Effect of aggregation state, temperature and phospholipids on photobleaching of photosynthetic pigments in spinach Photosystem II core complexes

Photosystem II (PSII) complex activity is known to decrease under strong white light illumination, and this photoinhibition phenomenon is connected to the photobleaching of the PSII photosynthetic pigments. In this work the pigment photobleaching has been studied on PSII core complexes, by observing the effects of different factors such as the aggregation state (PSII monomers and dimers were used), temperature (20 degrees C and 10 degrees C temperatures were tested) and the presence of the exogenous phospholipids (cardiolipin and phosphatidylglycerol). In particular, PSII resistance against white light stress was studied by means of UV/VIS Absorption and Fluorescence Emission measurements. It was found that PSII dimers resulted more resistant against photobleaching and that lower temperature reduces the pigment photodestruction. Moreover, the presence of phosphatidylglycerol or cardiolipin enhanced the PSII resistance to the photobleaching phenomenon, mainly at lower temperatures.     

Reconstruction of the water-oxidizing complex in manganese-depleted Photosystem II using synthetic manganese complexes

The efficiency of a trinuclear and two binuclear manganese complexes in reconstituting electron transport and O(2) evolution activity in Mn-depleted Photosystem II preparations is analyzed. The trinuclear Mn-complex is more efficient than two binuclear Mn-complexes in restoring oxygen evolution, but it is less effective as an electron donor than binuclear Mn-complexes. It is inferred from our results that recovery of electron transport and O(2) evolution with polynuclear Mn-complexes is affected with different factors. Moreover, the trinuclear Mn-complex is extremely sensitive to the addition of CaCl(2). It is suggested that there is an interaction between Ca(2+) and carboxyl within the trinuclear Mn-complex during photoactivation and this interaction benefits the ligation of Mn atom to the apo-WOC and form an active WOC. Binuclear Mn(III)Mn(III) complex shows slightly higher efficiency than binuclear Mn(III)Mn(IV) complex in restoration of O(2) evolution activity. The efficiency of three Mn-complexes in the reconstitution of WOC is in an order: trinuclear Mn(3)(III)>binuclear Mn(III)Mn(III)>binuclear Mn(III)Mn(IV).     

Light-harvesting and structural organization of Photosystem II: from individual complexes to thylakoid membrane

Photosystem II (PSII) is responsible for the water oxidation in photosynthesis and it consists of many proteins and pigment-protein complexes in a variable composition, depending on environmental conditions. Sunlight-induced charge separation lies at the basis of the photochemical reactions and it occurs in the reaction center (RC). The RC is located in the PSII core which also contains light-harvesting complexes CP43 and CP47. The PSII core of plants is surrounded by external light-harvesting complexes (lhcs) forming supercomplexes, which together with additional external lhcs, are located in the thylakoid membrane where they perform their functions. In this paper we provide an overview of the available information on the structure and organization of pigment-protein complexes in PSII and relate this to experimental and theoretical results on excitation energy transfer (EET) and charge separation (CS). This is done for different subcomplexes, supercomplexes, PSII membranes and thylakoid membranes. Differences in experimental and theoretical results are discussed and the question is addressed how results and models for individual complexes relate to the results on larger systems. It is shown that it is still very difficult to combine all available results into one comprehensive picture.     

Evidence for spatially-coherent trans-molecular electron tunnelling through two-dimensional arrays of Photosystem II core complexes

Localised spatially-coherent electron tunnelling through single Photosystem II complexes and into atomically-flat graphite is observed.     

Chemiluminescence of Mn(II) complexes in oscillatory redox processes

It has been shown that the red chemiluminescence (CL) in the Belousov-Zhabotinskii system with Mn(II, III) cannot be attributed to the formation of excited oxygen or its dimers during the process. Chemiluminescence has been discovered upon the reduction of Mn(III) by malonic acid, and its spectrum coincides with the spectrum of the CL in the oscillatory system (with a maximum at 680–720 nm) and is found in the same region as the photoluminescence of Mn(II),- which is known from the literature data. It has been concluded that the principal emitter of the oscillatory CL is Mn(II), which is formed in an excited state upon the reduction of Mn(III).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 191–197, March–April, 1989.     

