Introduction to Electron Transfer in Inorganic, Organic, and Biological Systems

Bolton, James R.; Mataga, Noboru; McLendon, George

doi:10.1021/ba-1991-0228.ch001

Cited by 117 publications

(191 citation statements)

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“…The classical Marcus theory of electron transfer (34,35) gives the ⌬G ‡ for a unimolecular reaction as the result of the reorganization energy () and the Gibbs free energy of reaction (⌬G°) according to Eq. 2.…”

Section: Discussionmentioning

confidence: 99%

“…4 where f is a reduced force constant and r R eq and r P eq are the equilibrium bond lengths in the reactant and product states, respectively. A dielectric continuum model, where the orientation polarization of the surroundings is slow, relative to the electronic polarization, frequently is used to approximate out (34,35). In its most general form, Eq.…”

Section: [3]mentioning

confidence: 99%

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Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase

Roth

Klinman

2002

Proc. Natl. Acad. Sci. U.S.A.

172

281

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Two prototropic forms of glucose oxidase undergo aerobic oxidation reactions that convert FADH ؊ to FAD and form H2O2 as a product. Limiting rate constants of kcat͞KM(O2) ‫؍‬ (5.7 ؎ 1.8) ؋ 10 2 M ؊1 ⅐s ؊1 and kcat͞KM(O2) ‫؍‬ (1.5 ؎ 0.3) ؋ 10 6 M ؊1 ⅐s ؊1 are observed at high and low pH, respectively. Reactions exhibit oxygen-18 kinetic isotope effects but no solvent kinetic isotope effects, consistent with mechanisms of rate-limiting electron transfer from flavin to O2. Site-directed mutagenesis studies reveal that the pH dependence of the rates is caused by protonation of a highly conserved histidine in the active site. Temperature studies (283-323 K) indicate that protonation of His-516 results in a reduction of the activation energy barrier by 6.0 kcal⅐mol ؊1 (0.26 eV). Within the context of Marcus theory, catalysis of electron transfer is attributed to a 19-kcal⅐mol ؊1 (0.82 eV) decrease in the reorganization energy and a much smaller 2.2-kcal⅐mol ؊1 (0.095 eV) enhancement of the reaction driving force. An explanation is advanced that is based on changes in outer-sphere reorganization as a function of pH. The active site is optimized at low pH, but not at high pH or in the H516A mutant where rates resemble the uncatalyzed reaction in solution. F lavins are highly versatile enzyme cofactors that undergo electron and proton-coupled electron transfer reactions (1-3). As a result, flavoenzymes are involved in an array of chemical and photochemical processes from COH oxidations (4) to electron transport (5) to repair of cross-linked DNA (6). Glucose oxidase (GO) is a homodimeric protein found predominantly in fungi (National Center for Biotechnology Information, www.ncbi.nlm.nih.gov). Each protein subunit contains an equivalent of noncovalently bound FAD Ϸ15 Å below the surface (7). GO mediates net hydride transfer from the anomeric COH bond of glucose to FAD in the reductive half-reaction (8, 9) and the oxidation of reduced cofactor (FADH Ϫ ) by O 2 in the oxidative half-reaction, forming H 2 O 2 as a product. All evidence points toward a rate-limiting electron transfer step during FADH Ϫ oxidation as shown in Eq. 1 (10). This reaction involves the transfer of negative charge from cofactor to superoxide ion with no net change in charge at the active site.To date, most mechanistic studies of O 2 activation have focused on metalloenzymes. In such reactions, electron transfer and electrostatic stabilization often occur within a single step (ref. 11 and references therein), causing rates to approach the diffusion limit (12). Additionally, ligands control metal coordination geometries and modulate redox potentials, thereby tuning reactivity toward O 2 (13). Enzymes that use organic cofactors do not enjoy such advantages, but may use specialized protein environments to help overcome the kinetic and thermodynamic barriers associated with activation of O 2 .The physical characterization of the protein dielectric is an area of growing interest (14-18) and may provide the key to understanding how proteins like GO facilita...

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Section: Discussionmentioning

confidence: 99%

Section: [3]mentioning

confidence: 99%

Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase

Roth

Klinman

2002

Proc. Natl. Acad. Sci. U.S.A.

