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1.
In Monoraphidium braunii, uptake of NO3?, NO2? and Cl? is associated with proton transport and triggered by blue light (BL). Only 10 s after cells able to reduce NO3? to NH4+ were irradiated with continuous, low-fluence BL in the presence of NO3?, an alkalinization of the medium began and only became interrupted by switching off the BL with a 60–90 s time lag. With 30 s BL pulses, the NO3?-dependent alkalinization lasted 3–5 min until it stopped. When the cells were exposed to continuous BL in the presence of Cl?, the alkalinization also started within 10 s but lasted only 3 min. After that, the pH remained constant and decreased when the BL was switched off. With 30 s BL pulses, the Cl?-dependent alkalinization lasted 3 min and then decreased to its initial value. The NO3?-dependent alkalinization shown by cells unable to reduce NO3? to NH4+ was similar to that observed in the presence of Cl?. These alkalinization rates fit the Bunsen-Roscoe reciprocity law. With 2 s pulses of high-fluence BL, the delay time of the NO3 - or Cl?-dependent alkalinizations was only 2 s, one of the fastest BL responses reported so far. The action spectra for Cl? and NO3? uptakes proved to be very similar and matched the absorption spectra of flavins, including the 267 nm peak.  相似文献   

2.
Abstract— Nitrate reductase from eukaryotes can be reversibly inactivated, blue light being an effective activating agent both in vitro and in vivo. Hydroxylamine proved to be a powerful inactivating agent of Ankistrodesmus braunii nitrate reductase. Irradiation with blue light of NH2OH-inactivated nitrate reductase, specially in the presence of μM amounts of FAD, promoted the recovery of the enzyme activity. Similarly, photoexcited methylene blue reactivated spinach nitrate reductase. On the other hand, in vitro nitrate reductase is highly susceptible to photodynamic inactivation caused by singlet O2. Aerobic incubation of the active spinach enzyme with either FMN or methylene blue under either blue or red light respectively led to its irreversible inactivation. Irradiation of frozen and thawed spinach leaf discs also promoted, in situ, an irreversible inactivation of nitrate reductase, provided that 62 was present in the incubation mixture. Thus, either in vitro or in situ, light can cause two quite different responses of nitrate reductase, its blue light-dependent photoactivation in a flavin sensitized reaction and its photodynamic inactivation in a singlet O2-dependent process.  相似文献   

3.
《化学:亚洲杂志》2017,12(10):1111-1119
The photoelectrochemical production and degradation properties of hydrogen peroxide (H2O2) were investigated on a WO3/BiVO4 photoanode in an aqueous electrolyte of hydrogen carbonate (HCO3). High concentrations of HCO3 species rather than CO32− species inhibited the oxidative degradation of H2O2 on the WO3/BiVO4 photoanode, resulting in effective oxidative H2O2 generation and accumulation from water (H2O). Moreover, the Au cathode facilitated two‐electron reduction of oxygen (O2), resulting in reductive H2O2 production with high current efficiency. Combining the WO3/BiVO4 photoanode with a HCO3 electrolyte and an Au cathode also produced a clean and promising design for a photoelectrode system specializing in H2O2 production (η anode(H2O2)≈50 %, η cathode(H2O2)≈90 %) even without applied voltage between the photoanode and cathode under simulated solar light through a two‐photon process; this achieved effective H2O2 production when using an Au‐supported porous BiVO4 photocatalyst sheet.  相似文献   

4.
Abstract— The action spectra for violaxanthin de-epoxidation and zeaxanthin epoxidation in New Zealand spinach leaf segments, Tetragonia expansa, were determined at equal incident quanta of 2·0 × 1015 quanta cm-2 sec-1. Precise action spectra were not obtained due to variable leaf activity. The de-epoxidation action spectrum had major peaks at approximately 480 and 648 nm. Blue light was slightly more effective than red light and little activity was observed beyond 700 nm. The epoxidation action spectrum showed major peaks at around 440 and 670 nm. Blue light was more effective than red light and light beyond 700 nm showed definite activity. The net result of de-epoxidation and epoxidation is a cyclic scheme, the violaxanthin cycle, which consumes O2 and photoproducts. The action spectra indicate that the violaxanthin cycle is more active in blue than in red light and therefore could account for O2 uptake stimulated by blue light. However, the violaxanthin cycle is not the pathway for O2 uptake by photosynthetic system 1. It was suggested that the violaxanthin cycle may function as a pathway for the consumption of excess photoproducts generated in blue light or the conversion of these photo-products to other forms of energy.  相似文献   

