Electron transfer in biological systems

Larsson, Sven

doi:10.1002/qua.560220736

Cited by 4 publications

(2 citation statements)

References 43 publications

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“…2,3,13,14,58,98,99 For thermochemistry and vibrational spectroscopy, harmonic-oscillator models form the basis of discussion, models that do not allow for chemical reactions. However, non-BO effects in ground-state chemical reactions are usually considered using methods developed for conical intersections, 13,14,99,100 although specific approaches such as the ''small polaron'' model have proven useful. 98 Further, it is well known that the effects of BO breakdown manifest quite differently during electron-transfer reactions in the ''normal'' and ''inverted'' regimes, 98 and we find that typical high-energy photochemical processes dominated by conical intersections are also fundamentally different.…”

Section: Introductionmentioning

confidence: 99%

Non-adiabatic effects in thermochemistry, spectroscopy and kinetics: the general importance of all three Born–Oppenheimer breakdown corrections

Reimers

McKemmish

McKenzie

et al. 2015

Phys. Chem. Chem. Phys.

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Using a simple model Hamiltonian, the three correction terms for Born-Oppenheimer (BO) breakdown, the adiabatic diagonal correction (DC), the first-derivative momentum non-adiabatic correction (FD), and the second-derivative kinetic-energy non-adiabatic correction (SD), are shown to all contribute to thermodynamic and spectroscopic properties as well as to thermal non-diabatic chemical reaction rates. While DC often accounts for >80% of thermodynamic and spectroscopic property changes, the commonly used practice of including only the FD correction in kinetics calculations is rarely found to be adequate. For electron-transfer reactions not in the inverted region, the common physical picture that diabatic processes occur because of surface hopping at the transition state is proven inadequate as the DC acts first to block access, increasing the transition state energy by (ℏω)(2)λ/16J(2) (where λ is the reorganization energy, J the electronic coupling and ω the vibration frequency). However, the rate constant in the weakly-coupled Golden-Rule limit is identified as being only inversely proportional to this change rather than exponentially damped, owing to the effects of tunneling and surface hopping. Such weakly-coupled long-range electron-transfer processes should therefore not be described as "non-adiabatic" processes as they are easily described by Born-Huang ground-state adiabatic surfaces made by adding the DC to the BO surfaces; instead, they should be called just "non-Born-Oppenheimer" processes. The model system studied consists of two diabatic harmonic potential-energy surfaces coupled linearly through a single vibration, the "two-site Holstein model". Analytical expressions are derived for the BO breakdown terms, and the model is solved over a large parameter space focusing on both the lowest-energy spectroscopic transitions and the quantum dynamics of coherent-state wavepackets. BO breakdown is investigated pertinent to: ammonia inversion, aromaticity in benzene, the Creutz-Taube ion, the bacterial photosynthetic reaction centre, BNB, the molecular conductor Alq3, and inverted-region charge recombination in a ferrocene-porphyrin-fullerene triad photosynthetic model compound. Throughout, the fundamental nature of BO breakdown is linked to the properties of the cusp catastrophe: the cusp diameter is shown to determine the magnitudes of all couplings, numerical basis-set and trajectory-integration requirements, and to determine the transmission coefficient κ used to understand deviations from transition-state theory.

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Section: Introductionmentioning

confidence: 99%

Non-adiabatic effects in thermochemistry, spectroscopy and kinetics: the general importance of all three Born–Oppenheimer breakdown corrections

Reimers

McKemmish

McKenzie

et al. 2015

Phys. Chem. Chem. Phys.

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“…The Marcus model − is a popular model among electrochemists and solar energy chemists. The theory is primarily a theory for electron transfer in mixed-valence systems in aqueous solution but has also been used in other chemical and biological systems, for example, in photosynthesis − and in electron transport in organic − and inorganic systems. ,− In solid state physics for conductivity problems and in solar energy research, − the model is indispensible since k -space methods are of limited value in local (correlated) systems, as we will see below. The Marcus model has previously been used by the present author as a hopping model to calculate the resistivity in transition metal oxides (TMOs) .…”

Section: Introductionmentioning

confidence: 99%

Correlations between Spectra and Resistivity in Transition Metal Oxides

Larsson

2019

J. Phys. Chem. B

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A comparison between photoconductivity spectra and resistivity in two transition metal oxides, La2–x Sr x CuO4 and La1–x Sr x VO3, is presented. The resistivities ρ(T) for x < 0.05 in the cuprate and x < 0.28 in the vanadate are typical for single electron transfer. For T > 100 K, ρ(T) – ρ(0) ∼ T 3/2. For higher dopings (x) the cuprate is a superconductor (x < 0.25) and the vanadate an ordinary metal. This tallies with the number of oxidation states and their spins when the electrons transfer locally. The insulator–metal transition and the vanishing of Cooper pairs are discussed in the conclusion.

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The effect of image force on the efficiency of electron tunneling through macromolecular structures

Петров

1993

Eur Biophys J

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Abstract. In electron tunneling (ET) along the boundary of two media with different high-frequency dielectric permittivities, the energy gap for the tunneling electron is affected by image forces. Macromolecules and macromolecular structures contain segments possessing different permittivities. Therefore, in any description of ET one must take image forces into account. Here, the spatial form of donor-acceptor ET through bridged molecular groups situated near macromolecular segments is investigated. It is shown that image forces can significantly reduce the energy levels of an electron on the bridge groups. As a result, the ET rate in the donor-bridge-acceptor system can increase by many orders of magnitude. The effect is more favorable for extended bridged chains. This fact may be used in explaining donor-acceptor conductivity of electron pathways in real macromolecular biological structures. Bridged groups in electron pathways may be provided by molecular groups whose affinity for the tunneling electron is higher than that of other groups. Furthermore, the electron overlap integral between the bridged groups should be large enough. That is, the role of bridge can be played by the polypeptide chain backbone, by side-chains of some amino acids (particularly those with aromatic rings), and by conjugated systems of the carotinoid type satuated near macromolecular segments or near the surfaces of membranes or channels.

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Electron transfer in biological systems

Cited by 4 publications

References 43 publications

Non-adiabatic effects in thermochemistry, spectroscopy and kinetics: the general importance of all three Born–Oppenheimer breakdown corrections

Non-adiabatic effects in thermochemistry, spectroscopy and kinetics: the general importance of all three Born–Oppenheimer breakdown corrections

Correlations between Spectra and Resistivity in Transition Metal Oxides

The effect of image force on the efficiency of electron tunneling through macromolecular structures

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