1
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Dunlap MK, Kringle L, Kay BD, Kimmel GA. Proton diffusion and hydrogen/deuterium exchange in amorphous solid water at temperatures from 114 to 134 K. J Chem Phys 2024; 161:244504. [PMID: 39723704 DOI: 10.1063/5.0233755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2024] [Accepted: 11/20/2024] [Indexed: 12/28/2024] Open
Abstract
The reaction coefficient for hydrogen/deuterium (H/D) exchange and the diffusion of hydrated excess protons within amorphous solid water (ASW) are characterized as a function of temperature. For these experiments, water films are deposited on a Pt(111) substrate at 108 K, and reactions with pre-adsorbed hydrogen atoms produce hydrated protons. Upon heating, protons diffuse within the water, and H/D exchange occurs when they encounter D2O probe molecules deposited in the films. The time-dependent concentration of D2O is monitored with infrared spectroscopy, and it indicates the protons diffusion from the substrate and establish an equilibrium distribution prior to significant H/D exchange for temperatures 114 K ≤T≤ 134 K. By controlling the distance between the D2O molecules and the substrate, we probe the distribution of protons within the film. It decays as x-2 for the examined range of x (12-52 nm) due to the electric field that develops between the diffusing protons and their image charges in the metal substrate. This agrees with the theoretical distance scaling for the equilibrated proton concentration in a dielectric near a metal boundary. From the proton concentration and the measured D2O decay rate, a lower bound for the proton diffusion coefficient ranging from 10-20 m2/s at 114 K to 10-18 m2/s at 134 K is estimated. The diffusion coefficient has an activation energy of 0.40 eV, which is comparable to energies reported for molecular translations and rotations of H2O, suggesting they may play a critical role in the proton diffusion mechanism within ASW.
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Affiliation(s)
- Megan K Dunlap
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Loni Kringle
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Bruce D Kay
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Greg A Kimmel
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
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2
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Gomez A, Thompson WH, Laage D. Neural-network-based molecular dynamics simulations reveal that proton transport in water is doubly gated by sequential hydrogen-bond exchange. Nat Chem 2024; 16:1838-1844. [PMID: 39164581 DOI: 10.1038/s41557-024-01593-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Accepted: 07/03/2024] [Indexed: 08/22/2024]
Abstract
The transport of excess protons in water is central to acid-base chemistry, biochemistry and energy production. However, elucidating its mechanism has been challenging. Recent nonlinear vibrational spectroscopy experiments could not be explained by existing models. Here we use both vibrational spectroscopy calculations and neural-network-based molecular dynamics simulations that account for nuclear quantum effects for all atoms to determine the proton transport mechanism. Our simulations reveal an equilibrium between two stable proton-localized structures with distinct Eigen-like and Zundel-like hydrogen-bond motifs. Proton transport follows a three-step mechanism gated by two successive hydrogen-bond exchanges: the first reduces the proton-acceptor water coordination, leading to proton transfer, and the second, the rate-limiting step, prevents rapid back-transfer by increasing the proton-donor coordination. This sequential mechanism is consistent with experimental characterizations of proton diffusion, explaining the low activation energy and the prolonged intermediate lifetimes in vibrational spectroscopy. These results are crucial for understanding proton dynamics in biochemical and technological systems.
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Affiliation(s)
- Axel Gomez
- PASTEUR, Department of Chemistry, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | - Ward H Thompson
- Department of Chemistry, University of Kansas, Lawrence, KS, USA
| | - Damien Laage
- PASTEUR, Department of Chemistry, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France.
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3
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Jin J, Noid WG, Li J, Kumar R, Cao J, Jang S, Paesani F, Reichman D. A Tribute to Gregory A. Voth. J Phys Chem B 2024; 128:7703-7706. [PMID: 39143864 DOI: 10.1021/acs.jpcb.4c04455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/16/2024]
Affiliation(s)
- Jaehyeok Jin
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - William G Noid
- Department of Chemistry, Penn State University, University Park, Pennsylvania 16802, United States
| | - Jianing Li
- Borch Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, United States
| | - Revati Kumar
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Jianshu Cao
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Seogjoo Jang
- Department of Chemistry and Biochemistry, Queens College, City University of New York, Queens, New York 11367, United States
- PhD Programs in Chemistry and Physics, Graduate Center of the City University of New York, New York, New York 10016, United States
| | - Francesco Paesani
- Department of Chemistry and Biochemistry, Materials Science and Engineering, Halicioğlu Data Science Institute, San Diego Supercomputer Center, University of California, San Diego, La Jolla, California 92093, United States
| | - David Reichman
- Department of Chemistry, Columbia University, New York, New York 10027, United States
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4
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Kaiser S, Yue Z, Peng Y, Nguyen TD, Chen S, Teng D, Voth GA. Molecular Dynamics Simulation of Complex Reactivity with the Rapid Approach for Proton Transport and Other Reactions (RAPTOR) Software Package. J Phys Chem B 2024; 128:4959-4974. [PMID: 38742764 PMCID: PMC11129700 DOI: 10.1021/acs.jpcb.4c01987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Revised: 05/05/2024] [Accepted: 05/06/2024] [Indexed: 05/16/2024]
Abstract
Simulating chemically reactive phenomena such as proton transport on nanosecond to microsecond and beyond time scales is a challenging task. Ab initio methods are unable to currently access these time scales routinely, and traditional molecular dynamics methods feature fixed bonding arrangements that cannot account for changes in the system's bonding topology. The Multiscale Reactive Molecular Dynamics (MS-RMD) method, as implemented in the Rapid Approach for Proton Transport and Other Reactions (RAPTOR) software package for the LAMMPS molecular dynamics code, offers a method to routinely sample longer time scale reactive simulation data with statistical precision. RAPTOR may also be interfaced with enhanced sampling methods to drive simulations toward the analysis of reactive rare events, and a number of collective variables (CVs) have been developed to facilitate this. Key advances to this methodology, including GPU acceleration efforts and novel CVs to model water wire formation are reviewed, along with recent applications of the method which demonstrate its versatility and robustness.
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Affiliation(s)
- Scott Kaiser
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Zhi Yue
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Yuxing Peng
- NVIDIA
Corporation, Santa
Clara, California 95051, United States
| | - Trung Dac Nguyen
- Research
Computing Center, The University of Chicago, Chicago, Illinois 60637, United States
| | - Sijia Chen
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Da Teng
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
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5
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Yan S, Wang B, Lin H. Reshaping the QM Region On-the-Fly: Adaptive-Shape QM/MM Dynamic Simulations of a Hydrated Proton in Bulk Water. J Chem Theory Comput 2024; 20:3462-3472. [PMID: 38671391 DOI: 10.1021/acs.jctc.4c00164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
Adaptive quantum mechanics/molecular mechanics (QM/MM) reclassifies on-the-fly a molecule or molecular fragment as QM or MM during dynamics simulations without abrupt changes in the energy or forces. Notably, the permuted adaptive-partitioning (PAP) algorithms have been applied to simulate a hydrated proton, with a mobile QM zone anchored at a pseudoatom called a proton indicator. The position of the proton indicator approximates the location of the delocalized excess proton, yielding a smooth trajectory of the proton diffusing via the Grotthuss mechanism in aqueous solutions. The mobile QM zone, which has been taken to be a sphere with a preset radius, follows the proton wherever it goes. Although the simulations are successful, the use of a spherical QM zone has one disadvantage: A large preset radius must be utilized to minimize the chance of missing water molecules that are important to proton translocation. A large radius leads to a large QM zone, which is computationally expensive. In this work, we report a new way to set up the QM zone, where one includes only the water molecules important to proton transfer. The importance of a given water molecule is quantified by its "weight" that depends on its relation to the reaction path of proton transfer. The weight varies smoothly, ensuring that a water molecule gradually appears in or disappears from the QM zone without abrupt changes, as required by the PAP method. Consequently, the shape of the QM zone evolves on-the-fly, keeping the QM zone as small as possible and as large as necessary. Test simulations demonstrate that the new algorithm significantly improves the computation efficiency while maintaining the proper descriptions of proton transfer in bulk water.
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Affiliation(s)
- Shengheng Yan
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 360015, P. R. China
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 360015, P. R. China
| | - Hai Lin
- Department of Chemistry, CB 194, University of Colorado Denver, Denver, P.O. Box 173364, Colorado 80217, United States
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6
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Dean JLS, Winkler VS, Boyer MA, Sibert EL, Fournier JA. Investigating Intramolecular H Atom Transfer Dynamics in β-Diketones with Ultrafast Infrared Spectroscopies and Theoretical Modeling. J Phys Chem A 2023; 127:9258-9272. [PMID: 37882618 DOI: 10.1021/acs.jpca.3c05417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2023]
Abstract
The vibrational signatures and ultrafast dynamics of the intramolecular H-bond in a series of β-diketones are investigated with 2D IR spectroscopy and computational modeling. The chosen β-diketones exhibit a range of H atom donor-acceptor distances and asymmetry along the H atom transfer coordinate that tunes the intramolecular H-bond strength. The species with the strongest H-bonds are calculated to have very soft H atom potentials, resulting in highly red-shifted OH stretch fundamental frequencies and dislocation of the H atom upon vibrational excitation. These soft potentials lead to significant coupling to the other normal mode coordinates and give rise to the very broad vibrational signatures observed experimentally. The 2D IR spectra in both the OH and OD stretch regions of the light and deuterated isotopologues reveal broadened and long-lived ground-state bleach signatures of the vibrationally hot molecules. Polarization-sensitive transient absorption measurements in the OH and OD stretch regions reveal notable isotopic differences in orientational dynamics. Orientational relaxation was measured to occur on ∼600 fs and ∼2 ps time scales for the light and deuterated isotopologues, respectively. The orientational dynamics are interpreted in terms of activated H/D atom transfer events driven by collective intramolecular structural rearrangements.
