Reorientional dynamics of water molecules in anionic hydration shells

Laage, Damien; Hynes, James T.

doi:10.1073/pnas.0701699104

Cited by 282 publications

(387 citation statements)

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“…The correlation times apparent from the 2D spectra and the mixed quantum-classical derived frequency calculations are well below the picosecond HB lifetimes reported here and in the literature, 14,22 i.e., we are able to discern sub-100 fs structural fluctuations from slower hydrogen bond exchange dynamics. Owing to the short vibrational lifetimes of 300 fs, these exchange processes do not contribute significantly to the observed 2D line shapes.…”

Section: Discussionmentioning

confidence: 66%

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Ultrafast phosphate hydration dynamics in bulk H2O

Costard

Tyborski

Fingerhut

et al. 2015

The Journal of Chemical Physics

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Phosphate vibrations serve as local probes of hydrogen bonding and structural fluctuations of hydration shells around ions. Interactions of H2PO4− ions and their aqueous environment are studied combining femtosecond 2D infrared spectroscopy, ab-initio calculations, and hybrid quantum-classical molecular dynamics (MD) simulations. Two-dimensional infrared spectra of the symmetric (νS(PO2−)) and asymmetric (νAS(PO2−)) PO2− stretching vibrations display nearly homogeneous lineshapes and pronounced anharmonic couplings between the two modes and with the δ(P-(OH)2) bending modes. The frequency-time correlation function derived from the 2D spectra consists of a predominant 50 fs decay and a weak constant component accounting for a residual inhomogeneous broadening. MD simulations show that the fluctuating electric field of the aqueous environment induces strong fluctuations of the νS(PO2−) and νAS(PO2−) transition frequencies with larger frequency excursions for νAS(PO2−). The calculated frequency-time correlation function is in good agreement with the experiment. The ν(PO2−) frequencies are mainly determined by polarization contributions induced by electrostatic phosphate-water interactions. H2PO4−/H2O cluster calculations reveal substantial frequency shifts and mode mixing with increasing hydration. Predicted phosphate-water hydrogen bond (HB) lifetimes have values on the order of 10 ps, substantially longer than water-water HB lifetimes. The ultrafast phosphate-water interactions observed here are in marked contrast to hydration dynamics of phospholipids where a quasi-static inhomogeneous broadening of phosphate vibrations suggests minor structural fluctuations of interfacial water.

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Section: Discussionmentioning

confidence: 66%

“…The mean HB lifetime has values of 1-2 ps in the bulk, limited by HB exchange events within 100 fs. 10,22 The role of ions in accelerating or retarding water dynamics has been discussed controversially. 23 2D IR spectra of water vibrations are spatially unselective, i.e., contain both hydration shell and bulk contributions.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast phosphate hydration dynamics in bulk H2O

Costard

Tyborski

Fingerhut

et al. 2015

The Journal of Chemical Physics

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“…From the measurement of l, it is not possible to independently determine j and j . It has been found from MD simulations of an aqueous 1 M NaCl solution that the jump angles of water molecules are 63°and 70°for switching their hydrogen bond partners from water to water and from Cl Ϫ to water, respectively (12,43). For j ϭ 63°, l ϭ 1.17 j , and for j ϭ 70°, l ϭ 1.03 j .…”

Section: Resultsmentioning

confidence: 99%

“…Recently, Laage and Hynes (12,43) have shown that the orientational relaxation of water molecules in pure water and ionic solutions is described by a jump reorientation model rather than Gaussian orientational diffusion. This model was recently applied to nanoscopic water in Nafion fuel cell membranes (19).…”

Section: Resultsmentioning

confidence: 99%

Hydrogen bond dynamics in aqueous NaBr solutions

Park

Fayer

2007

Proc. Natl. Acad. Sci. U.S.A.

