ENERGY TRANSFER BETWEEN THE PRIMARY DONOR BACTERIOCHLOROPHYLL AND CAROTENOIDS IN Rhodopseudomonas sphaeroides

Abstract— The temperature dependencies of the primary donor triplet state spectra are presented for the phorosynthetic bacteria Rhodopseudomonas sphaeroides wild type. GIC and R26. The data suggest that energy transfer from the primary donor triplet state to the reaction center carotenoid is dependent on the type of carotenoid present, reversible in the case of strain GIC, and best understood by a model depicting the kinetic processes that can occur between two potential energy surfaces; one representing the state ³BChl₂*Car and the other representing BChl₂³Car*. Furthermore, it is shown that the onset of spin lattice relaxation in the primary donor triplet is most likely coupled to the same energy vibrational mode as that which promotes triplet state energy transfer from the primary donor to the reaction center carotenoid     

CONFIGURATIONS OF CAROTENOIDS IN THE REACTION CENTER and THE LIGHT-HARVESTING COMPLEX OF Rhodospirillum rubrum. NATURAL SELECTION OF CAROTENOID CONFIGURATIONS BY PIGMENT PROTEIN COMPLEXES

Abstract— Carotenoids extracted from the reaction center (RC), the light-harvesting complex (LH), and the chromatophore membrane of Rhodospirillum rubrum SI were analyzed by high-performance liquid chromatography. The chemical structures and the configurations of major components were determined by means of mass, Raman, electronic absorption and ¹H-NMR spectroscopy. The results indicated: (1) 15- cis -spirilloxanthin is bound to RC; (2) both all-frans-spirilloxanthin and aII-(ran.s-3,4-dihydrospirilloxanthin are bound to LH and (3) 13-cK-spirilloxanthin is additionally present in the chromatophore membrane. The natural selection of the carotenoid configurations, i.e. 15-ris by RC and aW-trans by LH, is discussed in relation to the physiological functions and the photophysical properties of isomeric carotenoids.     

SPECTROSCOPIC CHARACTERIZATION OF TWO FORMS OF THE D1-D2-CYTOCHROME b559 COMPLEX FROM SUGAR BEET

Two D1-D2-cytochrome b559 complex forms, called RCIIa and RCIIb, with different pigment stoichi-ometry were characterized using absorption and surface-enhanced resonance Raman scattering spectroscopy and spectral gaussian deconvolution. Electronic absorption spectra of the RCIIb at 277 K showed significant differences compared to RCIIa, i.e . a strong decrease in the absorbance due to carotenoid and chlorophyll for the same amount of pheophytin. A reduced carotenoid and chlorophyll content in RCIIb was also observed in the surface-enhanced resonance Raman scattering spectra. Spectral deconvolution elicited three main absorption bands at 680, 672 and 669–670 nm, which were ascribed to P680, pheophytin and accessory chlorophyll, respectively. In addition, a minor component around 667 nm was observed in the RCIIb, most probably due to some reaction center inactivation. Calculation of the relative area under the gaussians together with pigment stoichiometry data suggest that the 680, 672 and 669–670 nm components contain, respectively, two chlorophylls, two pheophytins and four chlorophylls for the RCIIa, and two chlorophylls, two pheophytins and two chlorophylls for the RCIIb.     

THE REACTION CENTER OF PHOTOSYNTHETIC BACTERIA

Abstract. Investigations on the bacterial photosynthetic reaction center have recently made several important steps forward. Progress has been made in measuring the time course of the light-driven reactions, and in understanding the thermodynamics of these processes, in determining the chemical-structural properties of the protein and its constituents, and in elucidating the functional relationship of the reaction center with the chromatophore membrane. Although the well-characterized Rhodopseudomonas sphaeroides reaction center has been the main exploratory vehicle in many of these studies, we now have an ever increasing body of information from bacteria of other species and genera. This work is providing information from which we can underline features that are common to bacterial reaction centers, but it also reveals differences which may reflect different selection pressures on the separate species.
In this report we shall describe the early photochemical events of the reaction center, summarize the comparative biology of the reaction center, and discuss some of the current physical-chemical problems pertaining to the redox components of the reaction center.     

