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Gregory A. Voth - One of the best experts on this subject based on the ideXlab platform.
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Multiscale Simulation Reveals Passive Proton Transport Through SERCA on the Microsecond Timescale
Biophysical journal, 2020Co-Authors: Zhi Yue, L. Michel Espinoza-fonseca, Gregory A. VothAbstract:Abstract The sarcoplasmic reticulum Ca2+-ATPase (SERCA) Transports two Ca2+ ions from the cytoplasm to the reticulum lumen at the expense of ATP hydrolysis. In addition to Transporting Ca2+, SERCA facilitates bidirectional Proton Transport across the sarcoplasmic reticulum to maintain the charge balance of the Transport sites and to balance the charge deficit generated by the exchange of Ca2+. Previous studies have shown the existence of a transient water-filled pore in SERCA that connects the Ca2+ binding sites with the lumen, but the capacity of this pathway to sustain passive Proton Transport has remained unknown. In this study, we used the multiscale reactive molecular dynamics method and free energy sampling to quantify the free energy profile and timescale of the Proton Transport across this pathway while also explicitly accounting for the dynamically coupled hydration changes of the pore. We find that Proton Transport from the central binding site to the lumen has a microsecond timescale, revealing a novel passive cytoplasm-to-lumen Proton flow beside the well-known inverse Proton counterTransport occurring in active Ca2+ Transport. We propose that this Proton Transport mechanism is operational and serves as a functional conduit for passive Proton Transport across the sarcoplasmic reticulum.
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Water Assisted Proton Transport in Confined Nanochannels
The Journal of Physical Chemistry C, 2020Co-Authors: Alex B. F. Martinson, Gregory A. VothAbstract:Hydrated excess Protons under hydrophobic confinement are a critical component of charge Transport behavior and reactivity in nanoporous materials and biomolecular systems. Herein, excess Proton confinement effects are computationally investigated for sub-2 nm hydrophobic nanopores by varying the diameters (d = 0.81, 0.95, 1.09, 1.22, 1.36, 1.63, and 1.90 nm), lengths (l ∼3 and ∼5 nm), curvature, and chirality of cylindrical carbon nanotube (CNT) nanopores. CNTs with a combination of different diameter segments are also explored. The spatial distribution of water molecules under confinement is diameter-dependent; however, Proton solvation and Transport are consistently found to occur in the water layer adjacent to the pore wall, showing an “amphiphilic” character of the hydrated excess Proton hydronium-like structure. The Proton Transport free energy barrier also decreases significantly as the nanopore diameter increases and Proton Transport becomes almost barrierless in the d > 1 nm nanopores. Among the nanopores studied, the Zundel cation (H5O2+) is populated only in the d = 0.95 nm CNT (7,7) nanopore. The presence of the hydrated excess Proton and K+ inside the CNT (7,7) nanopore induces a water density increase by 40 and 20%, respectively. The K+ Transport through CNT nanopores is also consistently higher in the free energy barrier than Proton Transport. Interestingly, the evolution of excess Protonic charge defect distribution reveals a “frozen” single water wire configuration in the d = 0.81 nm CNT (6,6) nanopore (or segment), through which hydrated excess Protons can only shuttle via the Grotthuss mechanism. Vehicular diffusion becomes relevant to Proton Transport in the “flat” free energy regions and in the wider nanopores, where Protons do not primarily shuttle in the axial direction.
