@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 {2019|2139, title = {Effect of Ions on Water Dynamics in Dilute and Concentrated Aqueous Salt Solutions}, journal = {J Phys Chem B}, volume = {123}, year = {2019}, month = {Apr}, pages = {3312-3324}, abstract = {

Aqueous ionic solutions are ubiquitous in chemistry and in biology. Experiments show that ions affect water dynamics, but a full understanding of several questions remains needed: why some salts accelerate water dynamics while others slow it down, why the effect of a given salt can be concentration-dependent, whether the effect of ions is rather local or more global. Numerical simulations are particularly suited to disentangle these different effects, but current force fields suffer from limitations and often lead to a poor description of dynamics in several aqueous salt solutions. Here, we develop an improved classical force field for the description of alkali halides that yields dynamics in excellent agreement with experimental measurements for water reorientational and translational dynamics. These simulations are analyzed with an extended jump model, which allows to compare the effects of ions on local hydrogen-bond exchange dynamics and on more global properties like viscosity. Our results unambiguously show that the ion-induced changes in water dynamics are usually mostly due to a local effect on the hydrogen-bond exchange dynamics; in contrast, the change in viscosity leads to a smaller effect, which governs the retardation only for a minority of salts and at high concentrations. We finally show how the respective importance of these two effects can be directly determined from experimental measurements alone, thus providing guidelines for the selection of an electrolyte with specific dynamical properties.

}, doi = {10.1021/acs.jpcb.9b01053}, author = {Laage, Damien and Guillaume Stirnemann} } @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 {2017|2024, title = {Ab Initio Simulations of Water Dynamics in Aqueous TMAO Solutions: Temperature and Concentration Effects}, journal = {J Phys Chem B}, year = {2017}, month = {Dec}, abstract = {

We use ab initio molecular dynamics simulation to study the effect of hydrophobic groups on the dynamics of water molecules in aqueous solutions of trimethylamine N-oxide (TMAO). We show that hydrophobic groups induce a moderate (\<2-fold) slowdown of water reorientation and hydrogen-bond dynamics in dilute solutions, but that this slowdown rapidly increases with solute concentration. In addition, the slowdown factor is found to vary very little with temperature, thus suggesting an entropic origin. All of these results are in quantitative agreement with prior classical molecular dynamics simulations and with the previously suggested excluded-volume model. The hydrophilic TMAO headgroup is found to affect water dynamics more strongly than the hydrophobic moiety, and the magnitude of this slowdown is very sensitive to the strength of the water-solute hydrogen-bond.

}, doi = {10.1021/acs.jpcb.7b09989}, author = {Guillaume Stirnemann and Elise Dubou{\'e}-Dijon and Laage, Damien} } @article {2016|2027, title = {Orientational Dynamics of Water at an Extended Hydrophobic Interface}, journal = {J Am Chem Soc}, volume = {138}, year = {2016}, month = {May}, pages = {5551-60}, abstract = {

We report on the orientational dynamics of water at an extended hydrophobic interface with an octadecylsilane self-assembled monolayer on fused silica. The interfacial dangling OH stretch mode is excited with a resonant pump, and its evolution followed in time by a surface-specific, vibrationally resonant, infrared-visible sum-frequency probe. High sensitivity pump-probe anisotropy measurements and isotopic dilution clearly reveal that the decay of the dangling OH stretch excitation is almost entirely due to a jump to a hydrogen-bonded configuration that occurs in 1.61 $\pm$ 0.10 ps. This is more than twice as fast as the jump time from one hydrogen-bonded configuration to another in bulk H2O but about 50\% slower than the reported out-of-plane reorientation at the air/water interface. In contrast, the intrinsic population lifetime of the dangling OH stretch in the absence of such jumps is found to be \>10 ps. Molecular dynamics simulations of air/water and hexane/water interfaces reproduce the fast jump dynamics of interfacial dangling OH with calculated jump times of 1.4 and 1.7 ps for the air and hydrophobic interfaces, respectively. The simulations highlight that while the air/water and hydrophobic/water surfaces exhibit great structural similarities, a small stabilization of the OH groups by the hydrophobic interface produces the pronounced difference in the dynamics of dangling bonds.

}, doi = {10.1021/jacs.6b01820}, author = {Xiao, Shunhao and Figge, Florian and Guillaume Stirnemann and Laage, Damien and McGuire, John A} } @article {2013|1797, title = {Biomolecular hydration dynamics: a jump model perspective}, journal = {Chem. Soc. Rev.}, volume = {42}, number = {13}, year = {2013}, pages = {5672{\textendash}5683}, author = {Fogarty, Aoife C. and Elise Dubou{\'e}-Dijon and Sterpone, Fabio and Hynes, James T. and Laage, Damien} } @article {2013|1670, title = {Mechanisms of acceleration and retardation of water dynamics by ions}, journal = {J. Am. Chem. Soc.}, volume = {135}, year = {2013}, pages = {11824{\textendash}11831}, abstract = {