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Affiliation(s)
- Jessika L S Dean
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Valerie S Winkler
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Mark A Boyer
- Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin Madison, Madison, Wisconsin 53706, United States
| | - Edwin L Sibert
- Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin Madison, Madison, Wisconsin 53706, United States
| | - Joseph A Fournier
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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7
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Kratochvil HT, Watkins LC, Mravic M, Thomaston JL, Nicoludis JM, Somberg NH, Liu L, Hong M, Voth GA, DeGrado WF. Transient water wires mediate selective proton transport in designed channel proteins. Nat Chem 2023; 15:1012-1021. [PMID: 37308712 PMCID: PMC10475958 DOI: 10.1038/s41557-023-01210-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 04/19/2023] [Indexed: 06/14/2023]
Abstract
Selective proton transport through proteins is essential for forming and using proton gradients in cells. Protons are conducted along hydrogen-bonded 'wires' of water molecules and polar side chains, which, somewhat surprisingly, are often interrupted by dry apolar stretches in the conduction pathways, inferred from static protein structures. Here we hypothesize that protons are conducted through such dry spots by forming transient water wires, often highly correlated with the presence of the excess protons in the water wire. To test this hypothesis, we performed molecular dynamics simulations to design transmembrane channels with stable water pockets interspersed by apolar segments capable of forming flickering water wires. The minimalist designed channels conduct protons at rates similar to viral proton channels, and they are at least 106-fold more selective for H+ over Na+. These studies inform the mechanisms of biological proton conduction and the principles for engineering proton-conductive materials.
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Affiliation(s)
- Huong T Kratochvil
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA.
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
| | - Laura C Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, IL, USA
- Kemper Insurance, Chicago, IL, USA
| | - Marco Mravic
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
- Department of Integrative Structural and Computational Biology Scripps Research Institute, La Jolla, CA, USA
| | - Jessica L Thomaston
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
| | - John M Nicoludis
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
- Genentech, San Francisco, CA, USA
| | - Noah H Somberg
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, IL, USA.
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA.
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8
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Huo J, Chen J, Liu P, Hong B, Zhang J, Dong H, Li S. Microscopic Mechanism of Proton Transfer in Pure Water under Ambient Conditions. J Chem Theory Comput 2023. [PMID: 37365994 DOI: 10.1021/acs.jctc.3c00244] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
Water molecules and the associated proton transfer (PT) are prevalent in chemical and biological systems and have been a hot research topic. Spectroscopic characterization and ab initio molecular dynamics (AIMD) simulations have previously revealed insights into acidic and basic liquids. Presumably, the situation in the acidic/basic solution is not necessarily the same as in pure water; in addition, the autoionization constant for water is only 10-14 under ambient conditions, making the study of PT in pure water challenging. To overcome this issue, we modeled periodic water box systems containing 1000 molecules for tens of nanoseconds based on a neural network potential (NNP) with quantum mechanical accuracy. The NNP was generated by training a dataset containing the energies and atomic forces of 17 075 configurations of periodic water box systems, and these data points were calculated at the MP2 level that considers electron correlation effects. We found that the size of the system and the duration of the simulation have a significant impact on the convergence of the results. With these factors considered, our simulations showed that hydronium (H3O+) and hydroxide (OH-) ions in water have distinct hydration structures, thermodynamic and kinetic properties, e.g., the longer-lasting and more stable hydrated structure of OH- ions than that of H3O+, as well as a significantly higher free energy barrier for the OH--associated PT than that of H3O+, leading the two to exhibit completely different PT behaviors. Given these characteristics, we further found that PT via OH- ions tends not to occur multiple times or between many molecules. In contrast, PT via H3O+ can synergistically occur among multiple molecules and prefers to adopt a cyclic pattern among three water molecules, while it occurs mostly in a chain pattern when more water molecules are involved. Therefore, our studies provide a detailed and solid microscopic explanation for the PT process in pure water.
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Affiliation(s)
- Jun Huo
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, China
| | - Jianghao Chen
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, China
- School of Physics, National Laboratory of Solid State Microstructure, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Pei Liu
- School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210023, China
| | - Benkun Hong
- School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210023, China
| | - Jian Zhang
- School of Physics, National Laboratory of Solid State Microstructure, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Hao Dong
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, China
- State Key Laboratory of Analytical Chemistry for Life Science, Nanjing University, Nanjing 210023, China
- Institute for Brain Sciences, Nanjing University, Nanjing 210023, China
| | - Shuhua Li
- School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210023, China
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9
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Chen S, Li Z, Voth GA. Acidic Conditions Impact Hydrophobe Transfer across the Oil-Water Interface in Unusual Ways. J Phys Chem B 2023; 127:3911-3918. [PMID: 37084419 PMCID: PMC10166083 DOI: 10.1021/acs.jpcb.3c00828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 04/09/2023] [Indexed: 04/23/2023]
Abstract
Molecular dynamics simulation and enhanced free energy sampling are used to study hydrophobic solute transfer across the water-oil interface with explicit consideration of the effect of different electrolytes: hydronium cation (hydrated excess proton) and sodium cation, both with chloride counterions (i.e., dissociated acid and salt, HCl and NaCl). With the Multistate Empirical Valence Bond (MS-EVB) methodology, we find that, surprisingly, hydronium can to a certain degree stabilize the hydrophobic solute, neopentane, in the aqueous phase and including at the oil-water interface. At the same time, the sodium cation tends to "salt out" the hydrophobic solute in the expected fashion. When it comes to the solvation structure of the hydrophobic solute in the acidic conditions, hydronium shows an affinity to the hydrophobic solute, as suggested by the radial distribution functions (RDFs). Upon consideration of this interfacial effect, we find that the solvation structure of the hydrophobic solute varies at different distances from the oil-liquid interface due to a competition between the bulk oil phase and the hydrophobic solute phase. Together with an observed orientational preference of the hydroniums and the lifetime of water molecules in the first solvation shell of neopentane, we conclude that hydronium stabilizes to a certain degree the dispersal of neopentane in the aqueous phase and eliminates any salting out effect in the acid solution; i.e., the hydronium acts like a surfactant. The present molecular dynamics study provides new insight into the hydrophobic solute transfer across the water-oil interface process, including for acid and salt solutions.
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Affiliation(s)
- Sijia Chen
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, The James Franck Institute, and Institute
for Biophysical Dynamics, The University
of Chicago, Chicago, Illinois 60637, United States
| | - Zhefu Li
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, The James Franck Institute, and Institute
for Biophysical Dynamics, The University
of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, The James Franck Institute, and Institute
for Biophysical Dynamics, The University
of Chicago, Chicago, Illinois 60637, United States
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10
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Antalicz B, Versluis J, Bakker HJ. Observing Aqueous Proton-Uptake Reactions Triggered by Light. J Am Chem Soc 2023; 145:6682-6690. [PMID: 36940392 PMCID: PMC10064335 DOI: 10.1021/jacs.2c11441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/22/2023]
Abstract
Proton-transfer reactions in water are essential to chemistry and biology. Earlier studies reported on aqueous proton-transfer mechanisms by observing light-triggered reactions of strong (photo)acids and weak bases. Similar studies on strong (photo)base-weak acid reactions would also be of interest because earlier theoretical works found evidence for mechanistic differences between aqueous H+ and OH- transfer. In this work, we study the reaction of actinoquinol, a water-soluble strong photobase, with the water solvent and the weak acid succinimide. We find that in aqueous solutions containing succinimide, the proton-transfer reaction proceeds via two parallel and competing reaction channels. In the first channel, actinoquinol extracts a proton from water, after which the newly generated hydroxide ion is scavenged by succinimide. In the second channel, succinimide forms a hydrogen-bonded complex with actinoquinol and the proton is transferred directly. Interestingly, we do not observe proton conduction in water-separated actinoquinol-succinimide complexes, which makes the newly studied strong base-weak acid reaction essentially different from previously studied strong acid-weak base reactions.
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Affiliation(s)
- Balázs Antalicz
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Jan Versluis
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Huib J Bakker
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098 XG Amsterdam, The Netherlands
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11
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Jin J, Voth GA. Statistical Mechanical Design Principles for Coarse-Grained Interactions across Different Conformational Free Energy Surfaces. J Phys Chem Lett 2023; 14:1354-1362. [PMID: 36728761 PMCID: PMC9940719 DOI: 10.1021/acs.jpclett.2c03844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 01/27/2023] [Indexed: 06/18/2023]
Abstract
Systematic bottom-up coarse-graining (CG) of molecular systems provides a means to explore different coupled length and time scales while treating the molecular-scale physics at a reduced level. However, the configuration dependence of CG interactions often results in CG models with limited applicability for exploring the parametrized configurations. We propose a statistical mechanical theory to design CG interactions across different configurations and conditions. In order to span wide ranges of conformational space, distinct classical CG free energy surfaces for characteristic configurations are identified using molecular collective variables. The coupling interaction between different CG free energy surfaces can then be systematically determined by analogy to quantum mechanical approaches describing coupled states. The present theory can accurately capture the underlying many-body potentials of mean force in the CG variables for various order parameters applied to liquids, interfaces, and in principle proteins, uncovering the complex nature underlying the coupling interaction and imparting a new protocol for the design of predictive multiscale models.
