Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J04: Water Dynamics in Different Environments: Experiment and Theory IV. Bulk Water and Solute HydrationFocus
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Sponsoring Units: DCP DCOMP DBIO DSOFT Chair: Radha Boya, Univ of Manchester Room: 109 |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J04.00001: Systematic optimization of atomistic water models for molecular simulation using liquid/vapor surface tension data Invited Speaker: Lee-Ping Wang The heat of vaporization is one of the most important experimental properties that is used to train the parameters of empirical potentials (force fields) commonly used to simulate molecular liquids. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J04.00002: Kosmotrope and Chaotrope Salts Influence on Water Structural Relaxation and hydrogen Bond Dynamics Investigated by Coherent Quasielastic Neutron Scattering Antonio Faraone, Erkan Senses, Eugene Mamontov Salts can either increase or decrease the viscosity when dissolved in water. This phenomenon has been traditionally interpreted within the classification of the solutes as kosmotropes (structure makers) and chaotropes (structure breakers), with reference to their hypothesized property of enhancing or weakening the hydrogen bond network. However, at the molecular level the distinction is less clear as both kosmotropes and chaotropes affect the structure of the surrounding water molecules. Using coherent quasielastic neutron scattering, we have investigated the dynamics of NaCl/D O and KCl/D O, NaCl being a kosmotrope and KCl being a chaotrope, respectively. By probing the dynamics of these systems at the structure factor peak, we measured how different salts affect the structural relaxation of water. At the same time, by collecting data at the second peak in the deuterium intermolecular partial structure factor, the hydrogen bond dynamics was probed. Whereas the hydrogen bonding dynamics is largely unchanged by the presence of the salts, NaCl and KCl affect the structural relaxation differently: the former slows down the dynamics whereas the latter mostly leaves the relaxation unchanged. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J04.00003: The SCAN330 dataset of first-principles molecular dynamics simulations of water Michael D LaCount, Francois Gygi We present the SCAN330 dataset of first-principles molecular dynamics simulations of liquid water [1] obtained using the Qbox code [2] and the SCAN meta-GGA density functional [3] at a temperature of 330 K. The dataset consists of 16 independent simulations with a cumulative duration of 696 ps. Structural properties, polarizability, infrared and Raman spectra are compared with experiment and with previous results of PBE simulations carried out at 400 K, showing a substantial improvement in all computed properties. The availability of multiple independent trajectories provides a measure of the uncertainty associated with computed spectra. All simulation data and trajectories are available at http://quantum-simulation.org and provide uncorrelated configurations for use in further investigations of the electronic structure of water. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J04.00004: Sensitizing Hydration Shells of Ions by Analyzing Water Dynamics Using High Sensitive Dielectric Spectroscopy Djamila Lou, LUAn DOAN, Henry J. Kesting, Vinh Q Nguyen A variety of measurement techniques have provided evidence that ions and other solute molecules affect the structure and dynamics of water directly surrounding them. Most experiments use infrared spectroscopy to study the vibrational relaxation of hydration shells, which observe intramolecular vibrations. In response, we have employed a highly sensitive, high-resolution, frequency domain, MHz to THz dielectric spectrometer that is sensitive to intermolecular dynamics. We have confirmed that water dynamics over this range are best described by three Debye relaxation processes with three-time constants of 8.56, 1.1ps and 179fs. Our argument is also supported by studies of dielectric relaxation of aqueous salt solutions, which produce the same three-time constants but amplitudes that vary with solute concentration. The amplitude of each process provides information about the structure of hydration shells. While the amplitude of the first process is related to the structure of the first hydration layer, the amplitude of the second and the third are linked to the second and/or the third hydration layers. Our results shed light on the dynamics of hydration shells around solute molecules in a biologically relevant environment. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J04.00005: Spatio-temporal analysis of water molecules around DNA employing extended MHz-THz spectroscopy and MD simulations Abhishek K Singh, LUAn DOAN, Vinh Q Nguyen The molecular motion of water molecules within hydration shells around DNA strongly influences its functionality. However, the structure and dynamics of water molecules in their hydration shells are still controversially discussed among the research community. The understanding developed in this regard so far, is mostly due to computational/simulation studies, with far lesser experimental investigations. Here we present a temperature-dependent study for dynamics of water molecules around salmon testes DNA, employing extended megahertz-terahertz dielectric spectroscopic technique and Fourier transform infrared spectroscopy supported by MD simulations. We have observed that water molecules are heterogeneously distributed around DNA and they can be classified as “tightly” and “loosely” bound water molecules with the relaxation times of ~500 ps and ~70 ps, respectively. We are able to locate the successive hydration layers with respect to the DNA molecule. FTIR analysis of hydrogen bond fluctuations indicates that the DNA behaves like a “chaotropic” solute and reduces the structural order of water molecules with respect to the bulk water. |
Tuesday, March 3, 2020 3:54PM - 4:30PM |