There are fundamental and not yet fully resolved questions concerning the impact of solutes, ions in particular, on the structure and dynamics of water, which can be formulated as follows: Are the effects of ions local or long-ranged? Is the action of cations and anions on water cooperative or not? Here, we investigate how the reorientation and hydrogen-bond dynamics of water are affected by ions in dilute and concentrated aqueous salt solutions. By combining simulations and analytic modeling, we first show that ions have a short-ranged influence on the reorientation of individual water molecules and that depending on their interaction strength with water, they may accelerate or slow down water dynamics. A simple additive picture combining the effects of the cations and anions is found to provide a good description in dilute solutions. In concentrated solutions, we show that the average water reorientation time ceases to scale linearly with salt concentration due to overlapping hydration shells and structural rearrangements which reduce the translational displacements induced by hydrogen-bond switches and increase the solution viscosity. This effect is not ion-specific and explains why all concentrated salt solutions slow down water dynamics. Our picture, which is demonstrated to be robust vis-a-vis a change in the force-field, reconciles the seemingly contradictory experimental results obtained by ultrafast infrared and NMR spectroscopies, and suggests that there are no long-ranged cooperative ion effects on the dynamics of individual water molecules in dilute solutions.

}, issn = {00027863}, author = {Guillaume Stirnemann and Wernersson, Erik and Jungwirth, Pavel and Laage, Damien} } @article {2012|1676, title = {Communication: On the origin of the non-Arrhenius behavior in water reorientation dynamics}, journal = {J. Chem. Phys.}, volume = {137}, year = {2012}, abstract = {

We combine molecular dynamics simulations and analytic modeling to determine the origin of the non-Arrhenius temperature dependence of liquid water{\textquoteright}s reorientation and hydrogen-bond dynamics between 235 K and 350 K. We present a quantitative model connecting hydrogen-bond exchange dynamics to local structural fluctuations, measured by the asphericity of Voronoi cells associated with each water molecule. For a fixed local structure the regular Arrhenius behavior is recovered, and the global anomalous temperature dependence is demonstrated to essentially result from a continuous shift in the unimodal structure distribution upon cooling. The non-Arrhenius behavior can thus be explained without invoking an equilibrium between distinct structures. In addition, the large width of the homogeneous structural distribution is shown to cause a growing dynamical heterogeneity and a non-exponential relaxation at low temperature.

}, issn = {00219606}, author = {Guillaume Stirnemann and Laage, Damien} } @article {2012|1488, title = {Magnitude and molecular origin of water slowdown next to a protein}, journal = {J. Am. Chem. Soc.}, volume = {134}, year = {2012}, pages = {4116{\textendash}4119}, abstract = {

Hydration shell dynamics plays a critical role in protein folding and biochemical activity and has thus been actively studied through a broad range of techniques. While all observations concur with a slowdown of water dynamics relative to the bulk, the magnitude and molecular origin of this retardation remain unclear. Via numerical simulations and theoretical modeling, we establish a molecular description of protein hydration dynamics and identify the key protein features that govern it. Through detailed microscopic mapping of the water reorientation and hydrogen-bond (HB) dynamics around lysozyme, we first determine that 80\% of the hydration layer waters experience a moderate slowdown factor of \~{}2-3, while the slower residual population is distributed along a power-law tail, in quantitative agreement with recent NMR results. We then establish that the water reorientation mechanism at the protein interface is dominated by large angular jumps similar to the bulk situation. A theoretical extended jump model is shown to provide the first rigorous determination of the two key contributions to the observed slowdown: a topological excluded-volume factor resulting from the local protein geometry, which governs the dynamics of the fastest 80\% of the waters, and a free energetic factor arising from the water-protein HB strength, which is especially important for the remaining waters in confined sites at the protein interface. These simple local factors are shown to provide a nearly quantitative description of the hydration shell dynamics.

}, issn = {00027863}, author = {Fabio Sterpone and Guillaume Stirnemann 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|1690, title = {Dynamics of water in concentrated solutions of amphiphiles: Key roles of local structure and aggregation}, journal = {J. Phys. Chem. B}, volume = {115}, year = {2011}, pages = {3254{\textendash}3262}, abstract = {

Water translational and reorientational dynamics in concentrated solutions of amphiphiles are investigated through molecular dynamics simulations and analytic modeling. We evidence the critical importance of the solute concentration in determining the magnitude of the slowdown in water dynamics compared to the bulk situation. The comparison of concentrated aqueous solutions of tetramethylurea, which tends to aggregate, and of trimethylamine N-oxide, which does not, shows the dramatic impact of solute clustering on the water dynamics. No significant decoupling of the reorientation and translation dynamics of water is observed, even at very high solute concentrations. The respective roles of energetic and topological disorders in determining the translational subdiffusive water dynamics in these confining environments are discussed. The water reorientational dynamics is shown to be quantitatively described by an extended jump model which combines two factors determined by the local structure: the transition-state excluded volume and the transition-state hydrogen-bond strength.

