Stripping away ion hydration shells in electrical double-layer formation: Water networks matter

<div><br></div><div><p>The double layer at the solid/electrolyte interface is a key concept in electrochemistry. Here, we present an experimental study combined with simulations, which provides a molecular picture of the double-layer formation in operando processes. By THz spectroscopy we are able to follow the stripping off of the cation/anion hydration shells for a NaCl electrolyte at the Au surface when decreasing/increasing the bias potential. While Na<sup>+</sup> is attracted toward the electrode already at the smallest applied negative potentials, stripping-off of the Cl<sup>-</sup> hydration shell is observed only at higher potential values. These phenomena are directly measured by in operando THz spectroscopy with ultra-bright synchrotron light as a source and rationalized by accompanying molecular-dynamics simulations and electronic-structure calculations. </p></div>

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Stripping off of the Hydration Shells in the Double Layer Formation: Water Networks Matter

10.26434/chemrxiv.13721179.v1 ◽

2021 ◽

Author(s):

Serena Rosa Alfarano ◽

Simone Pezzotti ◽

Christopher Stein ◽

Zhou Lin ◽

federico sebastiani ◽

...

Keyword(s):

Double Layer ◽

Hydration Shell ◽

Thz Spectroscopy ◽

Layer Formation ◽

Hydration Shells ◽

Synchrotron Light ◽

In Operando ◽

Dynamics Simulations ◽

Anion Hydration ◽

Structure Calculations

<div><br></div><div><p>The double layer at the solid/electrolyte interface is a key concept in electrochemistry. Here, we present an experimental study combined with simulations, which provides a molecular picture of the double-layer formation in operando processes. By THz spectroscopy we are able to follow the stripping off of the cation/anion hydration shells for a NaCl electrolyte at the Au surface when decreasing/increasing the bias potential. While Na<sup>+</sup> is attracted toward the electrode already at the smallest applied negative potentials, stripping-off of the Cl<sup>-</sup> hydration shell is observed only at higher potential values. These phenomena are directly measured by in operando THz spectroscopy with ultra-bright synchrotron light as a source and rationalized by accompanying molecular-dynamics simulations and electronic-structure calculations. </p></div>

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Ion Hydration Under Pressure: A Molecular Dynamics Study

Zeitschrift für Naturforschung A ◽

10.5560/zna.2012-0093 ◽

2013 ◽

Vol 68 (1-2) ◽

pp. 112-122 ◽

Cited By ~ 1

Author(s):

Maksym Druchok ◽

Myroslav Holovko

Keyword(s):

Molecular Dynamics ◽

Aqueous Solutions ◽

Dynamic Properties ◽

Ion Hydration ◽

Coordination Numbers ◽

Self Diffusion ◽

Velocity Autocorrelation ◽

Hydration Behaviour ◽

Hydration Shells ◽

Dynamics Simulations

This study is intended to elucidate the role of pressure on the hydration behaviour of ions in aqueous solutions. Molecular dynamics simulations were performed for systems modelling CsF, CsCl, CsBr, and CsI aqueous solutions under ‘normal’ (105 Pa, 298 K) and ‘high pressure’ (4 ·109 Pa, 500 K) conditions. Structural details are discussed in terms of radial distributions functions, coordination numbers, and instantaneous configurations of the ionic hydration shells. The dynamic properties studied include the velocity autocorrelation functions and self-diffusion coefficients of the ions for both pressure regimes. The results indicate strong changes in the hydration behaviour and mobility of the ions.

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Kosmotropic Electrolyte (Na2CO3, NaF) Perturbs the Air/Water Interface through Anion Hydration Shell without Forming a Well-Defined Electric Double Layer

The Journal of Physical Chemistry B ◽

10.1021/acs.jpcb.0c11024 ◽

2021 ◽

Vol 125 (16) ◽

pp. 3977-3985

Author(s):

Subhadip Roy ◽

Jahur Alam Mondal

Keyword(s):

Double Layer ◽

Electric Double Layer ◽

Hydration Shell ◽

Water Interface ◽

Air Water Interface ◽

Anion Hydration

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Hyaluronan orders water molecules in its nanoscale extended hydration shells

Science Advances ◽

10.1126/sciadv.abf2558 ◽

2021 ◽

Vol 7 (10) ◽

pp. eabf2558

Author(s):

J. Dedic ◽

H. I. Okur ◽

S. Roke

Keyword(s):

