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Zhu X, Iyengar SS. Graph Theoretic Molecular Fragmentation for Multidimensional Potential Energy Surfaces Yield an Adaptive and General Transfer Machine Learning Protocol. J Chem Theory Comput 2022; 18:5125-5144. [PMID: 35994592 DOI: 10.1021/acs.jctc.1c01241] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Over a series of publications we have introduced a graph-theoretic description for molecular fragmentation. Here, a system is divided into a set of nodes, or vertices, that are then connected through edges, faces, and higher-order simplexes to represent a collection of spatially overlapping and locally interacting subsystems. Each such subsystem is treated at two levels of electronic structure theory, and the result is used to construct many-body expansions that are then embedded within an ONIOM-scheme. These expansions converge rapidly with many-body order (or graphical rank) of subsystems and have been previously used for ab initio molecular dynamics (AIMD) calculations and for computing multidimensional potential energy surfaces. Specifically, in all these cases we have shown that CCSD and MP2 level AIMD trajectories and potential surfaces may be obtained at density functional theory cost. The approach has been demonstrated for gas-phase studies, for condensed phase electronic structure, and also for basis set extrapolation-based AIMD. Recently, this approach has also been used to derive new quantum-computing algorithms that enormously reduce the quantum circuit depth in a circuit-based computation of correlated electronic structure. In this publication, we introduce (a) a family of neural networks that act in parallel to represent, efficiently, the post-Hartree-Fock electronic structure energy contributions for all simplexes (fragments), and (b) a new k-means-based tessellation strategy to glean training data for high-dimensional molecular spaces and minimize the extent of training needed to construct this family of neural networks. The approach is particularly useful when coupled cluster accuracy is desired and when fragment sizes grow in order to capture nonlocal interactions accurately. The unique multidimensional k-means tessellation/clustering algorithm used to determine our training data for all fragments is shown to be extremely efficient and reduces the needed training to only 10% of data for all fragments to obtain accurate neural networks for each fragment. These fully connected dense neural networks are then used to extrapolate the potential energy surface for all molecular fragments, and these are then combined as per our graph-theoretic procedure to transfer the learning process to a full system energy for the entire AIMD trajectory at less than one-tenth the cost as compared to a regular fragmentation-based AIMD calculation.
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Affiliation(s)
- Xiao Zhu
- Department of Chemistry and Department of Physics, Indiana University, 800 E. Kirkwood Avenue, Bloomington 47405, Indiana, United States
| | - Srinivasan S Iyengar
- Department of Chemistry and Department of Physics, Indiana University, 800 E. Kirkwood Avenue, Bloomington 47405, Indiana, United States
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2
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Omodemi O, Kaledin M, Kaledin AL. Permutationally invariant polynomial representation of polarizability tensor surfaces for linear regression analysis. J Comput Chem 2022; 43:1495-1503. [PMID: 35737590 DOI: 10.1002/jcc.26952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Accepted: 06/09/2022] [Indexed: 11/07/2022]
Abstract
A linearly parameterized functional form for a Cartesian representation of molecular dipole polarizability tensor surfaces (PTS) is described. The proposed expression for the PTS is a linearization of the recently reported power series ansatz of the original Applequist model, which by construction is non-linear in parameter space. This new approach possesses (i) a unique solution to the least-squares fitting problem; (ii) a low level of the computational complexity of the resulting linear regression procedure, comparable to those of the potential energy and dipole moment surfaces; and (iii) a competitive level of accuracy compared to the non-linear PTS model. Calculations of CH4 PTS, with polarizabilities fitted to 9000 training set points with the energies up to 14,000 cm-1 show an impressive level of accuracy of the linear PTS model obtained with ~1600 parameters: ~1% versus 0.3% RMSE for the non-linear vs. linear model on a test set of 1000 configurations.
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Affiliation(s)
- Oluwaseun Omodemi
- Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, Georgia, USA
| | - Martina Kaledin
- Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, Georgia, USA
| | - Alexey L Kaledin
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia, USA
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3
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Boutwell D, Pierre-Jacques D, Cochran O, Dyke J, Salazar D, Tyler C, Kaledin M. Intramolecular Proton Transfer in the Hydrogen Oxalate Anion and the Cooperativity Effects of the Low-Frequency Vibrations: A Driven Molecular Dynamics Study. J Phys Chem A 2022; 126:583-592. [PMID: 35049313 DOI: 10.1021/acs.jpca.1c09686] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report first-principles molecular dynamics (MD) and dipole-driven molecular dynamics (μ-DMD) simulations of the hydrogen oxalate anion at the MP2/aug-cc-pVDZ level of theory. We examine the role of vibrational coupling between the OH stretching bands, that is, the fundamental and a few combination bands spanning the 2900-3100 cm-1 range, and several of the low-frequency bending and stretching fundamental modes. The low-frequency modes between 300 and 825 cm-1 play a crucial role in the proton-transfer motion. Strong involvement of CO2 and CCO bending and the CC stretching vibrations indicate that these large amplitude motions cause the shortening of the O···O distance and thus promote H+ transfer to the other oxygen by bringing it over the 3.4 kcal/mol barrier. Analysis of resonant μ-DMD trajectories shows that the complex spectral feature near 825 cm-1, closely corresponding to both an overtone of two quanta of 425 cm-1 and a combination band of low-frequency CO2 rocking (300 cm-1) and CCO bending (575 cm-1) modes, is involved in the proton transfer. μ-DMD shows that exciting the system at these mode combinations leads to faster barrier activation than exciting at the OH fundamental mode.
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Affiliation(s)
- Dalton Boutwell
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Dominick Pierre-Jacques
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Olivia Cochran
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Jason Dyke
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Dayana Salazar
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Ciara Tyler
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Martina Kaledin
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
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4
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Hanson MD, Readnour JA, Hassanali AA, Corcelli SA. Coupled Local-Mode Approach for the Calculation of Vibrational Spectra: Application to Protonated Water Clusters. J Phys Chem Lett 2021; 12:9226-9232. [PMID: 34529914 DOI: 10.1021/acs.jpclett.1c02254] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Spectroscopic studies of protonated water clusters (PWCs) have yielded enormous insights into the fundamental nature of the hydrated proton. Here, we introduce a new coupled local-mode (CLM) approach to calculate PWC OH stretch vibrational spectra. The CLM method combines a sampling of representative configurations from density functional theory (DFT)-based ab initio molecular dynamics (AIMD) simulations with DFT calculations of local-mode vibrational frequencies and couplings. Calculations of inhomogeneous OH stretch vibrational spectra for H+(H2O)4 and H+(H2O)21 agree well with experiment and higher-level calculations, and decompositions of the calculated spectra in terms of the coupled modes aids in the interpretation of the spectra. This observation is consistent with the idea that capturing anharmonicity and coupling is as important to accuracy as the underlying level of electronic structure theory. The CLM calculations can easily discern the configuration that dominates the experimental measurement for H+(H2O)5, which can adopt several low-energy conformations.
