Ion-Specific Long-Range Correlations on Interfacial Water Driven by Hydrogen Bond Fluctuations

Enami, Shinichi; Colussi, A. J.

doi:10.1021/jp411385u

Cited by 13 publications

(12 citation statements)

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“…The related question of the propensity of ions in a liquid–vapor planar interface has been studied over several decades. − It is emphasized that the forces that determine the location of multiple ions in a planar interface are not the same as those in charged droplets regardless of their size. The reason is that the conductivity of the aqueous droplets drives the excess ions nearer to the surface and the counterions toward the interior .…”

Section: Introductionmentioning

confidence: 99%

Low Density Interior in Supercooled Aqueous Nanodroplets Expels Ions to the Subsurface

et al. 2021

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The interaction between water and ions within droplets plays a key role in the chemical reactivity of atmospheric and man-made aerosols. Here we report direct computational evidence that in supercooled aqueous nanodroplets a lower density core of tetrahedrally coordinated water expels the cosmotropic ions to the denser and more disordered subsurface. In contrast, at room temperature, depending on the nature of the ion, the radial distribution in the droplet core is nearly uniform or elevated toward the center. We analyze the spatial distribution of a single ion in terms of a reference electrostatic model. The energy of the system in the analytical model is expressed as the sum of the electrostatic and surface energy of a deformable droplet. The model predicts that the ion is subject to a harmonic potential centered at the droplet's center of mass. We name this effect "electrostatic confinement". The model's predictions are consistent with the simulation findings for a single ion at room temperature but not at supercooling. We anticipate this study to be the starting point for investigating the structure of supercooled (electro)sprayed droplets that are used to preserve the conformations of macromolecules originating from the bulk solution.

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Section: Introductionmentioning

confidence: 99%

Low Density Interior in Supercooled Aqueous Nanodroplets Expels Ions to the Subsurface

et al. 2021

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“…Some ions accumulate at a specific depth layer of water–hydrophobes (e.g., air, oil, and biomembranes) interfaces, while other ions prefer to remain in bulk water and react homogeneously. − Long-chain carboxylate ions, due to the amphiphilic property, − play key roles in the nucleation, growth, and photochemical aging process of atmospheric aerosol. − For example, bubble-bursting from surface of the ocean is responsible for enriching marine aerosols with long-chain carboxylate ions, ,,, thereby influencing the chemistry of marine boundary layers. ,− Long-chain carboxylate ions act as a film covering atmospheric particles, directly confirmed by field measurement studies. − Recent studies have suggested long-chain carboxylate ions could induce cloud droplet formation, thereby affecting global climate change. ,− Benzoate ion, C 6 H 5 -COO – , has been recently found to be one of the most abundant organic species observed in PM 2.5 of polluted areas, where the concentration on PM 2.5 exceeds 1 μg/m 3 …”

Section: Introductionmentioning

confidence: 99%

Carboxylate Ion Availability at the Air–Water Interface

et al. 2016

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Amphiphilic organic compounds at the air−water interface play key roles in the nucleation, growth, and aging process of atmospheric aerosol. Surface-active species are expected to react preferentially with atmospheric oxidants, such as the OH radical, at the air−water interface via specific mechanisms. Establishing the relative availability of the different amphiphilic species to gas-phase oxidants at the air−water interface under atmospherically relevant conditions is, however, challenging. Here we report the interfacial availability of atmospherically relevant carboxylate ions R n -COO − (n = 1−7) and n-, cyclo-, aromatic-R 6 -COO − at the air−water interface via a novel application of mass spectrometry of aqueous microjets. The breakup mechanism of microjets lets us determine the relative interfacial affinities of carboxylate ions in equimolar solutions of the corresponding carboxylic acids in the 1 μM to 1 mM range under ambient conditions. We find that the interfacial affinity of R n -COO − increases exponentially with both chain-length and solvent-accessible surface area (SASA) except in the case of R 1 -COO − . The relative interfacial affinities for n-heptanoate (n-R 6 -COO − ) > cyclohexanecarboxylate (c-R 6 -COO − ) > benzoate (Ar-R 6 -COO − ) are also determined. We attribute the smallest availability of Ar-R 6 -COO − at the air−water interface among the three carboxylate ions to a strong π−H bonding between the aromatic ring and water molecule. Molecular mechanisms on the availability of carboxylate ions at the air−water interface and the atmospheric implications are discussed.

