假根羽藻细胞色素b6f蛋白复合体中α-胡萝卜素的结构与功能

细胞色素b6f蛋白复合体（Cyt b6f）是光合链中连接两个光系统（PSII 和PSI）的中间电子载体蛋白复合物，其主要的生理功能是催化电子传递和质子跨膜转移，形成跨膜质子电化学梯度，为ATP的合成提供能量，在光合作用光能转化过程中占有很重要的地位。细菌和莱茵衣藻Cyt b6f的晶体结构已于2003年底获得了近原子水平的解析，但有关该复合物中两种色素（Chl a和β-Car）的生理功能及其机理尚无明确的解释。预计它们将成为今后几年的研究热点,因为揭示Cyt b6f蛋白复合体中Chl a和β-Car分子的生理功能对于进一步阐明光合作用高效转能及其调控的分子机理具十分重要的意义。鉴于目前尚未见到海洋绿藻Cyt b6f的报道，本文以海洋绿藻—假根羽藻（Bryopsis corticulans）类囊体膜上的Cyt b6f蛋白复合体为对象，对其中的类胡萝卜素的分子结构与生理功能进行了比较系统地研究。 首先，我们改进了原用于菠菜类囊体膜Cyt b6f的分离、纯化流程，在原流程的基础上增加了一次2 mol/L NaBr洗膜，彻底地去除了膜表面的杂蛋白;还调整了第二次硫酸铵分级沉淀时的饱和度，并将38-45%饱和度下的沉淀物确定为需要收集的Cyt b6f制剂。采用此改进的流程，我们首次从假根羽藻类囊体膜中分离纯化了高活性、高纯度的Cyt b6f制剂。SDS-PAGE分析的结果显示该制剂的4个多肽亚基 （Cytf 、Cyt b6 、Rieske[Fe-s]及亚基IV）的表观分子量分别为34.8、24.0、18.7和16.7 kD;Cyt b6 / f 比值接近2.0， 其纯度值为9.9 nmol cyt f/mg;其催化电子传递的活性 （C10-PQH2→PC）为73 e/s。HPLC 和共振拉曼光谱分析表明，假根羽藻Cyt b6f中的类胡萝卜素为α-胡萝卜素分子，它是一种在Cyt b6f中尚未报道过的类胡萝卜素。定量分析表明，每个假根羽藻Cyt b6f单体中全反式(all-trans)和9顺式（9-cis）α-胡萝卜素的含量分别为0.2和0.7个分子，另外还含有1.2分子的Chl a。CD光谱分析表明该9-cis-α-胡萝卜素处在一个不对称的蛋白环境中。TLC分析表明该制剂是一种缺脂的Cyt b6f蛋白复合体。 采用稳态荧光激发光谱，时间分辨吸收光谱及Chl a的光破坏实验对假根羽藻Cyt b6f中α-胡萝卜素的功能进行了研究。结果表明，Cyt b6f中α-胡萝卜素可以将它吸收的光能传递给Chl a，其能量传递效率为62.4%，提出α-胡萝卜素分子与Chl a分子之间的单线态能量传递是遵从Föster 机制进行的;α-胡萝卜素分子对Chl a分子有一定的光保护作用，这种保护作用是通过清除单线态氧来实现的。另外还发现Cyt b6f中的Chl a分子可能与其周围的氨基酸残基存在相互作用，认为这是其进行自我光保护的一种方式。 此外，还采用HPLC研究了光和暗交替对假根羽藻Cyt b6f中α-胡萝卜素构型的影响，并对假根羽藻Cyt b6f选择结合α-胡萝卜素的原因进行了初步的分析。

