptides-assisted transport of metal ions across liquid-organic membrane

The formation of alkali and alkaline-earth metal picrate complexes with cyclo(Pro-Gly)_n ionophores (1, n = 3; 2, n = 4) can facilitate the migration of metal ions across a bulk liquid CH₂Cl₂ membrane. The migration behavior was studied by measuring the solution absorption at 356 nm, using a UV/Vis spectrophotometer, and the rates can be determined by comparing the initial absorption of donor solutions with the absorption of the corresponding receiver solutions as the function of time. It was found that cyclic peptide 1 shows higher transport activity for the studied alkali and alkaline-earth metal ions than compound 2, which is related to the backbone flexibility of the cyclic peptides. The findings in this work suggest that the rate of ionophore-facilitated ion transport depends not only on the ability of complex formation in aqueous phase, but also on the ability of complex dissociation in organic phase.     

Thermal behavior of zirconia-dop ed mullite gel fibers

The zirconia-doped mullite gel fibers were prepared via a sol-gel method.The thermal behaviors of the gel fibers during pyrolysis were investigated by means of thermal gravitydifferential scanning calo...     

Effect of Cl- on photosynthetic bicarbonate uptake in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803

Photosynthetic inorganic carbon utilization was investigated in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803 grown in standing culture. Photosynthetic rates for the two algae reached about 10 times the theoretical CO₂ supply rate at low dissolved inorganic carbon (DIC) of 100 μmol/L, and the rates were unaffected by the addition of 20 mmol/L Na⁺, indicating that the two algae possessed Na+-independent HCO^-₃ utilization for photosynthesis under low DIC. Their photo- synthetic rates at low DIC were inhibited by higher Cl^- and the degrees of inhibition were increased with the rise of CI^- concentration, and in the presence of Diphenylamine-2-carboxylate (DPC), a reported Cl^- channel inhibitor, the rates decreased by 74%－82%, implying that putative DPC-sensitive Cl^- channels participate in Na+-independent HCO₃^- uptake for photosynthesis. The experiment of intracellular 14C-DIC accumulation for photosynthesis showed that internal DIC pools decreased by about 80% with 200 μmol/L DPC and by 64%－70% with 100 mmol/L Cl^-. The experiment of chlorophyll a fluorescence quenching showed that initial rates and extents of fluorescence quenching obviously decreased with 200 μmol/L DPC or 100 mmol/L Cl^-. The two experiments gave further evidence that putative DPC-sen- sitive Cl^- channels participate in Na+-independent HCO^-₃ uptake for photosynthesis in the two algae grown in standing culture.     

Tailoring impedance match and enhancing microwave absorption of Fe3O4/ Bi24Fe2O39/Bi hollow porous microrods by controlling their composition

A self-assembly/precipitate conversion/decomposition process was developed for the controllable synthesis of Fe_3O_4/Bi_(24)Fe_2O_(39)/Bi hollow porous microrods(HPMRs).The results demonstrated that the crystal size,component,and performances of HPMRs could be effectively modulated via changing Fe~(2+)/Bi~(3+)molar ratio(γ).Fe_3O_4/Bi_(24)Fe_2O_(39)/Bi HPMRs exhibited ferromagnetic behavior at room temperature.As Bi and Bi_(24)Fe_2O_(39)contents increased withγ,the saturation magnetization M_sand attenuation constantly decreased,whereas coercivity H_cand impedance matching ratio increased.Compounding Fe_3O_4with small quantities of Bi and Bi_(24)Fe_2O_(39)into HPMRs can significantly enhance microwave absorption.Fe_3O_4/Bi_(24)Fe_2O_(39)/Bi HPMRs formed atγ=1:0.25 exhibited the optimum microwave absorption performance.The minimum R_Lwas-47.3 dB at8.72 GHz,corresponding to 2.4 mm sample thickness.The absorption band with the reflection loss below-20 dB was up to 14.0 GHz for the absorber with a thickness of 1.4-8.0 mm.The results demonstrate that the introduction of electromagnetic transparent materials(Bi_(24)Fe_2O_(39)or Bi)can improve the microwave absorption performances of Fe_3O_4 composites owing to enhanced impedance matching rather than attenuation constant.     

Integrated Bi2O3 nanostructure modified with Au nanoparticles for enhanced photocatalytic activity under visible light irradiation

An integrated Bi_2O_3(i-Bi_2O_3) nanostructure with a particle size 10 nm inducing agglomerated structure were synthesized by dissolving bismuth nitrate pentahydrate in diethylene glycol at 180 ℃ with post heat treatment.The prepared i-Bi_2O_3 nanostructures were employed for the construction of Au/i-Bi_2O_3 composite system and characterized by X-ray diffraction pattern,UV-visible diffuse reflectance spectroscopy(DRS),and transmission electron microscopy,X-ray photoemission spectroscopy(XPS) and Energy dispersive X-ray spectroscopy(EDS).The i-Bi_2O_3 nanostructure and Au/i-Bi_2O_3 composite system were found to exhibit high photocatalytic activity than commercial Bi_2O_3 in decomposing salicylic acid under visible light irradiation.The high catalytic activity of i-Bi_2O_3 nanostructure was deduced to be caused by charge separation facilitated by electron hopping between the particles within the integrated structure and space-charge separation between i-Bi_2O_3 and Au.The charge separation behavior in i-Bi_2O_3 nanostructure was further bolstered by comparing the measured.OH radical produced in the solution with i-Bi_2O_3 nanostructure,commercial Bi_2O_3 and Au/i-Bi_2O_3 composite which readily react with 1,4-terephthalic acid(TA) inducing 2-hydroxy terephthalic acid(TAOH) that shows unique fluorescence peak at 426 nm.The space-charge separation between i-Bi_2O_3 and An was confirmed by measuring the electron spin resonance(ESR) spectra.     

阳极修饰对微生物燃料电池性能的影响

利用PW12/rGO复合材料负载于碳布表面制得PW12/rGO修饰阳极并构建单室空气阴极微生物燃料电池(microbial fuel cells,MFC),考察了PW12/rGO修饰阳极对MFC产电和高氯酸盐(ClO4-)还原性能的影响,并通过对阳极表面形态及其电化学特性的分析,探讨了PW12/rGO修饰阳极改善MFC产电性能的机理.结果 表明,当ClO4-浓度为700 mg/L时,PW12/rGO修饰阳极MFC的最大输出电压和ClO4-平均去除速率分别为200.18 mV和1.15 kg/(m3·d),分别是空白阳极MFC的4.4倍和1.06倍;扫描电镜(SEM)表征显示,PW12/rGO修饰阳极表面附着的微生物量远高于空白阳极;Tafel曲线、循环伏安曲线(CV)和交流阻抗谱(EIS)测试表明,PW12/rGO修饰阳极较空白阳极具有更高的交换电流密度、CV电活性面积以及更低的电荷转移电阻.PW12/rGO修饰阳极提高了阳极电子产量和电子传递速率,进而改善了MFC的产电性能.