Title

Biological Charge Transfer Via Flickering Resonance

Keywords

Coherence; Gated transport; Resonant tunneling pathways; Superexchange; Vibronic coupling

Abstract

Biological electron-transfer (ET) reactions are typically described in the framework of coherent two-state electron tunneling or multistep hopping. However, these ET reactions may involve multiple redox cofactors in van der Waals contact with each other and with vibronic broadenings on the same scale as the energy gaps among the species. In this regime, fluctuations of the molecular structures and of the medium can produce transient energy level matching among multiple electronic states. This transient degeneracy, or flickering electronic resonance among states, is found to support coherent (ballistic) charge transfer. Importantly, ET rates arising from a flickering resonance (FR) mechanism will decay exponentially with distance because the probability of energy matching multiple states is multiplicative. The distance dependence of FR transport thus mimics the exponential decay that is usually associated with electron tunneling, although FR transport involves real carrier population on the bridge and is not a tunneling phenomenon. Likely candidates for FR transport are macromolecules with ET groups in van der Waals contact: DNA, bacterial nanowires, multiheme proteins, strongly coupled porphyrin arrays, and proteins with closely packed redox-active residues. The theory developed here is used to analyze DNA charge-transfer kinetics, and we find that charge-transfer distances up to three to four bases may be accounted for with this mechanism. Thus, the observed rapid (exponential) distance dependence of DNA ET rates over distances of ≲15 Å does not necessarily prove a tunneling mechanism.

Publication Date

7-15-2014

Publication Title

Proceedings of the National Academy of Sciences of the United States of America

Volume

111

Issue

28

Number of Pages

10049-10054

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1073/pnas.1316519111

Socpus ID

84904325184 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/84904325184

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