Second Harmonic ◽

Hydration Shell ◽

Water Molecules ◽

Temperature Dependent ◽

Flexible Chain ◽

Optical Modeling ◽

Hydration Shells ◽

Second Harmonic Scattering ◽

Nuclear Quantum Effects ◽

Extracellular Environment

Hyaluronan (HA) is an anionic, highly hydrated bio-polyelectrolyte found in the extracellular environment, like the synovial fluid between joints. We explore the extended hydration shell structure of HA in water using femtosecond elastic second-harmonic scattering (fs-ESHS). HA enhances orientational water-water correlations. Angle-resolved fs-ESHS measurements and nonlinear optical modeling show that HA behaves like a flexible chain surrounded by extended shells of orientationally correlated water. We describe several ways to determine the concentration-dependent size and shape of a polyelectrolyte in water, using the amount of water oriented by the polyelectrolyte charges as a contrast agent. The spatial extent of the hydration shell is determined via temperature-dependent measurements and can reach up to 475 nm, corresponding to a length of 1600 water molecules. A strong isotope effect, stemming from nuclear quantum effects, is observed when light water (H2O) is replaced by heavy water (D2O), amounting to a factor of 4.3 in the scattered SH intensity.

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Structure and Interdigitation of Chain-Asymmetric Phosphatidylcholines and Milk Sphingomyelin in the Fluid Phase

Symmetry ◽

10.3390/sym13081441 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1441

Author(s):

Moritz P. K. Frewein ◽

Milka Doktorova ◽

Frederick A. Heberle ◽

Haden L. Scott ◽

Enrico F. Semeraro ◽

...

Keyword(s):

Chain Length ◽

Hydration Shell ◽

Fluid Phase ◽

Hydrocarbon Chain ◽

Specific Model ◽

Glycerol Backbone ◽

Membrane Composition ◽

Membrane Structures ◽

Hydrocarbon Chain Length ◽

Dynamics Simulations

We addressed the frequent occurrence of mixed-chain lipids in biological membranes and their impact on membrane structure by studying several chain-asymmetric phosphatidylcholines and the highly asymmetric milk sphingomyelin. Specifically, we report trans-membrane structures of the corresponding fluid lamellar phases using small-angle X-ray and neutron scattering, which were jointly analyzed in terms of a membrane composition-specific model, including a headgroup hydration shell. Focusing on terminal methyl groups at the bilayer center, we found a linear relation between hydrocarbon chain length mismatch and the methyl-overlap for phosphatidylcholines, and a non-negligible impact of the glycerol backbone-tilting, letting the sn1-chain penetrate deeper into the opposing leaflet by half a CH2 group. That is, penetration-depth differences due to the ester-linked hydrocarbons at the glycerol backbone, previously reported for gel phase structures, also extend to the more relevant physiological fluid phase, but are significantly reduced. Moreover, milk sphingomyelin was found to follow the same linear relationship suggesting a similar tilt of the sphingosine backbone. Complementarily performed molecular dynamics simulations revealed that there is always a part of the lipid tails bending back, even if there is a high interdigitation with the opposing chains. The extent of this back-bending was similar to that in chain symmetric bilayers. For both cases of adaptation to chain length mismatch, chain-asymmetry has a large impact on hydrocarbon chain ordering, inducing disorder in the longer of the two hydrocarbons.

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Origin and control of ionic hydration patterns in nanopores

Communications Materials ◽

10.1038/s43246-021-00162-x ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Miraslau L. Barabash ◽

William A. T. Gibby ◽

Carlo Guardiani ◽

Alex Smolyanitsky ◽

Dmitry G. Luchinsky ◽

...

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Distribution Functions ◽

Water Molecules ◽

Surrounding Water ◽

Ionic Hydration ◽

Hydration Shells ◽

Water Layers ◽

Dynamics Simulations ◽

And Control

AbstractIn order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

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X-ray transient absorption reveals the 1Au (nπ*) state of pyrazine in electronic relaxation

Nature Communications ◽

10.1038/s41467-021-25045-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Valeriu Scutelnic ◽

Shota Tsuru ◽

Mátyás Pápai ◽

Zheyue Yang ◽

Michael Epshtein ◽

...

Keyword(s):

Electronic Excitation ◽

Transient Absorption ◽

Transient Absorption Spectroscopy ◽

Electronic Relaxation ◽

Nonadiabatic Dynamics ◽

X Ray ◽

Organic Chromophores ◽

Dynamics Simulations ◽

X Ray Absorption ◽

Structure Calculations

AbstractElectronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computations. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated in 200 ± 50 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

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