Surface potentials of aqueous electrolyte solutions

Jarvis, N. L.; Scheiman, M. A.

doi:10.1021/j100847a014

Cited by 292 publications

(318 citation statements)

References 2 publications

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“…Addition of ethanol has similar effects, but in the opposite direction. In both cases, changes in the asymptotic values (Ϸ5 dynes͞cm for 2 M NaCl and Ϸ30 dynes͞cm for 40 mol% ethanol solution) are consistent with experimental data on vapor-liquid surface tensions of their aqueous solutions (57,58). Further, we find that the EgelstaffWidom lengthscale, ␥ ϱ b , increases somewhat with salt addition and decreases with ethanol addition, consistent with our calculations.…”

Section: (D) Shown Is the Ratio P N͞supporting

confidence: 90%

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Rajamani

Truskett

Garde

2005

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

277

329

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Small and large hydrophobic solutes exhibit remarkably different hydration thermodynamics. Small solutes are accommodated in water with minor perturbations to water structure, and their hydration is captured accurately by theories that describe density fluctuations in pure water. In contrast, hydration of large solutes is accompanied by dewetting of their surfaces and requires a macroscopic thermodynamic description. A unified theoretical description of these lengthscale dependencies was presented by Lum, Chandler, and Weeks [(1999) J. Phys. Chem. B 103, 4570 -4577]. Here, we use molecular simulations to study lengthscale-dependent hydrophobic hydration under various thermodynamic conditions. We show that the hydration of small and large solutes displays disparate dependencies on thermodynamic variables, including pressure, temperature, and additive concentration. Understanding these dependencies allows manipulation of the small-tolarge crossover lengthscale, which is nanoscopic under ambient conditions. Specifically, applying hydrostatic tension or adding ethanol decreases the crossover length to molecular sizes, making it accessible to atomistic simulations. With detailed temperaturedependent studies, we further demonstrate that hydration thermodynamics changes gradually from entropic to enthalpic near the crossover. The nanoscopic lengthscale of the crossover and its sensitivity to thermodynamic variables imply that quantitative modeling of biomolecular self-assembly in aqueous solutions requires elements of both molecular and macroscopic hydration physics. We also show that the small-to-large crossover is directly related to the Egelstaff-Widom lengthscale, the product of surface tension and isothermal compressibility, which is another fundamental lengthscale in liquids. molecular dynamics ͉ salt and additive effects ͉ density fluctuations ͉ nonpolar solvation B iological self-assembly processes in aqueous solutions are driven by water-mediated interactions between constituents taking part in the assembly. Of these, hydrophobic interactions have received particular attention because of their relevance to protein folding and interactions, micelle and membrane formation, and molecular recognition (1-5). Theoretical work in this direction has been focused on the modeling of primitive hydrophobic phenomena, such as hydration and association of small hydrophobic particles in water (6-13). However, biological assembly occurs over a spectrum of lengthscales from that of an amino acid to proteins and larger. Naturally, fundamental understanding of the lengthscale dependence of hydration and association of hydrophobic solutes in water will be relevant to the quantitative modeling of realistic macromolecular processes (14,15).Small hydrophobic solutes can be accommodated into the open hydrogen-bonded network of liquid water without significant perturbations. Indeed, theories that model density fluctuations over small lengthscales in pure water provide a quantitative description of the hydration thermodynamics of small...

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Section: (D) Shown Is the Ratio P N͞supporting

confidence: 90%

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Rajamani

Truskett

Garde

2005

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

277

329

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“…By contrast, for NaCl in the same channel was negligible. Our measured potentials of 0 and ÿ38 mV, respectively, for 1M NaCl and NaI are consistent with experimental surface potentials of roughly 0 and ÿ20 mV, respectively, for vapor-liquid interfaces of the same solutions [20]; for NaI is also of similar magnitude to the value of ÿ9 mV measured by electrophoresis of neutral liposomes in 1M KI [18], for which ionspecific effects should be smaller due to the greater simi- Although not shown in Fig. 3, we found that for 0 was not sensitive to electrolyte concentration.…”

