@article {2020|2141, title = {Water dynamics at electrified graphene interfaces: a jump model perspective}, journal = {Phys Chem Chem Phys}, year = {2020}, month = {Mar}, abstract = {

The reorientation dynamics of water at electrified graphene interfaces was recently shown [J. Phys. Chem. Lett., 2020, 11, 624-631] to exhibit a surprising and strongly asymmetric behavior: positive electrode potentials slow down interfacial water reorientation, while for increasingly negative potentials water dynamics first accelerates before reaching an extremum and then being retarded for larger potentials. Here we use classical molecular dynamics simulations to determine the molecular mechanisms governing water dynamics at electrified interfaces. We show that changes in water reorientation dynamics with electrode potential arise from the electrified interfaces\&$\#$39; impacts on water hydrogen-bond jump exchanges, and can be quantitatively described by the extended jump model. Finally, our simulations indicate that no significant dynamical heterogeneity occurs within the water interfacial layer next to the weakly interacting graphene electrode.

}, doi = {10.1039/d0cp00359j}, author = {Zhang, Yiwei and Guillaume Stirnemann and Hynes, James T and Laage, Damien} } @article {2018|2133, title = {Water dynamics in concentrated electrolytes: Local ion effect on hydrogen-bond jumps rather than collective coupling to ion clusters}, journal = {Proc Natl Acad Sci U S A}, volume = {115}, year = {2018}, month = {05}, pages = {E4953-E4954}, doi = {10.1073/pnas.1803988115}, author = {Guillaume Stirnemann and Jungwirth, Pavel and Laage, Damien} } @article {2012|1684, title = {Water jump reorientation and ultrafast vibrational spectroscopy}, journal = {J. Photochem. Photobiol. A}, volume = {234}, year = {2012}, pages = {75{\textendash}82}, abstract = {

The reorganization of water{\textquoteright}s hydrogen-bond (HB) network by breaking and making HBs lies at the heart of many of the pure liquid{\textquoteright}s special features and many aqueous media phenomena, including chemical reactions, ion transport and protein activity. An essential role in this reorganization is played by water molecule reorientation, long described by very small angular displacement Debye rotational diffusion. A markedly contrasting picture has been recently proposed, based on simulation and analytic modeling: a sudden, large amplitude jump mechanism, in which the reorienting water molecule rapidly exchanges HB partners in an activated process which has all the hallmarks of a chemical reaction. In this contribution, we offer a brief review of the jump mechanism together with a discussion of its application to, and probing by, modern ultrafast infrared spectroscopy experiments. Special emphasis is given to the direct characterization of the jumps via pioneering two-dimensional infrared spectroscopic measurements. ?? 2012 Elsevier B.V. All rights reserved.

}, keywords = {Hydrogen-bond dynamics, Pump-probe infrared spectroscopy, Two-dimensional infrared spectroscopy, Water dynamics}, issn = {10106030}, author = {Laage, Damien and Guillaume Stirnemann and Hynes, James T.} } @article {2012, title = {Water Jump Reorientation: From Theoretical Prediction to Experimental Observation}, journal = {Acc. Chem. Res.}, volume = {45}, number = {1}, year = {2012}, pages = {53{\textendash}62}, doi = {10.1021/ar200075u}, author = {Laage, Damien and Guillaume Stirnemann and Sterpone, Fabio and Hynes, James T.} } @article {2011|1739, title = {Water reorientation dynamics in the first hydration shells of F- and I-}, journal = {Phys. Chem. Chem. Phys.}, volume = {13}, year = {2011}, pages = {19895}, abstract = {

Molecular dynamics and analytic theory results are presented for the reorientation dynamics of first hydration shell water molecules around fluoride and iodide anions. These ions represent the extremes of the (normal) halide series in terms of their size and conventional structure-making and -breaking categorizations. The simulated reorientation times are consistent with NMR and ultrafast IR experimental results. They are also in good agreement with the theoretical predictions of the analytic Extended Jump Model. Analysis through this model shows that while sudden, large amplitude jumps (in which the reorienting water exchanges hydrogen-bond partners) are the dominant reorientation pathway for the I(-) case, they are comparatively less important for the F(-) case. In particular, the diffusive reorientation of an intact F(-)...H(2)O hydrogen-bonded pair is found to be most important for the reorientation time, a feature related to the greater hydrogen-bond strength for the F(-)...H(2)O pair. The dominance of this effect for e.g. multiply charged ions is suggested.

}, issn = {1463-9076}, author = {Boisson, Jean and Guillaume Stirnemann and Laage, Damien and Hynes, James T.} } @article {2010|1692, title = {Water hydrogen bond dynamics in aqueous solutions of amphiphiles}, journal = {J. Phys. Chem. B}, volume = {114}, year = {2010}, pages = {3052{\textendash}3059}, abstract = {

The hydrogen bond dynamics of water in a series of amphiphilic solute solutions are investigated through simulations and analytic modeling with an emphasis on the interpretation of experimentally accessible two-dimensional infrared (2D IR) photon echo spectra. We evidence that for most solutes the major effect in the hydration dynamics comes from the hydrophilic groups. These groups can retard the water dynamics much more significantly than can hydrophobic groups by forming strong hydrogen bonds with water. By contrast, hydrophobic groups are shown to have a very moderate effect on water hydrogen bond breaking kinetics. We also present the first calculation of the 2D IR spectra for these solutions. While 2D IR spectroscopy is a powerful technique to probe water hydrogen bond network fluctuations, interpretations of aqueous solution spectra remain ambiguous. We show that a complementary approach through simulations and calculation of the spectra lifts the ambiguity and provides a clear connection between the simulated molecular picture and the experimental spectroscopy data. For amphiphilic solute solutions, we show that, in contrast with techniques such as NMR or ultrafast anisotropy, 2D IR spectroscopy can discriminate between waters next to the solutes hydrophobic and hydrophilic groups. We also evidence that the water dynamics slowdown due to the hydrophilic groups is dramatically enhanced in the 2D IR spectral relaxation, because these groups can induce a slow chemical exchange with the bulk, even when recognized exchange signatures are absent. Implications for the understanding of water around chemically heterogeneous systems such as protein surfaces and for the interpretation of 2D IR spectra in these cases are discussed.

