Electron transfer across polypeptides. 5. Rapid rates of electron transfer between osmium(II) and cobalt(III) in complexes with bridging oligoprolines and other polypeptides

Isied, Stephan S.; Vassilian, Asbed; Magnuson, Roy H.; Schwarz, Harold A.

doi:10.1021/ja00311a035

Cited by 81 publications

(29 citation statements)

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“…In a natural protein, a proline-rich proline-IT helix serves as a spacer between other secondary structures or as an interdomain linker (13). Synthetic redox assemblies containing oligoproline spacers as long as Pros have been used to study distance effects in intramolecular electron transfer (14)(15)(16)(17).…”

Section: Resultsmentioning

confidence: 99%

Photochemical energy conversion in a helical oligoproline assembly.

McCafferty

Friesen

Danielson

et al. 1996

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

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A biological photosynthetic reaction center contains a spatially ordered array of chromophores, electron donors, and electron acceptors that efficiently separate reductive and oxidative equivalents upon irradiation with visible light. This fundamental process of redox separation has been modeled in redox assemblies based on metal-bipyridyl complexes (1) or porphyrin-quinone systems (2-5). We have described the synthesis and photophysical characterization of lysine-based donorchromophore-acceptor triads that undergo light-induced redox separation (6-9). We describe here a general method for designing and constructing a helical oligoproline assembly having a spatially ordered array of redox or other functional groups protruding from a proline-II helical rod. Solid-phase peptide synthesis (10) is an efficient method for assembling a modular chain containing functional sites at specific positions. An a-helical peptide chain can serve as a molecular framework to display functional sites in a spatially ordered array (9). Alternatively, a chain of nine or more proline residues folds into a stable proline-II helix even when several of the proline residues have large functional sites on their side chains (11). The distance between two functional sites is determined by their helical location and orientation. The position of a modified proline residue in the proline chain determines its location on the helical surface. The configuration and conformation of the modified proline residue determine its orientation on the helical surface. To illustrate this general method, we have assembled an oligoproline assembly (triad 1) bearing three different redox sites (Fig. 1). Folding of the peptide triad 1 into a proline-II helix places the donor, chromophore, and acceptor sites in a linear array on one side of the helical rod.

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Section: Resultsmentioning

confidence: 99%

Photochemical energy conversion in a helical oligoproline assembly.

McCafferty

Friesen

Danielson

et al. 1996

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

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“…9 Donor-acceptor dyads with proline bridges and distance dependences of k ET after reduction of the donor moieties (left-hand sides) with pulse radiolysis. The change from Os-Co 25 to Os-Ru 26 and Ru-Co systems 27 allowed a change in driving-force (DG 0 ET ) from À0.15 to À1.1 eV.…”

Section: Consequences For Light-to-chemical Energy Conversionmentioning

confidence: 99%

Unusual distance dependences of electron transfer rates

Kuss‐Petermann

Wenger

2016

Phys. Chem. Chem. Phys.

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Usually the rates for electron transfer (kET) decrease with increasing donor-acceptor distance, but Marcus theory predicts a regime in which kET is expected to increase when the transfer distance gets longer. Until recently, experimental evidence for such counter-intuitive behavior had been very limited, and consequently this effect is much less well-known than the Gaussian free energy dependence of electron transfer rates leading to the so-called inverted driving-force effect. This article presents the theoretical concepts that lead to the prediction of electron transfer rate maxima at large donor-acceptor distances, and it discusses conditions that are expected to favor experimental observations of such behavior. It continues with a consideration of specific recent examples in which electron transfer rates were observed to increase with increasing donor-acceptor distance, and it closes with a discussion of the importance of this effect in the context of light-to-chemical energy conversion.

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“…Decades of research in electron transfer (ET) have explored the particular variables which control long-range ET in proteins. , The kinetic effect of ET distance is described in the Marcus equation for non-adiabatic ET, , in which H DA is the electronic coupling matrix between the reactant and product states at the transition-state nuclear configuration for a distant ET reaction. Research in modified proteins and synthetic systems has shown that rate constants for ET decay exponentially with increasing distance between the donor and acceptor: where R is the distance between the electron donor and acceptor and k R 0 is the ET rate constant at donor–acceptor close contact. − The factor β describes the severity of the rate constant decay with increased distance, and is typically assumed to be a property of the type of bridge separating a donor (D) and acceptor (A) (i.e., saturated or unsaturated linkers) . Theoretical treatments of distance-dependent ET kinetics typically follow the McConnell superexchange model, where H DA is approximated as the product of the electronic couplings between the components of a donor–bridge–acceptor (D-b-A) system (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Shallow Distance Dependence for Proton-Coupled Tyrosine Oxidation in Oligoproline Peptides

et al. 2020

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We have explored the kinetic effect of increasing electron transfer distance in a biomimetic, proton coupled electron transfer system (PCET). Biological electron transfer is often simultaneous with proton transfer in order to avoid the high-energy, charged intermediates resulting from the stepwise transfer of protons and electrons. These concerted proton electron transfer (CPET) reactions are implicated in numerous biological electron transfer pathways. In many cases, proton transfer is coupled to long-range electron transfer. While many studies have shown that the rate of electron transfer is sensitive to the distance between the electron donor and acceptor, extensions to biological CPET reactions are sparse. The possibility of a unique electron transfer distance dependence for CPET reactions deserves further exploration, as this could have implications for how we understand biological electron transfer. We therefore explored the electron transfer distance dependence for the CPET oxidation of tyrosine in a model system. We prepared a series of metallopeptides with a tyrosine separated from a Ru(bpy) 3 2+ complex by an oligoproline bridge of increasing length. Rate constants for intramolecular tyrosine oxidation were measured using the flash-quench transient absorption technique in aqueous solutions. The rate constants for tyrosine oxidation decreased by 125-fold with three added prolines residues between tyrosine and the oxidant. By comparison, related intramolecular ET rate constants in very similar constructs were reported to decrease by 4-5 orders of magnitude over the same number of prolines. The observed shallow distance dependence for tyrosine oxidation is proposed to originate, at least in part, from the requirement for stronger oxidants, leading to a smaller hole transfer tunneling barrier height. The shallow distance dependence observed here and extensions to distance dependent CPET reactions have far-reaching implications for long-range charge transfers File list (2) download file view on ChemRxiv BMKoligoproline_manuscript_version7_unformatted_man... (1.02 MiB) download file view on ChemRxiv BMK_oligproline_SI_version6_02_04_2020.pdf (9.87 MiB)

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Electron transfer across polypeptides. 5. Rapid rates of electron transfer between osmium(II) and cobalt(III) in complexes with bridging oligoprolines and other polypeptides

Cited by 81 publications

References 0 publications

Photochemical energy conversion in a helical oligoproline assembly.

Photochemical energy conversion in a helical oligoproline assembly.

Unusual distance dependences of electron transfer rates

Shallow Distance Dependence for Proton-Coupled Tyrosine Oxidation in Oligoproline Peptides

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