1
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Gimbal-Zofka Y, González-Espinoza CE, Rumble CA, Wesolowski TA. Assessment of Approximations to the Embedding Potential in Frozen-Density Embedding Theory for the Calculation of Electric Field Gradients. J Chem Theory Comput 2024; 20:348-356. [PMID: 38116618 DOI: 10.1021/acs.jctc.3c00773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
The approximations to the embedding potential in frozen-density embedding theory (FDET) have been assessed for the first time for the calculation of the electric field gradient (EFG) at a nucleus. FDET-based methods using a hierarchy of approximations are applied to evaluate the EFG at the nuclei of an HCl molecule in several noncovalently bound clusters chosen to represent potential liquid or molecular crystal systems. A detailed assessment of such approximations is made for the Hartree-Fock treatment of electron-electron correlation (both in FDET and in the reference calculations for the whole cluster). The emerging choice of the optimal set of approximations is reconfirmed in calculations in which electron-electron calculations are treated at the MP2 level. Our optimized protocol produces average errors in the complexation-induced EFG shift on the order of 25% relative to conventional quantum mechanical calculations for the whole cluster. This protocol is shown to be numerically robust and leads to enormous computational savings compared to a complete quantum mechanical treatment of the embedded species and its environment. For a cluster comprising a Na+ cation and up to 24 water molecules, the computation time is reduced by a factor of 30,000 at the expense of introducing an error in the environment-induced EFG shift of 22%.
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Affiliation(s)
- Yann Gimbal-Zofka
- Départment de Chimie Physique, Université de Genève, 30, quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
| | | | - Christopher A Rumble
- Department of Chemistry, Altoona College, The Pennsylvania State University, 3000 Ivyside Park, Altoona, 16601 Pennsylvania, United States
| | - Tomasz A Wesolowski
- Départment de Chimie Physique, Université de Genève, 30, quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
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2
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Hoang Ngoc Minh T, Kim J, Pireddu G, Chubak I, Nair S, Rotenberg B. Electrical noise in electrolytes: a theoretical perspective. Faraday Discuss 2023; 246:198-224. [PMID: 37409620 DOI: 10.1039/d3fd00026e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/13/2023]
Abstract
Seemingly unrelated experiments such as electrolyte transport through nanotubes, nano-scale electrochemistry, NMR relaxometry and surface force balance measurements, all probe electrical fluctuations: of the electric current, the charge and polarization, the field gradient (for quadrupolar nuclei) and the coupled mass/charge densities. The fluctuations of such various observables arise from the same underlying microscopic dynamics of the ions and solvent molecules. In principle, the relevant length and time scales of these dynamics are encoded in the dynamic structure factors. However, modelling the latter for frequencies and wavevectors spanning many orders of magnitude remains a great challenge to interpret the experiments in terms of physical processes such as solvation dynamics, diffusion, electrostatic and hydrodynamic interactions between ions, interactions with solid surfaces, etc. Here, we highlight the central role of the charge-charge dynamic structure factor in the fluctuations of electrical observables in electrolytes and offer a unifying perspective over a variety of complementary experiments. We further analyze this quantity in the special case of an aqueous NaCl electrolyte, using simulations with explicit ions and an explicit or implicit solvent. We discuss the ability of the standard Poisson-Nernst-Planck theory to capture the simulation results, and how the predictions can be improved. We finally discuss the contributions of ions and water to the total charge fluctuations. This work illustrates an ongoing effort towards a comprehensive understanding of electrical fluctuations in bulk and confined electrolytes, in order to enable experimentalists to decipher the microscopic properties encoded in the measured electrical noise.
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Affiliation(s)
- Thê Hoang Ngoc Minh
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
| | - Jeongmin Kim
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
| | - Giovanni Pireddu
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
| | - Iurii Chubak
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
| | - Swetha Nair
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
| | - Benjamin Rotenberg
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France.
- Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France
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3
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Gravelle S, Beyer D, Brito M, Schlaich A, Holm C. Assessing the Validity of NMR Relaxation Rates Obtained from Coarse-Grained Simulations of PEG-Water Mixtures. J Phys Chem B 2023. [PMID: 37327109 DOI: 10.1021/acs.jpcb.3c01646] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
NMR relaxometry is a powerful and well-established experimental approach for characterizing dynamic processes in soft matter systems. All-atom (AA) resolved simulations are typically employed to gain further microscopic insights while reproducing the relaxation rates R1. However, such approaches are limited to time and length scales that prevent to model systems such as long polymer chains or hydrogels. Coarse graining (CG) can overcome this barrier at the cost of losing atomistic details that impede the calculation of NMR relaxation rates. Here, we address this issue by performing a systematic characterization of dipolar relaxation rates R1 on a PEG-H2O mixture at two different levels of details: AA and CG. Remarkably, we show that NMR relaxation rates R1 obtained at the CG level obey the same trends when compared to AA calculations but with a systematic offset. This offset is due to, on the one hand, the lack of an intramonomer component and, on the other hand, the inexact positioning of the spin carriers. We show that the offset can be corrected for quantitatively by reconstructing a posteriori the atomistic details for the CG trajectories.
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Affiliation(s)
- Simon Gravelle
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
| | - David Beyer
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
| | - Mariano Brito
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
| | - Alexander Schlaich
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
- Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart, D-70569 Stuttgart, Germany
| | - Christian Holm
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
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4
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Chubak I, Alon L, Silletta EV, Madelin G, Jerschow A, Rotenberg B. Quadrupolar 23Na + NMR relaxation as a probe of subpicosecond collective dynamics in aqueous electrolyte solutions. Nat Commun 2023; 14:84. [PMID: 36604414 PMCID: PMC9816157 DOI: 10.1038/s41467-022-35695-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 12/14/2022] [Indexed: 01/07/2023] Open
Abstract
Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and temperature ranges. We demonstrate that quadrupolar nuclear relaxation is sensitive to subpicosecond dynamics not captured by previous models based on water reorientation or cluster rotation. While ions affect the overall water retardation, experimental trends are mainly explained by dynamics in the first two solvation shells of sodium, which contain mostly water. This work thus paves the way to the quantitative understanding of quadrupolar relaxation in electrolyte and bioelectrolyte systems.
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Affiliation(s)
- Iurii Chubak
- Sorbonne Université CNRS, Physico-Chimie des électrolytes et Nanosystèmes Interfaciaux, F-75005, Paris, France
| | - Leeor Alon
- New York University School of Medicine, Department of Radiology, Center for Biomedical Imaging, 660 First Avenue, New York, NY, 10016, USA
- Center for Advanced Imaging Innovation and Research, Department of Radiology, New York University Grossman School of Medicine, New York, NY, 10016, USA
| | - Emilia V Silletta
- Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, Medina Allende s/n, X5000HUA, Córdoba, Argentina
- Instituto de Física Enrique Gaviola, CONICET, Medina Allende s/n, X5000HUA, Córdoba, Argentina
| | - Guillaume Madelin
- New York University School of Medicine, Department of Radiology, Center for Biomedical Imaging, 660 First Avenue, New York, NY, 10016, USA
- Center for Advanced Imaging Innovation and Research, Department of Radiology, New York University Grossman School of Medicine, New York, NY, 10016, USA
| | - Alexej Jerschow
- New York University, Department of Chemistry, 100 Washington Square E, New York, NY, 10003, USA.
| | - Benjamin Rotenberg
- Sorbonne Université CNRS, Physico-Chimie des électrolytes et Nanosystèmes Interfaciaux, F-75005, Paris, France.
