Ions at Aqueous Interfaces: From Water Surface to Hydrated Proteins

Jungwirth, Pavel; Winter, Bernd

doi:10.1146/annurev.physchem.59.032607.093749

Cited by 258 publications

(304 citation statements)

References 154 publications

(238 reference statements)

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“…Since sodium ions contain fewer electrons than chloride ions, our SAXS results suggest that water molecules are ''contracting'' locally more around acidic than around basic surface residues and that protein HS properties are a combined result of a residue-specific ionic interaction and structural changes of water molecules in their vicinity. Indeed, an important factor not taken into account by most SAXS/ SANS programs is the contribution of solvent ions in the vicinity of proteins, which may display concentrations that vary significantly from those in the bulk as a function of the local physicochemical protein surface properties (24,25). Recent MD simulations suggest that ions may either bind specifically and locally to oppositely charged protein surface residues (67,68) or accumulate at nonpolar surface patches (66) as a function of type (i.e., anions/cations) and size, an observation supported by SANS experiments with varying salt concentrations and type (5,33).…”

Section: Protein Hs Density and Ionic Composition Depend On The Surfamentioning

confidence: 99%

“…Increased water density in the first hydration shell (HS), as well as surface-specific differences in the organization of the hydration water, have been reported by MD simulations (17)(18)(19)(20) and have been described thermodynamically in terms of electrorestriction (21). MD studies involving nucleic acids (7,22,23) or proteins (24,25), as well as anomalous x-ray solution studies on proteins and nucleic acids (26,27), have revealed the specific recruitment of ions into their HSs.…”

Section: Introductionmentioning

confidence: 99%

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SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Kim

Martel

Girard

et al. 2016

Biophysical Journal

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Water molecules in the immediate vicinity of biomacromolecules, including proteins, constitute a hydration layer characterized by physicochemical properties different from those of bulk water and play a vital role in the activity and stability of these structures, as well as in intermolecular interactions. Previous studies using solution scattering, crystallography, and molecular dynamics simulations have provided valuable information about the properties of these hydration shells, including modifications in density and ionic concentration. Small-angle scattering of x-rays (SAXS) and neutrons (SANS) are particularly useful and complementary techniques to study biomacromolecular hydration shells due to their sensitivity to electronic and nuclear scattering-length density fluctuations, respectively. Although several sophisticated SAXS/SANS programs have been developed recently, the impact of physicochemical surface properties on the hydration layer remains controversial, and systematic experimental data from individual biomacromolecular systems are scarce. Here, we address the impact of physicochemical surface properties on the hydration shell by a systematic SAXS/SANS study using three mutants of a single protein, green fluorescent protein (GFP), with highly variable net charge (þ36, À6, and À29). The combined analysis of our data shows that the hydration shell is locally denser in the vicinity of acidic surface residues, whereas basic and hydrophilic/hydrophobic residues only mildly modify its density. Moreover, the data demonstrate that the density modifications result from the combined effect of residue-specific recruitment of ions from the bulk in combination with water structural rearrangements in their vicinity. Finally, we find that the specific surface-charge distributions of the different GFP mutants modulate the conformational space of flexible parts of the protein.

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Section: Protein Hs Density and Ionic Composition Depend On The Surfamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Kim

Martel

Girard

et al. 2016

Biophysical Journal

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“…[1,2,3,4,5] Recently, there have been a great deal of theoretical and experimental studies on the ion solvation and ion effects at the electrolyte aqueous solution surfaces. [1,2,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] Ions have long been considered to be depleted from the surface of an aqueous solution of simple electrolytes, such as the alkali halides. [30,31,32] According to the Gibbs adsorption equation, the increase of the surface tension of water with the addition of simple inorganic salts was explained by the assertion that the simple ions can only have a negative adsorption at the aqueous interface.…”

mentioning

confidence: 99%

Spectroscopic evidence for the specific Na+ and K+ interactions with the hydrogen-bonded water molecules at the electrolyte aqueous solution surfaces

