紫细菌B800缺失LH2能量传递模型的构建及性质

构建B800缺失LH2对于阐明光合作用中光能传递的分子机制与捕光复合体组装机制具有重要意义。采用吸收光谱、荧光光谱、分子筛层析、超滤和SDS-PAGE等方法研究了紫细菌两个典型种外周捕光复合体 (LH2) 约800 nm特征光谱 (B800) 细菌叶绿素 (BChl) 缺失能量传递模型的构建方法及性质。结果表明：在pH 8.0 Tris-HCl(10 mmol·L-1) 缓冲液中,0.08% SDS能够使来自Rhodobacter azotoformans的LH2 B800 BChl特异性解离,解离体系中加入10%(φ) 甲醇,通过超滤脱除游离BChl,构建了B800缺失LH2,但该缺失模型不够稳定。在pH 1.9缓冲液中,来自Rhodopseudomonas palustris的LH2 B800 BChl能够特异性解离,通过层析得到两个组分。一个组分的B800 BChl不能通过层析脱除,能够重新自组装成LH2。另一个组分为B800缺失LH2,该缺失模型稳定。两种LH2均存在2类以上B800 BChl结合位点,并得到了两类Rhodopseudomonas palustris B800 BChl解离的LH2,但未发现类似紫色硫细菌中的B800吸收光谱劈裂现象。B800缺失LH2均未呈现约800 nm特征荧光光谱。采用两种方法构建了两个物种B800缺失LH2能量传递模型。利用BChl与缺失B800 LH2结合能力不同的特性,将Rhodopseudomonas palustris中的LH2分成两个类型,实现了异质性亚基LH2的分离。     

紫细菌Rb.Sphaeroides 601外周捕光天线(LH2) B800吸收带的超快动力学研究

利用从紫细菌Rb.sphaeroides 601 所提取出的外周捕光天线LH2以及其不同pH值酸化样品(部分和全部去除B800分子LH2)并采用不同波长下的飞秒单色抽运探测技术详细研究了LH2中B800吸收带内的激发态动力学过程.通过对野生型与部分/完全去B800分子LH2的比较研究，分析了B800吸收带激发后所表现出的丰富变化的动力学过程，研究结果表明激发B800带的动力学过程中包含着B850上激子带的直接激发而产生的对激发态动力学的贡献. 关键词： 紫细菌外周捕光天线LH2 部分和全部去除B800分子LH2 激发态动力学的演变 飞秒抽运探测     

Effect of the mutation of carotenoids on the dynamics of energy transfer in light-harvesting complexes （LH2） from Rhodobacter sphaeroides 601 at room temperature

Energy transfers in two kinds of peripheral light-harvesting complexes (LH2) of {Rhodobacter sphaeroides} (RS) 601 are studied by using femtosecond pump--probe spectroscopy with tunable laser wavelength at room temperature. These two complexes are native LH2 (RS601) and green carotenoid mutated LH2 (GM309). The obtained results demonstrate that, compared with spheroidenes with ten conjugated double bonds in native RS601, carotenoid in GM309 containing neurosporenes with nine conjugated double bonds can lead to a reduction in energy transfer rate in the B800-to-B850 band and the disturbance in the energy relaxation processes within the excitonic B850 band.     

紫细菌捕光天线LH2中的超快光物理研究

采用飞秒泵浦探测技术研究了紫细菌外周捕光天线LH2中的超快光动力学过程.从B800蓝侧的激发态动力学中观察到B800到B850的能量传递时间,实验结果与理论计算结果的差别说明激发B800时可能引起B850上激子带的直接激发,或存在由B800到B850上激子态的能量传递通道.在B800红侧激发的动力学过程中,漂白信号前端存在的一个快速光吸收信号主要来源于B850上激子带的直接激发.在天然RS601和突变体GM309的LH2中,800 nm激发时的动力学过程都表现为一个类似的光漂白过程,动力学曲线的衰减时间常量在天然LH2中明显快于突变体中,说明在GM309中B800到B850的激发能传递速率有所降低.而在845 nm激发下两个样品中的快过程类似,但慢过程在GM309中有所增快,激发态中的能量重新分布包括逆向的能量传递也受到类胡萝卜素微结构的影响.     