PSII色素蛋白复合物的脂质体重组及反应中心的功能研究

光系统II（PSII）是存在于类囊体膜中的多亚基色素蛋白复合物，是吸收光能、催化光诱导水裂解释放氧气、质子和电子的重要机构。它在体内的基本单位是由外周天线蛋白（LHCII）与PSII核心复合物结合形成的PSII-LHCII超分子复合物，这一结构保证了LHCII吸收的能量能够快速有效的传递到PSII反应中心（RC），进行原初光化学反应。 本论文分为两部分：1、利用捕光色素蛋白复合物（LHCII）与PSII核心复合物在以DGDG、PG、SQDG三种类囊体膜脂形成的脂质体中重组的方法，研究了LHCII与PSII在脂膜上结构与功能的相互作用;2、通过研究光破坏和色素置换对PSII RC的影响，探讨了RC中不同色素的功能。主要结果如下： 1、LHCII与PSII核心复合物的蛋白脂质体研究： 将OECC（粗提核心复合物）、pdOE（纯化核心复合物）、LHCII（大量天线）制剂分别与脂质体重组并研究了其光谱性质。LHCII在与脂质体重组前表现出典型的聚集态光谱特征，重组后吸收和荧光发射峰发生明显蓝移;LHCII、OECC和pdOE三种蛋白脂质体与重组前的样品相比荧光发射强度增加;表明脂环境影响了色素蛋白复合物的聚集状态以及色素和蛋白之间的相互作用。 OECC和pdOE分别与LHCII在脂质体中重组，得到两种重组蛋白（LHCII-OECC和LHCII-pdOE）脂质体，用冰冻蚀刻电镜技术和低温荧光光谱的方法研究其结构和功能特征。LHCII和核心复合物（OECC或pdOE）结合形成PSII-LHCII重组颗粒，并在脂质体中均匀排布，阻止了LHCII晶格状结构的形成。重组蛋白脂质体的吸收光谱既有LHCII的吸收特征，又有核心复合物的特征吸收峰，但低温荧光光谱的主要发射峰是核心复合物的特征峰（684 nm-685 nm），而不是LHCII的特征峰（680 nm）;而且激发不同色素得到的荧光发射光谱基本一致，这些结果证明LHCII吸收的能量传递到了核心复合物中，在重组蛋白脂质体中不同色素蛋白复合物在结构和功能上都实现了相互偶联。 通过对OECC或pdOE与LHCII重组形成的蛋白脂质体放氧或DCPIP光还原活性的检测研究了PSII光化学活性特征。LHCII和核心复合物（OECC或pdOE）的重组蛋白脂质体与单独核心脂质体相比，在强光和弱光下光化学活性都明显提高。这从另一个角度证明了核心复合物与LHCII的功能偶联，LHCII的结合使捕光截面积增大，从而使PSII光化学活性增加。 用77K飞秒时间分辨荧光光谱分析了几种蛋白脂质体的能量传递和捕获情况。LHCII、OECC和pdOE三种蛋白脂质体的主要荧光衰减组分分别是670 ps（发射峰在680 nm）、650 ps（发射峰在690 nm）和570 ps（发射峰在685 nm）。LHCII-OECC和LHCII-pdOE脂质体的主要衰减组分分别是940 ps（发射峰在690 nm）和840 ps（发射峰在685 nm），并且出现了一个在核心复合物脂质体和LHCII脂质体中没有的40 ps组分，可以推测，这是LHCII和核心复合物之间达到平衡的时间组分，比激发态衰减的平均寿命要快得多，因此支持了PSII的trap-limited激发能衰减动力学模型。此外，可以看到天线的增大使Chl a荧光衰减的寿命延长，这一特性可能与PSII的光保护机制有关。 LHCII和OECC、LHCII和pdOE在脂质体中都成功的实现了重组，而且在结构和功能上没有明显差异;表明小天线以及23 kDa、17 kDa蛋白可能不是LHCII和核心复合物结合及能量传递所必需的。 2、受体侧光破坏和色素置换对PSII RC的影响： 在800 μmol.m-2 .s-1光照和无外加电子受体、供体的情况下，研究了PSII RC色素的受体侧光破坏情况。Chl a、Pheo和β-Car的光漂白几乎同时发生，其中在680 nm吸收的色素破坏最为显著，670 nm吸收的外周Chl比其他色素更加稳定。荧光发射强度呈先升高后降低的趋势，最大发射峰位逐渐蓝移，表明色素之间的能量传递受到破坏。用β-Car的主要吸收波长488 nm和514.5 nm激发得到两组谱带峰位和强度不同的拉曼光谱，表明在PSII RC中存在两个光谱性质不同的β-Car。光破坏过程中两组谱带的位置和带宽都没有明显变化，表明β-Car的光保护机制不涉及自身构象的变化。 将PSII RC与Cu-Chl a进行色素置换，得到了与Cu-Chl重组的RC（Cu-Chl-RC），含有0.5 Cu-Chl/2Pheo。与对照RC（按同样方式与Chl a置换的RC）和天然RC相比，Cu-Chl含量增加而Chl含量减少，660 nm的吸收增加而670 nm吸收降低，因此推测是外周Chl被替换。色素置换过程对RC的多肽组分及大部分的P680活性没有影响，CD光谱的变化也很小，表明产生CD信号的色素和蛋白环境也没有受到明显影响。但是Cu-Chl-RC的荧光发射强度明显降低，最大发射峰蓝移且峰形发生变化，Cu-Chl可能在重组RC中作为激发态的淬灭剂，阻碍了色素之间的能量传递。

