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Kurashov, Vasily N.,Allakhverdiev, Suleyman I.,Zharmukhamedov, Sergey K.,Nagata, Toshi,Klimov, Vyacheslav V.,Semenov, Alexey Yu.,Mamedov, Mahir D. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.2
An electrometric technique was used to investigate the generation of a photovoltage ($\Delta\psi$) by Mn-depleted spinach photosystem II (PS II) core particles incorporated into liposomes. In the presence of $MnCl_2$, the fast kinetically unresolvable phase of $\Delta\psi$ generation, related to electron transfer between the redox-active tyrosine $Y_Z$ and the primary plastoquinone acceptor $Q_A$ was followed by an additional electrogenic phase (${\tau}\;{\sim}\;20\;{\mu}s$, ~5% of the phase attributed to ${Y_Z}^{OX}{Q_A}^-$). The latter phase was ascribed to the transfer of an electron from the Mn, bound to the Mn-binding site of the PS II reaction center to the ${Y_Z}^{OX}$. An additional electrogenicity observed upon addition of synthetic trinuclear Mn complex-1 has a ${\tau}\;{\sim}\;50\;{\mu}s$ (~4% of the ${Y_Z}^{OX}Q_A$) and ${\tau}\;{\sim}\;160\;ms$ (~25%). The fast electrogenic component could be ascribed to reduction of ${Y_Z}^{OX}$ ox by Mn, delivered to the Mn-binding site in Mn-depleted samples after the release of the tripod ligands from the complex-1 while the slow electrogenic phase to the electron transfer from theMn-containing complex-1 attached to the protein-water boundary to the oxidized Mn at the protein-embedded Mn-binding site.
Hydrogen photoproduction by use of photosynthetic organisms and biomimetic systems
Allakhverdiev, Suleyman I.,Kreslavski, Vladimir D.,Thavasi, Velmurugan,Zharmukhamedov, Sergei K.,Klimov, Vyacheslav V.,Nagata, Toshi,Nishiharad, Hiroshi,Ramakrishna, Seeram Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.2
Hydrogen can be important clean fuel for future. Among different technologies for hydrogen production, oxygenic natural and artificial photosyntheses using direct photochemistry in synthetic complexes have a great potential to produce hydrogen, since both use clean and cheap sources: water and solar energy. Artificial photosynthesis is one way to produce hydrogen from water using sunlight by employing biomimetic complexes. However, splitting of water into protons and oxygen is energetically demanding and chemically difficult. In oxygenic photosynthetic microorganisms such as algae and cyanobacteria, water is split into electrons and protons, which during primary photosynthetic process are redirected by photosynthetic electron transport chain, and ferredoxin, to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, $e^-$ and $H^+$ recombine and form gaseous hydrogen. Biohydrogen activity of hydrogenase can be very high but it is extremely sensitive to photosynthetic $O_2$. In contrast, nitrogenase is insensitive to $O_2$, but has lower activity. At the moment, the efficiency of biohydrogen production is low. However, theoretical expectations suggest that the rates of photon conversion efficiency for $H_2$ bioproduction can be high enough (>10%). Our review examines the main pathways of $H_2$ photoproduction by using of photosynthetic organisms and biomimetic photosynthetic systems.