Electron bifurcation: progress and grand challenges

Abstract

Electron bifurcation moves electrons from a two-electron donor to reduce two spatially separated one-electron acceptors.

Universal free-energy landscape produces efficient and reversible electron bifurcation

“…The obstacle to realizing efficient electron bifurcation arises from the shortcircuiting reactions intrinsic to the bifurcating network, indicated in Fig. 1C (5,20,21). Short-circuit electron transfer reactions occur when an electron flows from the B − intermediate to the high-potential acceptor A H , or when electrons individually flow from the low-potential (high-energy) branch to reduce B − .…”

“…electron bifurcation | electron transfer | short-circuiting | bioenergetics | chemiosmotic hypothesis L iving systems depend crucially on the efficient interconversion of energy at the molecular scale. Electron bifurcation was recognized by Mitchell as being a key element of the Q cycle in mitochondria (1), but it now describes a broader class of chemical reactions--presently found only in biology--that oxidize a two-electron donor and reduce two spatially separated one-electron acceptors (2)(3)(4)(5). One of the electron transfer reactions from the bifurcating species can proceed thermodynamically "uphill" with respect to the two-electron (midpoint) reduction potential of the electron-bifurcating donor, provided that the other electron proceeds sufficiently downhill for the reaction to be spontaneous overall.…”

“…For example, electron bifurcation is used in the Q cycle of respiration (6) and photosynthesis (7), and to generate low-potential equivalents for CO 2 reduction in methanogenesis (8,9), nitrogen fixation by nitrogenase (10), hydrogen production by hydrogenases (11), and more (4,(12)(13)(14)(15)(16). This use of electron bifurcation by nature to achieve difficult chemical transformations highlights its fundamental place in the toolbox of biological energy transduction (2,5,17), and makes electron bifurcation an attractive candidate for biomimetic energy schemes that require the production of highly reducing or oxidizing species (3,5,18).…”

Rational Design of Fe2(μ‐PR2)2(L)6 Coordination Compounds Featuring Tailored Potential Inversion

“…[11][12][13][14][15][16][17][18][19][20][21] Even if a general consensus has not yet been reached, it has been proposed that one of the key functional thermodynamic features of electron bifurcation (EB) depends on the peculiar redox properties of the flavin cofactor. [11,13,18,22,23] Already in 1932 Michaelis noted that some heteronuclear aromatic compounds, such as quinones and flavins, are characterized by versatile 2electron redox properties. [24] Under certain conditions these compounds undergo two separated one electron redox transfers between the oxidized, the one-electron reduced and the "fully" two-electron reduced states; i. e. the redox midpoint potentials of the two individual transfers is consistent with the intuitive expectation that transfer of the second electron will take place at a lower reduction potential than the first one.…”

“…Even if a general consensus has not yet been reached, it has been proposed that one of the key functional thermodynamic features of electron bifurcation (EB) depends on the peculiar redox properties of the flavin cofactor . Already in 1932 Michaelis noted that some heteronuclear aromatic compounds, such as quinones and flavins, are characterized by versatile 2‐electron redox properties .…”