Single-shot ultrabroadband two-dimensional electronic spectroscopy of the light-harvesting complex LH2

Here we present two-dimensional (2D) electronic spectra of the light-harvesting complex LH2 from purple bacteria using coherent pulses with bandwidth of over 100 nm FWHM. This broadband excitation and detection has allowed the simultaneous capture of both the B800 and B850 bands using a single light source. We demonstrate that one laser pulse is sufficient to capture the entire 2D electronic spectrum with a high signal-to-noise ratio. At a waiting time of 800 fs, we observe population transfer from the B800 to B850 band as manifested by a prominent cross peak. These results will enable observation of the dynamics of biological systems across both ultrafast (<1 ps) and slower (>1 ms) timescales simultaneously.     

Coherence effects in the exciton transfer in LH2 unit

The LH2 subunit ofRps. acidophila consists of a ring of 9αβ heterodimers to which BChl’s are associated. We apply the strong exciton coupling model in which allαβ BChl₂ pairs are organized in a cyclic unit cell and strongly excitonically coupled. We investigate the exciton energy structure with heterogeneity both in the local BChl850 energies and in transfer integrals. We calculate the pure coherent memory functions of the LH2 subunit which enter the time nonlocal Generalized Master Equations in various regimes of the exciton transfer. We discuss the influence of the exciton interaction with a bath (phonons) on the time dependence of the memory functions and we show limits of the use of the time local Pauli Master Equations. We study also the influence of the heterogeneity in the local BChl850 energies and in transfer integrals on the delivery time of the exciton inside of the LH2. Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic, 26–30 May 1997. This work was supported by the Grants 105/95 of the Charles University and 1235/96 of the Development Fund.     

The study of photo-induced ultrafast dynamics in light-harvesting complex LH2 of purple bacteria

In this paper, we introduce the photo-induced ultrafast dynamics taking place in the peripheral light harvesting antenna LH2 from purple bacteria Rhodobacter sphaeroides by using absorption, fluorescence emission and ultrafast spectroscopic techniques. Three kinds of LH2 samples, pH treated LH2 (complete removal of B800 pigments), carotenoid mutated LH2 (GM 309) and electrochemical oxidation treated LH2 were used in comparison with native LH2 to investigate the mechanism of photo-induced ultrafast energy transfer within the LH2 complex.     

Exciton delocalization probed by excitation annihilation in the light-harvesting antenna LH2

Singlet-singlet annihilation is used to study exciton delocalization in the light harvesting antenna complex LH2 (B800-B850) from the photosynthetic purple bacterium Rhodobacter sphaeroides. The characteristic femtosecond decay constants of the high intensity isotropic and the low intensity anisotropy kinetics of the B850 ring are related to the hopping time tau(h) and the coherence length N(coh) of the exciton. Our analysis yields N(coh) = 2.8+/-0.4 and tau(h) = 0.27+/-0.05 ps. This approach can be seen as an extension to the concept of the spectroscopic ruler.     

Multivariate analysis of single-molecule spectra: surpassing spectral diffusion

The full exploitation of single-molecule spectroscopy in disordered systems is often hampered by spectral diffusion processes of the optical transitions due to structural fluctuations in the local environment of the probe molecule which leads to temporal averaging of the signal. Multivariate statistical pattern recognition techniques, originally developed for single-molecule cryoelectron microscopy, allow us to retrieve detailed information from optical single-molecule spectra. As an example, we present the phonon side band of the B800 excitations of the light-harvesting 2 (LH2) complex from Rhodospirillum molischianum, revealing the electron-phonon coupling strength for these transitions. The measured Debye-Waller factors, ranging from 0.4 to 0.9, fall in the regime of weak electron-phonon coupling.     

Site-selection optical spectra of bacteriochlorophyll and bacteriopheophytin in frozen solutions

Site-selection spectra of title compounds in different frozen solvents at 5K have been obtained: fluorescence spectra on selective excitation in vibronic as well as in the O-O absorption region and excitation spectra with narrow-band fluorescence recording. Frequencies of vibrational modes active in fluorescence and excitation spectra of bacteriochlorophyll a (BChl) and its metal-free derivative have been determined from these fine-line spectra. Most favourable vibronic line-to-background intensity ratios have been found in non-polar aprotic glassy environments (triethylamine, di-iso-amylether). The intensity of zero-phonon lines in microcrystallic protic matrices was low, indicating strong electron-phonon coupling. The vibrational frequencies of the excited electronic state characteristic of axially (at Mg atom) mono- and disolvated BChl species have been identified. Narrow spectral holes of about 20% of the initial absorption could be burned with ≈10^-4 quantum yield within the O-O band of BChl and bacteriopheophytin.     