5.
Abstract —The effects of various light/dark schedules on the time course of CO2 output by axenic cultures of the short-day plant Lemna perpusilla 6746 differ substantially depending on whether the medium is N-less or contains NH4 or NO3 as the sole N source. The steady-state pattern achieved with a daily 1/4 h light pulse in N-less medium is essentially the same whether the light is red or far-red; on NO3 or NH4, however, the red and far-red patterns differ in form and suggest the action of a ‘Pfr-hourglass’ timer. In darkness, following either continuous light or entrainment to kh red light daily, CO2 output oscillates for three or more circadian cycles on NH4 medium and for at least two on N-less, but damps after a single cycle on NO3. A schedule of 1/4 h red light every 12 h elicits a 24 h periodicity on NO3 or NH4 media and a 12 h periodicity on N-less medium, while a similar far-red schedule elicits a 12 h periodicity on all three. CO2 output patterns on each of the media respond differently to varying the daily span of light from 1/4 to 6 to 12 h. These results are probably due to differential effects of changing N status on the proportion of total C O2 arising from various metabolic reactions. They suggest that, rather than being a simple, unitary indicator, CO2 output can be made to reflect different processes on different media, increasing its value as a real-time indicator of events underlying photoperiodism.  相似文献   

6.
A stable visible‐light‐driven photocatalyst (λ≥450 nm) for water oxidation is reported. Rhodium substitution into the pyrochlore Y2Ti2O7 is demonstrated by monitoring Vegard′s law evolution of the unit‐cell parameters with changing rhodium content, to a maximum content of 3 % dopant. Substitution renders the solid solutions visible‐light active. The overall rate of oxygen evolution is comparable to WO3 but with superior light‐harvesting and surface‐area‐normalized turnover rates, making Y2Ti1.94Rh0.06O7 an excellent candidate for use in a Z‐scheme water‐splitting system.  相似文献   

7.
Chlamydomonas, like other organisms, regulates iron assimilation very tightly through differential expression of iron assimilation components. Nevertheless, in the presence of excess iron, cells do overaccumulate iron but without an evident phenotype. As iron toxicity is attributed to reactive oxygen species, we tested the impact of photon flux density (PFD) on cells with increased iron content. We noted that growth at >500 μmol m?2 s?1 is inhibited as iron content of the medium is increased, suggesting that high light exacerbates the systems of iron toxicity and vice versa. Cells grown in high light selectively down‐regulate the abundance of iron assimilation components, ferroxidase and FEA1, and storage protein ferritin1. At the RNA level, the abundance of ferroxidase (FOX1), iron reductase (FRE1), iron assimilatory protein (FEA1) and ferritin (FER1) mRNAs is also decreased. The time course of the response to high light compared to the response to Rose Bengal and H2O2 treatments suggests that both singlet oxygen and H2O2 may be implicated in the high light response. This hypothesis is supported by the recapitulation of some but not all of the high light responses in the carotenoid‐deficient, high light–sensitive npq1lor1 strain. We conclude that responses to iron nutrition and PFD are connected, and the determination of an optimum for photosynthetic growth for each is dependent on the other. This work defines a fourth stage of iron nutrition in Chlamydomonas, the iron excess situation, which can be molecularly and physiologically distinguished from the iron‐limited, iron‐deficient and iron‐replete stages, described previously.  相似文献   