}, issn = {15206106}, author = {Guillaume Stirnemann and Hynes, James T. and Laage, Damien} } @article {2010|1832, title = {Water hydrogen-bond dynamics around amino acids: the key role of hydrophilic hydrogen-bond acceptor groups}, journal = {J. Phys. Chem. B}, volume = {114}, number = {5}, year = {2010}, pages = {2083{\textendash}9}, abstract = {

Water hydrogen-bond (HB) dynamics around amino acids in dilute aqueous solution is investigated through molecular dynamics simulations and analytic modeling. We especially highlight the critical role played by hydrophilic HB acceptors: the strength of the HB formed with water has a pronounced effect on the HB dynamics, in accord with several experimental observations. In contrast, we evidence that hydrophilic HB donors induce a moderate slowdown in the water HB exchange dynamics due to an excluded volume effect, similar to that of hydrophobic groups. We present an analytic model which rationalizes the effect of all examined amino acid sites on the HB dynamics and whose predictions are in excellent agreement with the numerical simulations. This model provides the acceleration or retardation in the HB exchange time with respect to the bulk through the combination of the solute excluded volume factor with the solute-water HB strength factor, both referring to the HB exchange transition state.

}, author = {Sterpone, Fabio and Guillaume Stirnemann and Hynes, James T and Laage, Damien} } @article {2010|1649, title = {Water reorientation, hydrogen-bond dynamics and 2D-IR spectroscopy next to an extended hydrophobic surface.}, journal = {Farad. Discuss.}, volume = {146}, year = {2010}, pages = {263{\textendash}281}, abstract = {

The dynamics of water next to hydrophobic groups is critical for several fundamental biochemical processes such as protein folding and amyloid fiber aggregation. Some biomolecular systems, like melittin or other membrane-associated proteins, exhibit extended hydrophobic surfaces. Due to the strain these surfaces impose on the hydrogen (H)-bond network, the water molecules shift from the clathrate-like arrangement observed around small solutes to an anticlathrate-like geometry with some dangling OH bonds pointing toward the surface. Here we examine the water reorientation dynamics next to a model hydrophobic surface through molecular dynamics simulations and analytic modeling. We show that the water OH bonds lying next to the hydrophobic surface fall into two subensembles with distinct dynamical reorientation properties. The first is the OH bonds tangent to the surface; these exhibit a behavior similar to the water OHs around small hydrophobic solutes, i.e. with a moderate reorientational slowdown explained by an excluded volume effect due to the surface. The second is the dangling OHs pointing toward the surface: these are not engaged in any H-bond, reorient much faster than in the bulk, and exhibit an unusual anisotropy decay which becomes negative for delays of a few picoseconds. The H-bond dynamics, i.e. the exchanges between the different configurations, and the resulting anisotropy decays are analyzed within the analytic extended jump model. We also show that a recent spectroscopy technique, two-dimensional time resolved vibrational spectroscopy (2D-IR), can be used to selectively follow the dynamics of dangling OHs, since these are spectrally distinct from H-bonded ones. By computing the first 2D-IR spectra of water next to a hydrophobic surface, we establish a connection between the spectral dynamics and the dynamical properties that we obtain directly from the simulations.

}, issn = {1359-6640}, author = {Guillaume Stirnemann and Rossky, Peter J and Hynes, James T and Laage, Damien} } @article {2009|1693, title = {Why water reorientation slows without iceberg formation around hydrophobic solutes}, journal = {J. Phys. Chem. B}, volume = {113}, year = {2009}, pages = {2428{\textendash}2435}, abstract = {

The dynamics of water molecules next to hydrophobic solutes is investigated, specifically addressing the recent controversy raised by the first time-resolved observations, which concluded that some water molecules are immobilized by hydrophobic groups, in strong contrast to previous NMR conclusions. Through molecular dynamics simulations and an analytic jump reorientation model, we identify the water reorientation mechanism next to a hydrophobic solute and provide evidence that no water molecules are immobilized by hydrophobic solutes. Their moderate rotational slowdown compared to bulk water (e.g., by a factor of less than 2 at low solute concentration) is mainly due to slower hydrogen-bond exchange. The slowdown is quantitatively described by a solute excluded volume effect at the transition state for the key hydrogen-bond exchange in the reorientation mechanism. We show that this picture is consistent with both ultrafast anisotropy and NMR experimental results and that the transition state excluded volume theory yields quantitative predictions of the rotational slowdown for diverse hydrophobic solutes of varying size over a wide concentration range. We also explain why hydrophobic groups slow water reorientation less than do some hydrophilic groups.

}, author = {Laage, Damien and Guillaume Stirnemann and Hynes, James T.} }