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Water Assisted Proton Transport in Confined Nanochannels
arXiv: Materials Science, 2020Co-Authors: Alex B. F. Martinson, Gregory A. VothAbstract:Hydrated excess Protons under hydrophobic confinement are a critical component of charge Transport behavior and reactivity in nanoporous materials and biomolecular systems. Herein excess Proton confinement effects are computationally investigated for sub-2 nm hydrophobic nanopores by varying the diameters (d = 0.81, 0.95, 1.09, 1.22, 1.36, 1.63, and 1.90 nm), lengths (l ~3 and ~5 nm), curvature, and chirality of cylindrical carbon nanotube (CNT) nanopores. CNTs with a combination of different diameter segments are also explored. The spatial distribution of water molecules under confinement are diameter-dependent; however, Proton solvation and Transport is consistently found to occur in the water layer adjacent to the pore wall, showing an "amphiphilic" character of the hydrated excess Proton hydronium-like structure. The Proton Transport free energy barrier also decreases significantly as the nanopore diameter increases and Proton Transport becomes almost barrierless in the d > 1 nm nanopores. Among the nanopores studied, the Zundel cation (${H_{5}O_{2}}^{+}$) is populated only in the d = 0.95 nm CNT (7,7) nanopore. The presence of the hydrated excess Proton and $K^{+}$ inside the CNT (7,7) nanopore induces a water density increase by 40 and 20%, respectively. The $K^{+}$ Transport through CNT nanopores is also consistently higher in free energy barrier than Proton Transport. Interestingly, the evolution of excess Protonic charge defect distribution reveals a "frozen" single water wire configuration in the d = 0.81 nm CNT (6,6) nanopore (or segment), through which hydrated excess Protons can only shuttle via the Grotthuss mechanism. Vehicular diffusion becomes relevant to Proton Transport in the "flat" free energy regions and in the wider nanopores, where Protons do not primarily shuttle in the axial direction.
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Multiscale Simulations Reveal Key Aspects of the Proton Transport Mechanism in the ClC-ec1 Antiporter
Biophysical journal, 2016Co-Authors: Sangyun Lee, Jessica M. J. Swanson, Gregory A. VothAbstract:Multiscale reactive molecular dynamics simulations are used to study Proton Transport through the central region of ClC-ec1, a widely studied ClC Transporter that enables the stoichiometric exchange of 2 Cl– ions for 1 Proton (H+). It has long been known that both Cl– and Proton Transport occur through partially congruent pathways, and that their exchange is strictly coupled. However, the nature of this coupling and the mechanism of antiporting remain topics of debate. Here multiscale simulations have been used to characterize Proton Transport between E203 (Gluin) and E148 (Gluex), the internal and external intermediate Proton binding sites, respectively. Free energy profiles are presented, explicitly accounting for the binding of Cl– along the central pathway, the dynamically coupled hydration changes of the central region, and conformational changes of Gluin and Gluex. We find that Proton Transport between Gluin and Gluex is possible in both the presence and absence of Cl– in the central binding site, although it is facilitated by the anion presence. These results support the notion that the requisite coupling between Cl– and Proton Transport occurs elsewhere (e.g., during Proton uptake or release). In addition, Proton Transport is explored in the E203K mutant, which maintains Proton permeation despite the substitution of a basic residue for Gluin. This collection of calculations provides for the first time, to our knowledge, a detailed picture of the Proton Transport mechanism in the central region of ClC-ec1 at a molecular level.
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Mesoscale Study of Proton Transport in Proton Exchange Membranes: Role of Morphology
The Journal of Physical Chemistry C, 2015Co-Authors: Shule Liu, John Savage, Gregory A. VothAbstract:The influence of morphology on Proton Transport in Proton exchange membranes (PEM) is studied at the mesoscale using smoothed particle hydrodynamics (SPH), a mesh-free particle method for solving continuity equations. By solving the Nernst–Planck equation for Proton Transport in lamellar, cylinder, and cluster morphologies, we find that the Proton conductivity for cluster morphology is much lower than lamellar and cylinder morphology at all hydration levels. This suggests the porosity and tortuosity in PEM morphology can reduce Proton Transport significantly at the mesoscale. We also investigated the effect of including a position-dependent diffusion constant (PDDC) tied to the local morphology, which is usually ignored in studies of Proton Transport in confinement. We calculated the PDDC in lamellar PEM using both quantitative and phenomenological approaches. SPH calculations show that conductivities for PEM systems with a PDDC can vary compared with systems with uniform diffusion constant. Therefore, it...
Thomas A Zawodzinski - One of the best experts on this subject based on the ideXlab platform.