8.
光动力疗法(PDT)作为一种迅速发展的传统替代疗法,在抗癌治疗中显示出巨大的潜力.为增强靶向性和提高光催化杀伤效率,本研究设计了一种新型光敏剂Fe3O4-TiO2磁性纳米粒.在不同外磁场下,考察其在可见光和紫外光激发下对肝癌细胞的杀伤效应.同时利用流式细胞术检测纳米Fe3O4-TiO2对肝癌细胞凋亡率、细胞周期和线粒体膜电位的影响.根据纳米Fe3O4-TiO2和肝癌细胞的作用方式探讨其抗癌机制.结果表明,可见光激发纳米Fe3O4-TiO2可以杀伤癌细胞,且其杀伤效率与紫外光激发下无明显差别.此外,Fe3O4-TiO2比TiO2具有更高的细胞摄取率,从而使其具有更高的选择性和光催化杀伤效率.其作用机制是光催化纳米Fe3O4-TiO2产生活性氧ROS抑制癌细胞,然后通过阻滞细胞周期G0/G1期,降低线粒体膜电位,线粒体去极化,最终诱导细胞凋亡.  相似文献   

9.
新型红色荧光粉Sr3Al2O6的合成和发光性能研究   总被引:10,自引:0,他引:10  
稀土金属离子激活的多铝酸盐发光材料,在可见光区具有较高的量子效率犤1~4犦,充分显示出这类荧光发光材料,在高效节能、环保、电光源与新一代可见光显示器领域的应用前景犤4~9犦。特别是SrAl2O4∶Eu2+的持续发光现象的发现犤2,3犦,激起了对以稀土金属离子为激活剂,碱土铝酸盐为基质的长余辉无机发光材料体系的兴趣。研究表明其发光强度和余辉时间是传统硫化物发光材料的十倍以上,利用其长余辉储光-发光特性,有望开发新型发光油漆、涂料、发光陶瓷、发光塑料、薄膜、发光纸、发光纤维犤4犦。早在七十年代,荷兰菲利…  相似文献   

10.
采用EDTA-柠檬酸联合配位法制备一系列组成的(Sr1-xEux)2CaMoO6橙红色荧光粉。通过X射线衍射、拉曼光谱、扫描电镜及荧光光谱研究不同Eu3+离子掺杂浓度下Sr2CaMoO6∶Eu3+荧光粉的晶体结构、掺杂位置、形貌及其光致发光性能。Rietveld全谱拟合结果表明:掺杂后样品为(Ca/Mo)O6八面体少量倾斜的空间群为P21/n的正交双钙钛矿结构,随着Eu3+离子共掺杂浓度的增加,样品的晶胞体积减小;Eu3+离子取代八面体间隙的Sr2+位置致使双钙钛矿的T2g(1)拉曼振动模发生蓝移;在近紫外区宽而强电荷迁移带和蓝光激发下,该荧光粉分别发射以Eu3+离子5D0-7F1磁偶极跃迁为主的橙光和以5D0-7F2电偶极跃迁为主的红光,组成为(Sr0.98Eu0.02)2CaMoO6的荧光粉具有最强的橙红光发射强度,是一种潜在的适用于近紫外LED芯片的光转换红光材料。  相似文献   

11.
采用优化的高温固相方法制备了稀土离子Eu3+和Tb3+掺杂的La7O6(BO3)(PO42系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La7O6(BO3)(PO42:Eu3+材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D07F2特征能级跃迁,Eu3+的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La7O6(BO3)(PO42:Tb3+材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb3+5D47F5能级跃迁,Tb3+离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu3+和Tb3+掺杂的La7O6(BO3)(PO42荧光材料均具有良好的热稳定性。  相似文献   

12.
Abstract— Recently we reported on the stimulating effect of a cold, dark pretreatment on the processes of greening of dark-grown angiosperms under continuous white light (Schönbohm et al., 1988; Physiol. Plant. 72 ,541–546). These effects could be nullified by a subsequent second dark phase (25°C) which precedes the white light period. Our analysis was now focused on the effect of cold, dark pretreatments (with or without red-preirradiation) on the gas exchange (O2; CO2) of etiolated primary leaves of wheat during a subsequent white light period. The following results were obtained: (1) The net-O2-consumption under continuous white light decreased much more quickly after a cold than after a warm pretreatment. (2) This effect was enhanced by red-preirradiation. (3) The O2-compensation point was reached more quickly during the de-etiolation period when the leaves had been subjected to a cold instead to a warm pretreatment. (4) The “cold-effect” could be nullified by a subsequent warm, dark pretreatment (in this material the compensation point could not be reached within 8 h). (5) Cold treated material which had also been exposed to red light showed during the first 30 min of de-etiolation an extremely strong out-burst” of CO2. No correlation was apparent between the O2-uptake and this high CO2-release. (6) A cold, dark pretreatment induces a decrease of CO2-release during the second half of the de-etiolation period. This effect could be nullified by a secondary warm, dark treatment given after the cold, dark pretreatment. Our experiments indicate that red-preirradiation and cold, dark pretreatment stimulate chlorophyll synthesis (Schonbohm et al., 1988) and also photosynthetic O2-evolution and CO2-uptake. We also assume that this pretreatment causes CO2 release that is neither directly related to the respiratory electron transport chain nor to the photorespiration.  相似文献   