Upconversion in Highly Doped Er3+-Yb3+ Fiber Pumped by Ti:Sapphire Laser at 800 nm

The up-conversion processes were investigated in highly doped Er3+-Yb3+ silica fiber pumped by CW or mode-locked Ti:Sapphire laser at 800 nm band. The mechanism is different from that at 980 nm pumped band. The pumping wavelength and power dependences of green, blue and red fluorescence emission were obtained. The up-conversion efficiencies of different doped concentration were investigated. The strong infrared emissions, which limit the efficiency of up-conversion were observed.     

Upconversion in Highly Doped Er3+-Yb3+ Fiber Pumped by Ti:Sapphire Laser at 800 nm

The up-conversion processes were investigated in highly doped Er3+-Yb3+ silica fiber pumped by CW or mode-locked Ti:Sapphire laser at 800 nm band. The mechanism is different from that at 980 nm pumped band. The pumping wavelength and power dependences of green, blue and red fluorescence emission were obtained. The up-conversion efficiencies of different doped concentration were investigated. The strong infrared emissions, which limit the efficiency of up-conversion were observed.     

The Paths of Excitation Energy Deactivation in LH1 Reduced Mutant and Wild-Type Strains of Rhodobacter sphaeroides

The P3 mutant of Rhodobacter sphaeroides had an altered ratio of reaction center to core (LH1) and peripheral (LH2) antenna complexes compared to the wild-type strain. Intracytoplasmic membranes from these two strains were purified and then resuspended in buffer or immobilized in isotropic and stretched polymer film. The absorption, photoacoustic, and delayed luminescence spectra were measured. The ratios of infrared absorption and photoacoustic bands (located at about 880 nm for LH1 and at 850 and about 800 nm for LH2) as well as the half-width of these bands are different for the LH2 and LH1 mutants and wild-type strain. The whole yields of thermal deactivation of the two strains were comparable, but in the absorption region of LH2 it was slightly lower in the case of the mutant than for the wild-type strain. The delayed luminescence main maxima were observed at about 860 and 700 nm. The first one could be due to emission of bacteriochlorophyll a of LH2 complexes. The emission at about 700 nm is probably due to dihydromesochlorophyll, which is usually, to some extent, produced from bacteriochlorophyll a in bacterial complexes. The delayed luminescence emission is competing with excitation energy transfer to the reaction center. The intensity of the delayed luminescence of the mutant strain was higher than that of the wild-type strain when both samples were excited in a region of carotenoid absorption. The mutant contains less carotenoids than the wild-type strain. Carotenoids work as efficient antenna. When they at a lower concentration the excitation can be trapped more easily by some chlorophyll-like pigment isolated from the excitation energy chain. The dependences of delayed luminescence spectra on the light polarization and excitation wavelengths for the wild-type strain and for the mutant were different. The anisotropy of delayed luminescence showed that bacteriochlorophyll a molecules of different orientations were contributing to the mutant and the wild-type strain emission. All the results suggest that the excitation energy transfer from the antenna to the reaction center in the mutant and the wild-type strain is similar.     

太阳能分光发电系统的光学薄膜滤波片设计与仿真

由于不同材料的禁带宽度不同,对太阳光谱的吸收曲线也各不相同,探讨了用等效折射概念设计滤光片的原理和计算方法.针对非晶硅、单晶硅和砷化镓的吸收谱线设计了一组短波通滤光片,滤波片A在波长380～800nm处,平均透射率T＞90％;在波长880～1100 nm处截止,平均透射率T＜1％;滤波片B在380～500 nm处T＞9...     

紫色光合细菌中类胡萝卜素的选择性分布及功能

紫色光合细菌Rhodopseudomonas (Rps.) palustris光合膜中的外周捕光天线(LH2)及核心复合物(LH1-RC)中都含有多种类胡萝卜素分子(Crt)。研究不同种类的Crt在上述色素蛋白复合物中的分布及其生理学功能具有重要意义。采用了高效液相色谱(HPLC)手段分析了中等光强(～4 000 lux)培养条件下所获得的Rps. palustris的LH2及LH1-RC中的Crt组成,发现共轭双键数目(n)为11或12的类胡萝卜素分子(包括lycopene(n=11),Anhydrorhodivibrin(n=12)及Rhodopin(n=12)等,主要集中在LH2复合物中,而n=13的类胡萝卜素分子Spirilloxanthin则优先结合到LH1-RC中。通过将稳态吸收光谱及近红外荧光激发光谱在细菌叶绿素的Qx带处归一化,并比较两者的数值,发现在LH2中Crt从单重态向BChl的传能效率［30.9%(v=0),25.4%(v=1),30.4%(v=2)］明显高于在LH1-RC中的传能效率［10.7%(v=0),7.8%(v=1),11.4%(v=2)］。此外,本文还运用亚微秒时间分辨吸收光谱检测了类胡萝卜素三重态T_n←T₁吸收,发现伴随着532 nm激光脉冲激发,LH1-RC和LH2中Crt三重态的吸收主峰位于571及560 nm左右,它们分别归属于n=13和n=12的类胡萝卜素分子。通过对动力学衰减曲线进行单指数拟合,发现前者的衰减时间常数(1.6 μs)明显短于后者(2.2 μs)。上述研究结果表明,短链Crt易于结合到LH2中承担捕光的功能,而长链Crt优先结合到LH1-RC中发挥光保护功能。     