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Triazole and triazole derivatives as Proton Transport facilitators in polymer electrolyte membrane fuel cells
Solid State Ionics, 2009Co-Authors: Ram Subbaraman, Hossein Ghassemi, Thomas A ZawodzinskiAbstract:Some basic aspects pertaining to the application of triazole and its derivatives as Proton Transport facilitators for membranes for high temperature fuel cell operations are investigated. Performance as Proton Transport facilitators is studied for compounds in their native solid state and as a dopant in a polymer membrane. Some key parameters which influence the Proton Transport in the system are the Proton affinity, pKa or acidity, activation energy and the ease of formation of hydrogen bonding network. Theoretical calculations of the Proton affinity of the compounds are presented. The effect of Proton affinity of the compound on the activation energies for Proton Transport is investigated. Proton conductivity is measured for acid doped triazoles in both pellet form (powder triazole mixed with acid) and in composite forms wherein the acid group is contained in a polymer matrix. The effect of formation of a hydrogen bonding network by the triazoles and its impact on the Proton conductivity are studied. Also, the effect of ion exchange capacity (IEC) of the host polymeric electrolytes and loading of triazoles in the composites were investigated.
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defect structure for Proton Transport in a triflic acid monohydrate solid
Chemical Physics Letters, 2003Co-Authors: Michael Eikerling, Stephen J Paddison, Lawrence R Pratt, Thomas A ZawodzinskiAbstract:Abstract The mechanism of Proton Transport in a trifluoromethane sulfonic acid monohydrate solid is investigated using ab initio molecular dynamics. This system provides a model for Proton transfer in minimally hydrated sulfonic acid based polymer electrolyte membranes, materials of technological importance in fuel cells. As a mechanism of Proton Transport, these simulations identify a defect involving the formation of an H 5 O 2 + ion and the re-organization of neighboring sulfonate groups, which share a Proton between the oxygen atoms of the anionic sites. The energy of formation of this defect (0.3 eV) agrees with the experimentally determined activation energy for Proton Transport in minimally hydrated Nafion® of 0.36 eV.
John Savage - One of the best experts on this subject based on the ideXlab platform.
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Mesoscale Study of Proton Transport in Proton Exchange Membranes: Role of Morphology
The Journal of Physical Chemistry C, 2015Co-Authors: Shule Liu, John Savage, Gregory A. VothAbstract:The influence of morphology on Proton Transport in Proton exchange membranes (PEM) is studied at the mesoscale using smoothed particle hydrodynamics (SPH), a mesh-free particle method for solving continuity equations. By solving the Nernst–Planck equation for Proton Transport in lamellar, cylinder, and cluster morphologies, we find that the Proton conductivity for cluster morphology is much lower than lamellar and cylinder morphology at all hydration levels. This suggests the porosity and tortuosity in PEM morphology can reduce Proton Transport significantly at the mesoscale. We also investigated the effect of including a position-dependent diffusion constant (PDDC) tied to the local morphology, which is usually ignored in studies of Proton Transport in confinement. We calculated the PDDC in lamellar PEM using both quantitative and phenomenological approaches. SPH calculations show that conductivities for PEM systems with a PDDC can vary compared with systems with uniform diffusion constant. Therefore, it...
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Proton Transport Mechanism of Perfluorosulfonic Acid Membranes
The Journal of Physical Chemistry C, 2014Co-Authors: John Savage, Ying-lung Steve Tse, Gregory A. VothAbstract:An understanding of Proton Transport within perfluorosulfonic acid (PFSA) membranes is crucial to improve the efficiency of Proton exchange membrane fuel cells. Using reactive molecular dynamics si...
Takashi Tokumasu - One of the best experts on this subject based on the ideXlab platform.
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Nano/Microscale Simulation of Proton Transport in Catalyst Layer
ECS Transactions, 2019Co-Authors: Koichi Kobayashi, Takuya Mabuchi, Inoue, Takashi TokumasuAbstract:To spread polymer electrolyte fuel cells, improving the cell performance is required. The cell performance depends on various factors. One of the factors that lowers cell performance is Proton Transport resistance in catalyst layers. Catalyst layers have Nano/Microscale structures which influence on Proton Transport resistance. In this study, to investigate the relationship between structures of catalyst layers and cell performances, mass Transport and chemical reactions are calculated in the 3D catalyst layer models. The information about the ionomer thickness dependence on the diffusion coefficient of Protons based on the molecular dynamics simulation studies, is introduced to Transport calculation in order to analyze nanoscale structure influence on the cell performance. As a result, we have found that the output voltage increases over the whole range of current density with increasing ionomer/carbon ratio considering ionomer thickness dependence. This result suggests that the nanoscale structure in catalyst layer has a large influence on the cell performance.
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Relationship between Proton Transport and Morphology of Perfluorosulfonic Acid Membranes: A Reactive Molecular Dynamics Approach.