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Affiliation(s)
- Matthew D Hanson
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Janel A Readnour
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Ali A Hassanali
- Condensed Matter and Statistical Physics, International Centre for Theoretical Physics, Strada Costiera, 11 I - 34151 Trieste, Italy
| | - Steven A Corcelli
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
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5
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Pierre-Jacques D, Tyler C, Dyke J, Kaledin AL, Kaledin M. A polarizability driven ab initio molecular dynamics approach to stimulating Raman activity: Application to C20. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1939453] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
| | - Ciara Tyler
- Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, GA, USA
| | - Jason Dyke
- Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, GA, USA
| | - Alexey L. Kaledin
- Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, GA, USA
| | - Martina Kaledin
- Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, GA, USA
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6
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Zeng HJ, Johnson MA. Demystifying the Diffuse Vibrational Spectrum of Aqueous Protons Through Cold Cluster Spectroscopy. Annu Rev Phys Chem 2021; 72:667-691. [PMID: 33646816 DOI: 10.1146/annurev-physchem-061020-053456] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The ease with which the pH is routinely determined for aqueous solutions masks the fact that the cationic product of Arrhenius acid dissolution, the hydrated proton, or H+(aq), is a remarkably complex species. Here, we review how results obtained over the past 30 years in the study of H+⋅(H2O)n cluster ions isolated in the gas phase shed light on the chemical nature of H+(aq). This effort has also revealed molecular-level aspects of the Grotthuss relay mechanism for positive-charge translocation in water. Recently developed methods involving cryogenic cooling in radiofrequency ion traps and the application of two-color, infrared-infrared (IR-IR) double-resonance spectroscopy have established a clear picture of how local hydrogen-bond topology drives the diverse spectral signatures of the excess proton. This information now enables a new generation of cluster studies designed to unravel the microscopic mechanics underlying the ultrafast relaxation dynamics displayed by H+(aq).
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Affiliation(s)
- Helen J Zeng
- Sterling Chemistry Laboratory, Yale University, New Haven, Connecticut 06520, USA;
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, New Haven, Connecticut 06520, USA;
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7
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Parneix P, Maupin R, Attal L, Calvo F, Falvo C. Extracting vibrational anharmonicities from short driven molecular dynamics trajectories. Theor Chem Acc 2021. [DOI: 10.1007/s00214-021-02740-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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8
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Kumar R, Kumar A, Srivastava AK, Misra N. Ab initio investigations on the interaction of CO2 and non-metallic superalkalis: structure, stability and electronic properties. Mol Phys 2020. [DOI: 10.1080/00268976.2020.1841311] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Ratnesh Kumar
- Department of Physics, University of Lucknow, Lucknow, India
| | - Abhishek Kumar
- Department of Physics, University of Lucknow, Lucknow, India
| | | | - Neeraj Misra
- Department of Physics, University of Lucknow, Lucknow, India
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9
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Boutwell D, Okere O, Omodemi O, Toledo A, Barrios A, Olocha M, Kaledin M. Analysis of the Proton Transfer Bands in the Infrared Spectra of Linear N 2H +···OC and N 2D +···OC Complexes Using Electric Field-Driven Classical Trajectories. J Phys Chem A 2020; 124:7549-7558. [PMID: 32808782 DOI: 10.1021/acs.jpca.0c06756] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this work, we describe ab initio calculations and assignment of infrared (IR) spectra of hydrogen-bonded ion-molecular complexes that involve a fluxional proton: the linear N2H+···OC and N2D+···OC complexes. Given the challenges of describing fluxional proton dynamics and especially its IR activity, we use electric field-driven classical trajectories, i.e., the driven molecular dynamics (DMD) method that was developed by us in recent years and for similar applications, in conjunction with high-level electronic structure theory. Namely, we present a modified and a numerically efficient implementation of DMD specifically for direct (or "on the fly") calculations, which we carry out at the MP2-F12/AVDZ level of theory for the potential energy surface (PES) and MP2/AVDZ for the dipole moment surfaces (DMSs). Detailed analysis of the PES, DMS, and the time-dependence of the first derivative of the DMS, referred to as the driving force, for the highly fluxional vibrations involving H+/D+ revealed that the strongly non-harmonic PES and non-linear DMS yield remarkably complex vibrational spectra. Interestingly, the classical trajectories reveal a doublet in the proton transfer part of the spectrum with the two peaks at 1800 and 1980 cm-1. We find that their shared intensity is due to a Fermi-like resonance interaction, within the classical limit, of the H+ parallel stretch fundamental and an H+ perpendicular bending overtone. This doublet is also observed in the deuterated species at 1360 and 1460 cm-1.
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Affiliation(s)
- Dalton Boutwell
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Onyinye Okere
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Oluwaseun Omodemi
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Alexander Toledo
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Antonio Barrios
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Monique Olocha
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
| | - Martina Kaledin
- Department of Chemistry & Biochemistry, Kennesaw State University, 370 Paulding Ave NW, Box # 1203, Kennesaw, Georgia 30144, United States
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10
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Bertaina G, Di Liberto G, Ceotto M. Reduced rovibrational coupling Cartesian dynamics for semiclassical calculations: Application to the spectrum of the Zundel cation. J Chem Phys 2019; 151:114307. [PMID: 31542046 DOI: 10.1063/1.5114616] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study the vibrational spectrum of the protonated water dimer, by means of a divide-and-conquer semiclassical initial value representation of the quantum propagator, as a first step in the study of larger protonated water clusters. We use the potential energy surface from the work of Huang et al. [J. Chem. Phys. 122, 044308 (2005)]. To tackle such an anharmonic and floppy molecule, we employ fully Cartesian dynamics and carefully reduce the coupling to global rotations in the definition of normal modes. We apply the time-averaging filter and obtain clean power spectra relative to suitable reference states that highlight the spectral peaks corresponding to the fundamental excitations of the system. Our trajectory-based approach allows for the physical interpretation of the very challenging proton transfer modes. We find that it is important, for such a floppy molecule, to selectively avoid initially exciting lower energy modes, in order to obtain cleaner spectra. The estimated vibrational energies display a mean absolute error (MAE) of ∼29 cm-1 with respect to available multiconfiguration time-dependent Hartree calculations and MAE ∼ 14 cm-1 when compared to the optically active experimental excitations of the Ne-tagged Zundel cation. The reasonable scaling in the number of trajectories for Monte Carlo convergence is promising for applications to higher dimensional protonated cluster systems.