经不同pH值不同时间酸处理的DNA溶液拉曼光谱分析

小牛胸腺DNA被配制成pH 3.0,pH 2.0,pH 1.0的酸性溶液,在其进行水合的过程中分别测试了样品经过1,2,12和24 h后的拉曼谱图。实验结果表明,DNA分子内部发生了明显的质子化作用,其拉曼特征频率和强度均发生了不同程度的变化,而且随着不同的pH值和不同时间的酸处理它们的变化程度也不同。在pH 3.0的DNA溶液中仅在1 h处理后的拉曼谱图出现了微弱的A构型DNA的特征峰,溶液中主要以存在B构型为主,并有C构型特征峰的出现且随着水合时间的延长,该峰强增加。在pH 2.0的DNA溶液中仅见B构型和C构型特征峰,随着时间的增加,B型特征峰峰强逐渐减弱且伴随着C型特征峰峰强的增加。在pH 1.0的DNA溶液中B,C构型特征峰基本消失,出现了强度很大的891 cm-1峰以及1 265和1 418 cm-1峰,它们是Z构型的特征峰,891和1 265 cm-1峰随时间的延长峰强增加而1 418 cm-1随时间延长峰强减弱。从pH 3.0开始,随着酸性的增强和时间的延长,DNA溶液质子化程度逐渐加深,直到pH 1.0时其双螺旋结构遭到严重的修饰和发生变化。     

CdTe/CdO nH2O核壳纳米复合粒子的水相合成及光学特性.

"研究了CdTe/CdO?nH2O核壳纳米复合物的水相合成及其光学特性． 以巯基乙酸为稳定剂通过氯化镉和碲氢化钠反应制备了碲化镉纳米晶． 在反应过程中, 反应前驱溶液中镉离子与碲离子的摩尔浓度比对最终制备的碲化镉纳米晶的荧光强度起到了极其重要的作用． 在pH值为8.2, 镉离子与碲离子摩尔浓度比为4.0的情况下,制备出了具有最强荧光强度的碲化镉量子点．之后,CdTe/CdO?nH2O核壳纳米复合物在水相中制备出来．在适当的氢氧化镉沉积在碲化镉纳米粒子表面后,碲化镉量子点的荧光大大增强．所制备的CdTe/C     

Pulsed laser deposition of polymers doped with fluorescent molecular sensors

Pulsed laser deposition (PLD) has been used to obtain thin films of poly(methyl-methacrylate), PMMA, and polystyrene, PS, doped with fluorescent probes based in the amino aromatic compounds S6, DMA-2,4, Dans and Acrid-acryl. These compounds, both in solution and inserted in polymeric films, show solvatochromic emission band shifts upon changes of pH, polarity and viscosity in their micro-environment and, prepared in thin films, could prove advantageous for use as sensors of the presence of contaminating environmental agents. Deposits, obtained by irradiating targets consisting in films of doped PMMA and PS with a Ti:sapphire laser (800 nm, 120 fs pulse), were analyzed by optical and environmental scanning electron microscopy, fluorescence microscopy, laser-induced fluorescence, micro-Raman spectroscopy and flow injection analysis-mass spectrometry. Results show the effective transfer of the polymer and the probe to the substrate and the high dependence on film structure on the polymer used in the targets. Irradiation with a KrF laser (248 nm, 20 ns) of Dans-doped targets only produced deposits when using PMMA for target preparation. Results are discussed in terms of the participation of multiphoton processes in the fs IR irradiation, the influence of the linear absorption coefficient of the targets and of the different contributions of thermal and chemical effects in the IR femtosecond and UV nanosecond domains. PACS 81.15.Fg; 61.82.Pv