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Affiliation(s)
| | - Gregory A. Voth
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, Institute for Biophysical
Dynamics, and James Franck Institute, The
University of Chicago, Chicago, Illinois 60637, United States
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12
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Moses AA, Arntsen C. Ab initio molecular dynamics study of proton transport in imidazolium-based ionic liquids with added imidazole. Phys Chem Chem Phys 2023; 25:2142-2152. [PMID: 36562495 DOI: 10.1039/d2cp03262g] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Development of efficient anhydrous proton-conducting materials would expand the operational temperature ranges of hydrogen fuels cells (HFCs) and eliminate their dependence on maintaining sufficient hydration levels to function efficiently. Protic ionic liquids (PILs), which have high ionic densities and low vapor pressures, have emerged as a potential material for proton conducting layers in HFCs. In this work, we investigate proton transport via the Grotthuss mechanism in 1-ethylimidazolium bis-(trifluoromethanesulfonyl)imide ([C2HIm][TFSI]) protic ionic liquids with added imidazole (Im0) using ab initio molecular dynamics. In particular, we vary the composition of the systems studied from pure [C2HIm][TFSI] to those where the mole fraction of Im0 is 0.67. Given the large difference in pKa between C2HIm+ and HTFSI, TFSI- does not accept acidic protons from C2HIm+; conversely, imidazolium (HIm+) and C2HIm+ have very similar pKa values, and thus Im0 can readily accept protons. We find that the unprotonated nitrogen on Im0 dominates solvation of the labile protons on C2HIm+ and other Im0 species, resulting in formation of robust imidazole wires. Given the amphoteric nature of Im0, i.e. its ability to accept and donate protons, these wires provide conduits along which protons can rapidly traverse via the Grotthuss mechanism, thereby greatly increasing the proton coefficient of self-diffusion. We find that the average length of the wires increases with added Im0, and thus as the mole fraction of Im0 increases so too does the proton diffusion constant. Lastly, we analyze our trajectories to determine the energy and time scales associated with proton transfer.
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Affiliation(s)
- Aurelia A Moses
- Department of Chemical and Biological Sciences, Youngstown State University, Youngstown, OH, 44555, USA.
| | - Christopher Arntsen
- Department of Chemical and Biological Sciences, Youngstown State University, Youngstown, OH, 44555, USA.
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13
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Zuchniarz J, Liu Y, Li C, Voth GA. Accurate p Ka Calculations in Proteins with Reactive Molecular Dynamics Provide Physical Insight Into the Electrostatic Origins of Their Values. J Phys Chem B 2022; 126:7321-7330. [PMID: 36106487 PMCID: PMC9528908 DOI: 10.1021/acs.jpcb.2c04899] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 08/28/2022] [Indexed: 11/29/2022]
Abstract
Classical molecular dynamics simulations are a versatile tool in the study of biomolecular systems, but they usually rely on a fixed bonding topology, precluding the explicit simulation of chemical reactivity. Certain modifications can permit the modeling of reactions. One such method, multiscale reactive molecular dynamics, makes use of a linear combination approach to describe condensed-phase free energy surfaces of reactive processes of biological interest. Before these simulations can be performed, models of the reactive moieties must first be parametrized using electronic structure data. A recent study demonstrated that gas-phase electronic structure data can be used to derive parameters for glutamate and lysine which reproduce experimental pKa values in both bulk water and the staphylococcal nuclease protein with remarkable accuracy and transferability between the water and protein environments. In this work, we first present a new model for aspartate derived in similar fashion and demonstrate that it too produces accurate pKa values in both bulk and protein contexts. We also describe a modification to the prior methodology, involving refitting some of the classical force field parameters to density functional theory calculations, which improves the transferability of the existing glutamate model. Finally and most importantly, this reactive molecular dynamics approach, based on rigorous statistical mechanics, allows one to specifically analyze the fundamental physical causes for the marked pKa shift of both aspartate and glutamate between bulk water and protein and also to demonstrate that local steric and electrostatic effects largely explain the observed differences.
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Affiliation(s)
- Joshua Zuchniarz
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Yu Liu
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
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14
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Brünig FN, Rammler M, Adams EM, Havenith M, Netz RR. Spectral signatures of excess-proton waiting and transfer-path dynamics in aqueous hydrochloric acid solutions. Nat Commun 2022; 13:4210. [PMID: 35864099 PMCID: PMC9304333 DOI: 10.1038/s41467-022-31700-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 06/22/2022] [Indexed: 11/23/2022] Open
Abstract
The theoretical basis for linking spectral signatures of hydrated excess protons with microscopic proton-transfer mechanisms has so far relied on normal-mode analysis. We introduce trajectory-decomposition techniques to analyze the excess-proton dynamics in ab initio molecular-dynamics simulations of aqueous hydrochloric-acid solutions beyond the normal-mode scenario. We show that the actual proton transfer between two water molecules involves for relatively large water-water separations crossing of a free-energy barrier and thus is not a normal mode, rather it is characterized by two non-vibrational time scales: Firstly, the broadly distributed waiting time for transfer to occur with a mean value of 200-300 fs, which leads to a broad and weak shoulder in the absorption spectrum around 100 cm-1, consistent with our experimental THz spectra. Secondly, the mean duration of a transfer event of about 14 fs, which produces a rather well-defined spectral contribution around 1200 cm-1 and agrees in location and width with previous experimental mid-infrared spectra.
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Affiliation(s)
- Florian N Brünig
- Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany
| | - Manuel Rammler
- Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany
| | - Ellen M Adams
- Ruhr-Universität Bochum, Department of Physical Chemistry II, 44780, Bochum, Germany
| | - Martina Havenith
- Ruhr-Universität Bochum, Department of Physical Chemistry II, 44780, Bochum, Germany
| | - Roland R Netz
- Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
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15
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Liu R, Zhang C, Liang X, Liu J, Wu X, Chen M. Structural and Dynamic Properties of Solvated Hydroxide and Hydronium Ions in Water from Ab Initio Modeling. J Chem Phys 2022; 157:024503. [DOI: 10.1063/5.0094944] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Predicting the asymmetric structure and dynamics of solvated hydroxide and hydronium in water has been a challenging task from ab initio molecular dynamics (AIMD). The difficulty mainly comes from a lack of accurate and efficient exchange-correlation functional in elucidating the amphiphilic nature and the ubiquitous proton transfer behaviors of the two ions. By adopting the strongly-constrained and appropriately normed (SCAN) meta-GGA functional in AIMD simulations, we systematically examine the amphiphilic properties, the solvation structures, the electronic structures, and the dynamic properties of the two water ions. In particular, we compare these results to those predicted by the PBE0-TS functional, which is an accurate yet computationally more expensive exchange-correlation functional. We demonstrate that the general-purpose SCAN functional provides a reliable choice in describing the two water ions. Specifically, in the SCAN picture of water ions, the appearance of the fourth and fifth hydrogen bonds near hydroxide stabilizes the pot-like shape solvation structure and suppresses the structural diffusion, while the hydronium stably donates three hydrogen bonds to its neighbors. We apply a detailed analysis of the proton transfer mechanism of the two ions and find the two ions exhibit substantially different proton transfer patterns. Our AIMD simulations indicate hydroxide diffuses slower than hydronium in water, which is consistent with the experiments.
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Affiliation(s)
| | | | | | | | - Xifan Wu
- Physics, Temple University, United States of America
| | - Mohan Chen
- College of Engineering, Peking University, China
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16
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Mabuchi T. Revealing the Anticorrelation Behavior Mechanism between the Grotthuss and Vehicular Diffusions for Proton Transport in Concentrated Acid Solutions. J Phys Chem B 2022; 126:3319-3326. [PMID: 35468285 DOI: 10.1021/acs.jpcb.1c09742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this study, we performed reactive molecular dynamics simulations to characterize proton solvation and transport in concentrated hydrochloric acid solutions. The correlation contribution to the total proton mean square displacement is found to be negative for all acid concentrations, indicating the anticorrelation between the Grotthuss and vehicular diffusions. For the vehicular diffusion, the hydronium ions tend to move freely toward the lone pair side independent of acid concentrations, whereas for the Grotthuss diffusion, the proton hopping direction is limited to one of the hydrogen-bonded water molecules on the opposite side of the lone pair region, which are specifically oriented with respect to the neighboring hydronium ion at higher acid concentrations. This result is justified by our findings of the higher fraction of proton rattling with the single hopping event and longer hydrogen bond lifetimes at higher acid concentrations. However, the angular distribution for both the vehicular and Grotthuss diffusions is found to be rather broad and comparable for all acid concentrations, and thus, the anticorrelation shows a minimal dependence on the acid concentration. Our results reveal that the anticorrelation behavior between the vehicle and Grotthuss diffusions is attributed to the amphiphilic nature of hydronium ions and thus is independent of the acid concentrations in solutions.