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5
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Gimbal-Zofka Y, Karg B, Dziubinska-Kühn K, Kowalska M, Wesolowski TA, Rumble CA. Simulations of electric field gradient fluctuations and dynamics around sodium ions in ionic liquids. J Chem Phys 2022; 157:244502. [PMID: 36586985 DOI: 10.1063/5.0126693] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The T1 relaxation time measured in nuclear magnetic resonance experiments contains information about electric field gradient (EFG) fluctuations around a nucleus, but computer simulations are typically required to interpret the underlying dynamics. This study uses classical molecular dynamics (MD) simulations and quantum chemical calculations, to investigate EFG fluctuations around a Na+ ion dissolved in the ionic liquid 1-ethyl 3-methylimidazolium tetrafluoroborate, [Im21][BF4], to provide a framework for future interpretation of NMR experiments. Our calculations demonstrate that the Sternheimer approximation holds for Na+ in [Im21][BF4], and the anti-shielding coefficient is comparable to its value in water. EFG correlation functions, CEFG(t), calculated using quantum mechanical methods or from force field charges are roughly equivalent after 200 fs, supporting the use of classical MD for estimating T1 times of monatomic ions in this ionic liquid. The EFG dynamics are strongly bi-modal, with 75%-90% of the de-correlation attributable to inertial solvent motion and the remainder to a highly distributed diffusional processes. Integral relaxation times, ⟨τEFG⟩, were found to deviate from hydrodynamic predictions and were non-linearly coupled to solvent viscosity. Further investigation showed that Na+ is solvated by four tetrahedrally arranged [BF4]- anions and directly coordinated by ∼6 fluorine atoms. Exchange of [BF4]- anions is rare on the 25-50 ns timescale and suggests that motion of solvent-shell [BF4]- is the primary mechanism for the EFG fluctuations. Different couplings of [BF4]- translational and rotational diffusion to viscosity are shown to be the source of the non-hydrodynamic scaling of ⟨τEFG⟩.
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Affiliation(s)
- Yann Gimbal-Zofka
- Départment de Chimie Physique, Université de Genève, 30, quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
| | - Beatrice Karg
- Département de Physique Nucléaire et Corpusculaire, Université de Genève, CH-1211 Genève 4, Switzerland
| | | | | | - Tomasz A Wesolowski
- Départment de Chimie Physique, Université de Genève, 30, quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
| | - Christopher A Rumble
- The Pennsylvania State University - Altoona College, 3000 Ivyside Park, Altoona, Pennsylvania 16601, USA
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6
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Chubak I, Scalfi L, Carof A, Rotenberg B. NMR Relaxation Rates of Quadrupolar Aqueous Ions from Classical Molecular Dynamics Using Force-Field Specific Sternheimer Factors. J Chem Theory Comput 2021; 17:6006-6017. [PMID: 34570493 DOI: 10.1021/acs.jctc.1c00690] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nuclear magnetic resonance (NMR) relaxation of quadrupolar nuclei is governed by the electric field gradient (EFG) fluctuations at their position. In classical molecular dynamics (MD), the electron cloud contribution to the EFG can be included via the Sternheimer approximation, in which the full EFG at the nucleus that can be computed using quantum density functional theory (DFT) is considered to be proportional to that arising from the external, classical charge distribution. In this work, we systematically assess the quality of the Sternheimer approximation as well as the impact of the classical force field (FF) on the NMR relaxation rates of aqueous quadrupolar ions at infinite dilution. In particular, we compare the rates obtained using an ab initio parametrized polarizable FF, a recently developed empirical FF with scaled ionic charges and a simple empirical nonpolarizable FF with formal ionic charges. Surprisingly, all three FFs considered yield good values for the rates of smaller and less polarizable solutes (Li+, Na+, K+, Cl-), provided that a model-specific Sternheimer parametrization is employed. Yet, the polarizable and scaled charge FFs yield better estimates for divalent and more polarizable species (Mg2+, Ca2+, Cs+). We find that a linear relationship between the quantum and classical EFGs holds well in all of the cases considered; however, such an approximation often leads to quite large errors in the resulting EFG variance, which is directly proportional to the computed rate. We attempted to reduce the errors by including first order nonlinear corrections to the EFG, yet no clear improvement for the resulting variance has been found. The latter result indicates that more refined methods for determining the EFG at the ion position, in particular those that take into account the instantaneous atomic environment around an ion, might be necessary to systematically improve the NMR relaxation rate estimates in classical MD.