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Affiliation(s)
- G Bertaina
- Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133 Milano, Italy
| | - G Di Liberto
- Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133 Milano, Italy
| | - M Ceotto
- Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133 Milano, Italy
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11
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Hooper R, Boutwell D, Kaledin M. Assignment of Infrared-Active Combination Bands in the Vibrational Spectra of Protonated Molecular Clusters Using Driven Classical Trajectories: Application to N 4H + and N 4D . J Phys Chem A 2019; 123:5613-5620. [PMID: 31244119 DOI: 10.1021/acs.jpca.9b04480] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We investigate the utility of the driven molecular dynamics (DMD) approach to complex molecular vibrations by applying it to linear clusters with several degenerate vibrational modes and infrared (IR) intense combination bands. Here, the prominent features in N4H+ and N4D+ IR spectra, reported and described by others previously, have been characterized for the first time by DMD using recently published high-level potential and dipole moment surfaces. Namely, the calculations closely correlate the parallel proton stretch vibration in N4H+, at 750 cm-1, with the one observed experimentally at 743 cm-1. Second, the intense IR-active combination bands found in experimental spectra within 900-1100 cm-1 have been properly recovered by DMD at 950 cm-1 as strongly IR-active and confirmed as consisting of H+ asymmetric stretch and N2···N2 intermolecular symmetric stretch modes. Furthermore, we show that certain combination bands involving overtone transitions may be recovered by DMD using a hard-driving regime, such as the 1409 cm-1 band measured in N4H+, revealed by DMD at 1375 cm-1, and assigned to a progressive combination of the parallel H+ stretch and two quanta of N2···N2 stretch, in agreement with quantum mechanical studies reported previously by others.
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Affiliation(s)
- Reagan Hooper
- Department of Chemistry & Biochemistry , Kennesaw State University , 370 Paulding Avenue NW , Box # 1203, Kennesaw , Georgia 30144 , Unites States
| | - Dalton Boutwell
- Department of Chemistry & Biochemistry , Kennesaw State University , 370 Paulding Avenue NW , Box # 1203, Kennesaw , Georgia 30144 , Unites States
| | - Martina Kaledin
- Department of Chemistry & Biochemistry , Kennesaw State University , 370 Paulding Avenue NW , Box # 1203, Kennesaw , Georgia 30144 , Unites States
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12
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Quantum structural fluctuations of protonated water clusters (H2O) H+ (n = 1 − 4) studied by variational molecular dynamics method. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.03.170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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13
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Zeng HJ, Yang N, Johnson MA. Introductory lecture: advances in ion spectroscopy: from astrophysics to biology. Faraday Discuss 2019; 217:8-33. [PMID: 31094388 DOI: 10.1039/c9fd00030e] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This introduction provides a historical context for the development of ion spectroscopy over the past half century by following the evolution of experimental methods to the present state-of-the-art. Rather than attempt a comprehensive review, we focus on how early work on small ions, carried out with fluorescence, direct absorption, and photoelectron spectroscopy, evolved into powerful technologies that can now address complex chemical problems ranging from catalysis to biophysics. One of these developments is the incorporation of cooling and temperature control to enable the general application of "messenger tagging" vibrational spectroscopy, first carried out using ionized supersonic jets and then with buffer gas cooling in radiofrequency ion traps. Some key advances in the application of time-resolved pump-probe techniques to follow ultrafast dynamics are also discussed, as are significant benchmarks in the refinement of ion mobility to allow spectroscopic investigation of large biopolymers with well-defined shapes. We close with a few remarks on challenges and opportunities to explore molecular level mechanics that drive macroscopic behavior.
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Affiliation(s)
- Helen J Zeng
- Sterling Chemistry Laboratory, Yale University, New Haven, CT 06520, USA.
| | - Nan Yang
- Sterling Chemistry Laboratory, Yale University, New Haven, CT 06520, USA.
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, New Haven, CT 06520, USA.
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14
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Napoli JA, Marsalek O, Markland TE. Decoding the spectroscopic features and time scales of aqueous proton defects. J Chem Phys 2018; 148:222833. [PMID: 29907063 DOI: 10.1063/1.5023704] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Acid solutions exhibit a variety of complex structural and dynamical features arising from the presence of multiple interacting reactive proton defects and counterions. However, disentangling the transient structural motifs of proton defects in the water hydrogen bond network and the mechanisms for their interconversion remains a formidable challenge. Here, we use simulations treating the quantum nature of both the electrons and nuclei to show how the experimentally observed spectroscopic features and relaxation time scales can be elucidated using a physically transparent coordinate that encodes the overall asymmetry of the solvation environment of the proton defect. We demonstrate that this coordinate can be used both to discriminate the extremities of the features observed in the linear vibrational spectrum and to explain the molecular motions that give rise to the interconversion time scales observed in recent nonlinear experiments. This analysis provides a unified condensed-phase picture of the proton structure and dynamics that, at its extrema, encompasses proton sharing and spectroscopic features resembling the limiting Eigen [H3O(H2O)3]+ and Zundel [H(H2O)2]+ gas-phase structures, while also describing the rich variety of interconverting environments in the liquid phase.
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Affiliation(s)
- Joseph A Napoli
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
| | - Ondrej Marsalek
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
| | - Thomas E Markland
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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15
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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: 8.5] [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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16
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Esser TK, Knorke H, Asmis KR, Schöllkopf W, Yu Q, Qu C, Bowman JM, Kaledin M. Deconstructing Prominent Bands in the Terahertz Spectra of H 7O 3+ and H 9O 4+: Intermolecular Modes in Eigen Clusters. J Phys Chem Lett 2018; 9:798-803. [PMID: 29360366 DOI: 10.1021/acs.jpclett.7b03395] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report experimental vibrational action spectra (210-2200 cm-1) and calculated IR spectra, using recent ab initio potential energy and dipole moment surfaces, of H7O3+ and H9O4+. We focus on prominent far-IR bands, which postharmonic analyses show, arise from two types of intermolecular motions, i.e., hydrogen bond stretching and terminal water wagging modes, that are similar in both clusters. The good agreement between experiment and theory further validates the accuracy of the potential and dipole moment surfaces, which was used in a recent theoretical study that concluded that infrared photodissociation spectra of the cold clusters correspond to the Eigen isomer. The comparison between theory and experiment adds further confirmation of the need of postharmonic analysis for these clusters.