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confidence: 89%

Ion-Specific Anomalous Electrokinetic Effects in Hydrophobic Nanochannels

et al. 2007

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We demonstrate with computer simulations that anomalous electrokinetic effects, such as ion specificity and non-zero zeta potentials for uncharged surfaces, are generic features of electro-osmotic flow in hydrophobic channels. This behavior is due to the stronger attraction of larger ions to the "vapour-liquid-like" interface induced by a hydrophobic surface. An analytical model involving a modified Poisson-Boltzmann description for the ion density distributions is proposed, which allows the anomalous flow profiles to be predicted quantitatively. This description incorporates as a crucial component an ion-size-dependent hydrophobic solvation energy. These results provide an effective framework for predicting specific ion effects, with important implications for the modeling of biological problems.

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“…Moreover, it has been proposed that the salt-induced change of interfacial tension at protein/water interfaces may be either positive or negative depending on the particular salt (51). By contrast, the sodium salts of all these ions raise the surface tension at the air/water interface (37)(38)(39). As such, the slopes of the lines in Fig.…”

Section: Salt Concentration (M)mentioning

confidence: 97%

The inverse and direct Hofmeister series for lysozyme

Zhang

Cremer

2009

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

394

542

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Anion effects on the cloud-point temperature for the liquid؊liquid phase transition of lysozyme were investigated by temperature gradient microfluidics under a dark field microscope. It was found that protein aggregation in salt solutions followed 2 distinct Hofmeister series depending on salt concentration. Namely, under low salt conditions the association of anions with the positively charged lysozyme surface dominated the process and the phase transition temperature followed an inverse Hofmeister series. This inverse series could be directly correlated to the size and hydration thermodynamics of the anions. At higher salt concentrations, the liquid-liquid phase transition displayed a direct Hofmeister series that correlated with the polarizability of the anions. A simple model was derived to take both charge screening and surface tension effects into account at the protein/water interface. Fitting the thermodynamic data to this model equation demonstrated its validity in both the high and low salt regimes. These results suggest that in general positively charged macromolecular systems should show inverse Hofmeister behavior only at relatively low salt concentrations, but revert to a direct Hofmeister series as the salt concentration is increased.liquid-liquid phase transition ͉ protein aggregation P rotein-protein interactions can lead to aggregation. Such intermolecular contacts underlie the mechanistic basis for a variety of diseases (1-4) and are key to protein crystallization (5-7). An effective way to determine the strength of biomacromolecular interactions is to study the temperature-induced phase separation that occurs in concentrated protein solutions (8). When a concentrated protein solution is cooled below its cloud-point temperature, the system can separate into 2 coexisting liquid phases: 1 rich in protein and 1 poor. As coacervate droplets of the protein-rich phase grow, the solution turns cloudy (white) as a result of the scattering of visible light. Upon standing, the solution may completely separate by gravity into a protein-rich phase and a nearly pure aqueous phase above it. The temperature at which the initial cloud point occurs provides a simple physical measurement of the forces acting among biomacromolecules. Specifically, the higher the temperature at which the initial cloud point occurs, the stronger the putative attractive forces between the protein molecules should be.Dissolved salts in aqueous solutions have a strong influence on protein-protein interactions and the subsequent aggregated states which are formed. In fact, cloud-point temperatures typically follow a specific ion order according to the Hofmeister series (5,6,(9)(10)(11)(12)(13)(14). The relative effectiveness of anions to induce protein aggregation typically follows 1 of 2 trends depending on the pH of the solution (15, 16). Above a protein's isoelectric point, the macromolecule bears a net negative charge and a direct Hofmeister series is normally observed. In this case, chaotropes such as I Ϫ , ClO 4 Ϫ , and SCN Ϫ he...

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Surface potentials of aqueous electrolyte solutions

Cited by 292 publications

References 2 publications

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Ion-Specific Anomalous Electrokinetic Effects in Hydrophobic Nanochannels

The inverse and direct Hofmeister series for lysozyme

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