Feng

Bian

Guo

et al. 2009

The Journal of Chemical Physics

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Sum frequency generation vibrational spectra of the water molecules at the NaF and KF aqueous solution surfaces showed significantly different spectral features and different concentration dependence. This result is the first direct observation of the cation effects of the simple alkali cations, which have been believed to be depleted from the aqueous surface, on the hydrogen bonding structure of the water molecules at the electrolyte solution surfaces. These observations may provide important clue to understand the fundamental phenomenon of ions at the air/water interface. † Also Graduate University of the Chinese Academy of Sciences.* To whom correspondence should be addressed. E-mail: hongfei@iccas.ac.cn; Tel: 86-10-62555347; Fax:86-10-62563167. 1In this letter we would like to report the significantly different sum-frequency generation vibrational spectra of the NaF and KF aqueous solution surfaces. These results suggested that the ion effects on the interfacial water hydrogen bonding structure are quite different for the NaF and KF salts. These results may provide direct counterexamples to the physical picture based on the currently prevalent molecular dynamics (MD) simulations with the polarizable force field, which have predicted that the adsorption of the more polarizable anions, such as the I − and Br − anions, are significantly enhanced at the electrolyte aqueous solution surfaces, while the less polarizable anions, such as the F − and Cl − anions, and the non polarizable cations, such as the Na + and K + cations, are repelled from the electrolyte aqueous solution surfaces. [1,2,3,4,5] Recently, there have been a great deal of theoretical and experimental studies on the ion solvation and ion effects at the electrolyte aqueous solution surfaces. [1,2,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] It has been well established that the ssp SFG spectra for the neat air/water interface has two prominent features, one is the narrow peak centered at 3700cm −1 and the other is the fairly broad band in the 3000-3600cm −1 . The former is the signature of the non hydrogenbonded O-H group which sticks out of the liquid phase, i.e. the so called 'free O-H'; while the latter is the signature of the O-H stretching vibrations of the differently hydrogen-bonded water molecules on the liquid side in the vicinity of the air/water interface. [38,39,40,41,42] These signatures of the interfacial water molecules can be observed in the SFG-VS because the water molecules at the air/water interface are orientationally ordered. [38,39,40,41,42,46] It has been known that addition of the electrolytes into the bulk aqueous phase can introduce changes in the ssp SFG spectra in the hydrogen-bonded water region, i.e. 3000- [3,6,17,18,24,39,47] In order to systematically investigate the anion effects on the hydrogen-bonded water molecules at the electrolyte aqueous solution surfaces, the ssp 3 SFG-VS spectra of the NaF, NaCl, NaBr and NaI slat solution surfaces were measured by two independent groups. [17...

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“…As the surface has low dielectric, ions will not generally be preferred there compared with the high dielectric bulk. However, chaotropic ions with low surface charge density and/or high polarizability (such as Cl -, Br -, I -, HO 2 -and O 2 -) will favor the gas-liquid interfaces (Garrett, 2004;Jungwirth and Winter, 2008) as they only interact weakly with water but are influenced favorably by the highly polarized surface. Aqueous radicals also prefer to reside at such interfaces (Roeselová al, 2004), as do some molecular species that prefer to hydrogen bond on the outside of clathrate-like structures, like superoxide (Shi et al 2003).…”

Section: Surface Tension and Related Thermodynamicsmentioning

confidence: 99%

Untitled

2009

WATER

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SummaryThere is considerable disagreement over whether the gas/liquid surface of water is positive due to the presence of surface-active hydrogen ions or negative due to the presence of surface-active hydroxyl ions. Much has been written and many experimental and simulation studies have been undertaken. We critically analyze these studies to establish what is known unambiguously and what assumptions underlie these opposite views. The conclusion reached after this examination is that there is much misunderstanding over the strength of the evidence for hydrogen ions being surface active and less support for the positive surface than generally regarded. The surface of neutral water is negatively charged.

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Ions at Aqueous Interfaces: From Water Surface to Hydrated Proteins

Cited by 258 publications

References 154 publications

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell

Spectroscopic evidence for the specific Na+ and K+ interactions with the hydrogen-bonded water molecules at the electrolyte aqueous solution surfaces

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