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Affiliation(s)
- Takuya Mabuchi
- Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan.,Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
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17
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Park SY, Kim HY. Effect of lyophilized chive ( Allium wakegi Araki) supplementation to the frying batter mixture on quality attributes of fried chicken breast and tenderloin. Food Chem X 2022; 13:100216. [PMID: 35498993 PMCID: PMC9039885 DOI: 10.1016/j.fochx.2022.100216] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 12/24/2021] [Accepted: 01/14/2022] [Indexed: 01/10/2023] Open
Abstract
Batter mixtures for frying chicken breasts and tenderloins were supplemented with different amounts (0, 3, 5, and 7%) of lyophilized chives (Allium wakegi Araki). The viscosity of the batter mixture, crispness of the fried batter, fat and ash contents, caloric value, coating pickup, and frying yield were directly proportional, whereas the lightness, redness, yellowness, and pH were inversely proportional, to the amount of lyophilized chives in the batter. Principal component analysis revealed that the aromatic profiles varied between the 0%, 3%, and 5% lyophilized chive-supplemented groups in both the breast and tenderloin samples. However, the aromatic profiles of the 7% and 5% lyophilized chive-supplemented samples were similar. The taste profile of the 7% lyophilized chive-supplemented sample was different from those of the 0%, 3%, or 5% lyophilized chive-supplemented samples. The sensory characteristics of the 5% lyophilized chive-supplemented breast samples and 3% or 5% lyophilized chive-supplemented tenderloin samples received the best scores by sensory panelists.
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Affiliation(s)
- Sin-Young Park
- Department of Animal Resources Science, Kongju National University, Chungnam 32439, Republic of Korea
| | - Hack-Youn Kim
- Department of Animal Resources Science, Kongju National University, Chungnam 32439, Republic of Korea
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18
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Watkins LC, DeGrado WF, Voth GA. Multiscale Simulation of an Influenza A M2 Channel Mutant Reveals Key Features of Its Markedly Different Proton Transport Behavior. J Am Chem Soc 2022; 144:769-776. [PMID: 34985907 PMCID: PMC8834648 DOI: 10.1021/jacs.1c09281] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The influenza A M2 channel, a prototype for viroporins, is an acid-activated viroporin that conducts protons across the viral membrane, a critical step in the viral life cycle. Four central His37 residues control channel activation by binding subsequent protons from the viral exterior, which opens the Trp41 gate and allows proton flux to the interior. Asp44 is essential for maintaining the Trp41 gate in a closed state at high pH, resulting in asymmetric conduction. The prevalent D44N mutant disrupts this gate and opens the C-terminal end of the channel, resulting in increased conduction and a loss of this asymmetric conduction. Here, we use extensive Multiscale Reactive Molecular Dynamics (MS-RMD) and quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations with an explicit, reactive excess proton to calculate the free energy of proton transport in this M2 mutant and to study the dynamic molecular-level behavior of D44N M2. We find that this mutation significantly lowers the barrier of His37 deprotonation in the activated state and shifts the barrier for entry to the Val27 tetrad. These free energy changes are reflected in structural shifts. Additionally, we show that the increased hydration around the His37 tetrad diminishes the effect of the His37 charge on the channel's water structure, facilitating proton transport and enabling activation from the viral interior. Altogether, this work provides key insight into the fundamental characteristics of PT in WT M2 and how the D44N mutation alters this PT mechanism, and it expands understanding of the role of emergent mutations in viroporins.
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Affiliation(s)
- Laura C. Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, 94158, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States,Corresponding Author
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19
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Calio PB, Li C, Voth GA. Resolving the Structural Debate for the Hydrated Excess Proton in Water. J Am Chem Soc 2021; 143:18672-18683. [PMID: 34723507 DOI: 10.1021/jacs.1c08552] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
It has long been proposed that the hydrated excess proton in water (aka the solvated "hydronium" cation) likely has two limiting forms, that of the Eigen cation (H9O4+) and that of the Zundel cation (H5O2+). There has been debate over which of these two is the more dominant species and/or whether intermediate (or "distorted") structures between these two limits are the more realistic representation. Spectroscopy experiments have recently provided further results regarding the excess proton. These experiments show that the hydrated proton has an anisotropy reorientation time scale on the order of 1-2 ps. This time scale has been suggested to possibly contradict the picture of the more rapid "special pair dance" phenomenon for the hydrated excess proton, which is a signature of a distorted Eigen cation. The special pair dance was predicted from prior computational studies in which the hydrated central core hydronium structure continually switches (O-H···O)* special pair hydrogen-bond partners with the closest three water molecules, yielding on average a distorted Eigen cation with three equivalent and dynamically exchanging distortions. Through state-of-art simulations it is shown here that anisotropy reorientation time scales of the same magnitude are obtained that also include structural reorientations associated with the special pair dance, leading to a reinterpretation of the experimental results. These results and additional analyses point to a distorted and dynamic Eigen cation as the most prevalent hydrated proton species in aqueous acid solutions of dilute to moderate concentration, as opposed to a stabilized or a distorted (but not "dancing") Zundel cation.
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Affiliation(s)
- Paul B Calio
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
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20
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Li C, Voth GA. Accurate and Transferable Reactive Molecular Dynamics Models from Constrained Density Functional Theory. J Phys Chem B 2021; 125:10471-10480. [PMID: 34520198 PMCID: PMC8480781 DOI: 10.1021/acs.jpcb.1c05992] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Chemical reactions
constitute the central feature of many liquid,
material, and biomolecular processes. Conventional molecular dynamics
(MD) is inadequate for simulating chemical reactions given the fixed
bonding topology of most force fields, while modeling chemical reactions
using ab initio molecular dynamics is limited to
shorter time and length scales given its high computational cost.
As such, the multiscale reactive molecular dynamics method provides
one promising alternative for simulating complex chemical systems
at atomistic detail on a reactive potential energy surface. However,
the parametrization of such models is a key barrier to their applicability
and success. In this work, we present reactive MD models derived from
constrained density functional theory that are both accurate and transferable.
We illustrate the features of these models for proton dissociation
reactions of amino acids in both aqueous and protein environments.
Specifically, we present models for ionizable glutamate and lysine
that predict accurate absolute pKa values
in water as well as their significantly shifted pKa in staphylococcal nuclease (SNase) without any modification
of the models. As one outcome of the new methodology, the simulations
show that the deprotonation of ionizable residues in SNase can be
closely coupled with side chain rotations, which is a concept likely
generalizable to many other proteins. Furthermore, the present approach
is not limited to only pKa prediction
but can enable the fully atomistic simulation of many other reactive
systems along with a determination of the key aspects of the reaction
mechanisms.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
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21
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Li C, Voth GA. Using Constrained Density Functional Theory to Track Proton Transfers and to Sample Their Associated Free Energy Surface. J Chem Theory Comput 2021; 17:5759-5765. [PMID: 34468142 PMCID: PMC8444337 DOI: 10.1021/acs.jctc.1c00609] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Indexed: 11/30/2022]
Abstract
Ab initio molecular dynamics (AIMD) and quantum mechanics/molecular mechanics (QM/MM) methods are powerful tools for studying proton solvation, transfer, and transport processes in various environments. However, due to the high computational cost of such methods, achieving sufficient sampling of rare events involving excess proton motion-especially when Grotthuss proton shuttling is involved-usually requires enhanced free energy sampling methods to obtain informative results. Moreover, an appropriate collective variable (CV) that describes the effective position of the net positive charge defect associated with an excess proton is essential both for tracking the trajectory of the defect and for the free energy sampling of the processes associated with the resulting proton transfer and transport. In this work, such a CV is derived from first principles using constrained density functional theory (CDFT). This CV is applicable to a broad array of proton transport and transfer processes as studied via AIMD and QM/MM simulations.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, James Franck Institute,
and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, James Franck Institute,
and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
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22
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Stoppelman JP, McDaniel JG. Physics-based, neural network force fields for reactive molecular dynamics: Investigation of carbene formation from [EMIM +][OAc -]. J Chem Phys 2021; 155:104112. [PMID: 34525833 DOI: 10.1063/5.0063187] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Reactive molecular dynamics simulations enable a detailed understanding of solvent effects on chemical reaction mechanisms and reaction rates. While classical molecular dynamics using reactive force fields allows significantly longer simulation time scales and larger system sizes compared with ab initio molecular dynamics, constructing reactive force fields is a difficult and complex task. In this work, we describe a general approach following the empirical valence bond framework for constructing ab initio reactive force fields for condensed phase simulations by combining physics-based methods with neural networks (PB/NNs). The physics-based terms ensure the correct asymptotic behavior of electrostatic, polarization, and dispersion interactions and are compatible with existing solvent force fields. NNs are utilized for a versatile description of short-range orbital interactions within the transition state region and accurate rendering of vibrational motion of the reacting complex. We demonstrate our methodology for a simple deprotonation reaction of the 1-ethyl-3-methylimidazolium cation with acetate to form 1-ethyl-3-methylimidazol-2-ylidene and acetic acid. Our PB/NN force field exhibits ∼1 kJ mol-1 mean absolute error accuracy within the transition state region for the gas-phase complex. To characterize the solvent modulation of the reaction profile, we compute potentials of mean force for the gas-phase reaction as well as the reaction within a four-ion cluster and benchmark against ab initio molecular dynamics simulations. We find that the surrounding ionic environment significantly destabilizes the formation of the carbene product, and we show that this effect is accurately captured by the reactive force field. By construction, the PB/NN potential may be directly employed for simulations of other solvents/chemical environments without additional parameterization.
