Electron transfer , photosynthetic reaction applications

Liquid-crystalline media are important especially for technical and biomedical applications of electron-transfer reactions. Molecular electronic systems, photosynthetic processes, and some... 

The next two chapters are devoted to ultrafast radiationless transitions. In Chapter 5, the generalized linear response theory is used to treat the non-equilibrium dynamics of molecular systems. This method, based on the density matrix method, can also be used to calculate the transient spectroscopic signals that are often monitored experimentally. As an application of the method, the authors present the study of the interfadal photo-induced electron transfer in dye-sensitized solar cell as observed by transient absorption spectroscopy. Chapter 6 uses the density matrix method to discuss important processes that occur in the bacterial photosynthetic reaction center, which has congested electronic structure within 200-1500cm 1 and weak interactions between these electronic states. Therefore, this biological system is an ideal system to examine theoretical models (memory effect, coherence effect, vibrational relaxation, etc.) and techniques (generalized linear response theory, Forster-Dexter theory, Marcus theory, internal conversion theory, etc.) for treating ultrafast radiationless transition phenomena. 

A microscopic theory for describing ultrafast radiationless transitions in particular for, photo-induced ultrafast radiationless transitions is presented. For this purpose, one example system that well represents the ultrafast radiationless transaction problem is considered. More specifically, bacterial photosynthetic reaction centers (RCs) are investigated for their ultrafast electronic-excitation energy transfer (EET) processes and ultrafast electron transfer (ET) processes. Several applications of the density matrix method are presented for emphasizing that the density matrix method can not only treat the dynamics due to the radiationless transitions but also deal with the population and coherence dynamics. Several rate constants of the radiationless transitions and the analytic estimation methods of those rate... 

The second article also deals with PET in arranged media, however, this time by discussing comprehensively the various types of heterogeneous devices which may control supramolecular interactions and consequently chemical reactions. Before turning to such applications, photosynthetic model systems, mainly of the triad type, are dealt with in the third contribution. Here, the natural photosynthetic electron transfer process is briefly discussed as far as it is needed as a basis for the main part, namely the description of artificial multicomponent molecules for mimicking photosynthesis. In addition to the goal to learn more about natural photosynthetic energy conversion, these model systems may also have applications, which, for example, lie in the construction of electronic devices at the molecular level. 

This volume grew out of an American Chemical Society (ACS) symposium titled Bioenergetics. The ACS Division of Computers in Chemistry sponsored the symposium, whose goal was to bring together scientists from different disciplines to discuss current achievements and future directions in molecular-level simulations of electron and proton transfer. This volume provides a sampling of recently developed simulation methods, as well as their applications to prototypical biochemical systems such as the photosynthetic reaction center and bacteriorhodopsin. 

Early reports on interactions between redox enzymes and ruthenium or osmium compounds prior to the biosensor burst are hidden in a bulk of chemical and biochemical literature. This does not apply to the ruthenium biochemistry of cytochromes where complexes [Ru(NH3)5L] " , [Ru(bpy)2L2], and structurally related ruthenium compounds, which have been widely used in studies of intramolecular (long-range) electron transfer in proteins (124,156-158) and biomimetic models for the photosynthetic reaction centers (159). Applications of these compounds in biosensors are rather limited. The complex [Ru(NHg)6] has the correct redox potential but its reactivity toward oxidoreductases is low reflecting a low self-exchange rate constant (see Tables I and VII). The redox potentials of complexes [Ru(bpy)3] " and [Ru(phen)3] are way too much anodic (1.25 V vs. NHE) ruling out applications in MET. The complex [Ru(bpy)3] is such a powerful oxidant that it oxidizes HRP into Compounds II and I (160). The electron-transfer from the resting state of HRP at pH <10 when the hemin iron(III) is five-coordinate generates a 7i-cation radical intermediate with the rate constant 2.5 x 10 s" (pH 10.3)... 

The photocatalytic properties and electron/photon-induced processes related to natural systems treated in Chapters 13 and 14 have been researched in depth. Different single fundamental multi-electron catalytic processes and photoexcited state electron-transfer reactions, both in polymer matrixes, are described in relation to photosynthesis (Section 13.2). It is now necessary to combine these reactions step by step to produce artificial photosynthetic systems. Some photoinduced energy-transfer processes (photooxidations) have now reached the level of practical application for wastewater cleaning (Section 13.4) and should be extended to other reactions induced by irradiation with visible light. 

The intensity of fluorescence from an immobilized, isotropic sample of photosynthetic reaction centers (RCs) increases upon application of an electric field at 77 K [IJ. The change in fluorescence was found to be quadratic with the applied field strength, and the fluorescence in the field was found to become polarized [2]. The fluorescence increase is ascribed to a net decrease in the rate of the forward electron transfer reaction which competes with fluorescence from P. The field alters the free energy change for electron transfer, AG, and thus the rate because the energy of the dipolar product state... 

Electron transfer reactions are key processes responsible for the maintenance of fife. Certainly, supramolecular principles can help our understanding of the mechanisms of many biological processes such as photosynthetic reactions, oxidative phosphorylation, and many other events such those observed in the respiratory chain [1, 4]. Non-covalent functionalization of CNT has attracted investigation in technological applications as photovoltaic cells and light-emitting diodes (LEDs). 

Miguel et al. [56], in 2011, reported the application of triazole bridges created from the CuAAC reaction for the preparation of donor-acceptor conjugates, bearing zinc(II)porphyrins and fuUerenes (ZnP-Tri-Cgg), designed for artificial photosynthetic applications. It was found that the triazole bridge is excellent for efficient photoinduced electron transfer between a remote electron donor and acceptor moiety. 

M. Nonella and K. Schulten. Molecular dynamics simulation of electron transfer in proteins — theory and application to Qa Qb transfer in the photosynthetic reaction center. J. Phys. Chem., 95 2059-2067, 1990. 

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