Journal articles: 'Electron energy transfer rates'

1

Pavlov, A. V. "New electron energy transfer and cooling rates by excitation of O2." Annales Geophysicae 16, no. 8 (August 31, 1998): 1007–13. http://dx.doi.org/10.1007/s00585-998-1007-8.

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Abstract. In this work I present the results of a study of the electron cooling rate, the production rates of vibrationally excited O2, and the production frequency of the O2 vibrational quanta arising from the collisions of electrons with O2 molecules as functions of the electron temperature. The electron energy transfer and cooling rates by vibrational excitation of O2 have been calculated and fitted to analytical expressions by use of the revised vibrationally excited O2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations. It is also shown that the currently accepted rate of electron energy loss associated with rotational transitions in O2 must be decreased by a factor of 13.

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Jones, D. B., L. Campbell, M. J. Bottema, and M. J. Brunger. "New electron-energy transfer rates for vibrational excitation of O2." New Journal of Physics 5 (September 25, 2003): 114. http://dx.doi.org/10.1088/1367-2630/5/1/114.

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3

Tachiya, M., and A. V. Barzykin. "Energy gap law for electron transfer rates in polymer glasses." Chemical Physics 319, no. 1-3 (December 2005): 222–25. http://dx.doi.org/10.1016/j.chemphys.2005.03.036.

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Pavlov, A. V. "New electron energy transfer rates for vibrational excitation of N." Annales Geophysicae 16, no. 2 (1998): 176. http://dx.doi.org/10.1007/s005850050591.

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Skourtis, Spiros S., Chaoren Liu, Panayiotis Antoniou, Aaron M. Virshup, and David N. Beratan. "Dexter energy transfer pathways." Proceedings of the National Academy of Sciences 113, no. 29 (July 5, 2016): 8115–20. http://dx.doi.org/10.1073/pnas.1517189113.

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Energy transfer with an associated spin change of the donor and acceptor, Dexter energy transfer, is critically important in solar energy harvesting assemblies, damage protection schemes of photobiology, and organometallic opto-electronic materials. Dexter transfer between chemically linked donors and acceptors is bridge mediated, presenting an enticing analogy with bridge-mediated electron and hole transfer. However, Dexter coupling pathways must convey both an electron and a hole from donor to acceptor, and this adds considerable richness to the mediation process. We dissect the bridge-mediated Dexter coupling mechanisms and formulate a theory for triplet energy transfer coupling pathways. Virtual donor–acceptor charge-transfer exciton intermediates dominate at shorter distances or higher tunneling energy gaps, whereas virtual intermediates with an electron and a hole both on the bridge (virtual bridge excitons) dominate for longer distances or lower energy gaps. The effects of virtual bridge excitons were neglected in earlier treatments. The two-particle pathway framework developed here shows how Dexter energy-transfer rates depend on donor, bridge, and acceptor energetics, as well as on orbital symmetry and quantum interference among pathways.

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Fox, L. S., M. Kozik, J. R. Winkler, and H. B. Gray. "Gaussian Free-Energy Dependence of Electron-Transfer Rates in Iridium Complexes." Science 247, no. 4946 (March 2, 1990): 1069–71. http://dx.doi.org/10.1126/science.247.4946.1069.

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Pavlov, A. V. "New electron energy transfer and cooling rates by excitation of O." Annales Geophysicae 16, no. 8 (1998): 1007. http://dx.doi.org/10.1007/s005850050670.

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Closs, Gerhard L., Piotr Piotrowiak, Jean M. MacInnis, and Graham R. Fleming. "Determination of long-distance intramolecular triplet energy-transfer rates. Quantitative comparison with electron transfer." Journal of the American Chemical Society 110, no. 8 (April 1988): 2652–53. http://dx.doi.org/10.1021/ja00216a051.

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Fisher, T. S., and D. G. Walker. "Thermal and Electrical Energy Transport and Conversion in Nanoscale Electron Field Emission Processes." Journal of Heat Transfer 124, no. 5 (September 11, 2002): 954–62. http://dx.doi.org/10.1115/1.1494091.

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This paper considers the theory of electron field emission from nanoscale emitters with particular focus on thermal and electrical energy transport. The foundational theory of field emission is explored, and a model is presented that accounts explicitly for the energy band curvature produced by nanoscale tip emitters. The results indicate that the inclusion of band curvature strongly influences the energetic distribution of electrons for emitter radii less than 50 nm. The energy exchange process between emitted and replacement electrons is shown to allow high local energy transfer rates that can be exploited in direct thermal-to-electrical energy conversion processes. The dependence of energy conversion rates on material and operational parameters is demonstrated. Throughout the paper, opportunities for further research involving nanoscale heat transfer, materials development, and modeling are highlighted.

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Gray, Harry B., and Jay R. Winkler. "Electron tunneling through proteins." Quarterly Reviews of Biophysics 36, no. 3 (August 2003): 341–72. http://dx.doi.org/10.1017/s0033583503003913.

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1. History 3422. Activation barriers 3432.1 Redox potentials 3442.2 Reorganization energy 3443. Electronic coupling 3454. Ru-modified proteins 3484.1 Reorganization energy 3494.1.1 Cyt c 3494.1.2 Azurin 3504.2 Tunneling timetables 3525. Multistep tunneling 3576. Protein–protein reactions 3596.1 Hemoglobin (Hb) hybrids 3596.2 Cyt c/cyt b5 complexes 3606.3 Cyt c/cyt c peroxidase complexes 3606.4 Zn–cyt c/Fe–cyt c crystals 3617. Photosynthesis and respiration 3627.1 Photosynthetic reaction centers (PRCs) 3627.2 Cyt c oxidase (CcO) 3648. Concluding remarks 3659. Acknowledgments 36610. References 366Electron transfer processes are vital elements of energy transduction pathways in living cells. More than a half century of research has produced a remarkably detailed understanding of the factors that regulate these ‘currents of life’. We review investigations of Ru-modified proteins that have delineated the distance- and driving-force dependences of intra-protein electron-transfer rates. We also discuss electron transfer across protein–protein interfaces that has been probed both in solution and in structurally characterized crystals. It is now clear that electrons tunnel between sites in biological redox chains, and that protein structures tune thermodynamic properties and electronic coupling interactions to facilitate these reactions. Our work has produced an experimentally validated timetable for electron tunneling across specified distances in proteins. Many electron tunneling rates in cytochrome c oxidase and photosynthetic reaction centers agree well with timetable predictions, indicating that the natural reactions are highly optimized, both in terms of thermodynamics and electronic coupling. The rates of some reactions, however, significantly exceed timetable predictions; it is likely that multistep tunneling is responsible for these anomalously rapid charge transfer events.