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Affiliation(s)
- Tim K Esser
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig , Linnéstraße 2, 04103 Leipzig, Germany
| | - Harald Knorke
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig , Linnéstraße 2, 04103 Leipzig, Germany
| | - Knut R Asmis
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig , Linnéstraße 2, 04103 Leipzig, Germany
| | - Wieland Schöllkopf
- Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6, D-14195 Berlin, Germany
| | - Qi Yu
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States
| | - Chen Qu
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States
| | - Joel M Bowman
- Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University , Atlanta, Georgia 30322, United States
| | - Martina Kaledin
- Department of Chemistry and Biochemistry, Kennesaw State University , Kennesaw, Georgia 30144, United States
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17
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Vener MV, Chernyshov IY, Rykounov AA, Filarowski A. Structural and spectroscopic features of proton hydrates in the crystalline state. Solid-state DFT study on HCl and triflic acid hydrates. Mol Phys 2017. [DOI: 10.1080/00268976.2017.1380860] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- M. V. Vener
- Quantum Chemistry Department, Mendeleev University of Chemical Technology, Moscow, Russia
- Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - I. Yu. Chernyshov
- Quantum Chemistry Department, Mendeleev University of Chemical Technology, Moscow, Russia
- Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - A. A. Rykounov
- Theoretical Department, Russian Federal Nuclear Center – All-Russian Research Institute of Technical Physics (RFNC-VNIITF), Snezhinsk, Russia
| | - A. Filarowski
- Faculty of Chemistry, University of Wrocław, Wrocław, Poland
- Department of Physics, Industrial University of Tyumen, Tyumen, Russia
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18
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Pitsevich G, Malevich A, Kozlovskaya E, Shalamberidze E, Doroshenko I, Pogorelov V, Mahnach E, Sapeshko V, Balevicius V. MP4 study of the multimode coupling in protonated water dimer. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.03.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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19
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McDonald DC, Mauney DT, Leicht D, Marks JH, Tan JA, Kuo JL, Duncan MA. Communication: Trapping a proton in argon: Spectroscopy and theory of the proton-bound argon dimer and its solvation. J Chem Phys 2017; 145:231101. [PMID: 28010076 DOI: 10.1063/1.4972581] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ion-molecule complexes of the form H+Arn are produced in pulsed-discharge supersonic expansions containing hydrogen and argon. These ions are analyzed and mass-selected in a reflectron spectrometer and studied with infrared laser photodissociation spectroscopy. Infrared spectra for the n = 3-7 complexes are characterized by a series of strong bands in the 900-2200 cm-1 region. Computational studies at the MP2/aug-cc-pVTZ level examine the structures, binding energies, and infrared spectra for these systems. The core ion responsible for the infrared bands is the proton-bound argon dimer, Ar-H+-Ar, which is progressively solvated by the excess argon. Anharmonic vibrational theory is able to reproduce the vibrational structure, identifying it as arising from the asymmetric proton stretch in combination with multiple quanta of the symmetric argon stretch. Successive addition of argon shifts the proton vibration to lower frequencies, as the charge is delocalized over more ligands. The Ar-H+-Ar core ion has a first solvation sphere of five argons.
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Affiliation(s)
- D C McDonald
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - D T Mauney
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - D Leicht
- Lehrstuhl für Physikalische Chemie II, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - J H Marks
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - J A Tan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617, People's Republic of China
| | - J-L Kuo
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617, People's Republic of China
| | - M A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
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20
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Haycraft C, Li J, Iyengar SS. Efficient, “On-the-Fly”, Born–Oppenheimer and Car–Parrinello-type Dynamics with Coupled Cluster Accuracy through Fragment Based Electronic Structure. J Chem Theory Comput 2017; 13:1887-1901. [DOI: 10.1021/acs.jctc.6b01107] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Cody Haycraft
- Department of Chemistry and
Department of Physics, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Junjie Li
- Department of Chemistry and
Department of Physics, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Srinivasan S. Iyengar
- Department of Chemistry and
Department of Physics, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
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21
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Pitsevich G, Malevich A, Kozlovskaya E, Mahnach E, Doroshenko I, Pogorelov V, Pettersson LGM, Sablinskas V, Balevicius V. MP4 Study of the Anharmonic Coupling of the Shared Proton Stretching Vibration of the Protonated Water Dimer in Equilibrium and Transition States. J Phys Chem A 2017; 121:2151-2165. [PMID: 28187260 DOI: 10.1021/acs.jpca.7b00536] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structure and harmonic and anharmonic IR spectra of the protonated water dimer (PWD) were calculated in C1, C2, and Cs symmetry at the MP4/acc-pVTZ level of theory. We found that structure and IR spectra are practically identical in C2 and C1 symmetry, demonstrating that an equilibrium C1 configuration of the PWD is not realized. Anharmonic coupling of the shared proton stretching vibration with all other modes in the PWD in C2 and Cs symmetry was the focus of this investigation. For this purpose, 28 two-dimensional potential energy surfaces (2D PES) were built at the MP4/acc-pVTZ level of theory and the corresponding vibrational Schrödinger equations were solved using the DVR method. Differences in the coupling of the investigated mode with other modes in the C2 and Cs configurations, along with some factors that determine the red- or blue-shift of the stretching vibration frequency, were analyzed. We obtained a rather reasonable value of the stretching frequency of the bridging proton (1058.4 cm-1) unperturbed by Fermi resonance. The Fermi resonance between the fundamental vibration ν7 and the combined vibration ν2 + ν6 of the same symmetry was analyzed through anharmonic second-order perturbation theory calculations, as well as by 3D PES constructed using Q2, Q6, and Q7 as normal coordinates. A significant (up to 50%) transfer of intensity from the fundamental vibration to the combined one was found. We have estimated the frequency of the bridging proton stretching vibration in the Cs configuration of the PWD based on calculations of the intrinsic anharmonicity and anharmonic double modes interactions at the MP4/acc-pVTZ level of theory (1261 cm-1).
