scholarly journals Towards a full understanding of water splitting in photosynthesis

2004 ◽  
Vol 6 (2) ◽  
pp. 43-51 ◽  
Author(s):  
James Barber
Keyword(s):  
Water Splitting ◽  
Organic Molecules ◽  
Structural Basis ◽  
Photosynthetic Organisms ◽  
Redox Active ◽  
Proton Transfer Reactions ◽  
Primary Acceptor ◽  
Mn Cluster ◽  
Almost All ◽  
Electron Proton Transfer

The capture and conversion of solar radiation by photosynthetic organisms directly or indirectly provides energy for almost all life on our planet. About 2.5 billion years ago a remarkable biological “machine” evolved known as photosystem two (PSII). This machine can use the energy of visible light (actually red quanta of∼1.8 eV) to split water into dioxygen and “hydrogen”. The latter is made available as reducing equivalents, ultimately destined to convert carbon dioxide to organic molecules. In PSII, the “hydrogen” reduces plastoquinone (PQ) to plastoquinol(PQH2). The water splitting process takes place at a catalytic centre composed of 4 Mn atoms and the reactions involved are chemically and thermodynamically challenging. The process is driven by a photooxidised chlorophyll molecule(P680•+)and involves electron/proton transfer reactions aided by a redox active tyrosine residue situated between the 4 Mn cluster and P680. TheP680•+species is generated by light induced rapid electron transfer (a few picoseconds) to a primary acceptor, pheophytina, before being transferred to PQ acceptors. Electron and x-ray crystallographic studies are now starting to reveal the structural basis for these reactions including the light harvesting processes. The 4 Mn atom-cluster has been visualised as have the chlorophylls that constitute P680. The scene is now set to fully elucidate the reactions of PSII and possibly mimic them in an artificial photochemical system that could split water and produce hydrogen.

scholarly journals Electronic Communication between Dithiolato-Bridged Diiron Carbonyl and S-Bridged Redox-Active Centres

Inorganics ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 37 ◽  
Author(s):  
Cédric Tard ◽  
Stacey Borg ◽  
Shirley Fairhurst ◽  
Christopher Pickett ◽  
Stephen Best
Keyword(s):  
Rational Design ◽  
Spectroscopic Properties ◽  
Electronic Effects ◽  
Binding Studies ◽  
Proton Reduction ◽  
Catalytic Potential ◽  
Redox Sites ◽  
Redox Active ◽  
Proton Transfer Reactions ◽  
Electron Proton Transfer

The catalytic potential of linked redox centres is exemplified by the catalytic site of [FeFe]-hydrogenases, which feature a diiron subsite linked by a cysteinyl S atom to a 4Fe4S cube. The investigation of systems possessing similarly-linked redox sites is important because it provides a context for understanding the biological system and the rational design of abiological catalysts. The structural, electrochemical and spectroscopic properties of Fe2(CO)5(CH3C(CH2S)2CH2SPhNO2, I-bzNO2 and the aniline analogue, I-bzNH2, are described and IR spectroelectrochemical studies have allowed investigation of the reduction products and their reactions with CO and protons. These measurements have allowed identification of the nitrobenzenyl radical anion, quantification of the shifts of the (CO) bands on ligand-based reduction compared with NO2/NH2 exchange and protonation of the pendent ligand. The strength of thioether coordination is related to the electronic effects, where competitive binding studies with CO show that CO/thioether exchange can be initiated by redox processes of the pendent ligand. Stoichiometric multi electron/proton transfer reactions of I-bzNO2 localised on nitrobenzene reductions occur at mild potentials and a metal-centred reduction in the presence of protons does not lead to significant electrocatalytic proton reduction.

3D periodic polyimide nano-networks for ultrahigh-rate and sustainable energy storage

2021 ◽  
Author(s):  
Youngjin Ham ◽  
Nathan J. Fritz ◽  
Gayea Hyun ◽  
Young Bum Lee ◽  
Jong Seok Nam ◽  
...  
Keyword(s):  
Energy Storage ◽  
Organic Molecules ◽  
Sustainable Energy ◽  
Next Generation ◽  
Significant Progress ◽  
Redox Active

Organic molecules with redox-active motifs are of great interest for next-generation electrodes for sustainable energy storage. While there has been significant progress in designing redox-active molecules, the practical requirements of...

scholarly journals Predictions of diffusion rates of organic molecules in secondary organic aerosols using the Stokes-Einstein and fractional Stokes-Einstein relations

2019 ◽  
Author(s):  
Erin Evoy ◽  
Adrian M. Maclean ◽  
Grazia Rovelli ◽  
Ying Li ◽  
Alexandra P. Tsimpidi ◽  
...  
Keyword(s):  
Citric Acid ◽  
Organic Molecules ◽  
Transport Model ◽  
Reaction Rates ◽  
Einstein Relation ◽  
Acid Mixture ◽  
Chemical Transport Model ◽  
Order Of Magnitude ◽  
Diffusion Rates ◽  
Almost All