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Otsuki, Joe, Kenkichi Harada, Koji Araki, Kikuo Takatera, Tadashi Watanabe, Koji Toyama, Yoshio Hirose, and Manabu Seno. "Energy gap dependence of electron transfer rates in porphyrin–imide supramolecular assemblies." Chemical Communications, no. 15 (1998): 1515–16. http://dx.doi.org/10.1039/a801453a.

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12

Pavlov, A. V. "New electron energy transfer rates for vibrational excitation of N<sub>2</sub>." Annales Geophysicae 16, no. 2 (February 28, 1998): 176–82. http://dx.doi.org/10.1007/s00585-998-0176-9.

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Abstract. In this paper we present the results of a study of the electron cooling rate, the production rates of vibrationally excited N2(v), and the production frequency of the N2 vibrational quanta arising from the collisions of electrons with unexcited N2(0) and vibrationally excited N2(1) molecules as functions of the electron temperature. The electron energy transfer rates for vibrational excitation of N2 have been calculated and fit to analytical expressions by use of the revised vibrationally excited N2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations.Key words. Atmospheric composition and structure · Thermosphere · Ionosphere · Modeling and forecasting

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Harvey, Pierre D., Christine Stern, Claude P. Gros, and Roger Guilard. "Through space singlet energy transfers in light-harvesting systems and cofacial bisporphyrin dyads." Journal of Porphyrins and Phthalocyanines 14, no. 01 (January 2010): 55–63. http://dx.doi.org/10.1142/s1088424610001702.

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Recent discoveries from our research groups on the photophysics of a few cofacial bisporphyrin dyads for through space singlet and triplet energy transfers raised several important investigations about the mechanism of energy transfers and energy migration in light-harvesting devices, notably LH II, in the heavily investigated purple photosynthetic bacteria. The key feature is that for face-to-face and slipped dyads with controlled structure using rigid spacers or spacers with limited flexibilities, our fastest rates for singlet energy transfer are in the 10 × 109 s -1 (i.e. 100 ps time scale) for donor-acceptor distances of ~3.5–3.6 Å. The time scale for energy transfers between different bacteriochlorophylls, notably B800*→B850, is in the ps despite the long Mg ⋯ Mg separation (~18 Å). This short rate drastically contrasts with the well-accepted Förster theory. This review focuses on the photophysical processes and dynamics in LH II and compares these parameters with our investigated model dyads build upon octa-etio-porphyrin chromophores and rigid and semi-rigid spacers. The recently discovered role of the rhodopin glucoside (carotenoid) will be analyzed as possible relay for energy transfers, including the possibility of uphill processes at room temperature. In this context the concept of energy migration may be complemented by parallel relays and uphill processes. It is also becoming more obvious that the irreversible electron transfer at the reaction center (electron transfer from the special pair to the phaeophytin) renders the rates for energy transfer and migration faster precluding all possibility of back transfers.

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Hughes, Joseph L., and Elmars Krausz. "The Chemical Problem of Energy Change: Multi-Electron Processes." Australian Journal of Chemistry 65, no. 6 (2012): 591. http://dx.doi.org/10.1071/ch12105.

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This special issue is focussed on arguably the most important fundamental question in contemporary chemical research: how to efficiently and economically convert abundant and thermodynamically stable molecules, such as H2O, CO2, and N2 into useable fuel and food sources. The 3 billion year evolutionary experiment of nature has provided a blueprint for the answer: multi-electron catalysis. However, unlike one-electron transfer, we have no refined theories for multi-electron processes. This is despite its centrality to much of chemistry, particularly in catalysis and biology. In this article we highlight recent research developments relevant to this theme with emphasis on the key physical concepts and premises: (i) multi-electron processes as stepwise single-electron transfer events; (ii) proton-coupled electron transfer; (iii) stimulated, concerted, and co-operative phenomena; (iv) feedback mechanisms that may enhance electron transfer rates by minimizing activation barriers; and (v) non-linearity and far-from-equilibrium considerations. The aim of our discussion is to provide inspiration for new directions in chemical research, in the context of an urgent contemporary issue.

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van Wonderen, Jessica H., Katrin Adamczyk, Xiaojing Wu, Xiuyun Jiang, Samuel E. H. Piper, Christopher R. Hall, Marcus J. Edwards, et al. "Nanosecond heme-to-heme electron transfer rates in a multiheme cytochrome nanowire reported by a spectrally unique His/Met-ligated heme." Proceedings of the National Academy of Sciences 118, no. 39 (September 23, 2021): e2107939118. http://dx.doi.org/10.1073/pnas.2107939118.

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Proteins achieve efficient energy storage and conversion through electron transfer along a series of redox cofactors. Multiheme cytochromes are notable examples. These proteins transfer electrons over distance scales of several nanometers to >10 μm and in so doing they couple cellular metabolism with extracellular redox partners including electrodes. Here, we report pump-probe spectroscopy that provides a direct measure of the intrinsic rates of heme–heme electron transfer in this fascinating class of proteins. Our study took advantage of a spectrally unique His/Met-ligated heme introduced at a defined site within the decaheme extracellular MtrC protein of Shewanella oneidensis. We observed rates of heme-to-heme electron transfer on the order of 109 s−1 (3.7 to 4.3 Å edge-to-edge distance), in good agreement with predictions based on density functional and molecular dynamics calculations. These rates are among the highest reported for ground-state electron transfer in biology. Yet, some fall 2 to 3 orders of magnitude below the Moser–Dutton ruler because electron transfer at these short distances is through space and therefore associated with a higher tunneling barrier than the through-protein tunneling scenario that is usual at longer distances. Moreover, we show that the His/Met-ligated heme creates an electron sink that stabilizes the charge separated state on the 100-μs time scale. This feature could be exploited in future designs of multiheme cytochromes as components of versatile photosynthetic biohybrid assemblies.