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Affiliation(s)
- G Pitsevich
- Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus
| | - A Malevich
- Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus
| | - E Kozlovskaya
- Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus
| | - E Mahnach
- Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus
| | - I Doroshenko
- Taras Shevchenko National University of Kyiv , Volodymyrska str., 64\13, 01601, Kyiv, Ukraine
| | - V Pogorelov
- Taras Shevchenko National University of Kyiv , Volodymyrska str., 64\13, 01601, Kyiv, Ukraine
| | - Lars G M Pettersson
- Department of Physics, AlbaNova University Center, Stockholm University , S-106 91 Stockholm, Sweden
| | - V Sablinskas
- Faculty of Physics, Vilnius University , Sauletekio al. 9-3, LT-10222 Vilnius, Lithuania
| | - V Balevicius
- Faculty of Physics, Vilnius University , Sauletekio al. 9-3, LT-10222 Vilnius, Lithuania
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22
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Molčanov K, Jelsch C, Wenger E, Stare J, Madsen AØ, Kojić-Prodić B. Experimental evidence of a 3-centre, 2-electron covalent bond character of the central O–H–O fragment on the Zundel cation in crystals of Zundel nitranilate tetrahydrate. CrystEngComm 2017. [DOI: 10.1039/c7ce00501f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Charge density of the Zundel cation in the solid state reveals a covalent nature of its central O–H–O fragment.
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Affiliation(s)
| | - Christian Jelsch
- Cristallographie
- Résonance Magnétique et Modélisations CNRS
- UMR 7036
- Institut Jean Barriol
- CNRS and Université de Lorraine BP 70239
| | - Emmanuel Wenger
- Cristallographie
- Résonance Magnétique et Modélisations CNRS
- UMR 7036
- Institut Jean Barriol
- CNRS and Université de Lorraine BP 70239
| | - Jernej Stare
- National Institute of Chemistry
- Hajdrihova 19
- SI-1000 Ljubljana
- Slovenia
| | - Anders Ø. Madsen
- Department of Pharmacy
- University of Copenhagen
- 2100 København
- Denmark
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23
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Li J, Haycraft C, Iyengar SS. Hybrid Extended Lagrangian, Post-Hartree–Fock Born–Oppenheimer ab Initio Molecular Dynamics Using Fragment-Based Electronic Structure. J Chem Theory Comput 2016; 12:2493-508. [DOI: 10.1021/acs.jctc.6b00001] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Junjie Li
- Department of Chemistry and
Department of Physics, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405, United States
| | - Cody Haycraft
- Department of Chemistry and
Department of Physics, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405, United States
| | - Srinivasan S. Iyengar
- Department of Chemistry and
Department of Physics, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405, United States
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24
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Theoretical Modeling of Vibrational Spectra and Proton Tunneling in Hydrogen-Bonded Systems. ADVANCES IN CHEMICAL PHYSICS 2016. [DOI: 10.1002/9781119165156.ch6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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25
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Kaledin M, Wood CA. Ab Initio Studies of Structural and Vibrational Properties of Protonated Water Cluster H7O3(+) and Its Deuterium Isotopologues: An Application of Driven Molecular Dynamics. J Chem Theory Comput 2015; 6:2525-35. [PMID: 26613504 DOI: 10.1021/ct100122s] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In this work, we present infrared (IR) spectra of H7O3(+) and its deuterium isotopomers calculated by direct molecular dynamics (MD) simulations at the B3LYP/6-31+G** computational level. The calculated spectra obtained at 100, 300, and 500 K were compared to available experimental observations, and spectral features were assigned using normal-mode analysis (NMA) and driven molecular dynamics (DMD). Spectral peaks at 2410 and 2540 cm(-1) were assigned to asymmetric and symmetric stretches of the bridging hydrogen (BH) using NMA. The weak spectral features at 2166 and 2275 cm(-1) were assigned to a combination band of BH asymmetric stretch, H2O in phase wagging, OO stretch, and H3O(+) rocking vibrations by DMD simulations. Our observation of BH stretch vibrations as low as 2166 cm(-1) is in good agreement with the assignment of the low-resolution spectrum obtained by Schwarz at 2200-2300 cm(-1) [Schwarz, H. A. J. Chem. Phys. 1977, 67, 5525-5534] and vibrational predissociation spectrum by Lee et al. ∼2300 cm(-1) [Okumura, M.; Yeh, L. I.; Myers, J. D.; Lee, Y. T. J. Chem. Phys. 1990, 94, 3416-3427].
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Affiliation(s)
- Martina Kaledin
- Chemistry and Biochemistry, Kennesaw State University, 1000 Chastain Road, Box 1203, Kennesaw, Georgia 30144
| | - Christopher A Wood
- Chemistry and Biochemistry, Kennesaw State University, 1000 Chastain Road, Box 1203, Kennesaw, Georgia 30144
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26
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Li J, Iyengar SS. Ab Initio Molecular Dynamics Using Recursive, Spatially Separated, Overlapping Model Subsystems Mixed within an ONIOM-Based Fragmentation Energy Extrapolation Technique. J Chem Theory Comput 2015; 11:3978-91. [DOI: 10.1021/acs.jctc.5b00433] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Junjie Li
- Department of Chemistry and
Department of Physics, Indiana University, 800 E. Kirkwood Ave, Bloomington, Indiana 47405, United States
| | - Srinivasan S. Iyengar
- Department of Chemistry and
Department of Physics, Indiana University, 800 E. Kirkwood Ave, Bloomington, Indiana 47405, United States
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27
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Kaledin M, Adedeji DT. Driven molecular dynamics studies of the shared proton motion in the H5O2+·Ar cluster: the effect of argon tagging and deuteration on vibrational spectra. J Phys Chem A 2015; 119:1875-84. [PMID: 25686318 DOI: 10.1021/jp511305c] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report IR spectra of H5O2(+) and H5O2(+)·Ar and their deuterium isotopologues using ab initio molecular dynamics. The trajectories were propagated as microcanonical (NVE) ensembles at energies corresponding to temperatures 50 and 100 K. The potential energy surface is calculated on-the-fly at the MP2/aug-cc-pVDZ level of theory. The calculations show that adding an argon atom to H5O2(+) introduces symmetry breaking in the Zundel core ion, causes blueshift in the shared proton vibration by about 200 cm(-1), and leads to the splitting of the OH stretch vibrations into four bands. Driven molecular dynamics (DMD) method is used to assign the spectrum by coupling the dipole moment to an external electric field oscillating at frequency ω. The broad feature at 1100 cm(-1) in the H5O2(+)·Ar spectrum is ascribed to the large amplitude shared proton vibration coupled with torsion and wag modes. MD MP2 simulations predict the H/D redshift in the shared proton vibration and water bending vibration to be about 280 and 460 cm(-1), respectively, in good agreement with experimental observations.
