生物光化学中的几个问题

生物光化学是光生物学的基础。生物光化学归根结底是光感受体(即感光的物质)的光化学。但是光感受体范围极广,功能各异,例如有感受紫外光的生物大分子(如蛋白质与核酸);有感受长波紫外光的糠香豆素类物质;有感受可见光的视紫质类物质(如视觉中的视紫质,嗜盐菌紫膜中的菌紫质);植物光合作用的叶绿素以及执行光形态建成的光敏色素等等。     

超分子光化学的前景

近二十年来光化学研究取得了巨大进展.其基本状况可归纳为下列几个方面:一是大量的有机分子、配位化合物、金属有机化合物的光化学和光物理行为已被了解,并得到理论上的阐明,许多重要激发态在结构上、能量上以及动态学方面的研究也已相当深入和完善;另一方面,人们对自然界存在的某些重要的光生物过程也有了相当的认识,包括如光合作用,视觉过程等,但尚未完全弄清.     

凝聚态光化学研究的现状和动向

从史前人走出所居住的洞穴、到阳光下起,人们就已经意识到阳光对自身的作用以及对环境的影响。地球上许多生命过程如光合作用和视觉过程都和光化学过程有关,这不仅反映了太阳辐射是地球主要的能量来源这一事实,而且也说明光化学反应对人类生存的重要意义。现代光化学的开始,如果不考虑十八世纪末Hales对光合作用的报告和十九世纪中叶卤化银照相术的出现,应当认为本世纪初意大利的Clinician和Silber对在有机光化学中的研究     

光化学学术会议在北京举行

光化学是在六十年代蓬勃发展起来的一门新兴学科。它的发展是化学、物理学和生物学相互渗透的结果,也是新的实验技术和理论相结合的结果。光化学和新能源的开发利用、新材料的研制、环境保护、光疗、高分子降解、信息材料以及光合作用等重大科技问题都有     

对光合作用机制研究的一些展望与两点建议

今后我国光合作用研究既要全面开展又要重点突出。现拟就光合作用机制的研究作一些展望,并对重点工作作两点建议。光合作用原初反应的研究原初反应,即光能通过叶绿素转变为化学能的最初步骤,是光合作用的核心问题。自本世纪20年代Warburg将光化学的两个原则运用到光合作用研究开始,物理学家们即着手研究光量子对叶绿素分子激发的状态。和从固体物理学方面研究光对叶绿素的激发。     

有机光化学研究的现状

本文综述了有机光化学的新进展和研究现状。介绍了激发态行为的研究方法,激发态的化学活性,扩散控制的激发能迁移,重要的有机光化学体系,激光化学,生物光化学,有机金属光化学和太阳能的贮存。对许多有价值的课题,作了比较粗略的论述。     

纳米粒子在生物分析中的应用

纳米粒子探针与传统的有机染料相比有更好的光谱特性和光化学稳定性。本文介绍了3种类型的纳米粒子在生物分析中的应用，并评价了其作为生物荧光探针的发展前景。     

欢迎订阅《影像科学与光化学》

《影像科学与光化学》于1983年创刊,原名《感光科学与光化学》,双月刊。主要领域为:影像材料与技术、生物与医学成像、数字成像与器件、印刷技术、柔性电子、图像信息处理、遥感图像、信息材料、光学材料与器件、光谱学、辐射固化、光化学、光电化学、光生物、光医学等。     

人工光合作用

光合作用将太阳能储存在化学反应中,是绿色高效的能量转换途径。模拟自然光合作用系统活性中心的结构和功能,实现小分子物质(H₂O、CO₂、N₂等)中惰性化学键的活化转化,对于解决能源和环境等问题具有重要意义。本文综述了人工光合作用在水分解、二氧化碳及氮气还原领域取得的重要进展,分析了相关光化学转换体系的设计思路和工作原理,并对人工光合作用面临的挑战和未来发展方向进行讨论。     

生物光化学

生物光化学研究光在动植物体内所引起的生化现象。例如:经过各种不同波长的光辐照后的生命现象,生长规律,某些生理和病理过程,疾病的产生和治疗机理,细胞的辐射损伤和自然防御,以及光合色素在生物进化中的作用等。本文就光引起的现象:视觉、生物钟(光周期性)、植物的光合作用、辐射损伤及其修复、牛皮癣的治疗、新生儿黄疸病的治疗机理,以及光合色素——藻胆蛋白等七种现象,做了综述性的介绍。     

Design of synthetic molecular units including quinones towards the construction of artificial photosynthesis

Quinones are essential components in many biological systems, notably in photosynthesis. This is largely due to the characteristic proton-coupled redox chemistry of quinones. This review article overviews the use of quinones in studies on artificial photosynthesis, as one-electron electron acceptors, reversible proton/electron carriers, and replacements for sacrificial oxidant and reductants in photosynthetic chemical conversion. Topics included are the early attempts on intramolecular photoinduced electron transfer involving quinones, subsequent reactions after photoinduced electron transfer between pigments and quinones, photochemistry in molecular assemblies containing quinones, and photochemical quinone/hydroquinone interconversion.     