}, issn = {15206106}, author = {Guillaume Stirnemann and Fabio Sterpone and Laage, Damien} } @article {2011|1738, title = {Non-monotonic dependence of water reorientation dynamics on surface hydrophilicity: competing effects of the hydration structure and hydrogen-bond strength}, journal = {Phys. Chem. Chem. Phys.}, volume = {13}, year = {2011}, pages = {19911}, abstract = {

The reorientation dynamics of interfacial water molecules was recently shown to change non-monotonically next to surfaces of increasing hydrophilicity, with slower dynamics next to strongly hydrophobic (apolar) and very hydrophilic surfaces, and faster dynamics next to surfaces of intermediate hydrophilicities. Through a combination of molecular dynamics simulations and analytic modeling, we provide a molecular interpretation of this behavior. We show that this non-monotonic dependence arises from two competing effects induced by the increasing surface hydrophilicity: first a change in the hydration structure with an enhanced population of water OH bonds pointing toward the surface and second a strengthening of the water-surface interaction energy. The extended jump model, including the effects due to transition-state excluded volume and transition-state hydrogen-bond strength, provides a quasi-quantitative description of the non-monotonic changes in the water reorientation dynamics with surface hydrophilicity.

}, issn = {1463-9076}, author = {Guillaume Stirnemann and Castrillon, Santiago Romero-Vargas and Hynes, James T. and Rossky, Peter J. and Debenedetti, Pablo G. and Laage, Damien} } @article {2011|1383, title = {Reorientation and Allied Dynamics in Water and Aqueous Solutions}, journal = {Annu. Rev. Phys. Chem.}, volume = {62}, year = {2011}, pages = {395{\textendash}416}, abstract = {

The reorientation of a water molecule is important for a host of phenomena, ranging over?in an only partial listing?the key dynamic hydrogen-bond network restructuring of water itself, aqueous solution chemical reaction mechanisms and rates, ion transport in aqueous solution and membranes, protein folding, and enzymatic activity. This review focuses on water reorientation and related dynamics in pure water, and for aqueous solutes with hydrophobic, hydrophilic, and amphiphilic character, ranging from tetramethylurea to halide ions and amino acids. Attention is given to the application of theory, simulation, and experiment in the probing of these dynamics, in usefully describing them, and in assessing the description. Special emphasis is placed on a novel sudden, large-amplitude jump mechanism for water reorientation, which contrasts with the commonly assumed Debye rotational diffusion mechanism, characterized by small-amplitude angular motion. Some open questions and directions for further research are also discussed. Expected final online publication date for the Annual Review of Physical Chemistry Volume 62 is March 31, 2011. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.

}, isbn = {0066-426X 1545-1593}, issn = {0066-426X}, doi = {doi: 10.1146/annurev.physchem.012809.103503}, url = {http://www.annualreviews.org/doi/abs/10.1146/annurev.physchem.012809.103503$\backslash$nhttp://www.annualreviews.org.login.ezproxy.lib.purdue.edu/doi/pdf/10.1146/annurev.physchem.012809.103503}, author = {Laage, Damien and Guillaume Stirnemann and Fabio Sterpone and Rey, Rossend and Hynes, James T.} } @article {2011|1691, title = {On the reorientation and hydrogen-bond dynamics of Alcohols}, journal = {J. Phys. Chem. B}, volume = {115}, year = {2011}, pages = {12173{\textendash}12178}, abstract = {

The mechanism of the OH bond reorientation in liquid methanol and ethanol is examined. It is found that the extended jump model, recently developed for water, describes the OH reorientation in these liquids. The slower reorientational dynamics in these alcohols compared to water can be explained by two key factors. The alkyl groups on the alcohol molecules exclude potential partners for hydrogen bonding exchanges, an effect that grows with the size of the alkyl chain. This increases the importance of the reorientation of intact hydrogen bonds, which also slows with increasing size of the alcohol and becomes the dominant reorientation pathway.

}, issn = {15206106}, author = {Vartia, Anthony A. and Mitchell-Koch, Katie R. and Guillaume Stirnemann and Laage, Damien and Thompson, Ward H.} } @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|1696, title = {Direct evidence of angular jumps during water reorientation through two-dimensional infrared anisotropy}, journal = {J. Phys. Chem. Lett.}, volume = {1}, year = {2010}, pages = {1511{\textendash}1516}, abstract = {

Water reorientation was recently suggested via simulations to proceed through large angular jumps, but direct experimental evidence has so far remained elusive. Here we show that both infrared pump-probe and photon echo spectroscopies can provide such evidence through the measurement of the two-dimensional anisotropy decay. We calculate these two-dimensional anisotropies from simulations and show they can be interpreted as a vibrational frequency-dependent resolved orientation time-correlation function. We develop a frequency-dependent extended jump model to predict the nature of the angular jump signature in these anisotropies. This model provides a rigorous and unambiguous connection between ultrafast infrared experimental results and the presence of angular jumps in bulk water, and calls for new experiments.

}, issn = {19487185}, doi = {10.1021/jz100385r}, author = {Guillaume Stirnemann and Laage, Damien} } @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.} }