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Langlois, Adam, Hai-Jun Xu, Paul-Ludovic Karsenti, Claude P. Gros, and Pierre D. Harvey. "Very fast singlet and triplet energy transfers in a tri-chromophoric porphyrin dyad aided by the truxene platform." Journal of Porphyrins and Phthalocyanines 19, no. 01-03 (January 2015): 427–41. http://dx.doi.org/10.1142/s1088424615500327.

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A trichromophoric dyad composed of an octa-β-alkyl-palladium(II)porphyrin (donor) and two tri-meso-aryl-zinc(II)porphyrins (acceptors) held by a truxene spacer exhibits very fast rates for triplet energy transfers at 77 (kET(T1) = 1.63 × 108 s-1) and 298 K (kET(T1) = 3.44 × 108 s-1), whereas the corresponding singlet energy transfer rates, kET(S1) = 3.9 × 1010 s-1 (77 K) and kET(S1) = 6.0 × 1010 s-1 (298 K), are also considered fast. The interpretation for these results is that the energy transfer processes proceed via a through bond Dexter mechanism (i.e. double electron exchange) supported by comparison with literature data and evidence for a moderate MO coupling between the donor and acceptor chromophores in the frontier MOs.

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Suess, Christian J., Jonathan D. Hirst, and Nicholas A. Besley. "Quantum chemical calculations of tryptophan → heme electron and excitation energy transfer rates in myoglobin." Journal of Computational Chemistry 38, no. 17 (April 1, 2017): 1495–502. http://dx.doi.org/10.1002/jcc.24793.

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Saloma, Miguel, Martha Aguilar, and Manuel Salmón. "Electron‐Transfer Rates on Chemically Modified Conducting Polypyrrole Film Electrodes." Journal of The Electrochemical Society 132, no. 10 (October 1, 1985): 2379–81. http://dx.doi.org/10.1149/1.2113581.

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Pradhan, Ekadashi, Rudolph J. Magyar, and Alexey V. Akimov. "Scaling relationships for nonadiabatic energy relaxation times in warm dense matter: toward understanding the equation of state." Physical Chemistry Chemical Physics 18, no. 47 (2016): 32466–76. http://dx.doi.org/10.1039/c6cp06827h.

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20

Sarewicz, Marcin, Łukasz Bujnowicz, Satarupa Bhaduri, Sandeep K. Singh, William A. Cramer, and Artur Osyczka. "Metastable radical state, nonreactive with oxygen, is inherent to catalysis by respiratory and photosynthetic cytochromes bc1/b6f." Proceedings of the National Academy of Sciences 114, no. 6 (January 23, 2017): 1323–28. http://dx.doi.org/10.1073/pnas.1618840114.

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Oxygenic respiration and photosynthesis based on quinone redox reactions face a danger of wasteful energy dissipation by diversion of the productive electron transfer pathway through the generation of reactive oxygen species (ROS). Nevertheless, the widespread quinone oxido-reductases from the cytochrome bc family limit the amounts of released ROS to a low, perhaps just signaling, level through an as-yet-unknown mechanism. Here, we propose that a metastable radical state, nonreactive with oxygen, safely holds electrons at a local energetic minimum during the oxidation of plastohydroquinone catalyzed by the chloroplast cytochrome b6f. This intermediate state is formed by interaction of a radical with a metal cofactor of a catalytic site. Modulation of its energy level on the energy landscape in photosynthetic vs. respiratory enzymes provides a possible mechanism to adjust electron transfer rates for efficient catalysis under different oxygen tensions.

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Barklem, P. S. "Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen." Astronomy & Astrophysics 610 (February 2018): A57. http://dx.doi.org/10.1051/0004-6361/201731968.

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Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000–20 000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates.

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Lymar, Sergei V., Gerald F. Manbeck, and Dmitry E. Polyansky. "Hydrogen bonding between hydroxylic donors and MLCT-excited Ru(bpy)2(bpz)2+ complex: implications for photoinduced electron–proton transfer." Chemical Communications 55, no. 42 (2019): 5870–73. http://dx.doi.org/10.1039/c9cc01896d.

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Barklem, P. S. "Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron." Astronomy & Astrophysics 612 (April 2018): A90. http://dx.doi.org/10.1051/0004-6361/201732365.

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Data for inelastic processes due to hydrogen atom collisions with iron are needed for accurate modelling of the iron spectrum in late-type stars. Excitation and charge transfer in low-energy Fe+H collisions is studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau–Zener model. An extensive calculation including 166 covalent states and 25 ionic states is presented and rate coefficients are calculated for temperatures in the range 1000–20 000 K. The largest rates are found for charge transfer processes to and from two clusters of states around 6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p electrons undergoing transfer. Excitation and de-excitation processes among these two sets of states are also significant.

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Tvrdy, Kevin, Pavel A. Frantsuzov, and Prashant V. Kamat. "Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles." Proceedings of the National Academy of Sciences 108, no. 1 (December 13, 2010): 29–34. http://dx.doi.org/10.1073/pnas.1011972107.

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Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO2, TiO2, and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO2) were not the same as those which showed the highest photocurrent (TiO2). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

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Chen, Jing Ming, Tong Ing Ho, and Chung Yuan Mou. "Experimental investigation of excited-state electron-transfer reaction: effects of free energy and solvent on rates." Journal of Physical Chemistry 94, no. 7 (April 5, 1990): 2889–96. http://dx.doi.org/10.1021/j100370a030.

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Parson, William W. "Effects of Free Energy and Solvent on Rates of Intramolecular Electron Transfer in Organic Radical Anions." Journal of Physical Chemistry A 121, no. 38 (September 14, 2017): 7297–306. http://dx.doi.org/10.1021/acs.jpca.7b08579.

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Kirillov, A. S. "Application of Landau–Zener and Rosen–Zener approximations to calculate rates of electron energy transfer processes." Advances in Space Research 33, no. 6 (January 2004): 993–97. http://dx.doi.org/10.1016/j.asr.2003.06.009.

