Building Model Systems to Understand Proton-Coupled Electron Transfer in Heme PDF Download
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Author: Christina J. Hanson
Publisher:
ISBN:
Category :
Languages : en
Pages : 111
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Book Description
Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are coupled in a bidirectional system allowing for individual turning of the kinetics and thermodynamics. The target of interest is a biomimedic heme system allowing for a detailed mechanistic study of the formation of the oxidation states of heme, of particular interest the highly reactive Fe(IV)=O species. The bidirectional model is prepared using a hangman porphyrin with an axially coordinated to the metal center, and the electron transfer event is triggered by excitation of the porphyrin. The synthesis of this motif is discussed as well as initial studies into the binding of a coordinated electron acceptor to the metal center. In the future, the excited state of the acceptor will be used to trigger the electron transfer portion of the PCET event. To understand the signatures of different electron acceptors and binding to the metal center, a redox inactive zinc porphyrin is used as a model to allow for longer excited state lifetimes and well known transient signatures. Three diimide acceptors have been coordinated through a pyridine ring to the metal center of the porphyrin, and electron transfer was triggered both by excitation of the porphyrin and the acceptor. Lifetimes of the charge separated state were determined using picoseconds and nanosecond transient absorption. The acceptors are then coordinated to a symmetrical iron porphyrin in an attempt to understand the behavior of charge separation in the more complicated open d shell system. Spectroscopic data of both systems is shown.
Author: Christina J. Hanson
Publisher:
ISBN:
Category :
Languages : en
Pages : 111
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Book Description
Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are coupled in a bidirectional system allowing for individual turning of the kinetics and thermodynamics. The target of interest is a biomimedic heme system allowing for a detailed mechanistic study of the formation of the oxidation states of heme, of particular interest the highly reactive Fe(IV)=O species. The bidirectional model is prepared using a hangman porphyrin with an axially coordinated to the metal center, and the electron transfer event is triggered by excitation of the porphyrin. The synthesis of this motif is discussed as well as initial studies into the binding of a coordinated electron acceptor to the metal center. In the future, the excited state of the acceptor will be used to trigger the electron transfer portion of the PCET event. To understand the signatures of different electron acceptors and binding to the metal center, a redox inactive zinc porphyrin is used as a model to allow for longer excited state lifetimes and well known transient signatures. Three diimide acceptors have been coordinated through a pyridine ring to the metal center of the porphyrin, and electron transfer was triggered both by excitation of the porphyrin and the acceptor. Lifetimes of the charge separated state were determined using picoseconds and nanosecond transient absorption. The acceptors are then coordinated to a symmetrical iron porphyrin in an attempt to understand the behavior of charge separation in the more complicated open d shell system. Spectroscopic data of both systems is shown.
Author: Afua Nti
Publisher:
ISBN:
Category : Oxidation-reduction reaction
Languages : en
Pages : 210
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Book Description
Author: Mårten Wikström
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 216
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Book Description
Author: Ewuradjoa Gadzanku
Publisher:
ISBN:
Category : Electron donor-acceptor complexes
Languages : en
Pages : 84
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Book Description
Author: Sebastiao Formosinho
Publisher: Royal Society of Chemistry
ISBN: 1849733163
Category : Science
Languages : en
Pages : 169
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Book Description
Proton-coupled electron transfer (PCET) is emerging as an important new class of reactions and, over the past decade, great strides have been made in our understanding of them. PCET reactions are studied in many branches of chemistry and are omnipresent in biological processes. This book covers recent developments from both the theoretical and experimental points of view. It concentrates on the importance of PCET in biological systems and for bioenergetic conversion. The oxidation of water in Photosystem II to produce oxygen, and the reduction of protons to hydrogen by hydrogenase, for energy storage gets particular emphasis. Chemical reactivity is currently explained in terms of several scientific principles. One of them is the bond-breaking-bond-forming process and is conceptually based on potential energy surfaces. Another incorporates the role of Franck-Condon factors resulting from the overlap of vibrational wavefunctions. A third, the so-called solvent reorganization, involves solvent configuration around a charged species. PCET brings together such concepts and links them to quantum mechanical tunnelling of the electron particle. This book uses personal accounts of experimental examples to provide additional insight on this important topic. It starts by presenting a general overview of the main theoretical approaches and experimental applications. The chapters then go on to cover topics including: the application of the Marcus Cross Relation; the solvation of ionic systems; experimental approaches in biological redox systems; metal ion-coupled electron transfer, and electrochemical concerted proton-electron transfers.
