Quantum Transport in Conductive Bacterial Nanowires

Livernois, William; Anantram, M. P.

doi:10.1109/nmdc50713.2021.9677490

Cited by 9 publications

(17 citation statements)

References 15 publications

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“…79−81 Furthermore, decoherent quantum transport was found to be capable of explaining as much as 71% of the measured conductance. 82 Thermally activated hopping also seems at odds with the AFM-measured temperature dependence of electrical conductivity in OmcS (Figure 1, bottom). Instead of decreasing upon cooling as expected, the conductivity increased by a factor of 10 2 from 300 to 270 K. 80 To reconcile redox conduction with this anti-Arrhenius kinetics, a ″massive restructuring″ of intraprotein H-bonds upon cooling was computationally proposed to modulate heme redox potentials and, in turn, the activation energies for incoherent heme-toheme charge transfer.…”

Section: Introductionmentioning

confidence: 92%

“…If the hops were assumed to occur instead between nanometer-sized blocks of coherently coupled hemes, the predicted conductivity was able to approach the experimental value . However, it is unclear how a protein with 81% turns and loops comprising the secondary structure can be sufficiently rigid to preserve coherence among as many as two dozen hemes when the electronic coupling between any pair is less than thermal energy. − Furthermore, decoherent quantum transport was found to be capable of explaining as much as 71% of the measured conductance …”

Section: Introductionmentioning

confidence: 95%

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Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire

Guberman‐Pfeffer

2022

J. Phys. Chem. B

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A micrometers-long helical homopolymer of the outer-membrane cytochrome type S (OmcS) from Geobacter sulfurreducens is proposed to transport electrons to extracellular acceptors in an ancient respiratory strategy of biogeochemical and technological significance. OmcS surprisingly exhibits higher conductivity upon cooling (anti-Arrhenius kinetics), an effect previously attributed to H-bond restructuring and heme redox potential shifts. Herein, the temperature sensitivity of redox conductivity is more thoroughly examined with conventional and constant-redox and -pH molecular dynamics and quantum mechanics/ molecular mechanics. A 30 K drop in temperature constituted a weak perturbation to electron transfer energetics, changing electronic couplings (⟨H mn ⟩), reaction free energies (ΔG mn ), reorganization energies (λ mn ), and activation energies (E a ) by at most |0.002|, |0.050|, |0.120|, and |0.045| eV, respectively. Changes in ΔG mn reflected −0.07 ± 0.03 V shifts in redox potentials that were caused in roughly equal measure by altered electrostatic interactions with the solvent and protein.Changes in intraprotein H-bonding reproduced the earlier observations. Single-particle diffusion and multiparticle steady-state flux models, parametrized with Marcus theory rates, showed that biologically relevant incoherent hopping cannot qualitatively or quantitatively describe electrical conductivity measured by atomic force microscopy in filamentous OmcS. The discrepancy is attributed to differences between solution-phase simulations and solid-state measurements and the need to model intra-and intermolecular vibrations explicitly.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 95%

Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire

Guberman‐Pfeffer

2022

J. Phys. Chem. B

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“…It is currently unclear whether incoherent charge hopping can account for the conductivity of OmcS, 82, 83 or if coherence-assisted hopping 84 or decoherent quantum transport 85 mechanisms need to be invoked. Incoherent hopping was consistent with a measured linear-dependence of conductance on filament length, 83 but this is not an unambiguous metric.…”

Section: Discussionmentioning

confidence: 99%

“…Even so, proposed electrical conductivity mechanisms for the outer-membrane cytochrome type S (OmcS) filament range from incoherent charge hopping under physiological 82 or solid-state 83 measurement conditions, to coherence-assisted charge hopping, 84 and decoherent quantum transport. 85…”

Section: Introductionmentioning

confidence: 99%

Heme Hopping Falls Short: What Explains Anti-Arrhenius Conductivity in a Multi-heme Cytochrome Nanowire?