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Affiliation(s)
- Iurii Chubak
- Sorbonne Université CNRS, Physico-Chimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
| | - Laura Scalfi
- Sorbonne Université CNRS, Physico-Chimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
| | - Antoine Carof
- Universite de Lorraine, CNRS, LPCT, F-54000, Nancy, France
| | - Benjamin Rotenberg
- Sorbonne Université CNRS, Physico-Chimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
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7
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Mohammadi M, Benders S, Jerschow A. Nuclear magnetic resonance spin-lattice relaxation of lithium ions in aqueous solution by NMR and molecular dynamics. J Chem Phys 2020; 153:184502. [PMID: 33187429 DOI: 10.1063/5.0026450] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We study the aqueous solvation dynamics of lithium ions using nuclear magnetic resonance spectroscopy, molecular dynamics, and viscosity measurements. Several relaxation mechanisms are examined to explain the strong increases of spin-lattice relaxation toward high concentrations. The use of both 6Li and 7Li isotopes is helpful to identify the quadrupolar contribution to the relaxation rate. In particular, it is found that the quadrupolar interaction constitutes the strongest contribution above a concentration of ∼10 molal. The next-strongest contribution arises from interactions that scale with the square of the gyromagnetic ratio (mostly the dipolar interaction), and the experimental relaxation rates appear to be fully accounted for when these mechanisms are combined over the concentration range up to the saturation concentration. The study of solvation dynamics, particularly at high concentrations, could be of relevance for electrolyte dynamics in aqueous Li-ion rechargeable batteries.
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Affiliation(s)
- Mohaddese Mohammadi
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, USA
| | - Stefan Benders
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, USA
| | - Alexej Jerschow
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, USA
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8
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Philips A, Autschbach J. Quadrupolar NMR Relaxation of Aqueous 127I -, 131Xe, and 133Cs +: A First-Principles Approach from Dynamics to Properties. J Chem Theory Comput 2020; 16:5835-5844. [PMID: 32786904 DOI: 10.1021/acs.jctc.0c00581] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Quadrupolar NMR relaxation rates were computed for aqueous 133Cs+, 131Xe, and 127I- via Kohn-Sham (KS) density functional theory-based ab initio molecular dynamics and KS calculations of the electric field gradient (EFG) tensors along the trajectories. The resulting rates are within a factor of 1-3 of the experimental values and can be compared to available results from classical dynamics and EFGs from electrostatic models with corrections via Sternheimer antishielding factors. Relativistic effects are shown to have an enhancing effect on the magnitude of the EFGs. An analysis of the EFGs was carried out in terms of localized molecular orbitals to elucidate contributions from the solvent versus solute polarization and assess the validity of the Sternheimer approximation for these systems.
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Affiliation(s)
- Adam Philips
- Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, United States
| | - Jochen Autschbach
- Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, United States
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9
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Abella L, Philips A, Autschbach J. The Sodium Anion Is Strongly Perturbed in the Condensed Phase Even Though It Appears Like a Free Ion in Nuclear Magnetic Resonance Experiments. J Phys Chem Lett 2020; 11:843-850. [PMID: 31928009 DOI: 10.1021/acs.jpclett.9b03432] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Solvated sodium anions (Na-) were thought to behave essentially like isolated gas-phase ions that interact only weakly with their environments. For example, 23Na NMR signals for solvated Na- are very sharp, despite the potential for strong quadrupolar broadening. The sharp NMR signals appear to indicate a nearly spherical electron density of the ion. For the present study, ab initio molecular dynamics simulations and quadrupolar relaxation rate calculations were carried out for the Na-/Na+ [2.2.2]cryptand system solvated in methylamine, followed by detailed analyses of the electric field gradient at the sodium nuclei. It is found that Na- does not behave like a quasi-free ion interacting only weakly with its environment. Rather, the filled 3s shell of Na- interacts weakly with the ion's own core and the nucleus, causing Na- to appear in NMR experiments like a free ion.