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Affiliation(s)
- John P Stoppelman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
| | - Jesse G McDaniel
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
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23
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Watkins LC, DeGrado WF, Voth GA. Influenza A M2 Inhibitor Binding Understood through Mechanisms of Excess Proton Stabilization and Channel Dynamics. J Am Chem Soc 2020; 142:17425-17433. [PMID: 32933245 PMCID: PMC7564090 DOI: 10.1021/jacs.0c06419] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
![]()
Prevalent resistance to inhibitors
that target the influenza A
M2 proton channel has necessitated a continued drug design effort,
supported by a sustained study of the mechanism of channel function
and inhibition. Recent high-resolution X-ray crystal structures present
the first opportunity to see how the adamantyl amine class of inhibitors
bind to M2 and disrupt and interact with the channel’s water
network, providing insight into the critical properties that enable
their effective inhibition in wild-type M2. In this work, we examine
the hypothesis that these drugs act primarily as mechanism-based inhibitors
by comparing hydrated excess proton stabilization during proton transport
in M2 with the interactions revealed in the crystal structures, using
the Multiscale Reactive Molecular Dynamics (MS-RMD) methodology. MS-RMD,
unlike classical molecular dynamics, models the hydrated proton (hydronium-like
cation) as a dynamic excess charge defect and allows bonds to break
and form, capturing the intricate interactions between the hydrated
excess proton, protein atoms, and water. Through this, we show that
the ammonium group of the inhibitors is effectively positioned to
take advantage of the channel’s natural ability to stabilize
an excess protonic charge and act as a hydronium mimic. Additionally,
we show that the channel is especially stable in the drug binding
region, highlighting the importance of this property for binding the
adamantane group. Finally, we characterize an additional hinge point
near Val27, which dynamically responds to charge and inhibitor binding.
Altogether, this work further illuminates a dynamic understanding
of the mechanism of drug inhibition in M2, grounded in the fundamental
properties that enable the channel to transport and stabilize excess
protons, with critical implications for future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
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24
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Calio PB, Li C, Voth GA. Molecular Origins of the Barriers to Proton Transport in Acidic Aqueous Solutions. J Phys Chem B 2020; 124:8868-8876. [PMID: 32924490 DOI: 10.1021/acs.jpcb.0c06223] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The self-consistent iterative multistate empirical valence bond (SCI-MS-EVB) method is used to analyze the structure, thermodynamics, and dynamics of hydrochloric acid solutions. The reorientation time scales of irreversible proton transport are elucidated by simulating 0.43, 0.85, 1.68, and 3.26 M HCl solutions at 270, 285, 300, 315, and 330 K. The results indicate increased counterion pairing with increasing concentration, which manifests itself via a reduced hydronium oxygen-chloride (O*-Cl) structuring in the radial distribution functions. Increasing ionic concentration also reduces the diffusion of the hydrated excess protons, principally by reducing the contribution of the Grotthuss proton hopping (shuttling) mechanism to the overall diffusion process. In agreement with prior experimental findings, a decrease in the activation energy of reorientation time scales was also observed, which is explicitly explained by using activated rate theory and an energy-entropy decomposition of the state-averaged radial distribution functions. These results provide atomistic verification of suggestions from recent two-dimensional infrared spectroscopy experiments that chloride anions (as opposed to hydrated excess protons) create entropic barriers to proton transport.
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Affiliation(s)
- Paul B Calio
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
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25
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Carpenter WB, Yu Q, Hack JH, Dereka B, Bowman JM, Tokmakoff A. Decoding the 2D IR spectrum of the aqueous proton with high-level VSCF/VCI calculations. J Chem Phys 2020; 153:124506. [PMID: 33003749 DOI: 10.1063/5.0020279] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The aqueous proton is a common and long-studied species in chemistry, yet there is currently intense interest devoted to understanding its hydration structure and transport dynamics. Typically described in terms of two limiting structures observed in gas-phase clusters, the Zundel H5O2 + and Eigen H9O4 + ions, the aqueous structure is less clear due to the heterogeneity of hydrogen bonding environments and room-temperature structural fluctuations in water. The linear infrared (IR) spectrum, which reports on structural configurations, is challenging to interpret because it appears as a continuum of absorption, and the underlying vibrational modes are strongly anharmonically coupled to each other. Recent two-dimensional IR (2D IR) experiments presented strong evidence for asymmetric Zundel-like motifs in solution, but true structure-spectrum correlations are missing and complicated by the anharmonicity of the system. In this study, we employ high-level vibrational self-consistent field/virtual state configuration interaction calculations to demonstrate that the 2D IR spectrum reports on a broad distribution of geometric configurations of the aqueous proton. We find that the diagonal 2D IR spectrum around 1200 cm-1 is dominated by the proton stretch vibrations of Zundel-like and intermediate geometries, broadened by the heterogeneity of aqueous configurations. There is a wide distribution of multidimensional potential shapes for the proton stretching vibration with varying degrees of potential asymmetry and confinement. Finally, we find specific cross peak patterns due to aqueous Zundel-like species. These studies provide clarity on highly debated spectral assignments and stringent spectroscopic benchmarks for future simulations.
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Affiliation(s)
- William B Carpenter
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Qi Yu
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA
| | - John H Hack
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Bogdan Dereka
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Joel M Bowman
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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26
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Scivetti I, Sen K, Elena AM, Todorov I. Reactive Molecular Dynamics at Constant Pressure via Nonreactive Force Fields: Extending the Empirical Valence Bond Method to the Isothermal-Isobaric Ensemble. J Phys Chem A 2020; 124:7585-7597. [PMID: 32820921 DOI: 10.1021/acs.jpca.0c05461] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Empirical Valence Bond (EVB) method offers a suitable framework to obtain reactive potentials through the coupling of nonreactive force fields. In this formalism, most of the implemented coupling terms are built using functional forms that depend on spatial coordinates, while parameters are fitted against reference data to model the change of chemistry between the participating nonreactive states. In this work, we demonstrate that the use of such coupling terms precludes the computation of the stress tensor for condensed phase systems and prevents the possibility to carry out EVB molecular dynamics in the isothermal-isobaric (NPT) ensemble. Alternatively, we make use of coupling terms that depend on the energy gaps, defined as the energy differences between the participating nonreactive force fields, and derive a general expression for the EVB stress tensor suitable for computation. Implementation of this new methodology is tested for a model of a single reactive malonaldehyde solvated in nonreactive water. Mass densities and probability distributions for the values of the energy gaps computed in the NPT ensemble reveal a negligible role of the reactive potential in the limit of low concentrated solutions, thus corroborating for the first time the validity of approximations based on the canonical NVT ensemble, customarily adopted for EVB simulations. The presented formalism also aims to contribute to future implementations and extensions of the EVB method to research the limit of highly concentrated solutions.
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Affiliation(s)
- Ivan Scivetti
- Daresbury Laboratory, Sc. Tech., Keckwick Lane, Daresbury, Warrington WA4 4AD, U.K.,Department of Chemistry, University of Liverpool, Liverpool L69 3BX, U.K
| | - Kakali Sen
- Daresbury Laboratory, Sc. Tech., Keckwick Lane, Daresbury, Warrington WA4 4AD, U.K
| | - Alin M Elena
- Daresbury Laboratory, Sc. Tech., Keckwick Lane, Daresbury, Warrington WA4 4AD, U.K
| | - Ilian Todorov
- Daresbury Laboratory, Sc. Tech., Keckwick Lane, Daresbury, Warrington WA4 4AD, U.K
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27
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Kananenka AA, Skinner JL. Unusually strong hydrogen bond cooperativity in particular (H 2O) 20 clusters. Phys Chem Chem Phys 2020; 22:18124-18131. [PMID: 32761035 DOI: 10.1039/d0cp02343d] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Drawing upon an intuitive charge-transfer-based picture of hydrogen bonding, we demonstrate that cooperativity effects acting in concert can lead to unusually strong hydrogen bonds in neutral water clusters. The structure, vibrational, and NMR properties of a (H2O)20 pentagonal dodecahedron cluster containing such a strong hydrogen bond were studied using second-order perturbation theory and density functional theory. The hydrogen bond length was found to be shorter than 2.50 Å. A large redshift of over 2000 cm-1 with respect to the isolated water molecule was predicted for the OH stretching frequency of the donor water molecule. A large downfield shift to 13.5 ppm of the isotropic part of the 1H magnetic shielding tensor together with an unusually large shielding anisotropy of 49.9 ppm was obtained. The hydrogen bond energy was calculated using symmetry-adapted perturbation theory and was found to be more than three times stronger than a typical hydrogen bond in liquid water.
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Affiliation(s)
- Alexei A Kananenka
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
| | - J L Skinner
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, USA
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28
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Li C, Yue Z, Espinoza-Fonseca LM, Voth GA. Multiscale Simulation Reveals Passive Proton Transport Through SERCA on the Microsecond Timescale. Biophys J 2020; 119:1033-1040. [PMID: 32814059 DOI: 10.1016/j.bpj.2020.07.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 12/11/2022] Open
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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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - L Michel Espinoza-Fonseca
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois.
