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  • 1.
    Camisasca, Gaia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Galamba, Nuno
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Translational and rotational dynamics of high and low density TIP4P/2005 water2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 22, article id 224507Article in journal (Refereed)
    Abstract [en]

    We use molecular dynamics simulations using TIP4P/2005 to investigate the self- and distinct-van Hove functions for different local environments of water, classified using the local structure index as an order parameter. The orientational dynamics were studied through the calculation of the time-correlation functions of different-order Legendre polynomials in the OH-bond unit vector. We found that the translational and orientational dynamics are slower for molecules in a low-density local environment and correspondingly the mobility is enhanced upon increasing the local density, consistent with some previous works, but opposite to a recent study on the van Hove function. From the analysis of the distinct dynamics, we find that the second and fourth peaks of the radial distribution function, previously identified as low density-like arrangements, show long persistence in time. The analysis of the time-dependent interparticle distance between the central molecule and the first coordination shell shows that particle identity persists longer than distinct van Hove correlations. The motion of two first-nearest-neighbor molecules thus remains coupled even when this correlation function has been completely decayed. With respect to the orientational dynamics, we show that correlation functions of molecules in a low-density environment decay exponentially, while molecules in a local high-density environment exhibit bi-exponential decay, indicating that dynamic heterogeneity of water is associated with the heterogeneity among high-density and between high-density and low-density species. This bi-exponential behavior is associated with the existence of interstitial waters and the collapse of the second coordination sphere in high-density arrangements, but not with H-bond strength.

  • 2.
    Camisasca, Gaia
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Università Roma Tre, Italy.
    Iorio, Antonio
    De Marzio, Margherita
    Gallo, Paola
    Structure and slow dynamics of protein hydration water2018In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 268, p. 903-910Article in journal (Refereed)
    Abstract [en]

    We report results on the structure, local order and dynamics of water surrounding a lysozyme protein. The local order of water molecules is as much tetrahedral as in bulk water already at close vicinity of the protein but the number of hydrogen bonds depends more on the distance from the protein and gradually recovers bulk value upon moving outer. The dynamics of water seems in general to be more affected than its structure by the presence of the protein. An extremely long-relaxation detected in hydration water appears in the first monolayer around the protein, and the slow down is enhanced at low temperature. The dynamics of water within a layer of thickness 6 A is sub-diffusive up to about similar to 1 ns, above 1 ns we observe a crossover toward a hopping regime over a length-scale larger than that of nearest neighbors molecules. This hopping seems connected to transient trapping of water molecules on some specific protein domains.

  • 3.
    Camisasca, Gaia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Radial distribution functions of water: Models vs experiments2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044502Article in journal (Refereed)
    Abstract [en]

    We study the temperature behavior of the first four peaks of the oxygen-oxygen radial distribution function of water, simulated by the TIP4P/2005, MB-pol, TIP5P, and SPC/E models and compare to experimental X-ray diffraction data, including a new measurement which extends down to 235 K [H. Pathak et al., J. Chem. Phys. 150, 224506 (2019)]. We find the overall best agreement using the MB-pol and TIP4P/2005 models. We observe, upon cooling, a minimum in the position of the second shell simulated with TIP4P/2005 and SPC/E potentials, located close to the temperature of maximum density. We also calculated the two-body entropy and the contributions coming from the first, second, and outer shells to this quantity. We show that, even if the main contribution comes from the first shell, the contribution of the second shell can become important at low temperature. While real water appears to be less ordered at short distance than obtained by any of the potentials, the different water potentials show more or less order compared to the experiments depending on the considered length-scale.

  • 4.
    Camisasca, Gaia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Zhovtobriukh, Iurii
    Stockholm University, Faculty of Science, Department of Physics.
    Pitsevich, George
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    A proposal for the structure of high- and low-density fluctuations in liquid water2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 3, article id 034508Article in journal (Refereed)
    Abstract [en]

    Based on recent experimental data that can be interpreted as indicating the presence of specific structures in liquid water, we build and optimize two structural models which we compare with the available experimental data. To represent the proposed high-density liquid structures, we use a model consisting of chains of water molecules, and for low-density liquid, we investigate fused dodecahedra as templates for tetrahedral fluctuations. The computed infrared spectra of the models are in very good agreement with the extracted experimental spectra for the two components, while the extracted structures from molecular dynamics (MD) simulations give spectra that are intermediate between the experimentally derived spectra. Computed x-ray absorption and emission spectra as well as the O-O radial distribution functions of the proposed structures are not contradicted by experiment. The stability of the proposed dodecahedral template structures is investigated in MD simulations by seeding the starting structure, and remnants found to persist on an similar to 30 ps time scale. We discuss the possible significance of such seeds in simulations and whether they can be viable candidates as templates for structural fluctuations below the compressibility minimum of liquid water.