J04.00006: Transient Anisotropy of Liquid Water Invited Speaker: Fabio Novelli The solvation of molecules in water is pivotal for a myriad of molecular phenomena and is of crucial importance to understand diverse issues such as chemical reactivity and biomolecular function. It has been shown that laser techniques in the infrared (IR) and Terahertz (THz) frequency ranges offer fundamental insights into hydration from small solutes to proteins. In bulk liquid, motions of water molecules lead to ultrafast fluctuations at femto- to pico-second time scales. Underlying molecular processes range from diffusional motions spanning nanoseconds, rattling modes of anions and cations within their solvation shells on a ps time scale, the breaking and reformation of hydrogen bonds, and includes sub-100 fs librational motions. Here we report unprecedented non-linear THz experiments on water molecules in the liquid phase. This novel finding indicate that inducing anisotropy in bulk liquids is feasible. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J04.00007: Strong orbital interactions of the Zundel cation H5O2+ with hydration shell water Maria Ekimova, Carlo Kleine, Jan Ludwig, Miguel Ochmann, Thomas A. Gustafsson, Eve Kozari, EHUD PINES, Nils Huse, Philippe Wernet, Michael Odelius, Erik T. J. Nibbering We use O K-edge X-ray absorption spectroscopy in transmission to determine the electronic structure and hydrogen bond characteristics of the Zundel cation H5O2+ in solution. H5O2+ plays a key role in water-mediated proton transport in bulk water, hydrogen fuel cells and transmembrane proteins. For this, we elucidate spectroscopic signatures of O 1s core excitations to O-H σ* anti-bonding orbitals of hydrated protons. By a dedicated and previously established sample preparation procedure, we can systematically tune the hydration degree of the protons, starting from the Zundel cation solvated by acetonitrile, and exchange solvation layers with water, thus altering the hydrogen bond characteristics of H5O2+. The significant decrease of pre- and main-edge combined with a major increase of the post-edge transition cross sections point at strong interactions of the first hydration shell water molecules with the Zundel cation. With our flatjet system for x-ray absorption spectroscopy in transmission, now succesfully operating for the polar acetonitrile solvent, and in combination with previously obtained laboratory infrared spectroscopic data, we can establish a systematic structural approach to hydrated proton structures in solution. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J04.00008: Molten hydrate clathrates as a new class of macromolecular fluids. Carlos Lopez-Bueno, Carlos Herreros-Lucas, Marius Bittermann, Alfredo Amigo, Sander Woutersen, Maria del Carmen Giménez-López, Francisco Rivadulla Despite water being the most prominent liquid and a common reaction media of biological processes, the effect of hydrophobic solutes on its properties is not completely understood. For instance, apolar chains of tetrabutyl ammonium salts promote the formation of clathrate hydrates at low temperatures or high pressures. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J04.00009: A New Model for the Structure and Dynamics of the Hydrated Proton in Liquid Acetonitrile and Water Eve Kozari, Mark Sigalov, Dina Pines, Benjamin Philipp Fingerhut, EHUD PINES A new proton-solvation and -transport model in aqueous solutions is proposed based on our combined NMR and IR experiments and theoretical quantum–classical-molecular-dynamics findings. The H7+O3 solvate is at the center of the emerging model of the aqueous proton transport which is based on measurements made on protonated water solvates in liquid acetonitrile up to water-cluster size of at least 12 water molecules. The existence of structurally well-defined protonated water clusters in these solutions is unequivocally verified by NMR and FTIR spectroscopies of the hydrated proton. In contrast to the gas-phase where the H7+O3 unit is symmetric, the core H7+O3 unit in polar liquids is characterized by a chain of 3 water molecules with asymmetrically distorted oxygen-oxygen distances due the fluctuating solvent environment which does not allow a complete isotropic solvation of the proton. Such solvent-field-induced asymmetric distortion favors a Zundel-type, dimeric active proton solvation structure within the protonated water trimer unit. The dimeric solvation structure determines the (ultrafast) IR vibrational response of the genuine proton transfer mode in the ~ 1200 cm-1 region putting the model in harmony with recent fs-resolved 2D-IR experiments. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J04.00010: Determination of Ion–Water Correlated Motions in Aqueous Salt Solutions Yuya Shinohara, Ray Matsumoto, Matthew Thompson, Wojciech Dmowski, Chae Woo Ryu, Takuya Iwashita, Daisuke Ishikawa, Alfred Baron, Peter Thomas Cummings, Takeshi Egami We report on the real-space correlated motion of water molecules and ions in an aqueous salt solution. The Van Hove functions of aqueous salt solution were determined by high-resolution inelastic X-ray scattering (IXS) spectra and molecular dynamics simulation. (Pseudo-) Partial Van Hove function was determined to identify the element-specific correlated motions. Our results depict the distance-dependent correlated dynamics in the picosecond time-scale and identify the changes in the anion–water correlations. It is found that the anion–water correlations show a two-step relaxation. The fast term depends on the anion type, while the slow term is hardly dependent on the anion type. This result indicates that the process governing the molecular/ionic connectivity between the water molecules and the anions is almost independent of the type of anions. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J04.00011: Lysozyme Solution-State Tertiary Structure Measured in Protic and Aprotic Ionic Liquid Aqueous Mixtures Ian Reyes, Jose L Banuelos
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