13.
Iron(II), (Fe(H2O)62+, (FeII) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2, under environmental conditions containing bicarbonate (HCO3), which exists up to millimolar concentrations. In the absence and presence of HCO3, the formation of reactive oxygen species (O2, H2O2, and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3. The rate of the formation of CO3 may be expressed as d[CO3]/dt=[FeII[[O2][HCO3]2. The formation of reactive species was investigated using 1H nuclear magnetic resonance (1H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3 in the geochemical cycling of iron and carbon.  相似文献   

14.
采用优化的高温固相方法制备了稀土离子Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La_7O_6(BO_3)(PO_4)_2∶Eu~(3+)材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D0→7F2特征能级跃迁,Eu~(3+)的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La_7O_6(BO_3)(PO_4)_2∶Tb~(3+)材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb~(3+)的5D4→7F5能级跃迁,Tb~(3+)离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2荧光材料均具有良好的热稳定性。  相似文献   

15.
通过熔盐法制备TiB2载体,并采用简单的沉淀-沉积法制备了Co/TiB2磁性可回收纳米催化剂,用于室温催化氨硼烷(NH3BH3)溶液产氢及串联降解对硝基苯酚(4-NP)及偶氮染料酸性橙7(AO7)、酸性红1(AR1)和甲基橙(MO)等有机污染物。采用X射线衍射、扫描电子显微镜、透射电子显微镜、X射线光电子能谱、振动样品磁强计等表征方法对催化剂的微观形貌和结构等进行分析。结果表明,Co纳米粒子均匀地分布在TiB2载体表面,晶粒尺寸约为40 nm,并且被TiB2载体包覆,具有典型的金属-载体强相互作用。Co/TiB2表现出优异的室温催化NH3BH3溶液产氢活性,产氢速率为565.8 molH2·molcat-1·h-1。在串联降解有机污染物反应中,Co/TiB2在7 min内催化4-NP氨基化的转化率接近100%,反应速率常数高达0.72 min-1;降解AO7的反应速率常数在3种偶氮染料中最高(0.34 min-1)。通过EPR-DMPO(EPR=电子顺磁共振,DMPO=5,5-二甲基-1-吡咯啉-N-氧化物)自由基捕获实验检测出Co/TiB2+NH3BH3催化体系中产生大量的氢自由基(·H)。得益于·H的强还原性,Co/TiB2+NH3BH3催化体系能够将4-NP氨基化为具有更高价值的对氨基苯酚(4-AP),同时能够还原偶氮染料分子中的显色基团偶氮基(—N=N—)。  相似文献   

16.
The binding (dissociation) constant for HCO?3 to the photosystem II complex in maize chloroplasts is approximately 80 μM. One HCO?3 binds per 500–600 chlorophyll molecules. In the dark, formate is a competitive inhibitor of HCO?3 binding, while 3-(3′,4′-dichlorophenyl)-1, 1-dimethylurea (DCMU) inhibits HCO?3 binding non-competitively. Light decreases HCO?3 binding in the presence of formate. Light increases the binding of HCO?3 in the presence of DCMU. The high binding constant for HCO, discriminates strongly among the various hypotheses attempting to explain the “bicarbonate-effect” on photosystem II. The proposal by Stemler and Jursinic (Arch. Biochem. Biophys. 221, 227–237 1983), that HCO?3 is one of a class of monovalent anionic inhibitors of photosystem II, is favored. These anions compete for a specific binding site on the photosystem II complex.  相似文献   