FTIR study of manganese dimers with carboxylate donors as model complexes for the water oxidation complex in Photosystem II

The carboxylate stretching frequencies of two high-valent, di-μ-oxido bridged, manganese dimers has been studied with IR spectroscopy in three different oxidation states. Both complexes contain one monodentate carboxylate donor to each Mn ion, in one complex, the carboxylate is coordinated perpendicular to the Mn-(μ-O)(2)-Mn plane, and in the other complex, the carboxylate is coordinated in the Mn-(μ-O)(2)-Mn plane. For both complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequencies decrease for both the Mn(2)(IV,IV) to Mn(2)(III,IV) transition and the Mn(2)(III,IV) to Mn(2)(III,III) transition, with only minor differences observed between the two arrangements of the carboxylate ligand versus the Mn-(μ-O)(2)-Mn plane. The IR spectra also show that both carboxylate ligands are affected for each one electron reduction, i.e., the stretching frequency of the carboxylate coordinated to the Mn ion that is not reduced also shifts. These results are discussed in relation to FTIR studies of changes in carboxylate stretching frequencies in a one electron oxidation step of the water oxidation complex in Photosystem II.     

Functional Models for the Oxygen-Evolving Complex of Photosystem II

In the last ten years, a number of advances have been made in the study of the oxygen-evolving complex (OEC) of photosystem II (PSII). Along with this new understanding of the natural system has come rapid advance in chemical models of this system. The advance of PSII model chemistry is seen most strikingly in the area of functional models where the few known systems available when this topic was last reviewed has grown into two families of model systems. In concert with this work, numerous mechanistic proposals for photosynthetic water oxidation have been proposed. Here, we review the recent efforts in functional model chemistry of the oxygen-evolving complex of photosystem II.     

Detection of mercury(II) based on Hg2+ -DNA complexes inducing the aggregation of gold nanoparticles

A DNA-Au NP probe for sensing Hg2+ using the formation of DNA-Hg2+ complexes through thymidine (T)-Hg2+ -T coordination to control the negative charge density of the DNA strands-thereby varying their structures-adsorbed onto Au NPs.     

Photoinduced processes within compact dyads based on triphenylpyridinium-functionalized bipyridyl complexes of ruthenium(II)

As an alternative to conventional charge-separation functional molecular models based on long-range ET within redox cascades, a "compact approach" has been examined. To this end, spacer elements usually inserted between main redox-active units within polyad systems have been removed, allowing extended rigidity but at the expense of enhanced intercomponent electronic communication. The molecular assemblies investigated here are of the P-(theta (1))-A type, where the theta (1) twist angle is related to the degree of conjugation between the photosensitizer (P, of {Ru(bpy)(3)}(2+) type) and the electron-acceptor (A). 4-N- and 4-N-,4'-N-(2,4,6-triphenylpyridinio)-2,2'-bipyridine ligands (A(1)-bpy and A(2)-bpy, respectively) have been synthesized to give complexes with Ru(II), 1-bpy and 2-bpy, respectively. Combined solid-state analysis (X-ray crystallography), solution studies ((1)H NMR, cyclic voltammetry) and computational structural optimization allowed verifying that theta (1) angle approaches 90 degrees within 1-bpy and 2-bpy in solution. Also, anticipated existence of strong intercomponent electronic coupling has been confirmed by investigating electronic absorption properties and electrochemical behavior of the compounds. The capability of 1-bpy and 2-bpy to undergo PET process was evaluated by carrying out their photophysical study (steady state emission and time-resolved spectroscopy at both 293 and 77 K). The conformational dependence of photoinduced processes within P-(theta (1))-A systems has been established by comparing the photophysical properties of 1-bpy (and 2-bpy) with those of an affiliated species reported in the literature, 1-phen. A complementary theoretical analysis (DFT) of the change of spin density distribution within model [1-bpy(theta (1))](-) mono-reduced species as a function of theta (1) has been undertaken and the possibility of conformationally switching emission properties of P was derived.     