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Affiliation(s)
- Martina Kaledin
- Kennesaw State University , Chemistry & Biochemistry, 370 Paulding Avenue NW, Box No. 1203, Kennesaw, Georgia 30144, United States
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28
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Yamada T, Aida M. Fundamental frequency from classical molecular dynamics. Phys Chem Chem Phys 2015; 17:3227-40. [PMID: 25519091 DOI: 10.1039/c4cp04068f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We give a theoretical validation for calculating fundamental frequencies of a molecule from classical molecular dynamics (MD) when its anharmonicity is small enough to be treated by perturbation theory. We specifically give concrete answers to the following questions: (1) What is the appropriate initial condition of classical MD to calculate the fundamental frequency? (2) From that condition, how accurately can we extract fundamental frequencies of a molecule? (3) What is the benefit of using ab initio MD for frequency calculations? Our analytical approaches to those questions are classical and quantum normal form theories. As numerical examples we perform two types of MD to calculate fundamental frequencies of H2O with MP2/aug-cc-pVTZ: one is based on the quartic force field and the other one is direct ab initio MD, where the potential energies and the gradients are calculated on the fly. From those calculations, we show comparisons of the frequencies from MD with the post vibrational self-consistent field calculations, second- and fourth-order perturbation theories, and experiments. We also apply direct ab initio MD to frequency calculations of C-H vibrational modes of tetracene and naphthalene. We conclude that MD can give the same accuracy in fundamental frequency calculation as second-order perturbation theory but the computational cost is lower for large molecules.
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Affiliation(s)
- Tomonori Yamada
- Center for Quantum Life Sciences and Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan.
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29
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A Molecular Dynamic Simulation of Hydrated Proton Transfer in Perfluorosulfonate Ionomer Membranes (Nafion 117). J CHEM-NY 2015. [DOI: 10.1155/2015/169680] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A molecular dynamic model based on Lennard-Jones Potential, the interaction force between two particles, molecular diffusion, and radial distribution function (RDF) is presented. The diffusion of the hydrated ion, triggered by both Grotthuss and vehicle mechanisms, is used to study the proton transfer in Nafion 117. The hydrated ion transfer mechanisms and the effects of the temperature, the water content in the membrane, and the electric field on the diffusion of the hydrated ion are analyzed. The molecular dynamic simulation results are in good agreement with those reported in the literature. The modeling results show that when the water content in Nafion 117 is low, H3O+is the main transfer ion among the different hydrated ions. However, at higher water content, the hydrated ion in the form of H+(H2O)2is the main transfer ion. It is also found that the negatively charged sulfonic acid group as the fortified point facilitates the proton transfer in Nafion 117 better than the free water molecule. The diffusion of the hydrated ion can be improved by increasing the cell temperature, the water content in Nafion, and the electric field intensity.
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30
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Thaunay F, Dognon JP, Ohanessian G, Clavaguéra C. Vibrational mode assignment of finite temperature infrared spectra using the AMOEBA polarizable force field. Phys Chem Chem Phys 2015. [DOI: 10.1039/c5cp02270c] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The Driven Molecular Dynamics approach has been adapted and associated with the AMOEBA polarizable force field to assign and visualize vibrational modes in infrared spectra obtained by molecular dynamics simulations.
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Affiliation(s)
- Florian Thaunay
- Laboratoire de Chimie Moléculaire
- Ecole Polytechnique
- CNRS
- 91128 Palaiseau Cedex
- France
| | - Jean-Pierre Dognon
- CEA/Saclay
- DSM/IRAMIS/NIMBE
- CNRS
- UMR 3685
- Laboratoire de Chimie Moléculaire et de Catalyse pour l'Energie
| | - Gilles Ohanessian
- Laboratoire de Chimie Moléculaire
- Ecole Polytechnique
- CNRS
- 91128 Palaiseau Cedex
- France
| | - Carine Clavaguéra
- Laboratoire de Chimie Moléculaire
- Ecole Polytechnique
- CNRS
- 91128 Palaiseau Cedex
- France
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31
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Kulig W, Agmon N. Both Zundel and Eigen Isomers Contribute to the IR Spectrum of the Gas-Phase H9O4+ Cluster. J Phys Chem B 2013; 118:278-86. [DOI: 10.1021/jp410446d] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Waldemar Kulig
- The Fritz Haber Research
Center, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Noam Agmon
- The Fritz Haber Research
Center, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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32
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Molčanov K, Stare J, Vener MV, Kojić-Prodić B, Mali G, Grdadolnik J, Mohaček-Grošev V. Nitranilic acid hexahydrate, a novel benchmark system of the Zundel cation in an intrinsically asymmetric environment: spectroscopic features and hydrogen bond dynamics characterised by experimental and theoretical methods. Phys Chem Chem Phys 2013; 16:998-1007. [PMID: 24281720 DOI: 10.1039/c3cp54026j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Nitranilic acid (2,5-dihydroxy-3,6-dinitro-2,5-cyclohexadiene-1,4-dione) as a strong dibasic acid in acidic aqueous media creates the Zundel cation, H5O2(+). The structural unit in a crystal comprises (H5O2)2(+) (2,5-dihydroxy-3,6-dinitro-1,4-benzoquinonate)(2-) dihydrate where the Zundel cation reveals no symmetry, being an ideal case for studying proton dynamics and its stability. The Zundel cation and proton transfer dynamics are studied by variable-temperature X-ray diffraction, IR and solid-state NMR spectroscopy, and various quantum chemical methods, including periodic DFT calculations, ab initio molecular dynamics simulation, and quantization of nuclear motion along three fully coupled internal coordinates. The Zundel cation features a short H-bond with the O···O distance of 2.433(2) Å with an asymmetric placement of hydrogen. The proton potential is of a single well type and, due to the non-symmetric surroundings, of asymmetric shape. The formation of the Zundel cation is facilitated by the electronegative NO2 groups. The employed spectroscopic techniques supported by calculations confirm the presence of a short H-bond with a complex proton dynamics.
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33
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Maiorov VD, Kislina IS, Rykounov AA, Vener MV. The structure and vibrational features of proton disolvates in water-ethanol solutions of HCl: the combined spectroscopic and theoretical study. J PHYS ORG CHEM 2013. [DOI: 10.1002/poc.3251] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Vladimir D. Maiorov
- Semenov Institute of Chemical Physics; Russian Academy of Sciences; Moscow Russia
| | - Irina S. Kislina
- Semenov Institute of Chemical Physics; Russian Academy of Sciences; Moscow Russia
| | - Alexey A. Rykounov
- Snezhinsk Physics and Technology Institute; National Research Nuclear University MEPhI; Snezhinsk Russia
| | - Mikhail V. Vener
- Quantum Chemistry Department; Mendeleev University of Chemical Technology; Moscow Russia
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34
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Sigalov MV, Kalish N, Carmeli B, Pines D, Pines E. Probing Small Protonated Water Clusters in Acetonitrile Solutions by 1H NMR. ACTA ACUST UNITED AC 2013. [DOI: 10.1524/zpch.2013.0399] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Abstract
In a previous publication by Kalish et al. (J. Phys. Chem. A 115 (2011) 4063) the existence of well defined small protonated water clusters in acetonitrile has been established by IR spectroscopy. Here we report on a 1H NMR study of triflic acid, CF3SO3H, in acetonitrile-water solutions. Using NMR we are able to corroborate the general solvation scheme we have proposed for the hydrated proton in acetonitrile as a function of the molar ratio between the strong mineral acid and water, n = [H2O]/[acid]. According to this scheme, backed now by both IR absorption spectroscopy and NMR measurements, the very strong triflic acid completely dissociates in acetonitrile/water solutions to yield the aqueous proton and the triflate anion when n > 1. Furthermore, increasing n results in the proton solvated in increasingly larger water clusters formed within the acetonitrile solution.
