Reorientation and Allied Dynamics in Water and Aqueous Solutions

Laage, Damien; Stirnemann, Guillaume; Sterpone, Fabio; Rey, Rossend; Hynes, James T.

doi:10.1146/annurev.physchem.012809.103503

Cited by 332 publications

(525 citation statements)

References 144 publications

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“…We recognize that n k⊥ (t) undergoes librational motions and C ⊥ (t) decays on a timescale of 0.01 ps with a minimum at t = 0.023 ps. In liquid water, similar short-time behaviors with local minimum and maximum have been observed in various time-dependent quantities in simulations and experiments as manifestation of librational motions [38][39][40][41] .…”

Section: Orientation Time-correlation Functionssupporting

confidence: 70%

Fluctuations of local electric field and dipole moments in water between metal walls

Takae

Ōnuki

2015

The Journal of Chemical Physics

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We examine the thermal fluctuations of the local electric field E loc k and the dipole moment µ k in liquid water at T = 298 K between metal walls in electric field applied in the perpendicular direction. We use analytic theory and molecular dynamics simulation. In this situation, there is a global electrostatic coupling between the surface charges on the walls and the polarization in the bulk. Then, the correlation function of the polarization density pz(r) along the applied field contains a homogeneous part inversely proportional to the cell volume V . Accounting for the longrange dipolar interaction, we derive the Kirkwood-Fröhlich formula for the polarization fluctuations when the specimen volume v is much smaller than V . However, for not small v/V , the homogeneous part comes into play in dielectric relations. We also calculate the distribution of E loc k in applied field. As a unique feature of water, its magnitude |E loc k | obeys a Gaussian distribution with a large mean value E0 ∼ = 17 V/nm, which arises mainly from the surrounding hydrogen-bonded molecules. Since |µ k |E0 ∼ 30kBT , µ k becomes mostly parallel to E loc k . As a result, the orientation distributions of these two vectors nearly coincide, assuming the classical exponential form. In dynamics, the component of µ k (t) parallel to E loc k (t) changes on the timescale of the hydrogen bonds ∼ 5 ps, while its smaller perpendicular component undergoes librational motions on timescales of 0.01 ps.

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Section: Orientation Time-correlation Functionssupporting

confidence: 70%

Fluctuations of local electric field and dipole moments in water between metal walls

Takae

Ōnuki

2015

The Journal of Chemical Physics

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“…The resolution of this claim, however, depends on the water mode probed by the observations. There is a relatively insignificant slowing down of water's single-molecule rotational dynamics in hydration shells [67]. An attempt to find a separate dynamic process in density fluctuations (translations) probed by depolarized light scattering resulted in the realization that cross protein-water correlations, instead of a separate dynamic process, can explain the data [68].…”

Section: Discussion and Implications For The Protein Dynamical Trmentioning

confidence: 99%

Dynamical and orientational structural crossovers in low-temperature glycerol

2016

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Mean square displacements of hydrogen atoms in glass-forming materials and proteins, as reported by incoherent elastic neutron scattering, show kinks in their temperature dependence. This crossover, known as the dynamical transition, connects two approximately linear regimes. It is often assigned to the dynamical freezing of subsets of molecular modes at the point of equality between their corresponding relaxation times and the instrumental observation window. The origin of the dynamical transition in glass-forming glycerol is studied here by extensive molecular dynamics simulations. We find the dynamical transition to occur for both the center of mass translations and the molecular rotations at the same temperature, insensitive to changes of the observation window. Both the translational and rotational dynamics of glycerol show a dynamic crossover from the structural to a secondary relaxation at the temperature of the dynamical transition. A significant and discontinuous increase in the orientational Kirkwood factor and in the dielectric constant is observed in the same range of temperatures. We, however, do not find any indications of a true thermodynamic transition to an ordered low-temperature phase. We therefore suggest that all observed crossovers are dynamic in character. The increase in the dielectric constant is related to the dynamic freezing of dipolar domains on the time-scale of simulations.

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“…hydrophobic hydration | hydrogen bonding | IR spectroscopy | electrostatic screening | ab initio molecular dynamics D espite its great importance in numerous phenomena, the origin of hydrophobicity remains one of the most disputed topics in science (1)(2)(3)(4)(5). Experimental studies have shown that small purely hydrophobic solutes (alkanes and noble gases) in water increase the order (6,7) and restrict the mobility (8) of neighboring water molecules.…”

mentioning

confidence: 99%

“…Neutron diffraction (11,12) and extended X-ray absorption fine structure (EXAFS) (13) studies, however, show that the water molecules around small purely hydrophobic molecules do not differ significantly from those in pure liquid water. According to the dynamic view, the hydrophobic solute causes slowdown of the dynamics of the nearby water molecules by obstructing the jump mechanism of rotational relaxation, whereas water structure and H-bonding strength remain basically unchanged (5,14). The main problem of these two views is that there is essentially no direct experimental support for enhanced H bonding and resulting formation of icebergs in the hydration shell of small purely hydrophobic solutes (15) or a jump mechanism of rotational relaxation of the water molecules (5).…”

mentioning

confidence: 99%

Origin of hydrophobicity and enhanced water hydrogen bond strength near purely hydrophobic solutes

Grdadolnik

Merzel

Avbelj

2016

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

201

145

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Hydrophobicity plays an important role in numerous physicochemical processes from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that, in the presence of a hydrophobic solute, water forms transient microscopic "icebergs" arising from strengthened water hydrogen bonding, but there is no experimental evidence for enhanced hydrogen bonding and/or icebergs in such solutions. Here, we have used the redshifts and line shapes of the isotopically decoupled IR oxygen-deuterium (O-D) stretching mode of HDO water near small purely hydrophobic solutes (methane, ethane, krypton, and xenon) to study hydrophobicity at the most fundamental level. We present unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10-15 per methane molecule. Ab initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous, and more tetrahedrally oriented hydrogen bonds than those in bulk water and that their mobility is restricted. We show the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration.hydrophobic hydration | hydrogen bonding | IR spectroscopy | electrostatic screening | ab initio molecular dynamics D espite its great importance in numerous phenomena, the origin of hydrophobicity remains one of the most disputed topics in science (1-5). Experimental studies have shown that small purely hydrophobic solutes (alkanes and noble gases) in water increase the order (6, 7) and restrict the mobility (8) of neighboring water molecules. There are several opposing views on how to explain these data. The classical view is that a solute modifies water structure by forming transient, semiordered clathrate-like clusters ("icebergs"; used here only as a loose term) around it, arising from enhanced water hydrogen bonding (H bonding) (6, 7). This enhancement is brought about by either strengthening (9) or increasing the number of water to water H bonds (10). The classical view explains the characteristic changes in the thermodynamic variables of hydrophobic hydration (positive ΔG, ΔC p , negative ΔS, and ΔH) and the restricted mobility of water molecules observed by NMR (8). Neutron diffraction (11, 12) and extended X-ray absorption fine structure (EXAFS) (13) studies, however, show that the water molecules around small purely hydrophobic molecules do not differ significantly from those in pure liquid water. According to the dynamic view, the hydrophobic solute causes slowdown of t...

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Reorientation and Allied Dynamics in Water and Aqueous Solutions

Cited by 332 publications

References 144 publications

Fluctuations of local electric field and dipole moments in water between metal walls

Fluctuations of local electric field and dipole moments in water between metal walls

Dynamical and orientational structural crossovers in low-temperature glycerol

Origin of hydrophobicity and enhanced water hydrogen bond strength near purely hydrophobic solutes

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