Photosystem II fluorescence: slow changes--scaling from the past

With the advent of photoelectric devices (photocells, photomultipliers) in the 1930s, fluorometry of chlorophyll (Chl) a in vivo emerged as a major method in the science of photosynthesis. Early researchers employed fluorometry primarily for two tasks: to elucidate the role in photosynthesis, if any, of other plant pigments, such as Chl b, Chl c, carotenoids and phycobilins; and to use it as a convenient inverse measure of photosynthetic activity. In pursuing the latter task, it became apparent that Chl a fluorescence emission is influenced (i) by redox active Chl a molecules in the reaction center of photosystem (PS) II (photochemical quenching); (ii) by an electrochemical imbalance across the thylakoid membrane (high energy quenching); and (iii) by the size of the peripheral antennae of weakly fluorescent PSI and strongly fluorescent PSII in response to changes in the ambient light (state transitions). In this perspective we trace the historical evolution of our awareness of these concepts, particularly of the so-called 'State Transitions'.     

LaCl3提高菠菜光系统Ⅱ活性的作用机制

The effect of LaCl3 on the K3Fe(CN)6 (FeCy) reduction rate and the oxygen-evolving rate of PSU particles of spinach, and the spectral characterization of the D1/D2/Cytb559 of a PSII reaction center complex consisting of three polypeptides from spinach were studied. The experimental results showed that LaCl3 could significantly accelerate the transformation from light energy to electric energy, the electron transport, water photolysis and oxygen evolution of PSII of spinach, which was related to the spectral characterization of the D1/D2/Cytb559 complex.Soret band and Q band of Chl-a of UV-vis spectrum of D1/D2/Cytb559 complex were blue shifted, and the fluorescence emission peak was blue shifted in LaCl3 treated spinach compared with that in the control. The EXAFS (extended X-ray absorption fine structure spectroscopy) revealed that La^3 was coordinated with 8 nitrogen or oxygen atoms in the first coordination shell with La-N or La-O bond length of 0.254 nm, and with 6 nitrogen or oxygen atoms in the second coordination shell with La-N or La-O bond length of 0.321 nm in the D1/D2/Cytb559 complex. The CD suggested that the secondary structure of D1/D2/Cytb559 complex have been litfie affected by the treatment of LaCl3.     

光系统II(PSII)抑制剂的比较分子场研究

以光系统II抑制剂DISCO(DIStance COmparisons)模型的活性构象分子作为模板,利用比较分子场分析方法对三类结构不同的化合物进行了三维构效关系的研究.研究结果有助于对DISCO重叠模型的评估和新型PSII抑制剂的设计与合成.     

Luminescent platinum(II) terpyridyl complexes: effect of counter ions on solvent-induced aggregation and color changes

A series of platinum(II) terpyridyl complexes [Pt(tpy)(C triple bond C-C triple bond CH)]X, 1-X (X=OTf-; PF6-; ClO4-; BF4-; BPh4-); [Pt(tpy)(C triple bond CC6H5)]X, 2-X (X=OTf-; PF6-; ClO4-; BF4-); [Pt(tpy)(C triple bond CC6H4OCH3-4)]OTf, 3-OTf, and [Pt(4'-CH3O-tpy)(C triple bond CC6H5)]OTf, 4-OTf (tpy=2,2':6',2'-terpyridine, OTf=trifluoromethanesulfonate) were synthesized and their photophysical properties determined. Electronic absorption and emission studies showed the formation of a new band upon increasing the diethyl ether content in an acetonitrile/diethyl ether mixture. This was ascribed to the formation of complex aggregates, the solution color of which is dependent on the nature of the anions. This indicates that counter ions play an important role in governing the degree of aggregation and the extent of interactions within these aggregates. Addition of various anions to solutions of 1-OTf and 1-PF6 produced anion-induced color changes upon solvent-induced aggregation, indicating that these complexes may serve as potential colorimetric anion probes.     