Abstract. Information on the rate of diffusion of organic molecules within secondary organic aerosol (SOA) is needed to accurately predict the effects of SOA on climate and air quality. Often, researchers have predicted diffusion rates of organic molecules within SOA using measurements of viscosity and the Stokes-Einstein relation (D ∝ 1/η where D is the diffusion coefficient and η is viscosity). However, the accuracy of this relation for predicting diffusion in SOA remains uncertain. We measured diffusion coefficients over eight orders in magnitude in proxies of SOA including citric acid, sorbitol, and a sucrose-citric acid mixture. These results were combined with literature data to evaluate the Stokes-Einstein relation for predicting diffusion of organic molecules in SOA. Although almost all the data agrees with the Stokes-Einstein relation within a factor of ten, a fractional Stokes-Einstein relation (D ∝ C/ηt) with t = 0.93 and C = 1.66 is a better model for predicting diffusion of organic molecules in the SOA proxies studied. In addition, based on the output from a chemical transport model, the Stokes-Einstein relation can over predict mixing times of organic molecules within SOA by as much as one order of magnitude at an altitude ~ 3 km, compared to the fractional Stokes-Einstein relation with t = 0.93 and C = 1.66. These differences can be important for predicting growth, evaporation, and reaction rates of SOA in the middle and upper part of the troposphere. These results also have implications for other areas where diffusion of organic molecules within organic-water matrices is important.

scholarly journals A thylakoid membrane-bound and redox-active rubredoxin (RBD1) functions in de novo assembly and repair of photosystem II

2019 ◽  
Vol 116 (33) ◽  
pp. 16631-16640 ◽  
Author(s):  
José G. García-Cerdán ◽  
Ariel L. Furst ◽  
Kent L. McDonald ◽  
Danja Schünemann ◽  
Matthew B. Francis ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Thylakoid Membrane ◽  
De Novo Assembly ◽  
Biochemical Characterization ◽  
De Novo ◽  
Midpoint Potential ◽  
Photosynthetic Organisms ◽  
Redox Active ◽  
Photooxidative Damage

Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transmembrane α-helix (TMH) domain. RBD1 is an integral thylakoid membrane protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b559. Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.

Structural basis for blue-green light harvesting and energy dissipation in diatoms

Science ◽  
2019 ◽  
Vol 363 (6427) ◽  
pp. eaav0365 ◽  
Author(s):  
Wenda Wang ◽  
Long-Jiang Yu ◽  
Caizhe Xu ◽  
Takashi Tomizaki ◽  
Songhao Zhao ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Phaeodactylum Tricornutum ◽  
Light Harvesting ◽  
Green Light ◽  
Marine Diatom ◽  
Structural Basis ◽  
Aquatic Environments ◽  
Efficient Energy Transfer ◽  
Chl A ◽  
Photosynthetic Organisms

Diatoms are abundant photosynthetic organisms in aquatic environments and contribute 40% of its primary productivity. An important factor that contributes to the success of diatoms is their fucoxanthin chlorophyll a/c-binding proteins (FCPs), which have exceptional light-harvesting and photoprotection capabilities. Here, we report the crystal structure of an FCP from the marine diatom Phaeodactylum tricornutum, which reveals the binding of seven chlorophylls (Chls) a, two Chls c, seven fucoxanthins (Fxs), and probably one diadinoxanthin within the protein scaffold. Efficient energy transfer pathways can be found between Chl a and c, and each Fx is surrounded by Chls, enabling the energy transfer and quenching via Fx highly efficient. The structure provides a basis for elucidating the mechanisms of blue-green light harvesting, energy transfer, and dissipation in diatoms.

All-PEGylated redox-active metal-free organic molecules in non-aqueous redox flow battery

2020 ◽  
Vol 8 (31) ◽  
pp. 15715-15724 ◽  
Author(s):  
Jingchao Chai ◽  
Amir Lashgari ◽  
Xiao Wang ◽  
Caroline K. Williams ◽  
Jianbing “Jimmy” Jiang
Keyword(s):  
Organic Molecules ◽  
Redox Flow Battery ◽  
Flow Battery ◽  
Active Materials ◽  
Metal Free ◽  
Redox Active ◽  
Active Metal ◽  
Molecular Sizes ◽  
The Stability ◽  
Redox Active Metal

A non-aqueous redox flow battery based on all-PEGylated, metal-free compounds is presented. The PEGylation enhances the stability of the redox-active materials, alleviating crossover by increasing the anolyte and catholyte species’ molecular sizes.

High-Z′ structures of organic molecules: their diversity and organizing principles

2016 ◽  
Vol 72 (6) ◽  
pp. 807-821 ◽  
Author(s):  
Carolyn Pratt Brock
Keyword(s):  
Organic Molecules ◽  
Local Symmetry ◽  
Molecular Conformations ◽  
Space Group ◽  
Common Features ◽  
Different Types ◽  
Independent Molecules ◽  
Almost All ◽  
Careful Investigation ◽  
Organizing Principles

A list has been compiled of 284 well determined organic structures having more than four crystallographically independent molecules or formula units (i.e. Z′ > 4). Another 22 structures were rejected because the space group or unit cell was probably misassigned; the rate for that type of error is then only 7%. The space-group frequencies are unusual; half the structures are in Sohncke groups, partly because the fraction of enantiopure structures of resolvable enantiomers is higher than for lowerZ′ structures. Careful investigation of the 284 structures has shown that they are very diverse; no simple classification can describe them all. Organizing principles have, however, been recognized for almost all of them. The most common features are simple modulations and hydrogen-bonded aggregates; only 14% of the structures have neither. In 50% of the structuresnmolecules are related by a pseudotranslation that would be a crystallographic translation but for small molecular displacements and rotations. In 70% of the structures there are aggregates (e.g. n-mers, columns or layers) held together by strong intermolecular interactions; those aggregates usually have approximate local symmetry. Because then-fold modulations and then-mers often haven<Z′, 85% of the structures withZ′ > 5 have several features that combine to give the highZ′ value. The number of different molecular conformations is usually small,i.e.one or two in 84% of the structures. More exotic packing features, such as ordered faults and alternating layers of different types, are found inca30% of the structures. A very few structures are so complex that it is difficult to understand how the crystals could have formed.

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