Electron transfers in chemistry and biology

Marcus, R. A.; Sutin, Norman

doi:10.1016/0304-4173(85)90014-x

Cited by 8,235 publications

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“…64 Therefore, CR of the resulting ion pair should be more exergonic and thus slower, as predicted for electron-transfer processes in the inverted regime. 65 As illustrated in Figure 7C, the transient spectrum of B1 in NB is almost the same as that in MeOH except for a larger relative intensity in the 550 nm region and a red shift of the negative band. Interaction between R1 in the S 1 state and NB is supported by the strong reduction of the excited-state lifetime compared to MeOH.…”

Section: Resultsmentioning

confidence: 67%

Ultrafast Photoinduced Charge Separation in Naphthalene Diimide Based Multichromophoric Systems in Liquid Solutions and in a Lipid Membrane

et al. 2008

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The photophysical properties of multichromophoric systems consisting of eight red or blue naphthalene diimides (NDIs) covalently attached to a p-octiphenyl scaffold, as well as a blue bichromophoric system with a biphenyl scaffold, have been investigated in detail using femtosecond time-resolved spectroscopy. The blue octachromophoric systems have been recently shown to self-assemble as supramolecular tetramers in lipid bilayer membranes and to enable generation of a transmembrane proton gradient upon photoexcitation (Bhosale, S.; Sisson, A. L.; Talukdar, P.; Fürstenberg, A.; Banerji, N.; Vauthey, E.; Bollot, G.; Mareda, J.; Röger, C.; Würthner, F.; Sakai, N.; Matile, S. Science 2006, 313, 84). A strong reduction of the fluorescence quantum yield was observed when going from the single NDI units to the multichromophoric systems in methanol, the effect being even stronger in a vesicular lipid membrane. Fluorescence up-conversion measurements reveal ultrafast self-quenching in the multichromophoric systems, whereas the formation of the NDI radical anion, evidenced by transient absorption measurements, points to the occurrence of photoinduced charge separation. The location of the positive charge could not be established unambiguously from the transient absorption measurements, but energetic considerations indicate that charge separation should occur between two NDI units in the blue systems, whereas both an NDI unit and the p-octiphenyl scaffold could act as electron donor in the red system. The lifetime of the charge-separated state was found to increase from 22 to 45 ps by going from the bi-to the octachromophoric blue systems in methanol, while a 400 ps decay component was observed in the lipid membrane. This lifetime lengthening is explained in terms of charge migration that is most efficient when the octachromophoric systems are assembled as supramolecular tetramers in the lipid membrane. Furthermore, the average charge-separated state lifetime of the red system in methanol is even larger and amounts to 750 ps. This effect cannot be simply explained in terms of Marcus inverted regime as the driving force for charge recombination in the red system is only slightly larger than in the blue one. A better spatial separation of the charges in the red system stemming from the localization of the hole on the p-octiphenyl scaffold could additionally contribute to the slowing down of charge recombination.

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Section: Resultsmentioning

confidence: 67%

Ultrafast Photoinduced Charge Separation in Naphthalene Diimide Based Multichromophoric Systems in Liquid Solutions and in a Lipid Membrane

et al. 2008

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“…This implies that the electron transfer from cyt2+ c to cyt ox proceeds via state I1 and is governed by a potential difference of 0.54 V, taking into account the redox potentials of -0.41 V for cytlI 6cLS (Hildebrandt & Stockburger, 1989) and of 0.13 V for heme a, the primary electron acceptor of cyt ox (Wikstrom et al, 1981). A crude estimation based on classical Marcus theory (Marcus & Sutin, 1985) reveals that this large driving force corresponds to an electron-transfer rate constant for the oxidation of cyt2+ c that is by 2-3 orders of magnitude larger in state I1 than in state I ( E , = +0.02 V).…”

Section: Resultsmentioning

confidence: 99%

Cytochrome c at charged interfaces. 2. Complexes with negatively charged macromolecular systems studied by resonance Raman spectroscopy

Hildebrandt

Stockburger

1989

Biochemistry

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We have analyzed the structure of cytochrome c (cyt c) bound in a variety of complexes in which negatively charged molecular groups interact with the positively charged binding domain around the heme crevice of cyt c. Using resonance Raman spectroscopy, we could demonstrate that these interactions induce the same conformational changes as they were observed in the surface-enhanced resonance Raman experiments of cyt c adsorbed on the Ag electrode [Hildebrandt & Stockburger (1989) Biochemistry (preceding paper in this issue)]. When cyt c is bound to (As4W400140)27-, state I1 is stabilized, whereas in complexes with phosvitin and cytochrome b5 state I is formed. The complexes with phospholipid vesicles and inverted micelles reveal a mixture of both states. It is suggested that these systems as well as cyt c adsorbed on the Ag electrode may be regarded as model systems for the physiological complexes of cyt c with cytochrome oxidase and cytochrome reductase. On the basis of our findings it is proposed that the biological electron-transfer reactions are controlled by electric field induced conformational transitions of cyt c upon complex formation with its physiological redox partners.