Clearly distinguishable by NMR are the smallest protonated water clusters, the protonated water monomer, H3
+O, and the protonated water dimer, H5
+O2, which dominate the solution for n = 1,2,3. For larger n the NMR study indicates the gradual increase of the average protonated water cluster size as a function of n while the proton inner solvation core more closely retaining the characteristics of a deformed protonated water dimer, (H2O-H+⋯OH2)
s
than that of the protonated water monomer (H3
+O)
s
.
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Affiliation(s)
- Mark V. Sigalov
- Ben-Gurion University of the Negev, Department of Chemistry, Beer-Sheva 84125, Israel
| | - Noah Kalish
- Ben-Gurion University of the Negev, Department of Chemistry, Beer-Sheva 84125, Israel
| | - Benny Carmeli
- Ben-Gurion University of the Negev, Department of Chemistry, Beer-Sheva 84125, Israel
| | - Dina Pines
- Ben-Gurion University of the Negev, Department of Chemistry, Beer-Sheva 84125, Israel
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35
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36
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Madjet MEA, Li Z, Vendrell O. Ultrafast hydrogen migration in acetylene cation driven by non-adiabatic effects. J Chem Phys 2013; 138:094311. [DOI: 10.1063/1.4793215] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
| | - Zheng Li
- Center for Free-Electron Laser Science, DESY, Notkestrasse 85, D-22607 Hamburg, Germany
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
| | - Oriol Vendrell
- Center for Free-Electron Laser Science, DESY, Notkestrasse 85, D-22607 Hamburg, Germany
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37
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Dietrick SM, Iyengar SS. Constructing Periodic Phase Space Orbits from ab Initio Molecular Dynamics Trajectories to Analyze Vibrational Spectra: Case Study of the Zundel (H5O2+) Cation. J Chem Theory Comput 2012; 8:4876-90. [DOI: 10.1021/ct300695x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Scott M. Dietrick
- Department
of Chemistry and Department of Physics, Indiana University, Bloomington, Indiana
47405, United States
| | - Srinivasan S. Iyengar
- Department
of Chemistry and Department of Physics, Indiana University, Bloomington, Indiana
47405, United States
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38
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Niehues G, Kaledin AL, Bowman JM, Havenith M. Driving of a Small Solvated Peptide in the IR and THz Range—A Comparative Study of Energy Flow. J Phys Chem B 2012; 116:10020-5. [DOI: 10.1021/jp3021358] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Gudrun Niehues
- Lehrstuhl für Physikalische
Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Alexey L. Kaledin
- Cherry L. Emerson Center for
Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Joel M. Bowman
- Cherry L. Emerson Center for
Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Martina Havenith
- Lehrstuhl für Physikalische
Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany
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39
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Cheng TC, Bandyopadhyay B, Mosley JD, Duncan MA. IR Spectroscopy of Protonation in Benzene–Water Nanoclusters: Hydronium, Zundel, and Eigen at a Hydrophobic Interface. J Am Chem Soc 2012; 134:13046-55. [DOI: 10.1021/ja3038245] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Timothy C. Cheng
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | | | - Jonathan D. Mosley
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Michael A. Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
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40
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Xie HB, Jin L, Rudić S, Simons JP, Gerber RB. Computational Studies of Protonated β-d-Galactose and Its Hydrated Complex: Structures, Interactions, Proton Transfer Dynamics, and Spectroscopy. J Phys Chem B 2012; 116:4851-9. [DOI: 10.1021/jp3028325] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hong-bin Xie
- Key Laboratory of Industrial
Ecology and Environmental Engineering (MOE), School of Environmental
Science and Technology, Dalian University of Technology, Dalian 116024, China
- Department of Chemistry, University of California, Irvine, California 92697-2025,
United States
| | - Lin Jin
- Department of Chemistry, University of California, Irvine, California 92697-2025,
United States
| | - Svemir Rudić
- Department
of Chemistry, Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ,
U.K
| | - John P. Simons
- Department
of Chemistry, Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ,
U.K
| | - R. Benny Gerber
- Department of Chemistry, University of California, Irvine, California 92697-2025,
United States
- Institute of Chemistry
and The
Fritz Haber Research Center, The Hebrew University, Jerusalem 91904, Israel
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41
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Cazade PA, Huang J, Yosa J, Szymczak JJ, Meuwly M. Atomistic simulations of reactive processes in the gas- and condensed-phase. INT REV PHYS CHEM 2012. [DOI: 10.1080/0144235x.2012.694694] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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42
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Lutz S, Tubert-Brohman I, Yang Y, Meuwly M. Water-assisted proton transfer in ferredoxin I. J Biol Chem 2011; 286:23679-87. [PMID: 21531725 DOI: 10.1074/jbc.m111.230003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The role of water molecules in assisting proton transfer (PT) is investigated for the proton-pumping protein ferredoxin I (FdI) from Azotobacter vinelandii. It was shown previously that individual water molecules can stabilize between Asp(15) and the buried [3Fe-4S](0) cluster and thus can potentially act as a proton relay in transferring H(+) from the protein to the μ(2) sulfur atom. Here, we generalize molecular mechanics with proton transfer to studying proton transfer reactions in the condensed phase. Both umbrella sampling simulations and electronic structure calculations suggest that the PT Asp(15)-COOH + H(2)O + [3Fe-4S](0) → Asp(15)-COO(-) + H(2)O + [3Fe-4S](0) H(+) is concerted, and no stable intermediate hydronium ion (H(3)O(+)) is expected. The free energy difference of 11.7 kcal/mol for the forward reaction is in good agreement with the experimental value (13.3 kcal/mol). For the reverse reaction (Asp(15)-COO(-) + H(2)O + [3Fe-4S](0)H(+) → Asp(15)-COOH + H(2)O + [3Fe-4S](0)), a larger barrier than for the forward reaction is correctly predicted, but it is quantitatively overestimated (23.1 kcal/mol from simulations versus 14.1 from experiment). Possible reasons for this discrepancy are discussed. Compared with the water-assisted process (ΔE ≈ 10 kcal/mol), water-unassisted proton transfer yields a considerably higher barrier of ΔE ≈ 35 kcal/mol.