Rates of virtually self-exchange energy transfer processes of ruthenium(II) polypyridine complexes

The rate constants of electronic energy transfer from the lowest excited state of Ru(bpy)₂(L)²⁺ or Ru(bpy)(L)₂²⁺ 10 Ru(L)₃²⁺ (b     

pH-Dependent Extraction of Ca 2+ from Photosystem II Membranes and Thylakoid Membranes: Indication of a Ca 2+-Sensitive Site on the Acceptor Side of Photosystem II

The action of low pH treatment (pH 3.6) known to release Ca²⁺ from the oxygen-evolving complex in photosystem II (PSII) membranes and to induce Ca²⁺-revers-ible inhibition of electron transport at the acceptor side of PSII in thylakoid membranes (TM) was compared in PSII membranes and TM. The rate of the inactivation of electron transport by low pH was four times higher in TM than in PSII membranes. Ferricyanide accelerated the inactivation of PSII membranes but decreased it in the case of TM. Low pH treatment also greatly modified the fluorescence induction kinetics in both preparations, but significant differences have been found in the fluorescence induction kinetics of treated TM and PSII membranes. Calcium restored the electron transport activity and fluorescence induction kinetics in PSII membranes and TM, whereas diphenylcarbazide restored these functions only in PSII membranes. The reactivation of Ca-depleted PSII membranes was more effective in the dark, whereas the reactivation of TM required weak light. In the case of PSII membranes subjected to low pH citrate buffer, maximal reactivation was observed at 60 mM Ca²⁺ but for TM about 10 mM Ca²⁺ was required and 60 mM fully inhibited electron transport in TM during reactivation. These results indicate that the Ca-dependent inactivation of the acceptor side of PSII in TM after low pH treatment cannot be explained by the extraction of Ca²⁺ from the oxygen-evolving complex. It is rather suggested that the Ca²⁺ involved in this inhibition is bound to the acceptor side of the photosystem near to the Q_A-non-heme iron binding site and may participate in the binding of a polypeptide of the PSII light antenna complex to the PSII reaction center.     

AFM and electron microscopy study of the unusual aggregation behavior of metallosurfactants based on iron(II) complexes with bipyridine ligands

The aggregation behavior in water-rich solutions of five iron(II) complexes with alkylated derivatives of 2,2'-bipyridine was studied by electron microscopy (cryo-SEM, SEM, and TEM) and AFM. The results obtained by cryo-SEM on frozen colloidal solutions show that the morphology of the aggregates strongly depends on the length of the alkyl chains in the bipyridine ligands, with shorter alkyl chains forming rod-like structures, whereas for compounds with longer alkyl chains, only spherical structures were detected. The self-aggregates were further characterized by SEM and TEM. The results show that their overall morphology depends only on the length of the alkyl chain of the bipyridine ligands and that the samples show a broad size distribution. In addition, TEM and SEM were used to study the stability of the self-aggregates in solution, the effect of addition of methanol, and the temperature used in the preparation of the colloidal solutions. AFM studies of the aggregates either dried in ambient conditions or dehydrated by long drying under vacuum showed partially collapsed self-aggregates in the latter case, showing that the aggregates contain water in their core, indicating that the self-aggregation leads to vesicle-type structures.     

阴离子表面活性剂存在下光系统II中酪氨酸残基的性能研究

通过荧光光谱和富立叶变换红外(FT-IR)光谱研究了阴离子型表面活性剂－十 二烷基硫酸钠（SDS）与光系统II（PSII）的相互作用。结果表明,PSII表现出酪 氨酸荧光的特性。在PSII蛋白质内部,存在着232 nm处的组分与酪氨酸之间以及这 两种氨基酸列基与叶绿素a之间的能量传递。SDS的存在会使这些能量传递以及 PSII中蛋白的骨架结构和酪氨酸残基的结构发生改变,而变化方式又明显受SDS在 溶液中聚集状态的影响。低于其临界胶束浓度(cmc)时,SDS会促进蛋白质中232 nm外的组分与酪氨酸之间的能量传递,并且使酪氨酸残基外于极性更小的环境; 而大于cmc时,SDS却产生相反的效应。但不同浓度的SDS均会抑制酪氨酸残基至叶 绿素a的能量传递。     

Recent Advances in the Application of Chlorophyll a Fluorescence from Photosystem II

In the photosynthesis process, part of the absorbed photon energy in photosystem II (PSII) may be reemitted as chlorophyll a fluorescence (ChlF). Environmental and plant physiological changes affect the emission of ChlF, which makes ChlF a potentially useful tool to sense these changes. Volumes of research on ChlF are published each year and some published work has been controversial. To facilitate the application of ChlF, it is important to have a holistic picture of the field. This review summarizes ChlF applications published in the last 10 years.