Highly efficient photoluminescence of Er2SiO5 films grown by reactive magnetron sputtering method

E2SiO5 thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er2SiO5 crystalline structure was formed as sample treated at 1100 degrees C for 1 h in O-2 atmosphere. Through proper thermal treatment, the 1.53 mu m Er3+-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 degrees C. Analysis of pump-power dependence of Er3+ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 10(21) (photons/cm(2)/sec). Temperature-dependent photoluminescence (PL) of Er2SiO5 was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er2SiO5 films has been demonstrated with Er3+ concentration of 10(22)/cm(3), and it opens a promising way towards future Si-based light source for Si photonics. (C) 2009 Elsevier B.V. All rights reserved.

Role of Bi3+ ions for Er3+ ions efficient 1.54 mu m light emission in Er/Bi codoped SiO2 thin film prepared by sol-gel method

Er/Bi codoped SiO2 thin films were prepared by sol-gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 degrees C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er3+-related 1.54 mu m light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 gm reached maximum at 800 degrees C and decreased dramatically at 1000 degrees C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi3+ ions for Er3+ ions near infrared light emission. Through sol-gel method and thermal treatment, Bi3+ ions can provide a perfect environment for Er3+ ion light emission by forming Er-Bi-Si-O complex. Furthermore, energy transfer from Bi3+ ions to Er3+ ions is evidenced and found to be a more efficient way for Er3+ ions near infrared emission. This makes the Bi3+ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED

Strong visible and infrared photoluminescence from Er-implanted silicon nitride films

Silicon nitride films were deposited by plasma-enhanced chemical-vapour deposition. The films were then implanted with erbium ions to a concentration of 8 x 10(20) cm(-3). After high temperature annealing, strong visible and infrared photoluminescence (PL) was observed. The visible PL consists mainly of two peaks located at 660 and 750 nm, which are considered to originate from silicon nanocluster (Si-NCs) and Si-NC/SiNx interface states. Raman spectra and HRTEM measurements have been performed to confirm the existence of Si-NCs. The implanted erbium ions are possibly activated by an energy transfer process, leading to a strong 1.54 mu m PL.

Luminescence temperature and pressure studies of Zn2SiO4 phosphors doped with Mn2+ and Eu3+ ions

Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+ Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be -25.3 +/- 0.5 and -28.5 +/- 0.9 meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+ Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. (c) 2005 Elsevier B.V. All rights reserved.

Concentration effect of Mn2+ on the photoluminescence of ZnS : Mn nanocrystals

Mn-doped ZnS nanocrystals of about 3 nm diameter were synthesized by a wet chemical method. X-ray diffraction (XRD) measurements showed that the nanocrystals have the structure of cubic zinc blende. The broadening of the XRD lines is indicative of nanomaterials. Room temperature photoluminescence (PL) spectrum of the undoped sample only exhibited a defected-related blue emission band. But for the doped samples, an orange emission from the Mn2+ T-4(1)-(6)A(1) transition was also observed, apart from the blue emission. The peak position (600 nm) of the Mn2+ emission was shifted to longer wavelength compared to that (584 nm) of bulk ZnS:Mn. With the increase of the Mn2+ concentration, the PL of ZnS:Mn was significantly enhanced. The concentration quenching effect was not observed in our experiments. Such PL phenomena were attributed to the absence of Mn2+ pairs in a single ZnS:Mn nanocrystal, considering the nonradiative energy transfer between Mn2+ ions based on the Poisson approximation. (c) 2005 Elsevier B.V. All rights reserved.

Deep level and photoluminescence studies of Er-implanted GaN films

Deep level transient spectroscopy measurements were performed on the metal organic chemical vapor deposition epitaxially grown GaN before and after the implantation with Er. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300, 0.188, 0.600 and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees for 30 min. The origins of the deep defect levels were discussed. The photoluminescence (PL) properties of Er-implanted GaN thin films were also studied. After annealing at 900 degrees for 30 min in a nitrogen flow, Er-related 1.54 mu m luminescence peaks could be observed for the Er-implanted GaN sample. Moreover, the energy-transfer and recombination processes of the Er-implanted GaN film were described. (c) 2006 Elsevier B.V. All rights reserved.