ISOLATION AND PARTIAL CHARACTERIZATION OF THE PHOTOCHEMICAL REACTION CENTER OF CHROMATIUM VINOSUM (STRAIN D)

Abstract— –A preparation of the photochemical reaction center of Chromatiwn has been obtained by chromatography of lauryldimethylamineoxide-solubilized chromatophores on hydroxylapatite and Sepharose columns. The procedure has yielded a reaction center preparation from both carotenoid-containing and carotenoid-deficient Chromatium cells. Preliminary analysis of the isolated component indicates that the photochemical reaction center of the Thiorhodaceae is homologous to that of the Athiorhodaceae. In particular, the near infrared absorption spectrum of the Chromatium reaction center preparation shows the same triple-peaked spectrum observed for reaction center preparations from the Athiorhodaceae. The Chromatium preparation undergoes a rapid light-induced oxidation and dark reduction of the reaction center. The ratio of the reaction center to the two membrane-bound cytochromes (cytochrome c₅₅₂ and c₅₅₅) is greatly increased over the ratio observed in chromatophores or in other previously isolated, reaction center-enriched subchromatophore fractions of this organism.     

REVIEW CHARACTERISTIC REACTIONS OF THE ALKOXY GROUPS OF THE ACID DIESTERS OF PHOSPHOROUS ACID

Abstract

This review presents the characteristic reactions of the alkoxy group of the acid diesters of phosphorous acid (RO)₂ P(O)H: transesterification—with the phosphorus atom as the reaction center; alkylation—with the α-carbon atom as the reaction center; dealkylation—with the α-carbon atom as the reaction center. The possibilities of these reactions in the synthesis of end products with various structures and compositions are demonstrated. The perspectives for the practical application of these esters of phosphorous acid are discussed.     

CONFIGURATIONS OF NEUROSPORENE ISOMERS ISOLATED FROM THE REACTION CENTER AND THE LIGHT-HARVESTING COMPLEX OF Rhodobacter spheroides G1C. A RESONANCE RAMAN, ELECTRONIC ABSORPTION, AND 1H-NMR STUDY

Abstract— HPLC analysis of neurosporene extracted from the chromatophore membranes of Rhodobacter spheroides G1C showed two isomeric components 1 and 2. Extract from the light-harvesting complex (LH) gave only component 2, while extract from the reaction center (RC) mainly gave component 1. Both components were isolated, and their configurations were determined by means of (1) resonance Raman, (2) electronic absorption, and (3) ¹H-HMR spectroscopy. The configuration of component 2 originating from LH was determined to be all -trans and that of component 1 from RC was determined to be 15- cis . Thus, our previous configurational prediction of this particular carotenoid bound to RC, by means of resonance Raman spectroscopy, to be 15-cis [Y. Koyama, T. Takii, K. Saiki and K. Tsukida, Photobiochem. Photobiophys. 5 (1983)139–150] is confirmed.     

CHARGE ACCUMULATION IN THE REACTION CENTER OF PHOTOSYSTEM 2

Abstract— The significance of the accumulation of positive charge in the reaction center of the oxygen-evolving system of photosynthesis is discussed. Many experiments on delayed and prompt fluorescence are explained by the electric field caused by positive charges on the various components at the oxidizing side of the photosystem 2 reaction center. A molecular model for this reaction center is proposed.     

新型Ni催化剂催化乙烯聚合的中性机理

用密度泛函理论中的B3LYP LANL2MB方法 ,研究了Ni 水杨亚胺催化剂催化乙烯聚合的中性反应机理并和阳离子活性中心的催化反应机理进行了比较 .计算结果表明 ,整个中性催化机理类似于阳离子催化机理 ,但是也有不同 .两种机理都是从带空位的活性催化剂开始 ,乙烯以垂直于催化剂平面的方式占据空位 ,为了有利于甲基的迁移 ,乙烯向甲基的方向旋转 90° ,形成四元环过渡态 .插入反应发生后 ,Ni和 β C之间形成一种氢桥键 ,协助新空位的形成 ,实现链的增长 .乙烯与中性活性中心的相互作用远远强于乙烯与阳离子活性中心的相互作用 .中性催化机理较阳离子催化机理容易引发 .阳离子催化的过渡态所需的活化能比中性催化所需的活化能低 ,表明阳离子反应机理比中性反应机理容易进行 ,甲基在中性催化过渡态中的迁移明显不同于在酸性液化过渡态中的迁移 .β agostic相互作用在中性催化反应机理中 ,在主导烷基给合物中Ni所带的电荷方面 ,起着关键性的作用 .     

