Energetics and Kinetics of Primary Charge Separation in Bacterial Photosynthesis
We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentia...
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Veröffentlicht in: | The journal of physical chemistry. B 2008-08, Vol.112 (33), p.10322-10342 |
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description | We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair. |
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Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.</description><identifier>ISSN: 1520-6106</identifier><identifier>EISSN: 1520-5207</identifier><identifier>DOI: 10.1021/jp8016503</identifier><identifier>PMID: 18636767</identifier><language>eng</language><publisher>United States: American Chemical Society</publisher><subject>B: Biophysical Chemistry ; Bacterial Physiological Phenomena ; Bacteriochlorophylls - chemistry ; Biophysics - methods ; Electron Transport ; Electrons ; Kinetics ; Models, Statistical ; Molecular Conformation ; Photosynthesis ; Photosynthetic Reaction Center Complex Proteins - chemistry ; Rhodobacter sphaeroides - metabolism ; Static Electricity ; Temperature ; Thermodynamics ; Time Factors</subject><ispartof>The journal of physical chemistry. 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B</title><addtitle>J. Phys. Chem. B</addtitle><description>We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.</description><subject>B: Biophysical Chemistry</subject><subject>Bacterial Physiological Phenomena</subject><subject>Bacteriochlorophylls - chemistry</subject><subject>Biophysics - methods</subject><subject>Electron Transport</subject><subject>Electrons</subject><subject>Kinetics</subject><subject>Models, Statistical</subject><subject>Molecular Conformation</subject><subject>Photosynthesis</subject><subject>Photosynthetic Reaction Center Complex Proteins - chemistry</subject><subject>Rhodobacter sphaeroides - metabolism</subject><subject>Static Electricity</subject><subject>Temperature</subject><subject>Thermodynamics</subject><subject>Time Factors</subject><issn>1520-6106</issn><issn>1520-5207</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2008</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNpt0M9LwzAUB_AgipvTg_-A9KLgoZofbdIeXZk_cGhh8xyy5tVldm1NWnD_vR0t8-IhvDzehxfyReiS4DuCKbnf1BEmPMTsCI1JSLHfHXE83DnBfITOnNtgTEMa8VM0IhFnXHAxRumsBPsJjcmcp0rtvZqyb6rcS63ZKrvzkrXqiLeAWlnVmKr0TOlNVdaANarw0nXVVG5XNmtwxp2jk1wVDi6GOkEfj7Nl8uzP359ekoe5r1hIGj_WYa40DwOWAyOQxQIIU5gHVEdYsJUGoVmmGcOYKx2AoCsCVAQxDhSDmLEJuun31rb6bsE1cmtcBkWhSqhaJ3kc0JjQPbztYWYr5yzksu7_JQmW-_jkIb7OXg1L29UW9J8c8uqA3wPjGvg5zJX9kt1UhHKZLmTyRqdRQqYy7Px171Xm5KZqbdll8s_DvzjuhMY</recordid><startdate>20080821</startdate><enddate>20080821</enddate><creator>LeBard, David N</creator><creator>Kapko, Vitaliy</creator><creator>Matyushov, Dmitry V</creator><general>American Chemical Society</general><scope>BSCLL</scope><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7X8</scope></search><sort><creationdate>20080821</creationdate><title>Energetics and Kinetics of Primary Charge Separation in Bacterial Photosynthesis</title><author>LeBard, David N ; Kapko, Vitaliy ; Matyushov, Dmitry V</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a351t-9d5fad6543fe31ec97e13a0642d8073bde7d3cd33006ad4e72b1e274904a3e933</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2008</creationdate><topic>B: Biophysical Chemistry</topic><topic>Bacterial Physiological Phenomena</topic><topic>Bacteriochlorophylls - chemistry</topic><topic>Biophysics - methods</topic><topic>Electron Transport</topic><topic>Electrons</topic><topic>Kinetics</topic><topic>Models, Statistical</topic><topic>Molecular Conformation</topic><topic>Photosynthesis</topic><topic>Photosynthetic Reaction Center Complex Proteins - chemistry</topic><topic>Rhodobacter sphaeroides - metabolism</topic><topic>Static Electricity</topic><topic>Temperature</topic><topic>Thermodynamics</topic><topic>Time Factors</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>LeBard, David N</creatorcontrib><creatorcontrib>Kapko, Vitaliy</creatorcontrib><creatorcontrib>Matyushov, Dmitry V</creatorcontrib><collection>Istex</collection><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>MEDLINE - Academic</collection><jtitle>The journal of physical chemistry. B</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>LeBard, David N</au><au>Kapko, Vitaliy</au><au>Matyushov, Dmitry V</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Energetics and Kinetics of Primary Charge Separation in Bacterial Photosynthesis</atitle><jtitle>The journal of physical chemistry. B</jtitle><addtitle>J. Phys. Chem. B</addtitle><date>2008-08-21</date><risdate>2008</risdate><volume>112</volume><issue>33</issue><spage>10322</spage><epage>10342</epage><pages>10322-10342</pages><issn>1520-6106</issn><eissn>1520-5207</eissn><abstract>We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.</abstract><cop>United States</cop><pub>American Chemical Society</pub><pmid>18636767</pmid><doi>10.1021/jp8016503</doi><tpages>21</tpages></addata></record> |
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subjects | B: Biophysical Chemistry Bacterial Physiological Phenomena Bacteriochlorophylls - chemistry Biophysics - methods Electron Transport Electrons Kinetics Models, Statistical Molecular Conformation Photosynthesis Photosynthetic Reaction Center Complex Proteins - chemistry Rhodobacter sphaeroides - metabolism Static Electricity Temperature Thermodynamics Time Factors |
title | Energetics and Kinetics of Primary Charge Separation in Bacterial Photosynthesis |
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