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Ohkubo, Kei, and Shunichi Fukuzumi. "Long-lived charge-separated states of simple electron donor-acceptor dyads using porphyrins and phthalocyanines." Journal of Porphyrins and Phthalocyanines 12, no. 09 (September 2008): 993–1004. http://dx.doi.org/10.1142/s1088424608000376.

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Control of electron-transfer processes is described for a number of electron donor-acceptor dyads containing porphyrins or phthalocyanines as models for the photosynthetic reaction center. The rates for intramolecular electron transfer in the dyads are controlled by the driving force and reorganization energy of electron transfer. The small reorganization energy of electron transfer reactions and large driving force of charge recombination are required to form long-lived charge-separated states. A directly linked zinc chlorin-fullerene dyad, especially, has the longest lifetime of charge-separated state at 120 s at -150 °C, which is a much longer lifetime and higher energy than those of natural photosynthetic reaction centers. On the other hand, the charge-separated states of the phthalocyanine-based donor-acceptor dyads (silicon phthalocyanine-fullerene, and zinc phthalocyanine-perylenebisimide) are short-lived since charge recombination forms the low-lying triplet excited state of the chromophore. The energy of the charge-separated state of a zinc phthalocyanine-perylenebisimide dyad is decreased by binding of metal ions to the radical anion moiety in order to be lower than the triplet excited state. This results in formation of a long-lived charge-separated state. The mechanistic viability of formation of long-lived charge-separated states is demonstrated by a variety of examples based on the Marcus theory of electron transfer.

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GERICKE, D. O., M. S. MURILLO, and M. SCHLANGES. "Nonideality effects on temperature relaxation." Laser and Particle Beams 20, no. 4 (October 2002): 543–45. http://dx.doi.org/10.1017/s0263034602204012.

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The relaxation of two-temperature electron–ion systems is investigated. We apply a quantum kinetic approach which is suitable to treat strong electron–ion coupling and avoids any ad hoc cut-off procedures. A comparison with the usual Landau–Spitzer formula gives good agreement for Coulomb logarithms larger than three, whereas larger relaxation rates were found for strongly coupled plasmas. It is shown that the Landau–Spitzer theory can be greatly improved considering hyperbolic orbits. Numerical results for the energy transfer rates and the temporal behavior of the electron temperature are shown.

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Mantela, Marilena, Konstantinos Lambropoulos, Marina Theodorakou, and Constantinos Simserides. "Quasi-Periodic and Fractal Polymers: Energy Structure and Carrier Transfer." Materials 12, no. 13 (July 6, 2019): 2177. http://dx.doi.org/10.3390/ma12132177.

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We study the energy structure and the coherent transfer of an extra electron or hole along aperiodic polymers made of N monomers, with fixed boundaries, using B-DNA as our prototype system. We use a Tight-Binding wire model, where a site is a monomer (e.g., in DNA, a base pair). We consider quasi-periodic (Fibonacci, Thue–Morse, Double-Period, Rudin–Shapiro) and fractal (Cantor Set, Asymmetric Cantor Set) polymers made of the same monomer (I polymers) or made of different monomers (D polymers). For all types of such polymers, we calculate the highest occupied molecular orbital (HOMO) eigenspectrum and the lowest unoccupied molecular orbital (LUMO) eigenspectrum, the HOMO–LUMO gap and the density of states. We examine the mean over time probability to find the carrier at each monomer, the frequency content of carrier transfer (Fourier spectra, weighted mean frequency of each monomer, total weighted mean frequency of the polymer), and the pure mean transfer rate k. Our results reveal that there is a correspondence between the degree of structural complexity and the transfer properties. I polymers are more favorable for charge transfer than D polymers. We compare k ( N ) of quasi-periodic and fractal sequences with that of periodic sequences (including homopolymers) as well as with randomly shuffled sequences. Finally, we discuss aspects of experimental results on charge transfer rates in DNA with respect to our coherent pure mean transfer rates.

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Yoshimori, Akira, and Toshiaki Kakitani. "Energy Gap Dependence of the Solvent Dynamics Effect on Electron Transfer Rates in Non-Linear Response Systems." Journal of the Physical Society of Japan 61, no. 7 (July 15, 1992): 2577–92. http://dx.doi.org/10.1143/jpsj.61.2577.

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Shivaprasadachary, B., A. R. Ramya, Govind Reddy, and L. Giribabu. "Light induced intramolecular energy and electron transfer events in carbazole–corrole and phenothiazine-corrole dyads." Journal of Porphyrins and Phthalocyanines 24, no. 05n07 (May 2020): 693–704. http://dx.doi.org/10.1142/s1088424619501177.

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We report two corrole based donor–acceptor (D–A) dyads, Cbz-Cor and Ptz-Cor to understand the energy/electron transfer reactions. In these D–A systems, the donor, either carbazole (Cbz) or phenothiazine (Ptz), is covalently connected at the meso-phenyl position of 10-(phenyl)-5,15-bis-(pentafluorophenyl)corrole (Ph-Cor) by C–N linkage. Both the dyads were characterized by 1H NMR, MALDI-TOF MS, UV-vis, electrochemical, computational methods, study state fluorescence and TCSPC techniques. A comparison of absorption spectra with their reference monomeric compounds (Cbz-Ph, Ptz-Ph and Ph-Cor) revealed minimal ground-state interactions between chromophores in both dyads. Fluorescence studies suggested that singlet–singlet energy transfer from 1Cbz* to corrole is the major photochemical pathway in the Cbz-Cor dyad with a quenching efficiency of [Formula: see text]99%. Detailed analysis of the data suggests that Forster’s dipole–dipole mechanism does not adequately explain this energy transfer. However, at a 410 nm excitation, florescence quenching is detected in Ptz-Cor (49%) supporting a photo induced electron transfer (PET) process from the ground state of PTZ to the excited state of corrole macrocycle. The electron-transfer rates ([Formula: see text] of Ptz-Cor are found in the range [Formula: see text] to [Formula: see text] and are concluded to be solvent dependent.

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Cooper, Bridgette, Maria Tudorovskaya, Sebastian Mohr, Aran O’Hare, Martin Hanicinec, Anna Dzarasova, Jimena Gorfinkiel, et al. "Quantemol Electron Collisions (QEC): An Enhanced Expert System for Performing Electron Molecule Collision Calculations Using the R-Matrix Method." Atoms 7, no. 4 (October 17, 2019): 97. http://dx.doi.org/10.3390/atoms7040097.