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Affiliation(s)
- Stephan Lutz
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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43
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Biliškov N, Kojić-Prodić B, Mali G, Molčanov K, Stare J. A Partial Proton Transfer in Hydrogen Bond O−H···O in Crystals of Anhydrous Potassium and Rubidium Complex Chloranilates. J Phys Chem A 2011; 115:3154-66. [DOI: 10.1021/jp112380f] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Nikola Biliškov
- Rudjer Bošković Institute, POB 180, HR-10002 Zagreb, Croatia
| | | | - Gregor Mali
- National Institute of Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia
- EN-FIST Centre of Excellence, Dunajska c. 156, SI-1000 Ljubljana
| | | | - Jernej Stare
- National Institute of Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia
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44
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Kalish NBM, Shandalov E, Kharlanov V, Pines D, Pines E. Apparent stoichiometry of water in proton hydration and proton dehydration reactions in CH3CN/H2O solutions. J Phys Chem A 2011; 115:4063-75. [PMID: 21417385 DOI: 10.1021/jp110873t] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gradual solvation of protons by water is observed in liquids by mixing strong mineral acids with various amounts of water in acetonitrile solutions, a process which promotes rapid dissociation of the acids in these solutions. The stoichiometry of the reaction XH(+) + n(H(2)O) = X + (H(2)O)(n)H(+) was studied for strong mineral acids (negatively charged X, X = ClO(4)¯, Cl¯, Br¯, I¯, CF(3)SO(3)¯) and for strong cationic acids (uncharged X, X = R*NH(2), H(2)O). We have found by direct quantitative analysis preference of n = 2 over n = 1 for both groups of proton transfer reactions at relatively low water concentrations in acetonitrile. At high water concentrations, we have found that larger water solvates must also be involved in the solvation of the proton while the spectral features already observed for n = 2, H(+)(H(2)O)(2), remain almost unchanged at large n values up to at least 10 M of water.
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45
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Baer M, Marx D, Mathias G. Assigning Predissociation Infrared Spectra of Microsolvated Hydronium Cations H3O+⋅(H2)n (n=0, 1, 2, 3) by Ab Initio Molecular Dynamics. Chemphyschem 2011; 12:1906-15. [DOI: 10.1002/cphc.201000955] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Revised: 02/02/2011] [Indexed: 11/07/2022]
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46
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Guasco TL, Johnson MA, McCoy AB. Unraveling Anharmonic Effects in the Vibrational Predissociation Spectra of H5O2+ and Its Deuterated Analogues. J Phys Chem A 2011; 115:5847-58. [DOI: 10.1021/jp109999b] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Timothy L. Guasco
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Mark A. Johnson
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Anne B. McCoy
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States
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47
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Lankau T, Yu CH. A quantum description of the proton movement in an idealized NHN+ bridge. Phys Chem Chem Phys 2011; 13:12758-69. [DOI: 10.1039/c0cp02172e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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48
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Song D, Su H, Kong FA, Lin SH. Anharmonic RRKM Calculation for the Dissociation of (H2O)2H+ and Its Deuterated Species (D2O)2D+. J Phys Chem A 2010; 114:10217-24. [DOI: 10.1021/jp103782r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Di Song
- Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China, Institute of Applied Chemistry, Institute of Molecular Science, Chiao-Tung University, Hsin-Chu, Taiwan, Republic of China, and Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan, Republic of China,
| | - Hongmei Su
- Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China, Institute of Applied Chemistry, Institute of Molecular Science, Chiao-Tung University, Hsin-Chu, Taiwan, Republic of China, and Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan, Republic of China,
| | - Fan-ao Kong
- Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China, Institute of Applied Chemistry, Institute of Molecular Science, Chiao-Tung University, Hsin-Chu, Taiwan, Republic of China, and Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan, Republic of China,
| | - Sheng-Hsien Lin
- Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China, Institute of Applied Chemistry, Institute of Molecular Science, Chiao-Tung University, Hsin-Chu, Taiwan, Republic of China, and Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan, Republic of China,
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49
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Lee HM, Kumar A, Kołaski M, Kim DY, Lee EC, Min SK, Park M, Choi YC, Kim KS. Comparison of cationic, anionic and neutral hydrogen bonded dimers. Phys Chem Chem Phys 2010; 12:6278-87. [PMID: 20405079 DOI: 10.1039/b925551f] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Short Strong Hydrogen Bonds (SSHBs) play an important role in many fields of physics, chemistry and biology. Since it is known that SSHBs exist in many biological systems, the role of hydrogen bonding motifs has been particularly interesting in enzyme catalysis, bio-metabolism, protein folding and proton transport phenomena. To explore the characteristic features of neutral, anionic and cationic hydrogen bonds, we have carried out theoretical studies of diverse homogeneous and heterogeneous hydrogen bonded dimers including water, peroxides, alcohols, ethers, aldehydes, ketones, carboxylic acids, anhydrides, and nitriles. Geometry optimization and harmonic frequency calculations are performed at the levels of Density Functional Theory (DFT) and Møller-Plesset second order perturbation (MP2) theory. First principles Car-Parrinello molecular dynamics (CPMD) simulations are performed to obtain IR spectra derived from velocity- and dipole-autocorrelation functions. We find that the hydrogen bond energy is roughly inversely proportional to the fourth power of the r(O/N-H) distance. Namely, the polarization of the proton accepting O/N atom by the proton-donating H atom reflects most of the binding energy in these diverse cation/anion/neutral hydrogen bonds. The present study gives deeper insight into the nature of hydrogen-bonded dimers including SSHBs.
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Affiliation(s)
- Han Myoung Lee
- Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, 790-784 Pohang, South Korea
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50
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Douberly GE, Walters RS, Cui J, Jordan KD, Duncan MA. Infrared Spectroscopy of Small Protonated Water Clusters, H+(H2O)n (n = 2−5): Isomers, Argon Tagging, and Deuteration. J Phys Chem A 2010; 114:4570-9. [DOI: 10.1021/jp100778s] [Citation(s) in RCA: 143] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- G. E. Douberly
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, and Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260
| | - R. S. Walters
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, and Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260
| | - J. Cui
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, and Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260
| | - K. D. Jordan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, and Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260
| | - M. A. Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, and Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260
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