Hopping maps for photosynthetic reaction centers

Abstract

Photosynthetic reaction centers (PRCs) employ multiple-step tunneling (hopping) to separate electrons and holes that ultimately drive the chemistry required for metabolism. We recently developed hopping maps that can be used to interpret the rates and energetics of electron/hole hopping in three-site (donor-intermediate-acceptor) tunneling reactions, including those in PRCs. Here we analyze several key ET reactions in PRCs, including forward ET in the L-branch, and hopping that could involve thermodynamically uphill intermediates in the M-branch, which is ET-inactive in vivo. We also explore charge recombination reactions, which could involve hopping. Our hopping maps support the view that electron flow in PRCs involves strong electronic coupling between cofactors and reorganization energies that are among the lowest in biology (≤ 0.4 eV).

Bioinspired molecular electrets: bottom-up approach to energy materials and applications

“…[41][42][43][44][45][46] Conversely, arrays of cofactors and redox-active residues, such as tryptophan or tyrosine, make it possible to attain long-range ET. 47,48 That is, multiple short and efficient "electron hopping" steps along arrays of redox moieties allow ET to exceed the 2-nm tunneling limit. [48][49][50][51][52] Deoxyribonucleic acid (DNA) strands represent a class of biopolymers that can mediate CT at distances exceeding 2 nm.…”

“…47,48 That is, multiple short and efficient "electron hopping" steps along arrays of redox moieties allow ET to exceed the 2-nm tunneling limit. [48][49][50][51][52] Deoxyribonucleic acid (DNA) strands represent a class of biopolymers that can mediate CT at distances exceeding 2 nm. [53][54][55][56][57] Short efficient tunneling steps between closely situated bases, with relatively negative reduction potentials of their radical cations, mediate hole hopping.…”

Building blocks for bioinspired electrets: molecular-level approach to materials for energy and electronics

“…Tunneling, however, limits the distance of efficient CT to about 2 nm [37,38]. Sites where charges can temporarily reside (such as redox active cofactors, nucleotides, or amino-acid side chains) can greatly extend the CT distance beyond the 2-nm tunneling limit [5,44]. Good electronic coupling between a sequence of redox moieties ensures pathways for efficient multiple electron tunneling short steps allowing long-range CT to occur, i.e.…”

“…Good electronic coupling between a sequence of redox moieties ensures pathways for efficient multiple electron tunneling short steps allowing long-range CT to occur, i.e. long-range electron or hole hopping [5,44].…”

“…At a cellular level, CT is responsible for a range of chemical and biochemical transformations, and is essential for life on Earth to exist [1][2][3][4][5]. In addition to its vital role in living systems, CT resides at the heart of energy conversion, transduction and storage [6][7][8][9][10][11][12][13], and provides signal transduction for devices integral to our modern lifestyles [14,15].…”