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Affiliation(s)
- Laura Abella
- Department of Chemistry , University at Buffalo, State University of New York Buffalo , New York 14260-3000 , United States
| | - Adam Philips
- Department of Chemistry , University at Buffalo, State University of New York Buffalo , New York 14260-3000 , United States
| | - Jochen Autschbach
- Department of Chemistry , University at Buffalo, State University of New York Buffalo , New York 14260-3000 , United States
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10
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Philips A, Marchenko A, Ducati LC, Autschbach J. Quadrupolar 14N NMR Relaxation from Force-Field and Ab Initio Molecular Dynamics in Different Solvents. J Chem Theory Comput 2018; 15:509-519. [PMID: 30462503 DOI: 10.1021/acs.jctc.8b00807] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Quadrupolar NMR spin relaxation rates and corresponding line widths were computed for the quadrupolar nucleus 14N for neat acetonitrile as well as for 1-methyl-1,3-imidazole and 1-methyl-1,3,4-triazole in different solvents. Molecular dynamics (MD) was performed with forces from the Kohn-Sham (KS) theory (ab initio MD) and force-field molecular mechanics (classical MD), followed by KS electric field gradient (EFG) calculations. For acetonitrile the agreement of the 14N line width with experiment is very good. Relative line widths for the azole nitrogens are improved over simpler approximations used previously in conjunction with single-point calculations at the multiconfigurational self-consistent field level. Overall, the NMR line widths are computed within a factor of 2 of the experimental values, giving access to reasonable estimates both of the dynamic EFG variance in the solvated systems as well as the associated correlation times that determine the relaxation rates.
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Affiliation(s)
- Adam Philips
- Department of Chemistry , University at Buffalo, State University of New York , Buffalo , New York 14260-3000 , United States
| | - Alex Marchenko
- Department of Chemistry , University at Buffalo, State University of New York , Buffalo , New York 14260-3000 , United States
| | - Lucas C Ducati
- Department of Fundamental Chemistry Institute of Chemistry , University of São Paulo , Av. Prof. Lineu Prestes 748 , São Paulo , SP 05508-000 , Brazil
| | - Jochen Autschbach
- Department of Chemistry , University at Buffalo, State University of New York , Buffalo , New York 14260-3000 , United States
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11
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Philips A, Marchenko A, Truflandier LA, Autschbach J. Quadrupolar NMR Relaxation from ab Initio Molecular Dynamics: Improved Sampling and Cluster Models versus Periodic Calculations. J Chem Theory Comput 2017; 13:4397-4409. [PMID: 28719202 DOI: 10.1021/acs.jctc.7b00584] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Quadrupolar NMR relaxation rates are computed for 17O and 2H nuclei of liquid water, and of 23Na+, and 35Cl- in aqueous solution via Kohn-Sham (KS) density functional theory ab initio molecular dynamics (aiMD) and subsequent KS electric field gradient (EFG) calculations along the trajectories. The calculated relaxation rates are within about a factor of 2 of experimental results and improved over previous aiMD simulations. The relaxation rates are assessed with regard to the lengths of the simulations as well as configurational sampling. The latter is found to be the more limiting factor in obtaining good statistical sampling and is improved by averaging over many equivalent nuclei of a system or over several independent trajectories. Further, full periodic plane-wave basis calculations of the EFGs are compared with molecular-cluster atomic-orbital basis calculations. The two methods deliver comparable results with nonhybrid functionals. With the molecular-cluster approach, a larger variety of electronic structure methods is available. For chloride, the EFG computations benefit from using a hybrid KS functional.
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Affiliation(s)
- Adam Philips
- Department of Chemistry University at Buffalo, State University of New York , Buffalo, New York 14260-3000, United States
| | - Alex Marchenko
- Department of Chemistry University at Buffalo, State University of New York , Buffalo, New York 14260-3000, United States
| | - Lionel A Truflandier
- CNRS UMR 5255, Institut des Sciences Moléculaires Université Bordeaux , 351 cours de la Libération, 33405 Talence cedex, France
| | - Jochen Autschbach
- Department of Chemistry University at Buffalo, State University of New York , Buffalo, New York 14260-3000, United States
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12
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Carof A, Salanne M, Charpentier T, Rotenberg B. Collective water dynamics in the first solvation shell drive the NMR relaxation of aqueous quadrupolar cations. J Chem Phys 2017; 145:124508. [PMID: 27782645 DOI: 10.1063/1.4963682] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using molecular simulations, we analyze the microscopic processes driving the Nuclear Magnetic Resonance (NMR) relaxation of quadrupolar cations in water. The fluctuations of the Electric Field Gradient (EFG) experienced by alkaline and magnesium cations, which determine the NMR relaxation time, are mainly due to the dynamics of water molecules in their solvation shell. The dynamics of the ion plays a less important role, with the exception of the short-time dynamics in the lighter Li+ case, for which rattling in the solvent cage results in oscillations of the EFG autocorrelation function (ACF). Several microscopic mechanisms that may a priori contribute to the decay of the EFG-ACF occur in fact over too long time scales: entrance/exit of individual water molecules into/from the solvation shell, rotation of a molecule around the ion, or reorientation of the molecule. In contrast, the fluctuations of the ion-water distance are clearly correlated to that of the EFG. Nevertheless, it is not sufficient to consider a single molecule due to the cancellations arising from the symmetry of the solvation shell. The decay of the EFG-ACF, hence NMR relaxation, is in fact governed by the collective symmetry-breaking fluctuations of water in the first solvation shell.
