Selected biologically relevant ions at the air/water interface: A comparative molecular dynamics study

Hrobárik, Tomáš; Vrbka, Luboš; Jungwirth, Pavel

doi:10.1016/j.bpc.2006.04.010

Cited by 28 publications

(35 citation statements)

References 31 publications

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“…containing long alkyl chains, are also subject to the image force; however, they are attracted to the surface due their hydrophobicity. 19 But even for inorganic ions the picture turns out to be more complicated than Fig. 1 suggests.…”

Section: Inorganic Ions At the Air/water Interface 21 Simulations Of ...mentioning

confidence: 97%

Spiers Memorial Lecture : Ions at aqueous interfaces

Jungwirth

2009

Faraday Discuss.

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Studies of aqueous interfaces and of the behavior of ions therein have been profiting from a recent remarkable progress in surface selective spectroscopies, as well as from developments in molecular simulations. Here, we summarize and place in context our investigations of ions at aqueous interfaces employing molecular dynamics simulations and electronic structure methods, performed in close contact with experiment. For the simplest of these interfaces, i.e. the open water surface, we demonstrate that the traditional picture of an ion-free surface is not valid for large, soft (polarizable) ions such as the heavier halides. Both simulations and spectroscopic measurements indicate that these ions can be present and even enhanced at surface of water. In addition we show that the ionic product of water exhibits a peculiar surface behavior with hydronium but not hydroxide accumulating at the air/water and alkane/water interfaces. This result is supported by surface-selective spectroscopic experiments and surface tension measurements. However, it contradicts the interpretation of electrophoretic and titration experiments in terms of strong surface adsorption of hydroxide; an issue which is further discussed here. The applicability of the observed behavior of ions at the water surface to investigations of their affinity for the interface between proteins and aqueous solutions is explored. Simulations show that for alkali cations the dominant mechanism of specific interactions with the surface of hydrated proteins is via ion pairing with negatively charged amino acid residues and with the backbone amide groups. As far as halide anions are concerned, the lighter ones tend to pair with positively charged amino acid residues, while heavier halides exhibit affinity to the amide group and to non-polar protein patches, the latter resembling their behavior at the air/water interface. These findings, together with results for more complex molecular ions, allow us to formulate a local model of interactions of ions with proteins with the aim to rationalize at the molecular level ion-specific Hofmeister effects, e.g. the salting out of proteins.

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Section: Inorganic Ions At the Air/water Interface 21 Simulations Of ...mentioning

confidence: 97%

Spiers Memorial Lecture : Ions at aqueous interfaces

Jungwirth

2009

Faraday Discuss.

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“…The enhanced ability to be specifically adsorbed in carbon micropores as the alkyl chains in TAA + cations become longer is well understood, since the smallest of the quaternary ammonium series TMA + favors bulk solvation in aqueous solution, unlike the larger TEA + and TBA + cations, which show increased surface activity at the aqueous solution/air interface. [27] A common feature between this interface and the carbon/solution interface is that the hydrophobic interactions between the lengthy alkyl chains of the TAA + cations prevail over the solvation interactions, causing the appearance of a typical surfactant-type behavior on the essentially hydrophobic surfaces [27] (graphene planes of the microcrystallites of the carbon pores' walls are certainly hydrophobic at a low concentration of oxygen functional groups). [28] …”

Section: Ionic Fluxes As a Function Of Cation Size And Specific Adsormentioning

confidence: 99%

The Effect of Specific Adsorption of Cations and Their Size on the Charge-Compensation Mechanism in Carbon Micropores: The Role of Anion Desorption

et al. 2011

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Combined application of cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) technique reveals a complicated interplay between the adsorption of ammonium and lower molecular weight tetraalkyl ammonium cations and desorption of Cl(-) anions inside carbon micropores at low surface charge densities, which results in failure of their permselectivity. Higher negative surface charge densities induce complete exclusion (desorption) of the Cl(-) co-ions, which imparts purely permselective behavior on the carbon micropores. The second fundamental effect discovered herein relates to the dominant role of anion desorption (as compared to cation adsorption), that is, overwhelming failure of permselectivity extends to high negative charge densities of the electrode in the presence of bulky tetraalkyl ammonium cations, which tend to be confined in the micropores of the carbon. The results obtained are important for advancement of high power density carbon-based supercapacitors, nanofiltration technologies with porous carbon membranes, and studies of ionic transport across biological membranes.

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“…When comparing the behavior of the above ions at the protein/water and air/water interface we see a striking difference. For example, sodium, potassium, choline, and sulfate are all repelled from the open water surface but they all show (to varying degree) an affinity for the protein/water interface [145]. Moreover, calculations show that the interaction of these ions with protein surface is of a local nature.…”

Section: Protein/water Interface 31 Interfacial or Local Ion Behavior?mentioning

confidence: 99%

Ions at Aqueous Interfaces: From Water Surface to Hydrated Proteins

Jungwirth

Winter

2008

Annu. Rev. Phys. Chem.

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258

287

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The surfaces of aqueous solutions are traditionally viewed as devoid of inorganic ions. Molecular simulations and surface-selective spectroscopic techniques show, however, that large polarizable anions and hydronium cations can be found (and even enhanced) at the surface and are involved in chemistry at the air/water interface. Here, we review recent studies of ions at the air/water interface and compare from this perspective water with other polar solvents. For water, we focus in particular on the surface behavior of its ionic product (i.e., hydronium and hydroxide ions). We also investigate the feasibility of dielectric models for the description of the protein/water interface, in analogy to the air/water interface. Little correlation is found between these two interfaces in terms of ion segregation. Therefore, we suggest a local model of pairing of ions from the solution with charged and polar groups at the protein surface. We also describe corresponding results of experimental studies on aqueous model systems.

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Selected biologically relevant ions at the air/water interface: A comparative molecular dynamics study

Cited by 28 publications

References 31 publications

Spiers Memorial Lecture : Ions at aqueous interfaces

Spiers Memorial Lecture : Ions at aqueous interfaces

The Effect of Specific Adsorption of Cations and Their Size on the Charge-Compensation Mechanism in Carbon Micropores: The Role of Anion Desorption

Ions at Aqueous Interfaces: From Water Surface to Hydrated Proteins

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