TRIPLET FORMATION AND TRIPLET DECAY IN REACTION CENTERS FROM THE PHOTOSYNTHETIC BACTERIUM Rhodopseudomonas sphaeroides

Abstract— In the reaction center of photosynthetic bacteria, with the primary ubiquinone reduced, the triplet state P^R of the primary electron donor (a pair of bacteriochlorophylls named P) is PO ulated with a takes place in a few ns. We measured by flash absorption spectroscopy the influence of temperature on formation and decay kinetics of P^R and ³Car in the reaction center of several strains of R. sphaeroides . The rate of triplet energy transfer, measured as the decay of P^R after a flash, decreases when the temperature is lowered. Between 60 and 30 K the half-time of energy transfer becomes longer than the ³Car half-time decay (about 6 μs) and below 20 K the transfer is slower than the internal decay of P^R (about 100 μs). In several cases it is clear that P^R and ³Car decay independently and are not in thermal equilibrium. The singlet energy transfer from carotenoid to P occurs with a high efficiency at all temperatures.
The data can be accounted for on the basis of estimated energy levels of P^R and ³Car, in the context of the equilibrium ³P ←³D where ³P is the localized triplet state of P-870 and ³D is another triplet state. A reasonable kinetic scheme leads us to estimate that ³D is 0.0025 ± 0.005 eV above ³P. ³D may thus be the state observed by Shuvalov and Parson (1981). We propose that both triplet and singlet energy transfer between P and the carotenoid occur via a bacteriochlorophyll, to which the carotenoid should be tightly coupled via exchange interaction.     

Triplet State Energy Transfer Between the Primary Donor and the Carotenoid in Rhodobacter sphaeroides R-26.1 Reaction Centers Exchanged with Modified Bacteriochlorophyll Pigments and Reconstituted with Spheroidene

Abstract— The dynamics of triplet energy transfer between the primary donor and the carotenoid were measured on several photosynthetic bacterial reaction center preparations from Rhodobacter sphaeroides : (a) wild-type strain 2.4.1, (b) strain R-26.1, (c) strain R-26.1 exchanged with 13²-hy-droxy-[Zn]-bacteriochlorophyll at the accessory bacteriochlorophyll (BChl) sites and reconstituted with spheroidene and (d) strain R-26.1 exchanged with P-vinyl]-13²-hydroxy-bacteriochlorophyll at the accessory BChl sites and reconstituted with spheroidene. The rise and decay times of the primary donor and carotenoid triplet-triplet absorption signals were monitored in the visible wavelength region between 538 and 555 run as a function of temperature from 4 to 300 K. For the samples containing carotenoids, all of the decay times correspond well to the previously observed times for spheroidene (5 ± 2 us). The rise times of the carotenoid triplets were found in all cases to be biexponen-tial and comprised of a strongly temperature-dependent component and a temperature-independent component. From a comparison of the behavior of the carotenoid-con-taining samples with that from the reaction center of the carotenoidless mutant Rb. sphaeroides R-26.1, the temperature-independent component has been assigned to the buildup of the primary donor triplet state resulting from charge recombination in the reaction center. Arrhenius plots of the buildup of the carotenoid triplet states were used to determine the activation energies for triplet energy transfer from the primary donor to the carotenoid. A model for the process of triplet energy transfer that is consistent with the data suggests that the activation barrier is strongly dependent on the triplet state energy of the accessory BChl pigment, BChl_B.     

COMPARISON OF PHOTOTRAP COMPLEXES FROM CHROMATOPHORES OF RHODOSPIRILLUM RUBRUM, RHODOPSEUDOMONAS SPHEROIDES, AND THE R-26 MUTANT OF RHODOPSEUDOMONAS SPHEROIDES*

Abstract— After dissolution of the membrane structure of chromatophores from Rhodospirillum rubrum, Rhodopseudomonas spheroides , and the R-26 mutant of Rhodopseudomonas spheroides , active phototrap complexes from each have been purified by a column electrophoresis procedure. Phospholipids and transition metals were well separated from the phototrap complex in all three systems. The purified R. rubrum phototrap complex retained a full complement of antenna bacteriochlorophyll and carotenoid pigments which had nearly the same absorbance spectra as in the intact cell, and which delivered absorbed light energy to the phototrap with just as high efficiency as in the intact cell. Sodium dodecyl sulfate (SDS) disc gel electrophoresis using Tris buffer showed that these preparations often contained only two prominent polypeptides of 30,000 ± 2000 and 12,000 ± 4000 mol. wt., and a lesser amount of a third polypeptide of 21,000 ± 2000 mol. wt.
The phototrap complexes prepared from the wild type and the R-26 mutant of R. spheroides were similar, in that a partial separation from antenna pigments occurred during column electrophoresis. Both complexes had prominent polypeptides of 24,000 ± 2000 and 21,000 ± 2000 mol. wt., but no polypeptide of 30,000 mol. wt remained after electrophoresis. A third major polypeptide occurred with a mol. wt. of about 12,000 but seemed identifiable with an incompletely separated antenna pigment fraction. The phototrap complex prepared from the R-26 mutant had a typical reaction center spectrum.
In the case of wild type R. spheroides purification, two distinct protein-pigment complexes separated. Although the absorbance of the bacteriochlorophyll and carotenoid pigments were little changed from those of the in vivo system, different polypeptides in the two fractions were observed by SDS disc gel electrophoresis; only one fraction seemed to be intimately related with the phototrap complex.     

