Molecular insight into carboxylic acid–alkali metal cations interactions: reversed affinities and ion-pair formation revealed by non-linear optics and simulations

Sthoer, Adrien; Hladílková, Jana; Lund, Mikael; Tyrode, Eric

doi:10.1039/c9cp00398c

Cited by 66 publications

(144 citation statements)

References 83 publications

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“…The negative charge and accompanying surface potential result in surface proton concentrations that are several orders of magnitude higher than in the bulk. Moreover, the charging behavior upon addition of monovalent ion salts to solution has been shown to be consistent with the Gouy-Chapman theory for concentrations ≤50 mM 26,27 .…”

Section: Resultssupporting

confidence: 61%

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Identifying Eigen-like hydrated protons at negatively charged interfaces

2020

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Despite the importance of the hydrogen ion in a wide range of biological, chemical, and physical processes, its molecular structure in solution remains lively debated. Progress has been primarily hampered by the extreme diffuse nature of the vibrational signatures of hydrated protons in bulk solution. Using the inherently surface-specific vibrational sum frequency spectroscopy technique, we show that at selected negatively charged interfaces, a resolved spectral feature directly linked to the H 3 O + core in an Eigen-like species can be readily identified in a biologically compatible pH range. Centered at~2540 cm −1 , the band is seen to shift to~1875 cm −1 when forming D 3 O + upon isotopic substitution. The results offer the possibility of tracking and understanding from a molecular perspective the behavior of hydrated protons at charged interfaces.

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Section: Resultssupporting

confidence: 61%

“…The different polarizations provide complementary information about the surface species and their orientation. The assignements are taken from refs [26][27][28][29]. and this study (see text).…”

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confidence: 99%

Identifying Eigen-like hydrated protons at negatively charged interfaces

2020

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“…26 Previous VSFS studies using arachidic acid, a fatty acid with a twenty carbon alkyl chain, have shown that the charging behavior of the monolayer at pH 6 is in excellent agreement with the Gouy Chapman model predictions for ionic strengths ≤ 50 mM, 23 but deviates at salt concentrations ≥ 100 mM. 24 For the high salt concentrations, the data was instead consistent with the steric MPB model using an effective ion size of ~7.5 Å for Na + . 24 In those studies,…”

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confidence: 72%

“…24 For the high salt concentrations, the data was instead consistent with the steric MPB model using an effective ion size of ~7.5 Å for Na + . 24 In those studies,…”

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confidence: 74%

Interactions of Na+ Cations with a Highly Charged Fatty Acid Langmuir Monolayer: Molecular Description of the Phase Transition

Sthoer¹,

Tyrode

2019

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Vibrational sum frequency spectroscopy has been used to study the molecular properties upon compression of a highly charged arachidic acid Langmuir monolayer, which displays a first order phase transition plateau in the surface pressure - molecular area (p-A) isotherm. By targeting vibrational modes from the carboxylic acid headgroup, alkyl chain, and interfacial water molecules, information regarding the surface charge, surface potential, type of ion pair formed, and conformational order of the monolayer could be extracted. The monolayer in the liquid expanded phase is found to be fully charged until reaching the 2D-phase transition plateau, where partial reprotonation, as well as the formation of COO⎺ Na+ contact-ion pairs, start to take place. In the condensed phase after the transition, three headgroup species, mainly hydrated COO⎺, COOH, and COO⎺ Na+ contact-ion pairs could be identified and their proportions quantified. Comparison with theoretical models shows that despite the low ionic strengths used (i.e. 10 mM), the predictions from the Gouy Chapman model are only adequate for the lowest surface densities, when the surface charge does not exceed -0.1 C/m2. In contrast, a modified Poisson-Boltzmann (MPB) model that accounts for the steric effects associated with the finite ion-size, captures many of the experimental observables, including the partial reprotonation, and surface potential changes upon compression. The agreement highlights the importance of hydronium ion – carboxylate interactions, as well as the layer of sodium ions packed at the steric limit, for explaining the phase transition behavior. The MPB model, however, does not explicitly consider the formation of contact ion pairs with the sodium counterion. The experimental results provide a quantitative molecular insight that could be used to test potential extensions to the theory.

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“…Furthermore, most carbohydrate polymers have a positive chi‐parameter which means that their interaction with water is typically not stronger than interactions between water molecules . However, the added carboxyl groups on the surface of CNFs are strongly hydrated, but at a charge density of 0.6 mmol g −1 , the coverage is moderate and at low pH, most of the carboxyl groups are protonated and the chaotropic properties dominate …”

Section: Resultsmentioning

confidence: 99%

Ion‐Specific Assembly of Strong, Tough, and Stiff Biofibers

et al. 2019

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Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle.Many biological materials realize this objective through multiscale (i.e., atomic-to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials.I nspired from the architecture of such biological structures,w eh ere present flow-assisted organization and assembly of renewable native cellulose nanofibrils (CNFs), whichy ields highly anisotropic biofibers characterized by au nique combination of high strength (1010 MPa), high toughness (62 MJ m À3 )a nd high stiffness (57 GPa). We observed that properties of the fibers are primarily governed by specific ion characteristics such as hydration enthalpya nd polarizability.Afundamental facet of this study is thus to elucidate the role of specific anion binding following the Hofmeister series on the mechanical properties of wet fibrillar networks,a nd link this to the differences in properties of dry nanostructured fibers.T his knowledge is useful for rational design of nanomaterials and is critical for validation of specific ion effect theories.T he bioinspired assembly demonstrated here is relevant example for designing high-performance materials with absolute structural control.

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Molecular insight into carboxylic acid–alkali metal cations interactions: reversed affinities and ion-pair formation revealed by non-linear optics and simulations

Abstract: Alkali metal cations’ relative affinity to the carboxylic acid moiety is pH dependent, and typically remain hydrated.

Cited by 66 publications

References 83 publications

Identifying Eigen-like hydrated protons at negatively charged interfaces

Identifying Eigen-like hydrated protons at negatively charged interfaces

Interactions of Na+ Cations with a Highly Charged Fatty Acid Langmuir Monolayer: Molecular Description of the Phase Transition

Ion‐Specific Assembly of Strong, Tough, and Stiff Biofibers

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