Specific Ion Adsorption and Short-Range Interactions at the Air Aqueous Solution Interface

Viswanath, P.; Daillant, Jean; Belloni, Luc; Mora, Serge; Alba, M.; Konovalov, Oleg

doi:10.1103/physrevlett.99.086105

Cited by 80 publications

(79 citation statements)

References 23 publications

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“…Consequently, the NP − ion behaves very different than small atomic ions like Na + and Cl − . This follows the well-accepted trend where bulkier monovalent ions, such as iodide, tend to be less hydrated and therefore do not show the typical dielectric repulsion from a low-dielectric medium [48,49].…”

Section: A Adsorption Of Different Solutesmentioning

confidence: 88%

Selective solute adsorption and partitioning around single PNIPAM chains

Kanduč

Chudoba

Pałczynski

et al. 2017

Phys. Chem. Chem. Phys.

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Thermoresponsive polymer architectures have become integral building blocks of 'smart' functional materials in modern applications. For a large range of developments, e.g., for drug delivery or nanocatalytic carrier systems, the selective adsorption and partitioning of molecules (ligands or reactants) inside the polymeric matrix are key processes that have to be controlled and tuned for the desired material function. In order to gain insights into the nanoscale structure and binding details in such systems, we here employ molecular dynamics simulations of the popular poly(Nisopropylacrylamide) (PNIPAM) polymer in explicit water in the presence of various representative solute types with focus on aromatic model reactants. We model a PNIPAM polymer chain and explore the influence of its elongation, stereochemistry, and temperature on the solute binding affinities. While we find that the excess adsorption generally raises with the size of the solute, the temperaturedependent affinity to the chains is highly solute specific and has a considerable dependence on the polymer elongation (i.e., polymer swelling state). We elucidate the molecular mechanisms of the selective binding in detail and eventually present how the results can be extrapolated to macroscopic partitioning of the solutes in swollen polymer architectures, such as hydrogels.

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Section: A Adsorption Of Different Solutesmentioning

confidence: 88%

Selective solute adsorption and partitioning around single PNIPAM chains

Kanduč

Chudoba

Pałczynski

et al. 2017

Phys. Chem. Chem. Phys.

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“…The angle-dependent fluorescence intensity thus contains information on the interfacial element distribution (7). This principle has been exploited for the study of interfacial phenomena involving solid, liquid, and gas phases (8)(9)(10)(11)(12)(13)(14)(15)(16). High resolution perpendicular to the interface is implied by SWXF experiments in Bragg reflection configuration, in which case planar, nanometric multilayers are used to create strongly modulated standing waves above the terminal surface close to the Bragg condition (9,10).…”

mentioning

confidence: 99%

Atom-scale depth localization of biologically important chemical elements in molecular layers

Schneck

Scoppola

Drnec

et al. 2016

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

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In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.surfaces | interfaces | lipid membranes | protein adsorption | X-ray scattering N anometric biomolecular layers in interfacial geometries are key components of biological matter. Biological membranes, for example, are 2D molecular structures composed mainly of lipids and proteins in an aqueous environment (1, 2). Interfacial biomolecular layers are also important from a biotechnological perspective, where surfaces are often designed to selectively promote or prevent the adsorption of bio(macro)molecules from solution (3). To investigate the diverse behavior of biomolecules at interfaces, well-defined planar model systems of biological and biotechnologically relevant interfaces have been established (4, 5). Processes involving biomolecules at interfaces are typically accompanied by a spatial reorganization of molecules, changes in molecular conformations, or the adsorption of molecules in a chemically heterogeneous environment (6). Structural insight on the nanometer scale is therefore of paramount importance.X-ray and neutron scattering are uniquely suited for the structural investigation of biomolecular systems. Specular reflectometry reveals matter density profiles perpendicular to a planar interface. However, it is generally difficult to elucidate molecular conformations and elemental distributions from such "global" density profiles. In contrast, standing-wave X-ray fluorescence (SWXF) allows determining element-specific density profiles across an interface. The SWXF technique is based on the elementcharacteristic fluorescence induced by a standing X-ray wave. The latter is formed by interference of the incident and reflected waves and its shape depends o...

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“…3 and 4 and references therein, 5-9) and many experiments (10, ref. 11 and references therein, [12][13][14] suggest that certain small ions are in fact more concentrated near the liquid-vapor interface than in bulk aqueous solution. This counterintuitive phenomenon not only challenges the textbook understanding of ion solvation in polar liquids but also bears importantly on a wide range of important molecular processes, e.g., formation of sea salt aerosols and subsequent halogen-release mechanisms (15); regulation of action potentials across membranes (16); and exchange of ions near fuel-cell membranes (17).…”

mentioning

confidence: 99%

On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

Noah-Vanhoucke

Geissler

2009

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

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Contrary to the expectations from classic theories of ion solvation, spectroscopy and computer simulations of the liquid-vapor interface of aqueous electrolyte solutions suggest that ions little larger than a water molecule can prefer to reside near the liquid's surface. Here we advance the view that such affinity originates in a competition between strong opposing forces, primarily due to volume exclusion and dielectric polarization, that are common to all dense polar liquids. We present evidence for this generic mechanism from computer simulations of (i) water and (ii) a Stockmayer fluid near its triple point. In both cases, we show that strong surface enhancement of small ions, obtained by tuning solutes' size and charge, can be accentuated or suppressed by modest changes in either of those parameters. Statistics of solvent polarization, when the ion is held at and above the Gibbs dividing surface, highlight a basic deficiency in conventional models of dielectric response, namely, the neglect of interfacial flexibility. By distorting the solution's boundary, an ion experiences fluctuations in electrostatic potential and in electric field whose magnitudes attenuate much more gradually (as the ion is removed from the liquid phase) than for a quiescent planar interface. As one consequence, the collective responses that determine free energies of solvation can resolve very differently in nonuniform environments than in bulk. We show that this persistence of electric-field fluctuations additionally shapes the sensitivity of solute distributions to ion polarizability. dielectric continuum ͉ ion solvation ͉ liquid-vapor interface ͉ polarizability ͉ water S imple salts dissolve in water because the electrostatic reaction fields induced by separated ions in solution provide greatly favorable energies, more than sufficient to offset intrinsic costs of dissociation. These substantial solvation energies are captured with remarkable accuracy by simple linear response models for solvent polarization, for instance dielectric continuum theory (DCT) (1). Molecular simulations of bulk solutions further indicate that the presumption of Gaussian-distributed polarization fluctuations underlying these theories is appropriate even on microscopic scales (2). Based on these facts, one might expect small ions (little larger than a water molecule) to avoid interfaces with lower dielectric media, such as vapor, as predicted by straightforward DCT calculations. Surprisingly, a large body of computational work (pioneered by Jungwirth and Tobias) (refs. 3 and 4 and references therein, 5-9) and many experiments (10, ref. 11 and references therein, 12-14) suggest that certain small ions are in fact more concentrated near the liquid-vapor interface than in bulk aqueous solution. This counterintuitive phenomenon not only challenges the textbook understanding of ion solvation in polar liquids but also bears importantly on a wide range of important molecular processes, e.g., formation of sea salt aerosols and subsequent halogen-release mechani...

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Specific Ion Adsorption and Short-Range Interactions at the Air Aqueous Solution Interface

Cited by 80 publications

References 23 publications

Selective solute adsorption and partitioning around single PNIPAM chains

Selective solute adsorption and partitioning around single PNIPAM chains

Atom-scale depth localization of biologically important chemical elements in molecular layers

On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

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