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Affiliation(s)
- Antoine Carof
- Sorbonne Universités, UPMC Universités Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 place Jussieu, F-75005 Paris, France
| | - Mathieu Salanne
- Sorbonne Universités, UPMC Universités Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 place Jussieu, F-75005 Paris, France
| | - Thibault Charpentier
- NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette cedex, France
| | - Benjamin Rotenberg
- Sorbonne Universités, UPMC Universités Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 place Jussieu, F-75005 Paris, France
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13
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Carof A, Salanne M, Charpentier T, Rotenberg B. On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water. J Chem Phys 2016; 143:194504. [PMID: 26590539 DOI: 10.1063/1.4935496] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as (7)Li(+), (23)Na(+), (25)Mg(2+), (35)Cl(-), (39)K(+), or (133)Cs(+). Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.
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Affiliation(s)
- Antoine Carof
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 Place Jussieu, F-75005 Paris, France
| | - Mathieu Salanne
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 Place Jussieu, F-75005 Paris, France
| | - Thibault Charpentier
- CEA, IRAMIS, NIMBE, LSDRM, UMR CEA-CNRS 3685, F-91191 Gif-sur-Yvette Cedex, France
| | - Benjamin Rotenberg
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 Place Jussieu, F-75005 Paris, France
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14
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Zhang H, Farnan I. High temperature 35Cl nuclear magnetic resonance study of the LiCl–KCl system and the effect of CeCl3 dissolution. Faraday Discuss 2016; 190:367-85. [DOI: 10.1039/c6fd00003g] [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
This paper examines the dynamics of the LiCl–KCl system over a range of temperatures in order to understand the local structure surrounding chlorine, which is the common ion in these systems, during molten salt pyro-processing. Chlorine-35 nuclear magnetic resonance (NMR) is sensitive to the local environments of the resonant nuclei and their motion on a diffusive timescale. Thus, it is a good probe of the atomic scale processes controlling the viscosities, diffusivities and conductivities of these molten salts. The average isotropic chemical shifts (35Clδ) and spin-lattice relaxation times (T1) of 35Cl in (Li,K)Cl salt mixtures have been obtained over a compositional range of 0–100 mol% KCl with an interval of 10 mol% using high temperature nuclear magnetic resonance (NMR) spectroscopy from room temperature up to 890 °C. The 35Clδ in the two end member salts are consistent with the cation–anion radius ratio as previously measured on the solid halides and the average radius ratio of cation to anion, can be used to explain the variation of 35Clδ with composition. The quadrupolar interaction is found to be responsible for the spin-lattice relaxation of the 35Cl, and the activation energies for T1 relaxation have been obtained for all compositions. The measured T1 (35Cl) activation energies do not vary linearly with composition and peak at 50% KCl, which also coincides with the Chemla point for this system. They also are in good agreement with the values from equivalent conductivity measurements. To investigate the response of the system to solutes, 8 wt% of CeCl3 was added to the pure LiCl as a surrogate actinide. The shift induced was 120 ppm and the activation energy for the T1 (35Cl) increased by a factor of four. This is a promising preliminary result for probing the effect of actinide dissolution on the dynamics of these pyro-processing salts.
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Affiliation(s)
- H. Zhang
- Department of Earth Sciences
- University of Cambridge
- Cambridge
- UK
| | - I. Farnan
- Department of Earth Sciences
- University of Cambridge
- Cambridge
- UK
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