镉对植物光合作用的影响

从光合速率、叶绿体及叶绿素、光化学反应、电子传递、光合作用中CO2同化等方面概述了镉（Cd）对植物光合作用的影响，力图阐明Cd影响植物光合作用的生理机制。     

Protochlorophyllide a: A Comprehensive Photophysical Picture

The photochemistry of protochlorophyllide a, a precursor in the biosynthesis of chlorophyll and substrate of the light regulated enzyme protochlorophyllide oxidoreductase, is investigated by pump‐probe spectroscopy. Upon excitation into the lowest lying Q‐band the light induced changes are recorded over a wide range of probe wavelengths in the visible and near‐IR region between 500 and 1000 nm. Following excitation, an initial ultrafast 450 fs process is observed related to the motion out of the Franck‐Condon region on the excited state surface; thus directly unraveling previous suggestions based on time‐resolved fluorescence measurements (ChemPhysChem 2006 , 7, 1727–1733). Furthermore, the data reveals a previously concealed photointermediate, whose formation on a nanosecond timescale matches the overall fluorescence decay and is assigned to a triplet state. The implications of this finding with respect to the photochemistry of NADPH:protochlorophyllide oxidoreductase (POR) are discussed.     

Natural and artificial light-harvesting systems utilizing the functions of carotenoids

Carotenoids are essential pigments in natural photosynthesis. They absorb in the blue–green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and so expand the wavelength range of light that is able to drive photosynthesis. This process is an example of singlet–singlet energy transfer and so carotenoids serve to enhance the overall efficiency of photosynthetic light reactions. Carotenoids also act to protect photosynthetic organisms from the harmful effects of excess exposure to light. In this case, triplet–triplet energy transfer from (bacterio-)chlorophyll to carotenoid plays a key role in this photoprotective reaction. In the light-harvesting pigment–protein complexes from purple photosynthetic bacteria and chlorophytes, carotenoids have an additional role, namely the structural stabilization of those complexes. In this article we review what is currently known about how carotenoids discharge these functions. The molecular architecture of photosynthetic systems will be outlined to provide a basis from which to describe the photochemistry of carotenoids, which underlies most of their important functions in photosynthesis. Then, the possibility to utilize the functions of carotenoids in artificial photosynthetic light-harvesting systems will be discussed. Some examples of the model systems are introduced.     

高浓度LaCl3抑制黄瓜(Cucumis sativus Linn)光系统Ⅱ(PS Ⅱ)活性

研究了高浓度LaCl3对黄瓜（Cucumis sativus Linn）光系统Ⅱ（PSⅡ）光诱导荧光动力学参数、低温荧光光谱和放氧活性的影响。结果表明，随着黄瓜体内LaCl3浓度的升高、其荧光量子产率、PSⅡ最大光化学效率、放氧活性和电子传递速率都明显降低。低温荧光分析表明，低浓度LaCl3引起激发能更多的分配给PSⅡ。高浓度LaCl3对黄瓜幼茁的抑制作用表现在对类囊体膜结构的破坏。进而导致PSⅡ光合活性下降，并最终抑制黄瓜生长。     

THE PHOTOPHYSICS AND PHOTOCHEMISTRY OF THE NEAR-UV ABSORBING AMINO ACIDS-III. CYSTINE AND ITS SIMPLE DERIVATIVES

Abstract— The photochemistry of cystine and some of its analogues is reviewed. Topics discussed include the absorption spectra of disulfides, the photochemistry of alkyl disulfides and other more highly substituted disulfides including cystine, photooxidation of disulfides, and photochemical interactions of cystine derivatives with other molecules of biological interest.     

Excited‐State Charge Separation in the Photochemical Mechanism of the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase

The unique light‐driven enzyme protochlorophyllide oxidoreductase (POR) is an important model system for understanding how light energy can be harnessed to power enzyme reactions. The ultrafast photochemical processes, essential for capturing the excitation energy to drive the subsequent hydride‐ and proton‐transfer chemistry, have so far proven difficult to detect. We have used a combination of time‐resolved visible and IR spectroscopy, providing complete temporal resolution over the picosecond–microsecond time range, to propose a new mechanism for the photochemistry. Excited‐state interactions between active site residues and a carboxyl group on the Pchlide molecule result in a polarized and highly reactive double bond. This so‐called “reactive” intramolecular charge‐transfer state creates an electron‐deficient site across the double bond to trigger the subsequent nucleophilic attack of NADPH, by the negatively charged hydride from nicotinamide adenine dinucleotide phosphate. This work provides the crucial, missing link between excited‐state processes and chemistry in POR. Moreover, it provides important insight into how light energy can be harnessed to drive enzyme catalysis with implications for the design of light‐activated chemical and biological catalysts.     

Quantum effects in photosynthesis

In photosynthesis light is absorbed by the light-harvesting antenna and within several tens of picoseconds transferred to the photosynthetic reaction center (RC) where an ultrafast charge separation is initiated. Photosynthetic purple bacteria employ a single reaction center. In contrast, in photosynthesis of plants, algae and cyanobacteria, two reaction centers, Photosystem II (PSII) and Photosystem I (PSI), operate in series. PSII uses light to extract electrons from water (to produce oxygen); PSI uses light to reduce NADP + to NADPH. The electron transfer from PSII to PSI is coupled to the build-up of a proton motive force (pmf) that is used to form ATP. NADPH and ATP are required in the Calvin-Benson cycle to produce a reduced sugar. In the following we will discuss photosynthetic charge separation and photosynthetic light-harvesting with an emphasis on the role of quantum mechanics.     

PHOTOINHIBITION OF CHLOROPLAST REACTIONS

Abstract— An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent-treated chloroplasts were sensitive to a lower degree.
Photoinhibition irreversibly annihilated the 'variable' fraction of fluorescence emission —it decreased the steady state yield 2-3 fold and abolished the slow rise of the emission at the onset of illurnination.
It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre-illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry.