PICOSECOND TIME RESOLVED FLUORESCENCE OF CHLOROPHYLL IN VIVO

Abstract. The published data concerning the fluorescence kinetics of chlorophyll a in various photosynthetic species are reviewed. The effects of singlet-singlet and singlet-triplet annihilation induced by excessively high incident light intensities are discussed and related to the changes produced in the fluorescence lifetimes and quantum yields. We also review the fluorescence lifetimes of Chlorella pyrenoidosa and spinach chloroplast fragments under a variety of experimental conditions; these measurements were performed at single pulse excitation intensities of less than 5 × 10¹³ photons cm^–2 where distortion due to annihilation processes is negligible. Evidence for and against a time dependent rate equation for energy migration will be discussed with reference to the authors' work on in vitro systems.     

PICOSECOND ABSORPTION SPECTROSCOPY OF CHLOROPHYLL A DIHYDRATE

Abstract— The solution of chlorophyll a in hexane with more than 70% of chlorophyll molecules in the form of the dihydrate (CHl-a.2H₂O)_n is investigated at room temperature by picosecond absorption technique. The transient difference spectra and the kinetic dependences of the absorption changes are measured for several excitation and probe wavelengths. Creation of a new state with blue-shifted absorption band is observed in the system after excitation. A model of the behaviour of the system after excitation is proposed and checked by comparison of the computer-simulated spectral and time dependences with the experimental data. According to the model, about 30% of excited molecules are in the state with the 0.046 eV shift of the absorption band in comparison with the ground state absorption. The lifetime of this state has 170-ps component. The rest of the excited molecules are in the first excited state with the decay time component of 37 ps.     

A SINGLE PULSE PICOSECOND LASER STUDY OF EXCITON DYNAMICS IN CHLOROPLASTS

Abstract. Using single picosecond laser pulses at 610 nm, the fluorescence yield (φ) of spinach chloroplasts as a function of intensity ( I ) (10¹²-10¹⁶ photons/pulse/cm²) was studied in the range of 21–300 K. The quantum yield decreases with increasing intensity and the φ vs I curves are identical at the emission maxima of 685 and 735 nm. This result is interpreted in terms of singlet exciton-exciton annihilation on the level of the light-harvesting pigments which occurs before energy is transferred to the Photosystem I pigments which emit at 735 nm.
The yield φ is decreased by factors of 12 and 43 at 300 and 21 K, respectively. The shapes of the φ vs I curves are not well accounted for in terms of a model which is based on a Poisson distribution of photon hits in separate photosynthetic units, but can be satisfactorily described using a one-parameter fit and an exciton-exciton annihilation model. The bimolecular annihilation rate constant is found to be γ= (5–15) times 10^-9cm³s^-1 and to exhibit only a minor temperature dependence. Lower bound values of the singlet exciton diffusion coefficient (≥ 10^-3cm²s^-1), diffusion length (≥ 2 times 10^-6cm) and Förster energy transfer rates (≥ 3 ≥ 10¹⁰s^-1) are estimated from γ using the appropriate theoretical relationships.     

NEAR-INFRARED FOURIER-TRANSFORM RAMAN STUDY OF CHLOROPHYLL a IN SOLUTIONS

Abstract— The 1064 nm excited Fourier-transform (FT) Raman spectra have been measured for chlorophyll a (Chl- a ) in various solutions. Features of the obtained spectra are largely different from those of Soret-resonant Raman spectra of Chl- a . For example, a band due to the C=0 stretching mode of the 13-keto group is much stronger in the former than in the latter. Although the excitation wavelength is rather far from that of the Qy absorption of Chl- a , notable enhancements of bands due to the C=O stretching mode of the 13¹-keto group and to the C=C stretching mode of the vinyl group and those in the 1250–600 cm^-1 region suggest that the 1064 nm-excited Raman spectra of Chl- a are preresonance enhanced via the Qy band. Some of the marker bands for the coordination number of the central Mg atom, which have been used in the visible-excited resonance Raman spectra, are not valid in the 1064 nm-excited Raman spectra. Instead, new marker bands are found in the latter. The 1064-nm excited Raman spectra of Chl- a in a hydrated hexane solution reveal that the dehydrated oligomer of Chl- a as well as Chl- a -water micelles coexist in the solution. They also suggest that the size of the oligomer is considerably larger and the hydrogen bonding of the 13¹-keto group in the oligomer is weaker than that in the micelles.     