Deep level transient spectroscopy studies of Er and Pr implanted GaN films

Deep level transient spectroscopy measurements were used to characterize the electrical properties of metal organic chemical vapor deposition grown undoped, Er-implanted and Pr-implanted GaN films. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300 eV, 0.188 eV, 0.600 eV and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees C for 30 min, and four defect levels located at 0.280 eV, 0.190 eV, 0.610 eV and 0.390 eV below the conduction band were found in the Pr-implanted GaN films after annealing at 1050 degrees C for 30min. The origins of the deep defect levels are discussed. After annealing at 900 degrees C for 30min in a nitrogen flow, Er-related 1538nm luminescence peaks could be observed for the Er-implanted GaN sample. The energy-transfer and luminescence mechanism of the Er-implanted GaN film are described.

Diode-pumped passively Q-switched Yb : YAG microchip laser with a GaAs as saturable absorber

A passively Q-switched Yb: YAG microchip laser has been constructed by using a doped GaAs as the saturable absorber as well as the output coupler. At 13.5 W of pump power the device produces high-quality 3.4 muJ 52 ns pulses at 1030nm with a pulse repetition rate of 7.8kHz in a TEM00-mode.

Temperature and pressure dependences of the Mn2+ and donor-acceptor emissions in ZnS : Mn2+ nanoparticles

Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn2+ nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn2+ nanoparticles at 440 nm shifts to longer wavelengths while the Mn2+ emission (T-4(1)-(6)A(1)) shifts to shorter wavelengths. Both the DA and Mn2+ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn2+ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn2+ nanoparticles is approximately -3.2 meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn2+ emission in ZnS:Mn2+ nanoparticles is roughly -34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn2+ ions is mainly from the recombination of carriers localized at Mn2+ ions. (C) 2002 American Institute of Physics.

Photoluminescence of ZnO : Tb nanoparticles

Terbium-doped zinc oxide nanoparticles have been prepared by hydrolyzing zinc acetate and terbium acetate. Nanoparticle-matrix-facilitated photoluminescence which is related to Tb3+ ions has been observed for ZnO:Tb nanoparticles. The dependence of emission intensity on doping concentration of Tb3+ ions has been investigated. An energy transfer from excited states of ZnO hosts to dopants is disclosed by the fact that the emission intensity of Tb3+ centers increases with increasing Tb content at the expense of emission from defect states in ZnO matrix.

Stimulated luminescence and photo-gated hole burning in BaFCl0.8Br0.2 : Sm2+,Sm3+ phosphors

The photo- and thermo-stimulated luminescence (PSL and TSL) of BaFCl0.8Br0.2:Sm2+,Sm3+ phosphors were investigated. It is found that the stimulated luminescence intensity of Sm2+ is almost equal to that of Sm3+ even if the content of Sm2+ is much lower than that of Sm3+. Only the stimulated luminescence of Sm2+ is observed in the sample in which the content of Sm2+ is much higher than Sm3+, demonstrating that the PSL or TSL efficiency of Sm2+ is much higher than that of Sm3+. This is attributed to the effective overlap of the e-h emission with the absorption of Sm2+ centers which may make the energy transfer from the electron-hole pairs to Sm2+ effectively. In BaFCl0.8Br0.2:Sm2+,Sm3+ the stimulated luminescence is considered to be occurred via the recombination of photoreleased electrons with the [Sm2+ + h] or [Sm3+ + h] complex and the energy transfer from the electron-hole pairs to the luminescence centers (Sm2+ and Sm3+) is concerned to be the major step to determine the stimulated luminescence efficiency. The X-ray-induced stimulated luminescence is compared and connected to the photon gated hole burning. The net result of the two processes is quite similar and may be comparable. It is suggested from the observations of stimulated luminescence that electron migration between Sm2+ and Sm3+ is not the major process, color centers may play an important role in hole burning. The information from stimulated luminescence is helpful for the understanding of the hole burning mechanism. (C) 1999 Elsevier Science Ltd. All rights reserved.

Development of a self-thermal insulation miniature combustor

A novel miniature cylindrical combustor, whose chamber wall is made of porous material, has been designed and experimented for reducing heat loss and enhancing flame stability. The combustor has the function of reducing wall heat loss, extending residence time and avoiding radical chemical quenching with a self-thermal insulation concept in which heat loss reduction is obtained by the opposite flow directions between thermal energy transfer and mass flow. The methane/air mixture flames formed in the chamber are blue and tubular in shape. Between the flames and the porous wall, there is a thin unburned film that plays a significant role in reducing the flames' heat loss and keeping the flames stable. The porous wall temperature was 150-400 degrees C when the temperatures of the flames and exhaust gas were more than 1200 degrees C. When the equivalence ratio phi < 1.0, the methane conversion ratio was above 95%; the combustion efficiency was near 90%; and the overall sidewall heat loss was less than 15% in the 1.53 cm(3) chamber. Moreover, its combustion efficiency is stable in a wider combustion load (input power) range.