Guberman‐Pfeffer

2022

Preprint

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A helical homopolymer of the outer-membrane cytochrome type S (OmcS) was proposed to electrically connect a common soil bacterium, Geobacter sulfurreducens, with minerals and other microbes for biogeochemically important processes. OmcS exhibits a surprising rise in conductivity upon cooling from 300 to 270 K that has recently been attributed to a restructuring of H-bonds, which in turn modulates heme redox potentials. This proposal is more thoroughly examine herein by (1) analyzing H-bonding at 13 temperatures encompassing the entire experimental range; (2) computing redox potentials with quantum mechanics/molecular mechanics for 10-times more (3000) configurations sampled from 3-times longer (2 μs) molecular dynamics, as well as 3 μs of constant redox and pH molecular dynamics; and (3) modeling redox conduction with both single-particle diffusion and multi-particle flux kinetic schemes. Upon cooling by 30 K, the connectivity of the intra-protein H-bonding network was highly (86%) similar. An increase in the density and static dielectric constant of the filament's hydration shell caused a -0.002 V/K shift in heme redox potentials, and a factor of 2 decrease in charge mobility. Revision of a too-far negative redox potential in prior work (-0.521 V; expected = -0.350 - +0.150 V; new Calc. = -0.214 V vs. SHE) caused the mobility to be greater at high versus low temperature, opposite to the original prediction. These solution-phase redox conduction models failed to reproduce the experimental conductivity of electrode-absorbed, partially dehydrated, and possibly aggregated OmcS filaments. Some improvement was seen by neglecting reorganization energy from the solvent to model dehydration. Correct modeling of the physical state is suggested to be a prerequisite for reaching a verdict on the operative charge transport mechanism and the molecular basis of its temperature response.

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“…The LBP method has been originally developed to describe the coherentto-incoherent turnover of conduction in mesoscopic devices 23,24 . More recently, the LBP technique has been used to study thermally-assisted charge transport at the nanoscale, through organic 25,26 and biological molecules [27][28][29][30][31][32][33][34][35][36][37] . Applications of the LBP method to one-dimensional molecular junctions include studies of their electrical conductance 25 , nonlinear (high volt-age) characteristics 38,39 , thermopower 32 , and thermal conductance 40,41 .…”

Section: Introductionmentioning

confidence: 99%

Long-Range Charge Transport in Homogeneous and Alternating-Rigidity Chains

Liang,

Segal

2022

Preprint

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We study the interplay of intrinsic-electronic and environmental factors on long-range charge transport across molecular chains with up to N ∼ 80 monomers. We describe the molecular electronic structure of the chain with a tight-binding Hamiltonian. Thermal effects in the form of electron decoherence and inelastic scatterings are incorporated with the Landauer-Büttiker probe method. In short chains of up to 10 units we observe the crossover between coherent (tunneling, ballistic) motion and thermally-assisted conduction, with thermal effects enhancing the current beyond the quantum coherent limit. We further show that unconventional (nonmonotonic with size) transport behavior emerges when monomer-to-monomer electronic coupling is made large. In long chains, we identify a different behavior, with thermal effects suppressing the conductance below the coherent-ballistic limit. With the goal to identify a minimal model for molecular chains displaying unconventional and effective long-range transport, we simulate a modular polymer with alternating regions of high and low rigidity. Simulations show that, surprisingly, while charge correlations are significantly affected by structuring environmental conditions, reflecting charge delocalization, the electrical resistance displays an averaging effect, and it is not sensitive to this patterning. We conclude by arguing that efficient long-range charge transport requires engineering both internal electronic parameters and environmental conditions.

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Quantum Transport in Conductive Bacterial Nanowires

Cited by 9 publications

References 15 publications

Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire

Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire

Heme Hopping Falls Short: What Explains Anti-Arrhenius Conductivity in a Multi-heme Cytochrome Nanowire?

Long-Range Charge Transport in Homogeneous and Alternating-Rigidity Chains

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