172

281

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“…46,47 where 0 (donor,ox) -0 (acceptor,red) is the measured redox difference, and ∆E is the rubrene S 0 ,ν 0 f S 1 ,ν 0 excitation energy, taken as 543 nm, the wavelength where the rubrene absorption and fluorescence spectra overlap. 48 The last term in eq 8 is a Coulomb term that depends on the distance between the ions. The free energy change for the back transfer, ∆G b , was then determined by Details of the cyclic voltammetry measurements are given in ref 1.…”

Section: Methodsmentioning

confidence: 99%

Photoinduced Electron Transfer and Geminate Recombination in Liquids

et al. 1997

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The coupled processes of intermolecular photoinduced forward electron transfer and geminate recombination between donors (rubrene) and acceptors (duroquinone) are studied in two molecular liquids: dibutyl phthalate and diethyl sebacate. Time-correlated single-photon counting and fluorescence yield measurements give information about the depletion of the donor excited state due to forward transfer, while pump-probe experiments give direct information about the radical survival kinetics. A straightforward procedure is presented for removing contributions from excited-state-excited-state absorption to the pump-probe data. The data are analyzed with a previously presented model that includes solvent structure and hydrodynamic effects in a detailed theory of through-solvent electron transfer. Models that neglect these effects are incapable of describing the data. When a detailed description of solvent effects is included in the theory, agreement with the experimental results is obtained. Forward electron transfer is well-described with a classical Marcus form of the rate equation, though the precise values of the rate parameters depend on the details of the solvents' radial distribution function. The additional experimental results presented here permit a more accurate determination of the forward transfer parameters than those presented previously.1 The geminate recombination (back transfer) data are highly inverted and cannot be analyzed with a classical Marcus expression. Good fits are instead obtained with an exponential distance dependence model of the rate constant and also with a more detailed semiclassical treatment suggested by Jortner.2 Analysis of the pump-probe data, however, suggests that the geminate recombination cannot be described with a single solvent dielectric constant. Rather, a time-dependent dielectric constant is required to properly account for diffusion occurring in a time-varying Coulomb potential. A model using a longitudinal dielectric relaxation time is presented. Additionally, previously reported theoretical results 3 are rederived in a general form that permits important physical effects to be included more rigorously.

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“…Electron transfer (ET) processes have been a matter of huge interest since several decades [1]. It is a key process in photosynthesis [2][3][4] and peptides and proteins play an important role in the electron transport between the donor and the acceptor [4][5][6][7][8][9][10][11], with a recognized importance of the coupling between proton and electron transfer in some cases [12,13].…”

Section: Introductionmentioning

confidence: 99%

Vertical Ionization Energies of α-L-Amino Acids as a Function of Their Conformation: an Ab Initio Study

Dehareng

Dive

2004

IJMS

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Vertical ionization energies (IE) as a function of the conformation are determined at the quantum chemistry level for eighteen α-L-amino acids. Geometry optimization of the neutrals are performed within the Density Functional Theory (DFT) framework using the hybrid method B3LYP and the 6-31G**(5d) basis set. Few comparisons are made with wave-function-based ab initio correlated methods like MP2, QCISD or CCSD. For each amino acid, several conformations are considered that lie in the range 10-15 kJ/mol by reference to the more stable one. Their IE are calculated using the Outer-Valence-Green's-Functions (OVGF) method at the neutrals' geometry. Few comparisons are made with MP2 and QCISD IE. It turns out that the OVGF results are satisfactory but an uncertainty relative to the most stable conformer at the B3LYP level persists. Moreover, the value of the IE can largely depend on the conformation due to the fact that the ionized molecular orbitals (MO) can change a lot as a function of the nuclear structure.

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Introduction to Electron Transfer in Inorganic, Organic, and Biological Systems

Cited by 117 publications

References 0 publications

Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase

Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase

Photoinduced Electron Transfer and Geminate Recombination in Liquids

Vertical Ionization Energies of α-L-Amino Acids as a Function of Their Conformation: an Ab Initio Study

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Introduction to Electron Transfer in Inorganic, Organic, and Biological Systems

Cited by 117 publications

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Catalysis of electron transfer during activation of O 2 by the flavoprotein glucose oxidase

Catalysis of electron transfer during activation of O 2 by the flavoprotein glucose oxidase

Photoinduced Electron Transfer and Geminate Recombination in Liquids

Vertical Ionization Energies of α-L-Amino Acids as a Function of Their Conformation: an Ab Initio Study

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Product

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Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase

Catalysis of electron transfer during activation of O ₂ by the flavoprotein glucose oxidase