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Collisions of low energy electrons with molecules are important for understanding many aspects of the environment and technologies. Understanding the processes that occur in these types of collisions can give insights into plasma etching processes, edge effects in fusion plasmas, radiation damage to biological tissues and more. A radical update of the previous expert system for computing observables relevant to these processes, Quantemol-N, is presented. The new Quantemol Electron Collision (QEC) expert system simplifyies the user experience, improving reliability and implements new features. The QEC graphical user interface (GUI) interfaces the Molpro quantum chemistry package for molecular target setups, and the sophisticated UKRmol+ codes to generate accurate and reliable cross-sections. These include elastic cross-sections, super elastic cross-sections between excited states, electron impact dissociation, scattering reaction rates, dissociative electron attachment, differential cross-sections, momentum transfer cross-sections, ionization cross sections, and high energy electron scattering cross-sections. With this new interface we will be implementing dissociative recombination estimations, vibrational excitations for neutrals and ions, and effective core potentials in the near future.

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Fichtner, Horst, S. Ranga Sreenivasn, and Norbert Vormbrock. "Transfer integrals for fully ionized gases." Journal of Plasma Physics 55, no. 1 (February 1996): 95–120. http://dx.doi.org/10.1017/s0022377800018699.

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The general transfer integrals describing the collisional exchange of momentum and energy between the constituents of multicoimponent gases are evaluated for different plasma scenarios characterized by Maxwellian as well as non-Maxwellian distribution functions of the plasma species. Following a brief presentation of the standard approximation frequently employed in the literature, a comparison of numerical evaluations of the transfer integrals for various distribution functions reveals significant differences in the corresponding collisional momentum and energy exchange rates, which are shown to depend mainly on the core structure of the distributions. We demonstrate the inadequacy of the standard approximation and hence the importance of an accurate evaluation of the transfer integrals with an application to the electron proton as well as the helium proton interaction in the solar wind plasma.

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Peskin, Uri, Musa Abu-Hilu, and Shammai Speiser. "Approaches to molecular devices based on controlled intramolecular electronic energy and electron transfer. Electron transfer rates through flexible molecular bridges by a time-dependent super exchange model." Optical Materials 24, no. 1-2 (October 2003): 23–29. http://dx.doi.org/10.1016/s0925-3467(03)00100-9.

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Otten, Marijke F., John van der Oost, Willem N. M. Reijnders, Hans V. Westerhoff, Bernd Ludwig, and Rob J. M. Van Spanning. "Cytochromes c550,c552, and c1 in the Electron Transport Network of Paracoccus denitrificans: Redundant or Subtly Different in Function?" Journal of Bacteriology 183, no. 24 (December 15, 2001): 7017–26. http://dx.doi.org/10.1128/jb.183.24.7017-7026.2001.

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ABSTRACT Paracoccus denitrificans strains with mutations in the genes encoding the cytochrome c 550,c 552, or c 1 and in combinations of these genes were constructed, and their growth characteristics were determined. Each mutant was able to grow heterotrophically with succinate as the carbon and free-energy source, although their specific growth rates and maximum cell numbers fell variably behind those of the wild type. Maximum cell numbers and rates of growth were also reduced when these strains were grown with methylamine as the sole free-energy source, with the triple cytochromec mutant failing to grow on this substrate. Under anaerobic conditions in the presence of nitrate, none of the mutant strains lacking the cytochrome bc 1 complex reduced nitrite, which is cytotoxic and accumulated in the medium. The cytochrome c 550-deficient mutant did denitrify provided copper was present. The cytochromec 552 mutation had no apparent effect on the denitrifying potential of the mutant cells. The studies show that the cytochromes c have multiple tasks in electron transfer. The cytochrome bc 1 complex is the electron acceptor of the Q-pool and of amicyanin. It is also the electron donor to cytochromes c 550 andc 552 and to thecbb 3-type oxidase. Cytochromec 552 is an electron acceptor both of the cytochrome bc 1 complex and of amicyanin, as well as a dedicated electron donor to theaa 3-type oxidase. Cytochromec 550 can accept electrons from the cytochrome bc 1 complex and from amicyanin, whereas it is also the electron donor to both cytochromec oxidases and to at least the nitrite reductase during denitrification. Deletion of the c-type cytochromes also affected the concentrations of remaining cytochromes c, suggesting that the organism is plastic in that it adjusts its infrastructure in response to signals derived from changed electron transfer routes.

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Canton, S. E., X. Zhang, Y. Liu, J. Zhang, M. Pápai, A. Corani, A. L. Smeigh, et al. "Watching the dynamics of electrons and atoms at work in solar energy conversion." Faraday Discussions 185 (2015): 51–68. http://dx.doi.org/10.1039/c5fd00084j.

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The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium–cobalt dyads, which belong to the large family of donor–bridge–acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.

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Pandey, Kavita, Shams T. A. Islam, Thomas Happe, and Fraser A. Armstrong. "Frequency and potential dependence of reversible electrocatalytic hydrogen interconversion by [FeFe]-hydrogenases." Proceedings of the National Academy of Sciences 114, no. 15 (March 27, 2017): 3843–48. http://dx.doi.org/10.1073/pnas.1619961114.

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The kinetics of hydrogen oxidation and evolution by [FeFe]-hydrogenases have been investigated by electrochemical impedance spectroscopy—resolving factors that determine the exceptional activity of these enzymes, and introducing an unusual and powerful way of analyzing their catalytic electron transport properties. Attached to an electrode, hydrogenases display reversible electrocatalytic behavior close to the 2H+/H2 potential, making them paradigms for efficiency: the electrocatalytic “exchange” rate (measured around zero driving force) is therefore an unusual parameter with theoretical and practical significance. Experiments were carried out on two [FeFe]-hydrogenases, CrHydA1 from the green alga Chlamydomonas reinhardtii, which contains only the active-site “H cluster,” and CpI from the fermentative anaerobe Clostridium pasteurianum, which contains four low-potential FeS clusters that serve as an electron relay in addition to the H cluster. Data analysis yields catalytic exchange rates (at the formal 2H+/H2 potential, at 0 °C) of 157 electrons (78 molecules H2) per second for CpI and 25 electrons (12 molecules H2) per second for CrHydA1. The experiments show how the potential dependence of catalytic electron flow comprises frequency-dependent and frequency-independent terms that reflect the proficiencies of the catalytic site and the electron transfer pathway in each enzyme. The results highlight the “wire-like” behavior of the Fe–S electron relay in CpI and a low reorganization energy for electron transfer on/off the H cluster.

