Orientation‐Induced Adsorption of Hydrated Protons at the Air–Water Interface

Mamatkulov, Shavkat; Allolio, Christoph; Netz, Roland R.; Bonthuis, Douwe Jan

doi:10.1002/anie.201707391

Cited by 53 publications

(99 citation statements)

References 47 publications

(106 reference statements)

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“…Beyond this point, the positive hydrogen atoms point preferentially towards the cavity surface, and this trend in orientation is reinforced as the magnitude of negative charge further 6 increases. Similar observations have been made in simulation studies involving planar interfaces 2,3,29,30 .…”

Section: Excess Hydration Free Energy Of An Interface Based On Molecusupporting

confidence: 84%

Interfacial solvation can explain attraction between like-charged objects in aqueous solution

Kubincová

Hünenberger

Krishnan

2020

The Journal of Chemical Physics

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Over the past few decades the experimental literature has consistently reported observations of attraction between like-charged colloidal particles and macromolecules in solution. Examples include nucleic acids and colloidal particles in bulk solution and under confinement, and biological liquid-liquid phase separation. This observation is at odds with the intuitive expectation of an interparticle repulsion that decays monotonically with distance. Although attraction between like-charged particles can be theoretically rationalised in the strong-coupling regime, e.g., in the presence of multivalent counterions, recurring accounts of long-range attraction in aqueous solution containing monovalent ions at low ionic strength have posed an open conundrum. Here we show that the behaviour of molecular water at an interface -traditionally disregarded in the continuum electrostatics picture -provides a mechanism to explain attraction between like-charged objects in a broad spectrum of experiments. This basic principle will have important ramifications in the ongoing quest to better understand intermolecular interactions in solution.

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Section: Excess Hydration Free Energy Of An Interface Based On Molecusupporting

confidence: 84%

Interfacial solvation can explain attraction between like-charged objects in aqueous solution

Kubincová

Hünenberger

Krishnan

2020

The Journal of Chemical Physics

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“…To characterize the partitioning coefficient K for each ionic species from the measured , we consider H3O + and Xto have the surface ion densities and define their (36). A recent analysis of the surface tension data with the help of classical MD simulations gives another value of G ≈ -2.5 kJ/mol (37). G deduced from our spectroscopic work is within the range of these literature values, but, apparently, the estimates from the surface tension depend very much on the model adopted.…”

Section: Resultsmentioning

confidence: 99%

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment

Chiang

Dalstein

Wen

2020

J. Phys. Chem. Lett.

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ABTRACT:Protons at the water/vapor interface are relevant for atmospheric and environmental processes, yet to characterize their surface affinity on the quantitative level is still challenging.Here we utilize phase-sensitive sum-frequency vibrational spectroscopy to quantify the surface density of protons (or their hydronium form) at the intrinsic water/vapor interface, through inspecting the surface-field-induced alignment of water molecules in the electrical double layer of ions. With hydrogen halides in water, the surface adsorption of protons is found to be independent of specific proton-halide anion interactions and to follow a constant adsorption free energy, G ~ -3.74 (±0.56) kJ/mol, corresponding to a reduction of the surface pH with respect to the bulk value by 0.66 (±0.10), for bulk ion concentrations up to 0.3 M. Our spectroscopic study is not only of importance in atmospheric chemistry, but also offers a microscopic-level basis to develop advanced quantum-mechanical models for molecular simulations. MAIN TEXT:Protons at water/vapor interfaces play a key role in atmospheric chemistry and environmental science (1, 2). They have been the topics of extensive theoretical and experimental studies for decades (3-18), but good understanding of the surface affinity of protons on the microscopic and quantitative level is still lacking. Molecular dynamics (MD) simulations generally predicted that protons (H + ) could appear at the interface in the form of hydronium (H3O + ), while the quantitative details, such as the adsorption free energy and the depth profile of ion concentrations, depend very much on the molecular model and interaction potentials assumed (3-8). Several experimental approaches have been used to verify the qualitative conclusion from the simulations (9-18), but extension of these efforts to quantitative characterizations of the proton adsorption remains challenging (17). This largely limits our knowledge on the underlying mechanisms and the role of proton in many relevant interfacial processes. Technically, it is generally difficult to adopt macroscopic observables from surface tension, electrokinetic, and Kelvin probe measurements to yield molecular-level interfacial properties without crucial model assumption (17)(18)(19). For molecular-scale measurements, X-ray spectroscopies can examine the proton effect at water interfaces indirectly through probing relative concentration changes of the counterions (9, 10), but, yet, the surface affinity of protons has not been quantified from the results. Surface-specific optical sum frequency generation (SFG) and second harmonic generation (SHG) were widely employed to explore this issue (11)(12)(13)(14)(15)(16). But, in many reports, the proton propensity were only studied comparatively with respect to other ions without quantitative details (13)(14)(15). In the other, the surface concentration of protons was estimated by inspecting their reaction with extrinsic interfacial label molecules (16), whereas how the result is affected by the proton-label m...

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“…Proton transfer is facilitated when OH − is receiving three hydrogen bonds, but hindered with four bonds. However, simulating accurately the free energy of adsorption of hydrated hydroxide at interfaces is challenging and has been limited to date to the water/air interface 16,20,21 . Also, for this interface, comparison with experiments is delicate because of impurity effects 22 .…”

Section: Introductionmentioning

confidence: 99%

Versatile electrification of two-dimensional nanomaterials in water

2019

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The recent emergence of nanofluidics has highlighted the exceptional properties of graphene and its boron-nitride counterpart as confining nanomaterials for water and ion transport. Surprisingly, ionic transport experiments have unveiled a consequent electrification of the water/carbon surfaces, with a contrasting response for its water/boron-nitride homologue. In this paper, we report free energy calculations based on ab initio molecular dynamics simulations of hydroxide OH − ions in water near graphene and hexagonal boron nitride (h-BN) layers. Our results disclose that both surfaces get charged through hydroxide adsorption, but two strongly different mechanisms are evidenced. The hydroxide species shows weak physisorption on the graphene surface while it exhibits also strong chemisorption on the h-BN surface. Interestingly OH − is shown to keep very fast lateral dynamics and interfacial mobility within the physisorbed layer on graphene. Taking into account the large ionic surface conductivity, an analytic transport model allows to reproduce quantitatively the experimental data.

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Orientation‐Induced Adsorption of Hydrated Protons at the Air–Water Interface

Cited by 53 publications

References 47 publications

Interfacial solvation can explain attraction between like-charged objects in aqueous solution

Interfacial solvation can explain attraction between like-charged objects in aqueous solution

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment

Versatile electrification of two-dimensional nanomaterials in water

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