Author: Jay Lee Yang
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Book Description
Two new model systems for the study of orthogonal proton-coupled electron transfer (PCET) have been developed. The first model system is based on Ru"(HzO)(tpy)(bpy) (tpy = 2,2';6',2"terpyridine, bpy = 2,2'-bipyridine) where methyl viologen (MV2 ) electron acceptors were appended to the ruthenium aqua complex through the bpy. Picosecond transient absorption measurements show that electron transfer from the excited state of the ruthenium complex to MV2+ occurs with [tau] -200 ps. Experiments performed in water and buffered solution at pH = 7 show no evidence of the loss of proton from the aqua ligand to the bulk solvent or to the phosphate buffer. A minor kinetic isotope effect for the rate of charge separation was found with kH/kD = 1.8 + 0.1 ps. Preliminary synthetic attempts of coupling the ET event to the PT event was accomplished by appending xanthene "Hangman" scaffolds to the 4' position of the tpy. The feasibility of modifying the xanthene scaffold to accommodate various hanging groups has been demonstrated. The second model system is based on Re'(CO)3(phen)(pyr) (phen = 1,10phenanthroline, pyr = pyridine) where tyrosine was appended to the rhenium complex through the axial pyr ligand. Unlike previous Re'(CO)3(bpy)(CN) (CN = cyanide) systems, substitution to the more rigid phen extended the lifetime of the excited state of the rhenium complex to 3.0 ls, which allowed PCET to occur from the tyrosine to the rhenium metal center and hydrogenbonded base in dichloromethane. This was inferred from substantial emission quenching of the rhenium-tyrosine complex through the titration of base (base = pyridine, imidazole, 2,4,6trimethylpyridine). Equilibrium constants measuring the extent of formation of the [rheniumtyrosine---base]+ species were found to correlate with the strength of the base based on aqueous pKa values.
Author: Achim Müller
Publisher: Elsevier Publishing Company
ISBN:
Category : Science
Languages : en
Pages : 420
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Book Description
Various aspects of electron and proton transfer in chemistry and biology are described in this volume. The joint presentation was chosen for two reasons. Rapid electron and proton transfer govern cellular energetics in both the most primitive and higher organisms with photosynthetic and heterotrophic lifestyles. Further, biology has become the area where the various disciplines of science, which were previously diversified, are once again converging. The book begins with a survey of physicochemical principles of electron transfer in the gas and solid phase, with thermodynamic and photochemical driving force. Inner and outer sphere mechanisms and the coupling of electron transfer to nuclear rearrangements are reviewed. These principles are applied to construct artificial photosynthesis, leading to biological electron transfer involving proteins with transition metal and/or organic redox centres. The tuning of the free energy profile on the reaction trajectory through the protein by single amino acids or by the larger ensemble that determines the electrostatic properties of the reaction path is one major issue.Another one is the transformation of one-electron to paired-electron steps with protection against hazardous radical intermediates. The diversity of electron transport systems is represented in various chapters with emphasis on photosynthesis, respiration and nitrogenases. The book will be of interest to scientists in chemistry, physics and the life sciences.
Author: Elizabeth Renee Young
Publisher:
ISBN:
Category :
Languages : en
Pages : 266
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Book Description
Spectroscopic investigations of systems designed to advance the mechanistic interrogation of photo-induced proton coupled electron transfer (PCET) and proton-coupled (through-bond) energy transfer (PCEnT) are presented. PCET is ubiquitous in Nature, where it is at the heart of bioenergy conversion and catalysis (Chapter I). Systems of relevance to mechanistic studies of PCET and PCEnT are the central tenet of this work. In uni-directional PCET, electron transfer (ET) occurs from an electron donor (De) to an electron acceptor (Ae) through a hydrogen bonded proton interface. The proton interface plays a vital role in mediating ET. Thus, the exact ionization configuration of the interface must be uncovered to fuIIy realize the influence of the interface. SpecificaIIy, does the interface exists in the non-ionized (i.e. amidine-carboxylic acid) or ionized (i.e. amidinium-carboxylate) form. Strategies to spectraIIy monitor the interface ionization state by extending electronic communication from a porphyrinic chromophore to its pendant amidinium functionality are pursued through examination of an alkynylamidinium Ni(II) porphyrin (Chapter II) and an amidinium appended Zn(II) purpurin (Chapter III). With the ionization state of the interface resolved, mechanistic studies of photo-induced PCET between an identical De and Ae pair juxtaposed by a non-ionized (amidine-carboxylic acid) and an ionized (amidinium-sulfonate) interface are undertaken to reveal that PCET occurring through an ionized interface is more strongly coupled to the surrounding solvent environment (Chapter IV). Work on this system is extended to a second solvent of similar dielectric constant to establish that molecular variation of the solvent environment impacts PCET, likely through its interaction with the proton interface (Chapter V). Two water-soluble amidinium-appended ferrocene moieties are presented as building blocks for aqueous bi-directional PCET in which PT occurs to the bulk and ET occurs along a covalently bound coordinate (Chapter VI). ET and through-bond EnT are described by the semiclassical nonradiative decay formalism, meaning both processes should be sensitive to an intervening proton network. For the first time, PCEnT is established using ferrocenyl-amidine moieties bound through an amidinecarboxylic acid interface to Ru(II) polypyridyl complexes (Chapter VII).
Author: James A. Roberts
Publisher:
ISBN:
Category : Charge exchange
Languages : en
Pages : 384
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Book Description
Author: Bon Jun Koo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Proton-coupled electron transfer (PCET) combines proton transfer with electron transfer to bypass high-energy intermediates. The ribonucleotide reductase (RNR) family of enzymes catalyzes the conversion of ribonucleotides to deoxynucleotides using amino acid radicals. The enzyme contains an efficient PCET pathway that transfers an electron and proton over a 35 Å distance across two subunits, the longest PCET pathway known in biology. The enzyme func-tions with very high fidelity, performing >105 turnovers before radical loss.