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Howitt, D. G., D. L. Medlin, and M. M. Cluckie. "Low-energy displacement damage and the effect on the AEM of Ceramics." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 822–23. http://dx.doi.org/10.1017/s0424820100177246.

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The observation that the signal from light elements such as carbon, oxygen, and nitrogen decreases in strength with time is to be expected for displacement in ceramic materials at high voltage, not only because the momentum transfer from an electron is more favorable, but also because the lattices are often full of defects. Even though the sensitivities of these materials can be below that of close parked metals at high voltage, during analytical electron microscopy the beam currents are sufficiently intense that the effect can be substantial. The loss rates for the signal are however quite predictable in the early stages and need not interfere with quantitative assessments of composition.An example of the loss of carbon signal from titanium carbide is shown in Figure 1 and a determination of the overall cross-section for carbon loss at 100 keV indicates a value close to 0.3 barns. This is about the cross-section for carbon displacement at 20 eV which is a conservative estimate of the binding energy for carbon in the lattice. Early experiments on vanadium carbide (Venables, 1969) indicate a similar overall cross-section however the threshold energy for the electrons to induce the damage is about only 5 eV. These results are consistent with the transfer of about 5 eV from an incident electron inducing a very small displacement of the carbon atom, of the order of an interatomic distance, with a damage cross-section of about 200 barns. Since the process needs to be repeated several times before the carbon atom is lost from the specimen the measured cross-section is proportionality reduced.

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Cord-Ruwisch, Ralf, Derek R. Lovley, and Bernhard Schink. "Growth of Geobacter sulfurreducens with Acetate in Syntrophic Cooperation with Hydrogen-Oxidizing Anaerobic Partners." Applied and Environmental Microbiology 64, no. 6 (June 1, 1998): 2232–36. http://dx.doi.org/10.1128/aem.64.6.2232-2236.1998.

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ABSTRACT Pure cultures of Geobacter sulfurreducens and other Fe(III)-reducing bacteria accumulated hydrogen to partial pressures of 5 to 70 Pa with acetate, butyrate, benzoate, ethanol, lactate, or glucose as the electron donor if electron release to an acceptor was limiting. G. sulfurreducens coupled acetate oxidation with electron transfer to an anaerobic partner bacterium in the absence of ferric iron or other electron acceptors. Cocultures of G. sulfurreducens and Wolinella succinogenes with nitrate as the electron acceptor degraded acetate efficiently and grew with doubling times of 6 to 8 h. The hydrogen partial pressures in these acetate-degrading cocultures were considerably lower, in the range of 0.02 to 0.04 Pa. From these values and the concentrations of the other reactants, it was calculated that in this cooperation the free energy change available to G. sulfurreducens should be about −53 kJ per mol of acetate oxidized, assuming complete conversion of acetate to CO2 and H2. However, growth yields (18.5 g of dry mass per mol of acetate for the coculture, about 14 g for G. sulfurreducens) indicated considerably higher energy gains. These yield data, measurement of hydrogen production rates, and calculation of the diffusive hydrogen flux indicated that electron transfer in these cocultures may not proceed exclusively via interspecies hydrogen transfer but may also proceed through an alternative carrier system with higher redox potential, e.g., a c-type cytochrome that was found to be excreted byG. sulfurreducens into the culture fluid. Syntrophic acetate degradation was also possible with G. sulfurreducens and Desulfovibrio desulfuricans CSN but only with nitrate as electron acceptor. These cultures produced cell yields of 4.5 g of dry mass per mol of acetate, to which both partners contributed at about equal rates. These results demonstrate that some Fe(III)-reducing bacteria can oxidize organic compounds under Fe(III) limitation with the production of hydrogen, and they provide the first example of rapid acetate oxidation via interspecies electron transfer at moderate temperature.

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Klemme, J. H. "Photoproduction of Hydrogen by Purple Bacteria: A Critical Evaluation of the Rate Limiting Enzymatic Steps." Zeitschrift für Naturforschung C 48, no. 5-6 (June 1, 1993): 482–87. http://dx.doi.org/10.1515/znc-1993-5-613.

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Abstract The enzymatic mechanisms and energetics of nitrogenase-catalyzed photoproduction of hydrogen from organic C-compounds by purple bacteria are discussed in respect to the question of which of the following three enzymes or enzyme systems are rate limiting for H2-production: (a) the nitrogenase-complex; (b) the enzymes and electron transport proteins involved in hydrogen transfer from the organic substrate(s) to nitrogenase; and (c) the system of photosynthetic ATP-regeneration. Calculations of maximum in vivo rates of photosynthetic ATPregeneration (gATP-values derived from growth rates), and of ATP-consumption by nitrogenase- catalyzed H2-production, and comparison of these rates with the specific activities of the enzymes of hydrogen or electron transfer from the C-substrate to the nitrogenase-complex, make it very likely that, in Rhodospirillum rubrum, nitrogenase-catalyzed H2-formation is limited by the availability of ATP and, possibly, of reducing power. In two other nonsulfur purple bacterial species (Rhodobacter capsulatus and Rhodobacter sphaeroides), H2-photoproduction is probably not energy-limited.

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Honma, Kenji, and David E. Clemmer. "The Importance of Electron Transfer Mechanism in Reactions of Neutral Transition Metal Atoms." Laser Chemistry 15, no. 2-4 (January 1, 1995): 209–20. http://dx.doi.org/10.1155/1995/25319.