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“…According to the Marcus theory, the increase of the rate of an ET reaction may be caused (14) by (i) a larger intrinsic driving force of the reaction through an increase in the difference of the redox potentials of the donor/acceptor pair, (ii) a decrease of the distance between the donor and acceptor, (iii) lowering the reorganization energy λ, (iv) lowering the decay factor by providing orbitals for an optimal ET path, or (v) modification of the chemistry of the reaction. On the basis of our kinetic, thermodynamic, and structural studies, the feasibility of some mode will be discussed.…”

Section: Discussionmentioning

confidence: 99%

Radical Phosphate Transfer Mechanism for the Thiamin Diphosphate- and FAD-Dependent Pyruvate Oxidase from Lactobacillus plantarum. Kinetic Coupling of Intercofactor Electron Transfer with Phosphate Transfer to Acetyl-thiamin Diphosphate via a Transient FAD Semiquinone/Hydroxyethyl-ThDP Radical Pair

et al. 2005

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The thiamin diphosphate (ThDP)-and flavin adenine dinucleotide (FAD)-dependent pyruvate oxidase from Lactobacillus plantarum catalyses the conversion of pyruvate, inorganic phosphate, and oxygen to acetyl-phosphate, carbon dioxide, and hydrogen peroxide. Central to the catalytic sequence, two reducing equivalents are transferred from the resonant carbanion/enamine forms of R-hydroxyethylThDP to the adjacent flavin cofactor over a distance of approximately 7 Å, followed by the phosphorolysis of the thereby formed acetyl-ThDP. Pre-steady-state and steady-state kinetics using time-resolved spectroscopy and a 1 H NMR-based intermediate analysis indicate that both processes are kinetically coupled. In the presence of phosphate, intercofactor electron-transfer (ET) proceeds with an apparent first-order rate constant of 78 s -1 and is kinetically gated by the preceding formation of the tetrahedral substrateThDP adduct 2-lactyl-ThDP and its decarboxylation. No transient flavin radicals are detectable in the reductive half-reaction. In contrast, when phosphate is absent, ET occurs in two discrete steps with apparent rate constants of 81 and 3 s -1 and transient formation of a flavin semiquinone/hydroxyethyl-ThDP radical pair. Temperature dependence analysis according to the Marcus theory identifies the second step, the slow radical decay to be a true ET reaction. The redox potentials of the FAD ox /FAD sq (E 1 ) -37 mV) and FAD sq /FAD red (E 2 ) -87 mV) redox couples in the absence and presence of phosphate are identical. Both the Marcus analysis and fluorescence resonance energy-transfer studies using the fluorescent N3′-pyridyl-ThDP indicate the same cofactor distance in the presence or absence of phosphate. We deduce that the exclusive 10 2 -10 3 -fold rate enhancement of the second ET step is rather due to the nucleophilic attack of phosphate on the kinetically stabilized hydroxyethyl-ThDP radical resulting in a low-potential anion radical adduct than phosphate in a docking site being part of a through-bonded ET pathway in a stepwise mechanism of ET and phosporolysis. Thus, LpPOX would constitute the first example of a radical-based phosphorolysis mechanism in biochemistry.Pyruvate oxidase from Lactobacillus plantarum (LpPOX, 1 EC 1.2.3.3) belongs to a superfamily of enzymes that utilize the cofactor thiamin diphosphate (ThDP), the biologically active derivative of vitamin B 1 . In addition to ThDP, LpPOX contains a flavin adenine dinucleotide (FAD) that is positioned at a distance of approximately 7 Å from the thiamin cofactor (Figure 1) (1).Pyruvate oxidase (POX) catalyses the conversion of pyruvate, inorganic phosphate, and oxygen to the high-energy metabolite acetyl phosphate, carbon dioxide, and hydrogen peroxide (2). Catalysis can be assumed to follow the typical Breslow mechanism of ThDP enzymes (Scheme 1). After ionization of the acidic C2-H of the thiazolium ring, pyruvate enters the active site where it reacts with the C2

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Electron transfers in chemistry and biology

Abstract: The reduced force constant for the C0(NH3)36 +/2+ couple was used in calculating the inner-sphere reorganization energy for the Co(bpy)33 +/2+ couple.

Cited by 8,235 publications

References 275 publications

Ultrafast Photoinduced Charge Separation in Naphthalene Diimide Based Multichromophoric Systems in Liquid Solutions and in a Lipid Membrane

Ultrafast Photoinduced Charge Separation in Naphthalene Diimide Based Multichromophoric Systems in Liquid Solutions and in a Lipid Membrane

Cytochrome c at charged interfaces. 2. Complexes with negatively charged macromolecular systems studied by resonance Raman spectroscopy

Radical Phosphate Transfer Mechanism for the Thiamin Diphosphate- and FAD-Dependent Pyruvate Oxidase from Lactobacillus plantarum. Kinetic Coupling of Intercofactor Electron Transfer with Phosphate Transfer to Acetyl-thiamin Diphosphate via a Transient FAD Semiquinone/Hydroxyethyl-ThDP Radical Pair

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