294

403

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Hydrogen bond dynamics of water in NaBr solutions are studied by using ultrafast 2D IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments. The hydrogen bond structural dynamics are observed by measuring spectral diffusion of the OD stretching mode of dilute HOD in H2O in a series of high concentration aqueous NaBr solutions with 2D IR vibrational echo spectroscopy. The time evolution of the 2D IR spectra yields frequency-frequency correlation functions, which permit quantitative comparisons of the influence of NaBr concentration on the hydrogen bond dynamics. The results show that the global rearrangement of the hydrogen bond structure, which is represented by the slowest component of the spectral diffusion, slows, and its time constant increases from 1.7 to 4.8 ps as the NaBr concentration increases from pure water to Ϸ6 M NaBr. Orientational relaxation is analyzed with a wobbling-in-a-cone model describing restricted orientational diffusion that is followed by complete orientational randomization described as jump reorientation. The slowest component of the orientational relaxation increases from 2.6 ps (pure water) to 6.7 ps (Ϸ6 M NaBr). Vibrational population relaxation of the OD stretch also slows significantly as the NaBr concentration increases.ultrafast 2D IR spectroscopy ͉ water dynamics in ionic solutions W ater plays an important role in chemical and biological processes. In aqueous solutions, water molecules dissolve ionic compounds, charged chemical species, and biomolecules by forming hydration shells (layers) around them. Pure water undergoes rapid structural evolution of the hydrogen bond network that is responsible for water's unique properties (1). A question of fundamental importance is how the dynamics of water in the immediate vicinity of an ion or ionic group differ from those of pure water. For monatomic ions, molecular ions, charged groups of large molecules, or charged amino acids on the surfaces of proteins, the basic structure of hydration shells is determined by ion-dipole interactions between water molecules and the charged group (2, 3). Such ion-dipole interactions will influence both the structure and dynamics of water in the proximity of ions. Water dynamics in ion hydration shells play a significant role in the nature of systems such as proteins and micelles (3) and in processes such as ion transport through transmembrane proteins (4).Over the last several years, the application of ultrafast IR vibrational echo spectroscopy (5, 6), particularly 2D IR vibrational echo experiments, (7, 8) combined with molecular dynamics (MD) simulations (9-12) have greatly enhanced understanding of the hydrogen bond dynamics in pure water. These experiments directly examine the dynamics of water rather than study the indirect influence of water dynamics on a probe molecule (13). The ultrafast 2D IR vibrational echo experiments on water (7, 8) and other hydrogen-bonded systems (14) build upon earlier IR pump-probe experiments that have been extensively used to study ...

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“…However, ultrafast infrared pump-probe studies and their theoretical analysis have come to the surprising conclusion that the diffusive orientational relaxation of water outside the first solvation shell of the ions is hardly affected by the presence of salts. 3,10 This has been shown in aqueous solutions of Mg(ClO 4 ) 2 , NaClO 4 , and Na 2 SO 4 . 3 In all of these cases, infrared pump-probe experiments measure a 2.5 ps decay time for the orientational relaxation of water molecules in bulk water as distinct from water molecules in the relatively stable hydration shells surrounding the cations.…”

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confidence: 99%

Glasslike behavior in aqueous electrolyte solutions

Turton

Hunger

Hefter

et al. 2008

The Journal of Chemical Physics

108

162

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When salts are added to water, the viscosity generally increases suggesting the ions increase the strength of the water's hydrogen-bond network. However, infrared pump-probe measurements on electrolyte solutions have found that ions have no influence on the rotational dynamics of water molecules implying no enhancement or breakdown of the hydrogen-bond network. Here we report optical Kerr-effect and dielectric relaxation spectroscopic measurements, which have enabled us to separate the effects of rotational and transitional motions of the water molecules. These data show that electrolyte solutions behave like a supercooled liquid approaching a glass transition in which rotational and translational molecular motions are decoupled. It is now possible to understand previously conflicting viscosity data, nuclear magnetic resonance relaxation, and ultrafast infrared spectroscopy in a single unified picture.It is well known that when salts are added to water the viscosity typically increases, suggesting that the ions alter the hydrogen-bond network of the water, 1 which appears to be confirmed by, for example, neutron diffraction experiments. 2 However, recent ultrafast infrared pump-probe measurements on electrolyte solutions have found that ions do not influence the rotational dynamics of water molecules suggesting that there is no enhancement or breakdown of the hydrogen-bond network in liquid water. 3 As the effect of ions and ionic moieties on the structure of water is important for understanding protein stability, enzymatic reactions, and substrate binding, it is crucial to resolve this paradox. 4 Here we report ultrafast optical Kerr effect 5 (OKE) and dielectric relaxation 6 (DR) spectroscopy measurements, which show that salt solutions behave like a supercooled liquid approaching a glass transition, where rotational and translational molecular motions become decoupled. The rotational motions of bulk water molecules -observed as an -relaxation in DR -are essentially independent of concentration. The translational motions seen in OKE spectroscopy can be understood as a -relaxation 7 and their dynamics become increasingly inhomogeneous with increasing salt concentration. This insight reconciles previously conflicting viscosity data, 8 nuclear magnetic resonance relaxation, 9 and ultrafast infrared spectroscopy 3 data in a single unifying picture.When simple inorganic salts are added to water, the viscosity typically increases ( see FIG. 1). In the relatively low concentration range (up to ~0.5 M), this is described by the semi-empirical Jones-Dole equation, 1 , which expresses the shear viscosity in terms of the viscosity of pure water 0 , salt concentration c, and parameters A and B. For many salts additional terms have to be added to describe the rapid increase in viscosity at higher concentrations. The obvious conclusion to draw from this behavior is that ions alter the structure of water. Indeed, the empirical Jones-Dole B coefficient is often used to classify ions as either structure makers (kosmotropes...

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Reorientional dynamics of water molecules in anionic hydration shells

Cited by 282 publications

References 36 publications

Ultrafast phosphate hydration dynamics in bulk H2O

Ultrafast phosphate hydration dynamics in bulk H2O

Hydrogen bond dynamics in aqueous NaBr solutions

Glasslike behavior in aqueous electrolyte solutions

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