Triplet Energy Transfer between the Primary Donor and Carotenoids in Rhodobacter sphaeroides R-26.1 Reaction Centers Incorporated with Spheroidene Analogs Having Different Extents of π-Electron Conjugation

Abstract— Three carotenoids, spheroidene, 3,4-dihydrospheroidene and 3,4,5,6-tetrahydrospheroidene, having 8, 9 and 10 conjugated carbon-carbon double bonds, respectively, were incorporated into Rhodobacter (Rb.) sphaeroides R-26.1 reaction centers. The extents of binding were found to be 95±5% for spheroidene, 65±5% for 3,4-dihydrospheroidene and 60±10% for 3,4,5,6-tetrahydrospheroidene. The dynamics of the triplet states of the primary donor and carotenoid were measured at room temperature by flash absorption spectroscopy. The carotenoid, spheroidene, was observed to quench the primary donor triplet state. The triplet state of spheroidene that was formed subsequently decayed to the ground state with a lifetime of 7.0±0.5 μs. The primary donor triplet lifetime in the Rb. sphaeroides R-26.1 reaction centers lacking carotenoids was 60±5 μs. Quenching of the primary donor triplet state by the carotenoid was not observed in the Rb. sphaeroides R-26.1 reaction centers containing 3,4-dihydrospheroidene nor in the R-26.1 reaction centers containing 3,4,5,6-tetrahydrospheroidene. Triplet-state electron paramagnetic resonance was also carried out on the samples. The experiments revealed carotenoid triple-state signals in the Rb. sphaeroides R-26.1 reaction centers incorporated with spheroidene, indicating that the primary donor triplet is quenched by the carotenoid. No carotenoid signals were observed from Rb. sphaeroides R-26.1 reaction centers incorporating 3,4-dihydrospheroidene nor in reaction centers incorporating 3,4,5,6-tetrahydrospheroidene. Circular dichroism, steady-state absorbance band shifts accompanying the primary photochemistry in the reaction center and singlet energy transfer from the carotenoid to the primary donor confirm that the carotenoids are bound in the reaction centers and interacting with the primary donor. These studies provide a systematic approach to exploring the effects of carotenoid structure and excited state energy on triplet transfer between the primary donor and carotenoids in reaction centers from photosynthetic bacteria.     

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。     

四氢呋喃阳离子聚合向丁二酸酐链转移反应的研究

四氢呋喃阳离子聚合向丁二酸酐链转移反应的研究魏斌，赵庆香，栗方星（南开大学化学系天津３０００７１）关键词聚四氢呋喃，五氯化锑，表现链转移速率常数，表现聚合反应速率常数前言在用ＣＨ３ＣＯＳｂＣｌ５引发的四氢呋喃阳离子聚合［１］过程中，我们发现存在着活性...     

Time-dependent changes in the carotenoid composition and preferential binding of spirilloxanthin to the reaction center and anhydrorhodovibrin to the LH1 antenna complex in Rhodobium marinum

Carotenoids were isolated from the cells of Rhodobium marinum, and their structures were determined by mass spectrometry and 1H nuclear magnetic resonance spectroscopy; the carotenoids include lycopene, rhodopin, anhydrorhodovibrin, rhodovibrin and spirilloxanthin. Time-dependent changes in the carotenoid composition in the reaction center (RC) and the light-harvesting complex 1 (LH1) were traced by high-performance liquid chromatography analysis of the extracts. The carotenoid composition changed according to the spirilloxanthin biosynthetic pathway. However, spirilloxanthin having the longest conjugated chain was always preferentially bound to the RC, and anhydrorhodovibrin and other precursors to the LH1.     

TRANS-MEMBRANE LOCALIZATION OF REACTION CENTER PROTEINS IN RHODOPSEUDOMONAS SPHAEROIDES CHROMATOPHORES

Abstract— Rhodopseudomonas sphaeroides NCIB 8253 chromatophores were treated with trypsin and pronase to determine which of the three reaction center subunits was exposed at the outer surface and susceptible to digestion. Trypsin (37°C, 60min) produced no detectable digestion of any subunit, based on SDS polyacrylamide gel electrophoresis analysis. Pronase (37°C, 60min) digested the H (28 kdalton) subunit but left the M (22 kdalton) and L (19 kdalton) subunits intact. We conclude that the H subunit is significantly exposed at the outer chromatophore surface but that the M and L subunits are probably not externally exposed. Chromatophores which had been pronase-treated were fully photochemically active, as measured by light-induced carotenoid bandshift at 522 nm. The H subunit is apparently unnecessary for primary photochemistry in situ.     