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Reaction kinetics of ground, Ti(a3F) and V(a4F), and excited, Ti(a5F) and V(a6D), states atoms with some simple molecules have been studied by a discharge-flow tube technique. Laser-induced fluorescence (LIF) was used to determine the concentration of the metal atoms as a function of the flow rate of the reactant molecule to obtain effective bimolecular rate constants. The rate constants of reactions with OX (X = O, N, N2) and H2S show strong inverse correlation with effective ionization potentials (I.P.-Eel, where I.P. and Eel are ionization potential and electronic energy of metal atom) of the metal atoms. This result suggests that the electron transfer mechanism plays an important role in these reactions. The large rate constants for electronic excited states can be explained by the crossing between ionic and flat neutral potential energy surfaces. The inefficient reaction rates measured for ground states can be explained by the repulsive nature of 4s2 configuration which can result in a potential barrier.

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Kulkarni, Gargi, Donna M. Kridelbaugh, Adam M. Guss, and William W. Metcalf. "Hydrogen is a preferred intermediate in the energy-conserving electron transport chain ofMethanosarcina barkeri." Proceedings of the National Academy of Sciences 106, no. 37 (September 1, 2009): 15915–20. http://dx.doi.org/10.1073/pnas.0905914106.

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Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F420H2dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However,Methanosarcina barkeriΔfpomutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Δfrhmutants lacking the cytoplasmic F420-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Δfpo/Δfrhmutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless,M. barkeridoes have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Δfrhmutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth ofM. barkeri.

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Abe, Ryu, Kazuhiro Sayama, and Hideki Sugihara. "Effect of Water/Acetonitrile Ratio on Dye-Sensitized Photocatalytic H2 Evolution under Visible Light Irradiation." Journal of Solar Energy Engineering 127, no. 3 (October 28, 2004): 413–16. http://dx.doi.org/10.1115/1.1878854.

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H 2 production in a water-acetonitrile solution containing iodide as an electron donor was investigated over dye-sensitized Pt∕TiO2 photocatalysts under visible light irradiation, as a potential water-splitting system based on an iodide redox mediator. The rates of H2 evolution decreased with increasing proportion of water in the solutions, because of a decrease in the energy gap between the redox potential of I3−∕I− and the highest occupied molecular orbital levels of the dyes, which decreases the efficiency of electron transfer from I− to dye.

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Moe, Agnes, Justin Di Trani, John L. Rubinstein, and Peter Brzezinski. "Cryo-EM structure and kinetics reveal electron transfer by 2D diffusion of cytochrome c in the yeast III-IV respiratory supercomplex." Proceedings of the National Academy of Sciences 118, no. 11 (March 8, 2021): e2021157118. http://dx.doi.org/10.1073/pnas.2021157118.

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Energy conversion in aerobic organisms involves an electron current from low-potential donors, such as NADH and succinate, to dioxygen through the membrane-bound respiratory chain. Electron transfer is coupled to transmembrane proton transport, which maintains the electrochemical proton gradient used to produce ATP and drive other cellular processes. Electrons are transferred from respiratory complexes III to IV (CIII and CIV) by water-soluble cytochrome (cyt.) c. In Saccharomyces cerevisiae and some other organisms, these complexes assemble into larger CIII2CIV1/2 supercomplexes, the functional significance of which has remained enigmatic. In this work, we measured the kinetics of the S. cerevisiae supercomplex cyt. c-mediated QH2:O2 oxidoreductase activity under various conditions. The data indicate that the electronic link between CIII and CIV is confined to the surface of the supercomplex. Single-particle electron cryomicroscopy (cryo-EM) structures of the supercomplex with cyt. c show the positively charged cyt. c bound to either CIII or CIV or along a continuum of intermediate positions. Collectively, the structural and kinetic data indicate that cyt. c travels along a negatively charged patch on the supercomplex surface. Thus, rather than enhancing electron transfer rates by decreasing the distance that cyt. c must diffuse in three dimensions, formation of the CIII2CIV1/2 supercomplex facilitates electron transfer by two-dimensional (2D) diffusion of cyt. c. This mechanism enables the CIII2CIV1/2 supercomplex to increase QH2:O2 oxidoreductase activity and suggests a possible regulatory role for supercomplex formation in the respiratory chain.

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D'Souza, Francis, Suresh Gadde, Mohamed E. El-Khouly, Melvin E. Zandler, Yasuyaki Araki, and Osamu Ito. "A supramolecular Star Wars Tie Fighter Ship: electron transfer in a self-assembled triad composed of two zinc naphthalocyanines and a fullerene." Journal of Porphyrins and Phthalocyanines 09, no. 10 (October 2005): 698–705. http://dx.doi.org/10.1142/s1088424605000812.

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Photoactive supramolecules composed of electron donor and electron acceptor entities are important for light energy harvesting applications. In the present study, a Star Wars Tie Fighter Ship shaped supramolecular triad was constructed by self-assembling two zinc naphthalocyanines to a fulleropyrrolidine bearing two pyridine entities using an axial coordination approach. Optical absorption and emission studies revealed stable complex formation, and the experimentally determined free-energy change revealed the possibility of electron transfer from singlet excited zinc naphthalocyanine to the fulleropyrrolidine. The picosecond time-resolved emission technique was utilized to evaluate the kinetics of charge separation while nanosecond transient absorption spectral studies provided evidence for electron transfer quenching. The measured charge-separation rate, k CS and quantum yield, Φ CS were found to be 5.7 × 109 s −1 and 0.93 in toluene, respectively, indicating an efficient process within the supramolecular triad. The charge recombination rate (k CR ) of the supramolecular ion-pair calculated from the nanosecond transient absorption technique was found to be 3.5 × 107 s −1 yielding a lifetime for the radical ion-pair (τ RIP ) of about 30 ns. Changing the solvent from the noncoordinating toluene to the coordinating benzonitrile or THF destroyed the supramolecular structure, and under these experimental conditions, only intermolecular electron transfer from the triplet excited zinc naphthalocyanine to fulleropyrrolidine could be observed. Under these conditions, the measured electron transfer rates, k et , T inter , were found to be 2.6 × 107 M −1. s −1 in benzonitrile and 1.2 × 107 M −1. s −1 in THF, respectively.

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Orłowski, Rafał, John A. Clark, James B. Derr, Eli M. Espinoza, Maximilian F. Mayther, Olga Staszewska-Krajewska, Jay R. Winkler, et al. "Role of intramolecular hydrogen bonds in promoting electron flow through amino acid and oligopeptide conjugates." Proceedings of the National Academy of Sciences 118, no. 11 (March 11, 2021): e2026462118. http://dx.doi.org/10.1073/pnas.2026462118.