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29
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Sofronov O, Bakker HJ. Slow Proton Transfer in Nanoconfined Water. ACS CENTRAL SCIENCE 2020; 6:1150-1158. [PMID: 32724849 PMCID: PMC7379388 DOI: 10.1021/acscentsci.0c00340] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Indexed: 06/11/2023]
Abstract
The transport of protons in nanoconfined environments, such as in nanochannels of biological or artificial proton conductive membranes, is essential to chemistry, biology, and nanotechnology. In water, proton diffusion occurs by hopping of protons between water molecules. This process involves the rearrangement of many hydrogen bonds and as such can be strongly affected by nanoconfinement. We study the vibrational and structural dynamics of hydrated protons in water nanodroplets stabilized by a cationic surfactant using polarization-resolved femtosecond infrared transient absorption spectroscopy. We determine the time scale of proton hopping in the center of the water nanodroplets from the dynamics of the anisotropy of the transient absorption signals. We find that in small nanodroplets with a diameter <4 nm, proton hopping is more than 10 times slower than in bulk water. Even in relatively large nanodroplets with a diameter of ∼7 nm, we find that the rate of proton hopping is slowed by ∼4 times compared with bulk water.
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30
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Li C, Swanson JMJ. Understanding and Tracking the Excess Proton in Ab Initio Simulations; Insights from IR Spectra. J Phys Chem B 2020; 124:5696-5708. [PMID: 32515957 PMCID: PMC7448536 DOI: 10.1021/acs.jpcb.0c03615] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Proton transport in aqueous media is ubiquitously important in chemical and biological processes. Although ab initio molecular dynamics (AIMD) simulations have made great progress in characterizing proton transport, there has been a long-standing challenge in defining and tracking the excess proton, or more properly, the center of excess charge (CEC) created when a hydrogen nucleus distorts the electron distributions of water molecules in a delocalized and highly dynamic nature. Yet, defining (and biasing) such a CEC is essential when combining AIMD with enhanced sampling methods to calculate the relevant macroscopic properties via free-energy landscapes, which is the standard practice for most processes of interest. Several CEC formulas have been proposed and used, but none have yet been systematically tested or rigorously derived. In this paper, we show that the CEC can be used as a computational tool to disentangle IR features of the solvated excess proton from its surrounding solvent, and in turn, how correlating the features in the excess charge spectrum with the behavior of CEC in simulations enables a systematic evaluation of various CEC definitions. We present a new definition of CEC and show how it overcomes the limitations of those currently available both from a spectroscopic point of view and from a practical perspective of performance in enhanced sampling simulations.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jessica M. J. Swanson
- Department of Chemistry, Biological Chemistry Program, and Center for Cell and Genome Science, The University of Utah, Salt Lake City, Utah 84112, United States
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31
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Stoppelman JP, McDaniel JG. Proton Transport in [BMIM+][BF4–]/Water Mixtures Near the Percolation Threshold. J Phys Chem B 2020; 124:5957-5970. [DOI: 10.1021/acs.jpcb.0c02487] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- John P. Stoppelman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia30332-0400, United States
| | - Jesse G. McDaniel
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia30332-0400, United States
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32
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Li Z, Li C, Wang Z, Voth GA. What Coordinate Best Describes the Affinity of the Hydrated Excess Proton for the Air-Water Interface? J Phys Chem B 2020; 124:5039-5046. [PMID: 32426982 DOI: 10.1021/acs.jpcb.0c03288] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Molecular dynamics simulations and free energy sampling are employed in this work to investigate the surface affinity of the hydrated excess proton with two definitions of the interface: The Gibbs dividing interface (GDI) and the Willard-Chandler interface (WCI). Both the multistate empirical valence bond (MS-EVB) reactive molecular dynamics method and the density functional theory-based ab initio molecular dynamics (AIMD) were used to describe the hydrated excess proton species, including "vehicular" (standard diffusion) transport and (Grotthuss) proton hopping transport and associated structures of the hydrated excess proton net positive charge defect. The excess proton is found to exhibit a similar trend and quantitative free energy behavior in terms of its surface affinity as a function of the GDI or WCI. Importantly, the definitions of the two interfaces in terms of the excess proton charge defect are highly correlated and far from independent of one another, thus undermining the argument that one interface is superior to the other when describing the proton interface affinity. Moreover, the hydrated excess proton and its solvation shell significantly influence the location and local curvature of the WCI, making it difficult to disentangle the interfacial thermodynamics of the excess proton from the influence of that species on the instantaneous surface curvature.
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Affiliation(s)
- Zhefu Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute of Biophysics Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute of Biophysics Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Zhi Wang
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute of Biophysics Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute of Biophysics Dynamics, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
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33
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Roy S, Schenter GK, Napoli JA, Baer MD, Markland TE, Mundy CJ. Resolving Heterogeneous Dynamics of Excess Protons in Aqueous Solution with Rate Theory. J Phys Chem B 2020; 124:5665-5675. [DOI: 10.1021/acs.jpcb.0c02649] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Santanu Roy
- Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37830, United States
| | - Gregory K. Schenter
- Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
| | - Joseph A. Napoli
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305, United States
| | - Marcel D. Baer
- Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
| | - Thomas E. Markland
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305, United States
| | - Christopher J. Mundy
- Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
- Affiliate Professor, Department of Chemical Engineering, University of Washington, Seattle, United States
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34
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Zeng Y, Li A, Yan T. Hydrogen Bond Dynamics in the Solvation Shell on Proton Transfer in Aqueous Solution. J Phys Chem B 2020; 124:1817-1823. [DOI: 10.1021/acs.jpcb.0c00990] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Yonghui Zeng
- Institute of New Energy Material Chemistry, School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin 300350, China
| | - Ailin Li
- College of Science, Civil Aviation University of China, Tianjin 300300, China
| | - Tianying Yan
- Institute of New Energy Material Chemistry, School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin 300350, China
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35
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Shao Y, Hellström M, Yllö A, Mindemark J, Hermansson K, Behler J, Zhang C. Temperature effects on the ionic conductivity in concentrated alkaline electrolyte solutions. Phys Chem Chem Phys 2020; 22:10426-10430. [PMID: 31895378 DOI: 10.1039/c9cp06479f] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Alkaline electrolyte solutions are important components in rechargeable batteries and alkaline fuel cells. As the ionic conductivity is thought to be a limiting factor in the performance of these devices, which are often operated at elevated temperatures, its temperature dependence is of significant interest. Here we use NaOH as a prototypical example of alkaline electrolytes, and for this system we have carried out reactive molecular dynamics simulations with an experimentally verified high-dimensional neural network potential derived from density-functional theory calculations. It is found that in concentrated NaOH solutions elevated temperatures enhance both the contributions of proton transfer to the ionic conductivity and deviations from the Nernst-Einstein relation. These findings are expected to be of practical relevance for electrochemical devices based on alkaline electrolyte solutions.
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Affiliation(s)
- Yunqi Shao
- Department of Chemistry -Ångström Laboratory, Uppsala University, Box 538, 751 21 Uppsala, Sweden.
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36
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Multistate Reactive Molecular Dynamics Simulations of Proton Diffusion in Water Clusters and in the Bulk. J Phys Chem B 2019; 123:9846-9861. [PMID: 31647873 DOI: 10.1021/acs.jpcb.9b03258] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The molecular mechanics with proton transfer (MMPT) force field is combined with multistate adiabatic reactive molecular dynamics (MS-ARMD) to describe proton transport in the condensed phase. Parametrization for small protonated water clusters based on electronic structure calculations at the MP2/6-311+G(2d,2p) level of theory and refinement by comparing with infrared spectra for a protonated water tetramer yields a force field which faithfully describes the minimum energy structures of small protonated water clusters. In protonated water clusters up to (H2O)100H+, the proton hopping rate is around 100 hops/ns. This rate converges for 21 ≤ n ≤ 31, and no further speedup in bulk water is found. This indicates that bulklike behavior requires the solvation of a Zundel motif by ∼25 water molecules, which corresponds to the second solvation sphere. For smaller cluster sizes, the number of available states (i.e., the number of proton acceptors) is too small and slows down proton-transfer rates. The cluster simulations confirm that the excess proton is typically located on the surface. The free-energy surface as a function of the weights of the two lowest states and a configurational parameter suggests that the "special pair" plays a central role in rapid proton transport. The barriers between this minimum-energy structure and the Zundel and Eigen minima are sufficiently low (∼1 kcal/mol, consistent with recent experiments and commensurate with a hopping rate of ∼100/ns or 1 every 10 ps), leading to a highly dynamic environment. These findings are also consistent with recent experiments which find that Zundel-type hydration geometries are prevalent in bulk water.
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37
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Bresnahan CG, David R, Milet A, Kumar R. Ion Pairing in HCl-Water Clusters: From Electronic Structure Investigations to Multiconfigurational Force-Field Development. J Phys Chem A 2019; 123:9371-9381. [PMID: 31589444 DOI: 10.1021/acs.jpca.9b07775] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the bulk, condensed-phase HCl exists as a dissociated Cl- ion and a proton that is delocalized over solvating water molecules. However, in the gas phase, HCl is covalent, and even on the introduction of hydrating water molecules, the HCl covalent state dominates small clusters and is relevant at larger clusters including 21 water molecules. Electronic structure calculations (at the MP2 level) and ab initio metadynamics simulations (at the DFT level) have been carried out on HCl-(H2O)n clusters with n = 2-22 to investigate distinct solvation environments in clusters from covalent HCl structure, to contact ion pairs and solvent-separated ion pairs. The data were further used to train and validate a multiconfigurational force-field for HCl-water clusters that incorporates covalent HCl states into the MS-EVB3.2 formalism. Additionally, the many-body interaction of the Cl- ion with water and the excess proton was modeled by the introduction of two geometric three-body terms that incorporates the dominant many-body interaction in an efficient noniterative manner.