A FLASH PHOTOLYSIS STUDY OF INTERMEDIATES IN PHOTOCHEMICAL REACTIONS OF CHLOROPHYLL

Abstract— The photochemical reactions of chlorophyll intermediates in vitro have been studied by the flash photolysis method. The flash excitation of pigment solutions has been shown to involve the population of a chlorophyll triplet state where the oxidation-reduction processes occur. The mechanism and kinetics of pigment triplet decay have been investigated from 20°to — 50°C and the ability of chlorophyll molecules to carry out triplet-triplet energy transfer has been established. The latter phenomenon has been used to show up the role of chlorophyll triplets in the reversible photooxidation reaction with P -quinone. There have been studied initial products of pigment photoreduction with ascorbic acid and phenylhydrazine. Experimental data of the mechanism of the initial oxidation and reduction in chlorophyll photosensitized reactions have been analysed. There have been also obtained the differential spectra of chlorophyll triplets and radicals. A calculation has been made of rate constants for a few elementary reactions.     

A STUDY OF CHLOROPHYLL FLUORESCENCE IN VIVO BY A FLOW METHOD

Abstract— A flow method has been devised for the study of fluorescence transients during the induction period of photosynthetic systems. The principle of transformation of time-transients into space-transients is quantitatively worked out and the characteristics and mode of operation of the apparatus is described and illustrated with experimental results.
With this method spectroscopic and kinetic investigation of in vivo chlorophyll fluorescence have been undertaken. The fluorescence emission can be split into two componmts—a variable part and a constant part—with different spectral distributions. The excitation spectrum of the light induced fluorescence changes shows that the variable part is sensitized by system 11, whereas the constant part mainly sensitized by system II has a small component originating from system I. The light-induced fluorescence change decays in darkness with half-time of about 10 ^-2 s; this decay is highly sensitive to the action of inhibitors of oxygen evolution.
The flow method can be extended to measurements of oxygen, luminescence, absorption differences. It permits using high-intensity analytic beams with no actinic action; it is well suited for the integration of low level signals.     

ON THE NATURE OF CHLOROPHYLL a IN AQUEOUS MICELLAR SYSTEMS

Abstract— Absorption and fluorescence spectra of chlorophyll a in aqueous micellar solutions were studied. Solutions in anionic micelles gave an absorption band at 740 nm, attributable to microcrystal- line chlorophyll a. Solutions in cationic and nonionic micelles do not show this band. The positions of the spectral bands in anionic micelles and the possible structure of microcrystalline form are discussed. A comparison is made of the behaviour of microcrystalline form in hydrocarbon solvents and in micellar solutions.     

甲基苯热裂解机理的理论研究

在半经验UAM1方法及从头算UHF／3－21G*水平的基础上,用考虑了电子相关效应的密度泛函UB3LYP／3－21G＊方法对碳前驱体甲基苯的热裂解反应机理进行了研究,并对反应物、产物自由基及过渡态的结构进行了能量梯度法全优化。计算结果表明,甲基苯的热裂解温度较低时,首先支持苯环甲基上的C－H键断裂,继而发生生成联二甲苯的反应。随着温度的提高,生成苯自由基的反应比例将增加,同时发生少量的苯环上C－H键断裂的反应。该反应机理与实验结果相一致;用密度泛函方法UB3LYP／3－21G*计算的反应标准焓变ΔH与实验值吻合较好。     

FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF THE STRUCTURE OF CHLOROPHYLL a and CHLOROPHYLL b IN HIGHLY DILUTE WATER-SATURATED CARBON TETRACHLORIDE SOLUTIONS