The journal of physical chemistry. B, 2018Co-Authors: Takuya Mabuchi, Takashi TokumasuAbstract:A reactive molecular dynamics simulation has been performed for the characterization of the relationship between Proton Transport and water clustering in polymer electrolyte membranes. We have demonstrated that the anharmonic two-state empirical valence bond model is capable of describing efficiently excess Proton Transport through the Grotthuss hopping mechanism within the simplicity of the theoretical framework. To explore the long-time diffusion behavior in perfluorosulfonic acid membranes with statistical certainty, simulations that are longer than 10 ns are needed. The contribution of the Grotthuss mechanism to the Proton Transport yields a larger fraction compared to the vehicular mechanism, when the estimated percolation threshold of λ = 5.6 is surpassed. The cluster analyses elicit a consistent outlook in regard to the relationship between the connectivity and the confinement of water clusters and Proton Transport. The cluster growth behavior findings reveal that, below the percolation threshold, ...
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Effects of Water Structure on Proton Transport in Nafion Thin Films with Molecular Dynamics Simulations
ECS Transactions, 2015Co-Authors: Joji Aochi, Takuya Mabuchi, Takashi TokumasuAbstract:Proton Transport properties in Nafion thin films have been investigated using molecular dynamics simulations to characterize the nanoscopic flow phenomena in the electrode of polymer electrolyte fuel cell. Protons transfer in the ionomer by a combination of the Vehicle mechanism and the Grotthuss mechanism. In this study, the Grotthuss mechanism is described using the anharmonic two-state empirical valence bond method to evaluate quantitative Proton Transport within the framework of classical molecular dynamics simulations. The electrode consists of platinum-supported carbon and ionomers, and it is well known that the wettability of supported carbon depends on materials and operating environment. Our results suggested that the wettability affects morphology of the ionomer and Proton Transport.
Peidong Yang - One of the best experts on this subject based on the ideXlab platform.
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Gated Proton Transport in aligned mesoporous silica films
Nature Materials, 2008Co-Authors: Rong Fan, Seong Huh, Ruoxue Yan, John Arnold, Peidong YangAbstract:Modulated Proton Transport has a significant role in biological processes such as ATP synthesis and in electrochemical energy conversion. Electrostatic gating of Proton conduction that can be actively modulated is now shown in aligned mesoporous silica thin-films. Modulated Proton Transport plays significant roles in biological processes^ 1 such as ATP synthesis^ 2 , 3 as well as in technologically important applications including, for example, hydrogen fuel cells^ 4 , 5 . The state-of-the-art Proton-exchange membrane is the sulphonated tetrafluoroethylene copolymer Nafion developed by DuPont in the late 1960s, with a high Proton conductivity^ 6 . However, actively switchable Proton conduction, a functional mimic of the ion Transport within a cell membrane, has yet to be realized. Herein, we report the electrostatic gating of Proton Transport within aligned mesoporous silica thin film. It is observed that surface-charge-mediated Transport is dominant at low Proton concentrations. We have further demonstrated that the Proton conduction can be actively modulated by two–fourfold with a gate voltage as low as 1 V. Such artificial gatable ion Transport media could have potential applications in nanofluidic chemical processors, biomolecular separation and electrochemical energy conversion.
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Gated Proton Transport in aligned mesoporous silica films
Nature materials, 2008Co-Authors: Rong Fan, Seong Huh, Ruoxue Yan, John Arnold, Peidong YangAbstract:Modulated Proton Transport plays significant roles in biological processes such as ATP synthesis as well as in technologically important applications including, for example, hydrogen fuel cells. The state-of-the-art Proton-exchange membrane is the sulphonated tetrafluoroethylene copolymer Nafion developed by DuPont in the late 1960s, with a high Proton conductivity. However, actively switchable Proton conduction, a functional mimic of the ion Transport within a cell membrane, has yet to be realized. Herein, we report the electrostatic gating of Proton Transport within aligned mesoporous silica thin film. It is observed that surface-charge-mediated Transport is dominant at low Proton concentrations. We have further demonstrated that the Proton conduction can be actively modulated by two-fourfold with a gate voltage as low as 1 V. Such artificial gatable ion Transport media could have potential applications in nanofluidic chemical processors, biomolecular separation and electrochemical energy conversion.