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Affiliation(s)
- Caitlin G Bresnahan
- Department of Chemistry , 232 Choppin Hall , Louisiana State University , Baton Rouge , Louisiana 70803 , United States
| | - Rolf David
- Department of Chemistry , 232 Choppin Hall , Louisiana State University , Baton Rouge , Louisiana 70803 , United States.,Univ. Grenoble Alpes, CNRS, DCM , 38000 Grenoble , France
| | - Anne Milet
- Univ. Grenoble Alpes, CNRS, DCM , 38000 Grenoble , France
| | - Revati Kumar
- Department of Chemistry , 232 Choppin Hall , Louisiana State University , Baton Rouge , Louisiana 70803 , United States
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38
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Roget SA, Kramer PL, Thomaz JE, Fayer MD. Bulk-like and Interfacial Water Dynamics in Nafion Fuel Cell Membranes Investigated with Ultrafast Nonlinear IR Spectroscopy. J Phys Chem B 2019; 123:9408-9417. [PMID: 31580076 DOI: 10.1021/acs.jpcb.9b07592] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The water confined in the hydrophilic domains of Nafion fuel cell membranes is central to its primary function of ion transport. Water dynamics are intimately linked to proton transfer and are sensitive to the structural features and length scales of confinement. Here, ultrafast polarization-selective pump-probe and two-dimensional infrared vibrational echo (2D IR) experiments were performed on fully hydrated Nafion membranes with sodium counterions to explicate the water dynamics. Like aerosol-OT reverse micelles (AOT RMs), the water dynamics in Nafion are attributed to bulk-like core water in the central region of the hydrophilic domains and much slower interfacial water. Population and orientational dynamics of water in Nafion are slowed by polymer confinement. Comparison of the observed dynamics to those of AOT RMs helps identify local interactions between water and sulfonate anions at the interface and among water molecules in the core. This comparison also demonstrates that the well-known spherical cluster morphology of Nafion is not appropriate. Spectral diffusion of the interfacial water, which arises from structural dynamics, was obtained from the 2D IR experiments taking the core water to have dynamics similar to bulk water. Like the orientational dynamics, spectral diffusion was found to be much slower at the interface compared to bulk water. Together, the dynamics indicate slow reorganization of weakly hydrogen-bonded water molecules at the interface of Nafion. These results provide insights into proton transport mechanisms in fuel cell membranes, and more generally, water dynamics near the interface of confining systems.
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Affiliation(s)
- Sean A Roget
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Patrick L Kramer
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Joseph E Thomaz
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Michael D Fayer
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
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39
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Yu Q, Carpenter WB, Lewis NHC, Tokmakoff A, Bowman JM. High-Level VSCF/VCI Calculations Decode the Vibrational Spectrum of the Aqueous Proton. J Phys Chem B 2019; 123:7214-7224. [PMID: 31361141 DOI: 10.1021/acs.jpcb.9b05723] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The hydrated excess proton is a common species in aqueous chemistry, which complexes with water in a variety of structures. The infrared spectrum of the aqueous proton is particularly sensitive to this array of structures, which manifests as continuous IR absorption from 1000 to 3000 cm-1 known as the "proton continuum". Because of the extreme breadth of the continuum and strong anharmonicity of the involved vibrational modes, this spectrum has eluded straightforward interpretation and simulation. Using protonated water hexamer clusters from reactive molecular dynamics trajectories, and focusing on their central H+(H2O)2 structures' spectral contribution, we reproduce the linear IR spectrum of the aqueous proton with a high-level local monomer quantum method and highly accurate many-body potential energy surface. The accuracy of this approach is first verified in the vibrational spectra of the two isomers of the protonated water hexamer in the gas phase. We then apply this approach to 800 H+(H2O)6 clusters, also written as [H+(H2O)2](H2O)4, drawn from multistate empirical valence bond simulations of the bulk liquid to calculate the infrared spectrum of the aqueous proton complex. Incorporation of anharmonic effects to the vibrational potential and quantum mechanical treatment of the proton produces a better agreement to the infrared spectrum compared to that of the double-harmonic approximation. We assess the correlation of the proton stretching mode with different atomistic coordinates, finding the best correlation with ⟨ROH⟩, the expectation value of the proton-oxygen distance ROH. We also decompose the IR spectrum based on normal mode vibrations and ⟨ROH⟩ to provide insight on how different frequency regions in the continuum report on different configurations, vibrational modes, and mode couplings.
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Affiliation(s)
- Qi Yu
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation , Emory University , Atlanta , Georgia 30322 , United States
| | - William B Carpenter
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Nicholas H C Lewis
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Andrei Tokmakoff
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Joel M Bowman
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation , Emory University , Atlanta , Georgia 30322 , United States
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40
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Sofronov OO, Bakker HJ. Vibrational Relaxation Dynamics of the Core and Outer Part of Proton-Hydration Clusters. J Phys Chem B 2019; 123:6222-6228. [PMID: 31265298 PMCID: PMC6661761 DOI: 10.1021/acs.jpcb.9b02067] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
We study the ultrafast
relaxation dynamics of hydrated proton clusters
in acetonitrile using femtosecond mid-infrared pump-probe spectroscopy.
We observe a strong dependence of transient absorption dynamics on
the frequency of excitation. When we excite the OH vibrations with
frequencies ≤3100 cm–1, we observe an ultrafast
energy relaxation that leads to the heating of the local environment
of the proton. This response is assigned to the OH vibrations of the
water molecules in the core of the hydrated proton cluster. When we
excite with frequencies ≥3200 cm–1, we observe
a relatively slow vibrational relaxation with a T1 time constant ranging from 0.22 ± 0.04 ps at νex = 3200 cm–1 to 0.37 ± 0.02 ps at
νex = 3520 cm–1. We assign this
response to water molecules in the outer part of the hydrated proton
cluster.
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Affiliation(s)
| | - Huib J Bakker
- AMOLF , Science Park 104 , 1098 XG Amsterdam , The Netherlands
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41
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Farrell KM, Zanni MT. Observing Aqueous Proton Transfer Dynamics. ACS CENTRAL SCIENCE 2019; 5:1114-1116. [PMID: 31403065 PMCID: PMC6661868 DOI: 10.1021/acscentsci.9b00603] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
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42
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Yuan R, Napoli JA, Yan C, Marsalek O, Markland TE, Fayer MD. Tracking Aqueous Proton Transfer by Two-Dimensional Infrared Spectroscopy and ab Initio Molecular Dynamics Simulations. ACS CENTRAL SCIENCE 2019; 5:1269-1277. [PMID: 31403075 PMCID: PMC6661862 DOI: 10.1021/acscentsci.9b00447] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2019] [Indexed: 05/26/2023]
Abstract
Proton transfer in water is ubiquitous and a critical elementary event that, via proton hopping between water molecules, enables protons to diffuse much faster than other ions. The problem of the anomalous nature of proton transport in water was first identified by Grotthuss over 200 years ago. In spite of a vast amount of modern research effort, there are still many unanswered questions about proton transport in water. An experimental determination of the proton hopping time has remained elusive due to its ultrafast nature and the lack of direct experimental observables. Here, we use two-dimensional infrared spectroscopy to extract the chemical exchange rates between hydronium and water in acid solutions using a vibrational probe, methyl thiocyanate. Ab initio molecular dynamics (AIMD) simulations demonstrate that the chemical exchange is dominated by proton hopping. The observed experimental and simulated acid concentration dependence then allow us to extrapolate the measured single step proton hopping time to the dilute limit, which, within error, gives the same value as inferred from measurements of the proton mobility and NMR line width analysis. In addition to obtaining the proton hopping time in the dilute limit from direct measurements and AIMD simulations, the results indicate that proton hopping in dilute acid solutions is induced by the concerted multi-water molecule hydrogen bond rearrangement that occurs in pure water. This proposition on the dynamics that drive proton hopping is confirmed by a combination of experimental results from the literature.
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Affiliation(s)
- Rongfeng Yuan
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Joseph A. Napoli
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Chang Yan
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Ondrej Marsalek
- Charles
University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
| | - Thomas E. Markland
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Michael D. Fayer
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
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43
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Carpenter WB, Lewis NHC, Fournier JA, Tokmakoff A. Entropic barriers in the kinetics of aqueous proton transfer. J Chem Phys 2019; 151:034501. [PMID: 31325917 DOI: 10.1063/1.5108907] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Aqueous proton transport is uniquely rapid among aqueous processes, mediated by fluctuating hydrogen bond reorganization in liquid water. In a process known as Grotthuss diffusion, the excess charge diffuses primarily by sequential proton transfers between water molecules rather than standard Brownian motion, which explains the anomalously high electrical conductivity of acidic solutions. Employing ultrafast IR spectroscopy, we use the orientational anisotropy decay of the bending vibrations of the hydrated proton complex to study the picosecond aqueous proton transfer kinetics as a function of temperature, concentration, and counterion. We find that the orientational anisotropy decay exhibits Arrhenius behavior, with an apparent activation energy of 2.4 kcal/mol in 1M and 2M HCl. Interestingly, acidic solutions at high concentration with longer proton transfer time scales display corresponding decreases in activation energy. We interpret this counterintuitive trend by considering the entropic and enthalpic contributions to the activation free energy for proton transfer. Halide counteranions at high concentrations impose entropic barriers to proton transfer in the form of constraints on the solution's collective H-bond fluctuations and obstruction of potential proton transfer pathways. The corresponding proton transfer barrier decreases due to weaker water-halide H-bonds in close proximity to the excess proton, but the entropic effects dominate and result in a net reduction in the proton transfer rate. We estimate the activation free energy for proton transfer as ∼1.0 kcal/mol at 280 K.