Abstract— Fourier-transform (FT) infrared (IR) absorption spectra have been measured for chlorophyll a (Chi a ), chlorophyll b (Chi b ), pheophytin a (Pheo a ), and pheophytin b (Pheo b ) in highly dilute (10^-5-10^-6 M ) water-saturated carbon tetrachloride solutions. Frequencies of IR bands due to C=O stretching modes of the 9-keto group indicate that Chi a assumes largely a dimeric structure in the concentrated (10^-2-10^-3 M ) water-saturated carbon tetrachloride solutions but it remains mostly a monomer with one or two coordinated water molecules in dilute (10^-5-10^-6 M ) solutions. Although it seems that Chi b also assumes predominantly dimeric form in concentrated solutions and monomelic form in dilute solutions, the relative intensity change of two C=O stretching bands ascribed to the free and coordinated 3-aldehyde groups with decreasing concentration suggests that the aldehyde group is also involved in formation of the dimer. The relative intensity of two C=O stretching bands due to the free and coordinated aldehyde groups changes significantly for Pheo b in water-saturated carbon tetrachloride solutions. This observation suggests that some of Pheo b also assume dimeric form via the aldehyde group in concentrated solutions.     

光透电极叶绿素夹层电池的研究

报道了光透电极叶绿素夹层电池SnO_2/chla/PVA/SnO_2的光电特性, 讨论了电池发生光电效应的机理, 说明了电池的暗整流作用和光照时电荷分离的结点为chla/PVA. 测量了电池的输出参数并用氢醌等物质对电池进行改进, 使电池短路电流和能量转化率提高一个数量级以上.     

SPECTROSCOPIC STUDY OF CHLOROPHYLL a IN ORGANIC SOLVENTS AND POLYMERIZED ANHYDROUS POLYVINYL MATRIX

In this paper we present a spectroscopic study of chlorophyll a in solutions and in anhydrous polyvinyl alcohol films. Absorption, excitation and emission spectra, combined with fluorescence lifetime and time-resolved anisotropy measurements show that chlorophyll a in anhydrous polyvinyl alcohol films exists in a purely monomeric state. Furthermore, it appears that the monomeric chlorophyll a exhibits an efficient excitation energy transfer in this polyvinyl alcohol matrix. These results are rationalized in terms of a model in which the chlorophyll a molecules are located within pockets, formed by the polymer chains. It is concluded that the chlorophyll a-anhydrous polyvinyl alcohol film is a suitable system for studying energy transfer processes, especially because the factors governing energy transfer such as mutual orientation and separation of the molecules can easily be controlled.     

THE THEORETICAL STUDY OF ADSORPTION OF METAL IONS ON CHITOSAN

1. INTRODUCTION Chitin, the most abundant natural amino polysaccharide and estimated to be produced annually almost as much as cellulose, is well known to consist of 2-acetamido-2-deoxy-β-D- glucose through α, β(1→4) linkage. Chitin is the major source of surface pollution in coastalareas. Chitosan is the N-deacetylated derivative of chitin and their structures are shown in Fig. 1. Fig. 1 Structures of Chitin and Chitosan Because of the excellent properties such as biocompatibility…     

THE THEORETICAL STUDY OF ADSORPTION OF METAL IONS ON CHITOSAN

The interactions between metal ions such as Zn2+, Pb2+, Mn2+, Hg2+, Cd2+, Ni2+ and chitosan have been investigated using the model cluster model method and density functional method. Full optimization and frequency analysis of all cluster models have been performed employing B3LYP hybrid method at 3-21G basis set level except metal ions which were invoked to use effective core potential (ECP) method. The energy changes, and the main structural parameters have been obtained during the theoretical study of the adsorption of metal ions on the chitosan. The calculations showed that the coordination modes of metal ions with chitosan models were different, the geometries of Mn2+, Zn2+, Cd2+, Hg2+, Pb2+ ions coordinated with two nitrogen atoms and two oxygen atoms were distorted tetrahedral, while the square planar structure of Ni2+ coordinated two nitrogen atoms and two oxygen atoms was observed. The heat of reaction between six metal ions and chitosan models showed the order: Mn2+ ＞Ni2+ ＞Zn2+ ＞Pb2+ ＞Hg2+ ＞Cd2+, this suggested that the coordination strength of Mn2+ ＞Ni2+ ＞Zn2+ ＞Pb2+ ＞Hg2+ ＞Cd2+.     