INTENSITY AND TIME-DEPENDENCE OF THE CAROTENOID TRIPLET QUENCHING UNDER LIGHT FLASHES OF RECTANGULAR SHAPE IN CHLORELLA

Abstract— As is known the chlorophyll fluorescence of photosynthetizing plants is strongly quenched by carotenoid triplet states if the exciting light intensity is high enough (> 10 kW/m²). This light-induced quenching process was studied by measuring the relative yield of chlorophyll fluoresccncc excited with a pulsed argon laser at 20 C in light adapted algae as function of time (within lo μ s ) and exciting light intensity (<400 kW/m²). The experimental yield against time and yield against intensity curves have been adequately explained by a statistical model of Photosystem 2 (PS 2) units based upon the existence of freely moving excitons according to which the carotenoid triplet quenchers are randomly distributed and are perfect traps for excitons. Accepting the hypothesis that carotenoid triplet quenching occurs only in PS 2 units. it could be concluded that the height of the true zero level of PS 2 fluorescence is somewhat lower than the half value of the fluorescence level of the dark adapted state.     

ELECTROCHROMIC BAND SHIFTS OF CAROTENOID IN A BLUE-GREEN ALGA

Abstract— The excitation with a short flash of cells of a blue-green alga, Synechococcus sp., induced, besides photooxidation of cytochrome c -553 and P-700, small absorption changes of complex kinetics in the wavelength region between 450 and 570 nm. The absorption changes were resolved into two kinetic components different in their sensitivity to gramicidin D.
The ionophore-sensitive component (Gs), which rose very rapidly on flash illumination and decayed with a half-time of 3 ms, has spectral features indicating a red shift of carotenoid absorption bands. Gs was sensitive to valonomycin but not to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). The relaxation rate of Gs was markedly slowed down in the presence of tri- n -butyltin chloride. Phenazine methosulfate induced a secondary slow rise following the initial rapid rise. A similar slow rise appeared in the dark-starved cells but disappeared on the addition of methyl viologen. It is concluded from these results that Gs is an electrochromic band shift of carotenoid responding to the electric field formed by the primary charge separation of the photosystem I reaction center and its decay is related to the proton translocation through a proton channel of the membrane.
The ionophore-resistant component rose and decayed with the half-times of 0.2 and 2 ms, respectively. Its difference spectrum suggests a blue band shift of carotenoid. The ionophore-resistant component was also insensitive to DCMU. However, this component may be related in some way to flash-induced electron flow, because the photoresponse was altered by dibromothymoquinone, bathophenanthroline and 2- n -heptyl-hydroxyquinoline- N -oxide or the dark starvation of cells, which were all effective in inhibiting the cytochrome c -553 reduction.     

RESONANCE RAMAN EVIDENCE FOR 15-cis TO MA,-trans PHOTOISOMERIZATION OF SPIRILLOXANTHIN BOUND TO A REDUCED FORM OF THE REACTION CENTER OF Rhodospirillum rubrum SI

The reaction center (RC) of Rhodospirillum rubrum SI, which was prepared by ultrafiltration, showed one peak in molecular-sieve HPLC, but it showed two peaks in diethylaminoethyl (DEAE) ion-exchange HPLC; they were named as RC-α and RC-β in the order of elution, Nonequilibrated isoelectric electrophoresis, together with DEAE ion-exchange HPLC, showed that RC-β is electronically more negative than RC-α. Oxidation of RC-β by addition of ferricyanide caused its transformation into RC-α, while reduction of RC-α by adding ascorbate and subsequent illumination caused its transformation into RC-β. Resonance Raman spectroscopy of the RC at liquid nitrogen temperature detected the all-trans and the 15-cis isomers in a ratio of 1:1, but HPLC analyses of the carotenoid extracted from the RC before and after the Raman measurements detected the pair of isomers in a ratio of 1:6. Thus, the 15-cis to all-trans isomerization takes place during irradiation at liquid nitrogen temperature, while the reverse isomerization takes place in the dark. The isolated RC-α and RC-β exhibited the bleaching of the 868 nm band, and contained the H, M and L subunits and 1.2-1.4 molecules of ubiquinone-10 per RC. Each RC slowly equilibrated in the dark toward a mixture of RC-α and RC-β. Generation of the all-trans isomer in the light was found not in RC-α but in RC-β.