17.
王挺  吴礼光  蒋新 《无机化学学报》2011,27(8):1477-1482
利用吸附相反应技术制备得到了掺杂不同浓度的Fe2O3的TiO2复合光催化剂。通过透射电子显微镜(TEM)、紫外可见光谱和X射线衍射(XRD)研究不同掺杂浓度对TiO2形貌和结晶过程的影响,并利用3种波长光源下的甲基橙光降解实验考评了各个复合光催化剂的催化活性。结果表明,掺杂后复合光催化剂中Fe2O3分散性较好较均匀。在TiO2紫外可见吸收光谱中由于Fe2O3的掺杂而出现了红移,而且随着掺杂浓度增加红移越来越明显,复合光催化剂的禁带宽度也越来越小。在焙烧过程中无定形Fe2O3或Fe3+进入了TiO2的晶格结构,从而抑制了TiO2的结晶过程。半导体禁带宽度的减少以及TiO2结晶过程的抑制作用,都导致紫外光下复合光催化剂催化活性的降低。但Fe2O3的掺杂也使得复合光催化剂在可见光区出现了一定的光催化活性。  相似文献   

18.
采用三种低温溶胶-凝胶法制备了具有不同Fe3O4掺杂量的磁靶向纳米Fe3O4-TiO2复合物, 通过X射线衍射(XRD)、透射电镜(TEM)、傅里叶变换红外(FTIR)光谱、紫外-可见(UV-Vis)光谱、荧光光谱(FS)及磁性能分析等表征方法筛选出包覆均匀、分散性好、磁性能优异及光催化活性较高的纳米Fe3O4-TiO2复合物. 以四甲基偶氮唑蓝(MTT)法检测肝癌细胞(HepG2)的存活率, 考察纳米Fe3O4-TiO2复合物在外磁场作用下对HepG2 细胞的光催化杀伤效应. 结果表明: 采用方法三制备的5%(质量分数)Fe3O4-TiO2复合物具备核-壳结构, 在混悬液中分散性较好, 平均粒径约为50 nm, 具有较强的光催化活性和良好的磁响应性, 同时将纳米TiO2的光响应范围拓宽至444 nm; 在外磁场作用下, 紫外光和可见光激发纳米Fe3O4-TiO2复合物对HepG2细胞的杀伤效应差异不大, 且均强于纳米TiO2; 其杀伤效应在0-1.0 T范围内随着外磁场强度的增大而增强.  相似文献   

19.
Cu2+ binding on γ-Al2O3 is modulated by common electrolyte ions such as Mg2+, , and in a complex manner: (a) At high concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg2+ and Cu2+ ions for the SO surface sites of γ-Al2O3. (b) At low concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 can be enhanced. This is due to synergistic coadsorption of Cu2+ and electrolyte anions, and . This results in the formation of ternary surface species (SOH2SO4Cu)+, (SOH2PO4Cu), and (SOH2HPO4Cu)+ which enhance Cu2+ uptake at pH < 6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH  pHPZC, Cu2+ coordinates to one SO group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH  pHPZC Cu2+ may coordinate to two SO groups. At pH  pHPZC electrolyte ions and are bridging one O-atom from the γ-Al2O3 surface and one Cu2+ ion forming ternary [γ-Al2O3/elecrolyte/Cu2+] species.  相似文献   

20.
Hydrogen production from coal gasification provides a cleaning approach to convert coal resource into chemical energy, but the key procedures of coal gasification and thermal catalytic water–gas shift (WGS) reaction in this energy technology still suffer from high energy cost. We herein propose adopting a solar–driven WGS process instead of traditional thermal catalysis, with the aim of greatly decreasing the energy consumption. Under light irradiation, the CuOx/Al2O3 delivers excellent catalytic activity (122 μmol gcat?1 s?1 of H2 evolution and >95 % of CO conversion) which is even more efficient than noble‐metal‐based catalysts (Au/Al2O3 and Pt/Al2O3). Importantly, this solar‐driven WGS process costs no electric/thermal power but attains 1.1 % of light‐to‐energy storage. The attractive performance of the solar‐driven WGS reaction over CuOx/Al2O3 can be attributed to the combined photothermocatalysis and photocatalysis.  相似文献   

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