  • 5. Iorio, A.
    et al.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Rovere, M.
    Gallo, P.
    Characterization of hydration water in supercooled water-trehalose solutions: The role of the hydrogen bonds network2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044507Article in journal (Refereed)
    Abstract [en]

    The structural and dynamical properties of hydration water in aqueous solutions of trehalose are studied with molecular dynamics simulation. We simulate the systems in the supercooled region to investigate how the interaction with the trehalose molecules modifies the hydrogen bond network, the structural relaxation, and the diffusion properties of hydration water. The analysis is performed by considering the radial distribution functions, the residence time of water molecules in the hydration shell, the two body excess entropy, and the hydrogen bond water-water and water-trehalose correlations of the hydration water. The study of the two body excess entropy shows the presence of a fragile to strong crossover in supercooled hydration water also found in the relaxation time of the water-water hydrogen bond correlation function, and this is in agreement with predictions of the mode coupling theory and of previous studies of the oxygen-oxygen density correlators [A. Iorio et al., J. Mol. Liq. 282, 617 (2019); Sci. China: Phys., Mech. Astron. 62, 107011 (2019)]. The water-trehalose hydrogen bond correlation function instead evidences a strong to strong crossover in the relaxation time, and this crossover is related to a trehalose dynamical transition. This signals the role that the strong interplay between the soluted molecules and the surrounding solvent has in determining the dynamical transition common to both components of the system that happens upon cooling and that is similar to the well known protein dynamical transition. We connect our results with the cryoprotecting role of trehalose molecules.

  • 6. Iorio, Antonio
    et al.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Gallo, Paola
    Glassy dynamics of water at interface with biomolecules: A Mode Coupling Theory test2019In: Science China Physics, mechanics & astonomy, ISSN 1674-7348, Vol. 62, no 10, article id 107011Article in journal (Refereed)
    Abstract [en]

    We study the slow dynamics of hydration water upon cooling in two di ff erent biological aqueous solutions, one containing a molecule of lysozyme and another with trehalose molecules. In particular we test if the glassy behaviour of these solutions ful fi ls the predictions of the popular Mode Coupling Theory of glassy dynamics. In particular we test the Time Temperature Superposition Principle and the matching of the exponents of the theory. Our results con fi rm that this theory is able to describe the dynamical behaviour of supercooled water also in non ideal cases as the ones under investigation in the region of mild supercooling.

  • 7. Iorio, Antonio
    et al.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Gallo, Paola
    Slow dynamics of hydration water and the trehalose dynamical transition2019In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 282, p. 617-625Article in journal (Refereed)
    Abstract [en]

    We present results from molecular dynamics simulations of a solution of water and trehalose, a cryoprotecting disaccharide, upon cooling. We focus our attention on both the dynamics of hydration water and of the trehalose. Hydration water presents two slow relaxations. One is the a relaxation typical of glass formers and the second one is a long relaxation that was also found in proteins hydration water and appears coupled to the movement of the surface of trehaloses. Below 280 K trehalose aggregates and upon further cooling we find a dynamical transition for the trehalose aggregate at around 250 K similar to the well known Protein Dynamical Transition. When this transition happens the long relaxation time has a dynamical crossover. We hypothesize that this dynamical transition is a general feature that can be found not only in proteins but also in aggregates that interact with water and that have a flexible structure. In fact this feature has already been found not only in proteins hydration water but also in a colloidal microgel. In the known cases, including the one that we present here, water enhances movements of the surface of these aggregates above a certain temperature. The temperature of this dynamical transition ranges between 260 K and 220 K in all known cases.

  • 8.
    Mariedahl, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Benmore, Chris
    Pettersson, Lars Gunnar Moody
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Arnann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 30, p. 7616-7624Article in journal (Refereed)
    Abstract [en]

    The structure factor and oxygen-oxygen pair distribution functions of amorphous ices at liquid nitrogen temperature (T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 angstrom, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 angstrom, respectively, with high accuracy due to measurements up to a large momentum transfer of 23 angstrom(-1). Similarities in pair-distribution functions between LDA and supercooled water at 254.1 K, HDA and liquid water at 365.9 K, and VHDA and high-pressure liquid water were found up to around 8 angstrom, but beyond that at longer distances, the similarities were lost. In addition, the structure of the high-density amorphous ices was compared to high-pressure crystalline ices IV, IX, and XII, and conclusions were drawn about the local ordering.

  • 9.
    Perakis, Fivos
    et al.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Camisasca, Gaia
    Stockholm University, Faculty of Science, Department of Physics.
    Lane, Thomas J.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas A.
    Lehmkühler, Felix
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Amann-Winkel, Katrin
    Stockholm University, Faculty of Science, Department of Physics.
    Schreck, Simon
    Stockholm University, Faculty of Science, Department of Physics.
    Song, Sanghoon
    Sato, Takahiro
    Sikorski, Marcin
    Eilert, Andre
    McQueen, Trevor
    Ogasawara, Hirohito
    Nordlund, Dennis
    Roseker, Wojciech
    Koralek, Jake
    Nelson, Silke
    Hart, Philip
    Alonso-Mori, Roberto
    Feng, Yiping
    Zhu, Diling
    Robert, Aymeric
    Grübel, Gerhard
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Coherent X-rays reveal the influence of cage effects on ultrafast water dynamics2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1917Article in journal (Refereed)
    Abstract [en]

    The dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.

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