叶绿素、染料体系光电效应的研究

叶绿素光电性质的研究有特殊意义.70年代开始国内外已有很多报道, 它们有整流、光导、光伏和光解水制取氢和氧等性质^[1-5].我们也报道过叶绿素a/聚乙烯醇夹层电池的研究^[6-8]。     

质子化硼烷正离子体系电子结构的理论研究

本文用a b initio计算法和近似a b initio计算法(PRDDO)研究了质子化硼烷正离子体系的电子结构,给出了一些正离子体系的优化几何构型并讨论了它们的成键情况。计算的硼烷分子质子亲和势与实验值相当吻合。     

Ziegler-Natta催化配位聚合反应中AlR_3组分对催化剂活性影响的理论研究

本文采用ASED-MO法对Ziegler-Natta型催化剂催化的α-烯烃聚合过程中AlR_3组分对催化剂活性的影响进行了研究.得到了无AlR_3组分存在和一系列不同AlR_3存在时链增长过程的能量变化和相应的活化能.通过比较看出,AlR_3存在可以明显增强催化剂活性.同时运用分子轨道分析的方法探讨了AlR_3增强催化活性的原因.     

A TWOFOLD ACTION OF PHYTOCHROME IN CONTROLLING CHLOROPHYLL a ACCUMULATION

Abstract— A pretreatment with light prior to continuous illumination with high intensity white light eliminates the lag phase in chlorophyll a accumulation and increases the steady-state rate of chlorophyll a accumulation. In mustard seedlings ( Sinapis alba L.) the effect of a pretreatment can be fully attributed to phytochrome. The effect of phytochrome on chlorophyll a accumulation is twofold. It is possible to separate the effect on the lag phase from the effect on the steady-state rate of accumulation. While the effect on the lag phase is a relatively fast process (occurring within less than 3 h) the effect on the rate requires a considerable period of time (at least 12 h) to become manifest.     

乙叉到乙炔重排反应的反应途径的理论研究

本文用Morokuma提出的数值方案, 基于SCF MO ab initio(STO-3G), 求得了乙叉到乙炔重排反应的内禀反应坐标IRC(Fukui提出的与坐标系无关的反应途径), 并对反应过程中几何构型的改变进行了讨论, 在用MINDD/3方法对诚反应进行研究时, 发现反应过程中有其它中间体存在, 本文也对这种不正确的结果进行了讨论。
本文优化得到的反应物、产物和过渡态几何构型与更精确的理论方法所得的结果定性相符, 用单行列式和CID(考虑所有双激发组态的组态相互作用)所得该反应的位垒分别为123.85和95.81 kJ mol~(-1), 也与更精确方法得到的值相符; 本文还得到了该反应的过渡态的振动频率和正则振动模式。     

THEORETICAL STUDY OF VARIOUS ADSORPTION STATES OF OXYGEN ON SILVER SURFACE

The various adsorption states of oxygen on different sites of silver surfaces have been studied using CNDO method. The result shows that a fairly strong, adsorption bond is formed when oxygen molecule is adsorbed, in lying down position with its axis parallel to the surface, at the surface bridge site having larger silver-silver distance. In this case, the adsorbed oxygen molecule has fairly strong tendency to dissociate. The most favorite sites on Ag(110) and Ag(111) surfaces for oxygen molecules or atoms to be adsorbed have been suggested after calculation and analysis. The differences of oxygen adsorption on these two surfaces mentioned above have been compared. The most stable adsorption states of oxygen are O_2~(2-), O~(2-) on Ag(110) and O_2~-, O~-on Ag(111). On silver film or polycrystalline silver, O_2~(2-), O_2~-, O~(2-), O~- may coexist. The results are in agreement with experiments.