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Elucidating the factors that control charge transfer rates in relatively flexible conjugates is of importance for understanding energy flows in biology as well as assisting the design and construction of electronic devices. Here, we report ultrafast electron transfer (ET) and hole transfer (HT) between a corrole (Cor) donor linked to a perylene-diimide (PDI) acceptor by a tetrameric alanine (Ala)4. Selective photoexcitation of the donor and acceptor triggers subpicosecond and picosecond ET and HT. Replacement of the (Ala)4 linker with either a single alanine or phenylalanine does not substantially affect the ET and HT kinetics. We infer that electronic coupling in these reactions is not mediated by tetrapeptide backbone nor by direct donor–acceptor interactions. Employing a combination of NMR, circular dichroism, and computational studies, we show that intramolecular hydrogen bonding brings the donor and the acceptor into proximity in a “scorpion-shaped” molecular architecture, thereby accounting for the unusually high ET and HT rates. Photoinduced charge transfer relies on a (Cor)NH…O=C–NH…O=C(PDI) electronic-coupling pathway involving two pivotal hydrogen bonds and a central amide group as a mediator. Our work provides guidelines for construction of effective donor–acceptor assemblies linked by long flexible bridges as well as insights into structural motifs for mediating ET and HT in proteins.

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Jiao, Dongbin, Liangjun Ke, Shengbo Liu, and Felix Chan. "Optimal Energy-Delay in Energy Harvesting Wireless Sensor Networks with Interference Channels." Sensors 19, no. 4 (February 14, 2019): 785. http://dx.doi.org/10.3390/s19040785.

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In this work, we investigate the capacity allocation problem in the energy harvesting wireless sensor networks (WSNs) with interference channels. For the fixed topologies of data and energy, we formulate the optimization problem when the data flow remains constant on all data links and each sensor node harvests energy only once in a time slot. We focus on the optimal data rates, power allocations and energy transfers between sensor nodes in a time slot. Our goal is to minimize the total delay in the network under two scenarios, i.e., no energy transfer and energy transfer. Furthermore, since the optimization problem is non-convex and difficult to solve directly, by considering the network with the relatively high signal-to-interference-plus-noise ratio (SINR), the non-convex optimization problem can be transformed into a convex optimization problem by convex approximation. We attain the properties of the optimal solution by Lagrange duality and solve the convex optimization problem by the CVX solver. The experimental results demonstrate that the total delay of the energy harvesting WSNs with interference channels is more than that in the orthogonal channel; the total network delay increases with the increasing data flow for the fixed energy arrival rate; and the energy transfer can help to decrease the total delay.

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Onuchic, José N., Chigusa Kobayashi, Osamu Miyashita, Patricia Jennings, and Kim K. Baldridge. "Exploring biomolecular machines: energy landscape control of biological reactions." Philosophical Transactions of the Royal Society B: Biological Sciences 361, no. 1472 (July 14, 2006): 1439–43. http://dx.doi.org/10.1098/rstb.2006.1876.

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For almost 15 years, our Pathway model has been the most powerful model in terms of predicting the tunnelling mechanism for electron transfer (ET) in biological systems, particularly proteins. Going beyond the conventional Pathway models, we have generalized our method to understand how protein dynamics modulate not only the Franck–Condon factor, but also the tunnelling matrix element. We have demonstrated that when interference among pathways modulates the electron tunnelling interactions in proteins (particularly destructive interference), dynamical effects are of critical importance. Tunnelling can be controlled by protein conformations that lie far from equilibrium—those that minimize the effect of destructive interference during tunnelling, for example. In the opposite regime, electron tunnelling is mediated by one (or a few) constructively interfering pathway tubes and dynamical effects are modest. This new mechanism for dynamical modulation of the ET rate has been able to explain and/or predict several rates that were later confirmed by experiment. However, thermal fluctuations can also affect these molecular machines in many other ways. For example, we show how global transformations, which control protein functions such as allostery, may involve large-scale motion and possibly partial unfolding during the reaction event.

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Maes, Mio, Hisahiro Sasabe, Nobuhiro Kihara, Yasuyuki Araki, Yoshio Furusho, Kazuhiko Mizuno, Toshikazu Takata, and Osamu Ito. "Photoinduced electron and energy transfer processes in rotaxanes containing zinc porphyrin as pendant and [60]fullerene and ferrocene as axle ends." Journal of Porphyrins and Phthalocyanines 09, no. 10 (October 2005): 724–34. http://dx.doi.org/10.1142/s1088424605000836.

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Photoinduced electron-transfer processes of a newly synthesized rotaxane containing porphyrinatozinc ( ZnP ), [60]fullerene ( C 60), and ferrocene ( Fc ) have been studied in terms of the time-resolved fluorescence and transient absorption measurements in polar and nonpolar solvents. In this rotaxane, ( ZnP ; C 60- Fc ) rotax , ZnP was chosen as a pendant of a crown-ether necklace, through which an axle with C 60 and Fc at both termini was penetrated. By the selective excitation of the ZnP moiety in a nonpolar solvent, energy transfer predominantly takes place to the C 60 moiety of ( ZnP ; C 60- Fc ) rotax . In polar solvents, charge-separation process takes place via the excited singlet state of the ZnP moiety in addition to the energy-transfer process. From the nanosecond transient absorption spectra, a clear absorption band of the C 60•− moiety was observed at 1000 nm as well as a broad absorption in the 600-800 nm region due to ZnP •+, suggesting the generation of ( ZnP •+; C 60•−- Fc ) rotax in the first step. Afterward, the hole-transferring process from ZnP •+ to Fc is thermodynamically possible, although this process is not fast because of its through-space process character. The final lifetimes of the C 60•− moiety were evaluated to be 290 and 370 ns in benzonitrile and DMF, respectively. The ratios of the charge-separation rates to charge-recombination rates were ca. 1000, indicating that ( ZnP ; C 60- Fc ) rotax affords an efficient photosynthetic model.

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Journal articles on the topic 'Electron energy transfer rates'

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