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Affiliation(s)
- William B Carpenter
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Nicholas H C Lewis
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Joseph A Fournier
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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44
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Teschke O, de Castro JR, Gomes WE, Soares DM. Hydrated excess protons and their local hydrogen bond transport network as measured by translational, librational, and vibrational frequencies. J Chem Phys 2019; 150:234501. [PMID: 31228923 DOI: 10.1063/1.5098314] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A clear molecular description of excess hydrated protons and their local hydrogen bond transport network remains elusive. Here, the hydrogen bond network of excess hydrated protons in water bridges was probed by measuring their Raman spectra and comparing them to the spectra of protons in ice and water. The proton vibrational spectrum and the hydrogen bond network translational and librational spectra were recorded. The spectra of the water bridge and water exhibit clear differences, indicating the presence of a structure in water bridges when subjected to an electric field of ∼106 V/m that has not been previously reported. The intermolecular Raman spectrum of the floating water bridge exhibits a hydrogen bond stretching band at 150-250 cm-1, librational bands within the 300-1000 cm-1 spectral range, and a large band at 1500-3000 cm-1, which corresponds to the vibrational signature of excess hydrated protons in the water bridge structure. The excess protons are shown to move predominantly at the air/water interface, and the effect of this distribution is a measurable change in the air/water interfacial tension from ∼80 to ∼32 N/m. Therefore, hydrated protons must have a unique water arrangement that enables them to propagate without sinking into bulk water. This local polarized hydrogen bond network in the interfacial water region is characterized by a translational spectrum similar to that of ice V.
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Affiliation(s)
- Omar Teschke
- Laboratório de Nanoestruturas e Interfaces, Instituto de Física, UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Jose Roberto de Castro
- Laboratório de Nanoestruturas e Interfaces, Instituto de Física, UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Wyllerson Evaristo Gomes
- Pontificia Universidade Catolica de Campinas, Faculdade de Quimica, 13012-970 Campinas, SP, Brazil
| | - David Mendez Soares
- Laboratório de Nanoestruturas e Interfaces, Instituto de Física, UNICAMP, 13083-859 Campinas, SP, Brazil
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Fischer SA, Gunlycke D. Analysis of Correlated Dynamics in the Grotthuss Mechanism of Proton Diffusion. J Phys Chem B 2019; 123:5536-5544. [DOI: 10.1021/acs.jpcb.9b02610] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Sean A. Fischer
- Chemistry Division, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Daniel Gunlycke
- Chemistry Division, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States
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Thaunay F, Calvo F, Nicol E, Ohanessian G, Clavaguéra C. Infrared Spectra of Deprotonated Dicarboxylic Acids: IRMPD Spectroscopy and Empirical Valence‐Bond Modeling. Chemphyschem 2019; 20:803-814. [PMID: 30695125 DOI: 10.1002/cphc.201800947] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 01/28/2019] [Indexed: 01/08/2023]
Abstract
Experimental infrared multiple-photon dissociation (IRMPD) spectra recorded for a series of deprotonated dicarboxylic acids, HO2 (CH2 )n CO 2 - (n=2-4), are interpreted using a variety of computational methods. The broad bands centered near 1600 cm-1 can be reproduced neither by static vibrational calculations based on quantum chemistry nor by a dynamical description of individual structures using the many-body polarizable AMOEBA force field, strongly suggesting that these molecules experience dynamical proton sharing between the two carboxylic ends. To confirm this assumption, AMOEBA was combined with a two-state empirical valence-bond (EVB) model to allow for proton transfer in classical molecular dynamics simulations. Upon suitable parametrization based on ab initio reference data, the EVB-AMOEBA model satisfactorily reproduces the experimental infrared spectra, and the finite temperature dynamics reveals a significant amount of proton sharing in such systems.
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Affiliation(s)
| | - Florent Calvo
- LIPhyUniversité Grenoble Alpes, CNRS, LiPhy 38000 Grenoble France
| | - Edith Nicol
- LCM, CNRSEcole Polytechnique 91128 Palaiseau Cedex France
| | | | - Carine Clavaguéra
- Laboratoire de Chimie PhysiqueCNRS – Université Paris Sud, Université Paris-Saclay 15 avenue Jean Perrin 91405 Orsay Cedex France
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McDonnell MT, Keffer DJ. Reactive molecular dynamics simulations of an excess proton in polyethylene glycol-water solutions. MOLECULAR SIMULATION 2018. [DOI: 10.1080/08927022.2018.1557328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
| | - David J. Keffer
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA
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Chen C, Arntsen C, Voth GA. Development of reactive force fields using ab initio molecular dynamics simulation minimally biased to experimental data. J Chem Phys 2018; 147:161719. [PMID: 29096465 DOI: 10.1063/1.4985903] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Incorporation of quantum mechanical electronic structure data is necessary to properly capture the physics of many chemical processes. Proton hopping in water, which involves rearrangement of chemical and hydrogen bonds, is one such example of an inherently quantum mechanical process. Standard ab initio molecular dynamics (AIMD) methods, however, do not yet accurately predict the structure of water and are therefore less than optimal for developing force fields. We have instead utilized a recently developed method which minimally biases AIMD simulations to match limited experimental data to develop novel multiscale reactive molecular dynamics (MS-RMD) force fields by using relative entropy minimization. In this paper, we present two new MS-RMD models using such a parameterization: one which employs water with harmonic internal vibrations and another which uses anharmonic water. We show that the newly developed MS-RMD models very closely reproduce the solvation structure of the hydrated excess proton in the target AIMD data. We also find that the use of anharmonic water increases proton hopping, thereby increasing the proton diffusion constant.
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Affiliation(s)
- Chen Chen
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Christopher Arntsen
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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Biswas R, Carpenter W, Fournier JA, Voth GA, Tokmakoff A. IR spectral assignments for the hydrated excess proton in liquid water. J Chem Phys 2018; 146:154507. [PMID: 28433032 DOI: 10.1063/1.4980121] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The local environmental sensitivity of infrared (IR) spectroscopy to a hydrogen-bonding structure makes it a powerful tool for investigating the structure and dynamics of excess protons in water. Although of significant interest, the line broadening that results from the ultrafast evolution of different solvated proton-water structures makes the assignment of liquid-phase IR spectra a challenging task. In this work, we apply a normal mode analysis using density functional theory of thousands of proton-water clusters taken from reactive molecular dynamics trajectories of the latest generation multistate empirical valence bond proton model (MS-EVB 3.2). These calculations are used to obtain a vibrational density of states and IR spectral density, which are decomposed on the basis of solvated proton structure and the frequency dependent mode character. Decompositions are presented on the basis of the proton sharing parameter δ, often used to distinguish Eigen and Zundel species, the stretch and bend character of the modes, the mode delocalization, and the vibrational mode symmetry. We find there is a wide distribution of vibrational frequencies spanning 1200-3000 cm-1 for every local proton configuration, with the region 2000-2600 cm-1 being mostly governed by the distorted Eigen-like configuration. We find a continuous red shift of the special-pair O⋯H+⋯O stretching frequency, and an increase in the flanking water bending intensity with decreasing δ. Also, we find that the flanking water stretch mode of the Zundel-like species is strongly mixed with the flanking water bend, and the special pair proton oscillation band is strongly coupled with the bend modes of the central H5O2+moiety.
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Affiliation(s)
- Rajib Biswas
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - William Carpenter
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Joseph A Fournier
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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Carpenter WB, Fournier JA, Lewis NHC, Tokmakoff A. Picosecond Proton Transfer Kinetics in Water Revealed with Ultrafast IR Spectroscopy. J Phys Chem B 2018; 122:2792-2802. [PMID: 29452488 DOI: 10.1021/acs.jpcb.8b00118] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Aqueous proton transport involves the ultrafast interconversion of hydrated proton species that are closely linked to the hydrogen bond dynamics of water, which has been a long-standing challenge to experiments. In this study, we use ultrafast IR spectroscopy to investigate the distinct vibrational transition centered at 1750 cm-1 in strong acid solutions, which arises from bending vibrations of the hydrated proton complex. Broadband ultrafast two-dimensional IR spectroscopy and transient absorption are used to measure vibrational relaxation, spectral diffusion, and orientational relaxation dynamics. The hydrated proton bend displays fast vibrational relaxation and spectral diffusion timescales of 200-300 fs; however, the transient absorption anisotropy decays on a remarkably long 2.5 ps timescale, which matches the timescale for hydrogen bond reorganization in liquid water. These observations are indications that the bending vibration of the aqueous proton complex is relatively localized, with an orientation that is insensitive to fast hydrogen bonding fluctuations and dependent on collective structural relaxation of the liquid to reorient. We conclude that the orientational relaxation is a result of proton transfer between configurations that are well described by a Zundel-like proton shared between two flanking water molecules.
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Affiliation(s)
- William B Carpenter
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Joseph A Fournier
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Nicholas H C Lewis
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
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