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“…7-10 These concentration (or structural) fluctuations are brief (tens of picoseconds) inhomogeneities in the ∼1 nm scale that happen to peak in the concentration ranges that give rise to thermodynamic and transport properties anomalies in binary mixtures. [11][12][13][14][15][16][17] milliseconds to years) non-covalent aggregates detected by dynamic light scattering experiments in many systems. [18][19][20][21][22] These aggregates also appear in the mass spectra of liquid jets produced by adiabatic expansion of solutions of hydrophobic species in aqueous organic mixtures.…”

Section: Introductionmentioning

confidence: 99%

Chemical signatures of surface microheterogeneity on liquid mixtures

Enami

Ishizuka

Colussi

2019

The Journal of Chemical Physics

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Many chemical reactions in Nature, the laboratory, and chemical industry occur in solvent mixtures that bring together species of dissimilar solubilities. Solvent mixtures are visually homogeneous, but are not randomly mixed at the molecular scale. In the allimportant binary water-hydrotrope mixtures, small-angle neutron and dynamic light scattering experiments reveal the existence of short-lived (<50 ps), short-ranged (∼1 nm) concentration fluctuations. The presence of hydrophobic solutes stabilizes and extends such fluctuations into persistent, mesoscopic (10-100 nm) inhomogeneities. While the existence of inhomogeneities is well established, their impacts on reactivity are not fully understood. Here, we search for chemical signatures of inhomogeneities on the surfaces of W:X mixtures (W = water; X = acetonitrile, tetrahydrofuran, or 1,4-dioxane) by studying the reactions of Criegee intermediates (CIs) generated in situ from O 3 (g) addition to a hydrophobic olefin (OL) solute. Once formed, CIs isomerize to functionalized carboxylic acids (FC) or add water to produce α-hydroxy-hydroperoxides (HH), as detected by surface-specific, online pneumatic ionization mass spectrometry. Since only the formation of HH requires the presence of water, the dependence of the R = HH/FC ratio on water molar fraction x w expresses the accessibility of water to CIs on the surfaces of mixtures. The finding that R increases quasi-exponentially with x w in all solvent mixtures is consistent with CIs being preferentially produced (from their OL hydrophobic precursor) in X-rich, long-lived OL:X m W n interfacial clusters, rather than randomly dispersed on W:X surfaces. R vs x w dependences therefore reflect the average m, n composition of OL:X m W n interfacial clusters, as weighted by cluster reorganization dynamics. Water in large, rigid clusters could be less accessible to CIs than in smaller but more flexible clusters of lower water content. Since mesoscale inhomogeneities are intrinsic to most solvent mixtures, these phenomena should be quite general.Published under license by AIP Publishing. https://doi.org/10.1063/1.5055684The addition of solutes to binary mixtures generates the larger (in the 10-100 nm mesoscale), more persistent (from ARTICLE scitation.org/journal/jcpIn our experiments, (β-C + NaCl) solutions in W:X mixtures are injected (at 100 µl min −1 ) as liquid microjets (v y = 21 cm/s, see Fig. S1) into the spraying chamber of the mass spectrometer (ES-MS, Agilent 6130 Quadrupole LC/MS Electrospray System at NIES, Japan) through an electrically grounded stainless-steel syringe needle (100 µm bore). The ARTICLE scitation.org/journal/jcp (2017).

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Ion-Specific Long-Range Correlations on Interfacial Water Driven by Hydrogen Bond Fluctuations

Cited by 13 publications

References 100 publications

Low Density Interior in Supercooled Aqueous Nanodroplets Expels Ions to the Subsurface

Low Density Interior in Supercooled Aqueous Nanodroplets Expels Ions to the Subsurface

Carboxylate Ion Availability at the Air–Water Interface

Chemical signatures of surface microheterogeneity on liquid mixtures

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