Interacting Ions in Biophysics: Real is not Ideal

Eisenberg, Robert S.

doi:10.1016/j.bpj.2013.03.049

Cited by 57 publications

(67 citation statements)

References 291 publications

(324 reference statements)

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“…Our results suggest that this trend may be due to the progressive formation of effectively neutral ionic networks involving large numbers of strongly interacting ions. Over the longer term, our results may also prove useful for deciphering how electrostatic interactions maintain such a dominant role near the active sites of proteins, ion channels, and similar self-assembling biological systems (2), where local effective salt concentrations can exceed 10 M. samples were dried under vacuum at 373 K for at least 72 h. After drying, a droplet of RTIL (50-100 μL) was immediately injected between mica surfaces in a gas-tight SFA under dry nitrogen purge conditions, and the SFA was resealed. All experiments were performed in the presence of a reservoir of the desiccant phosphorous pentoxide (P 2 O 5 ).…”

Section: Discussionmentioning

confidence: 91%

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Long-range electrostatic screening in ionic liquids

Gebbie

Dobbs

Valtiner

et al. 2015

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

242

302

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Electrolyte solutions with high concentrations of ions are prevalent in biological systems and energy storage technologies. Nevertheless, the high interaction free energy and long-range nature of electrostatic interactions makes the development of a general conceptual picture of concentrated electrolytes a significant challenge. In this work, we study ionic liquids, single-component liquids composed solely of ions, in an attempt to provide a novel perspective on electrostatic screening in very high concentration (nonideal) electrolytes. We use temperature-dependent surface force measurements to demonstrate that the long-range, exponentially decaying diffuse double-layer forces observed across ionic liquids exhibit a pronounced temperature dependence: Increasing the temperature decreases the measured exponential (Debye) decay length, implying an increase in the thermally driven effective free-ion concentration in the bulk ionic liquids. We use our quantitative results to propose a general model of long-range electrostatic screening in ionic liquids, where thermally activated charge fluctuations, either free ions or correlated domains (quasiparticles), take on the role of ions in traditional dilute electrolyte solutions. This picture represents a crucial step toward resolving several inconsistencies surrounding electrostatic screening and charge transport in ionic liquids that have impeded progress within the interdisciplinary ionic liquids community. More broadly, our work provides a previously unidentified way of envisioning highly concentrated electrolytes, with implications for diverse areas of inquiry, ranging from designing electrochemical devices to rationalizing electrostatic interactions in biological systems.electrostatic interactions | intermolecular interactions | interfacial phenomena | Boltzmann distribution | activation energy E lectrolyte solutions are multicomponent liquids that are composed of ions (solutes) dissolved in a liquid phase (solvent), a classic example being salt water. Like any ideal mixture, the driving force for the dissolution of ions in electrolyte solutions is entropic. Unlike ideal mixtures, the long-range nature and high interaction free energy of the electrostatic interactions between ions ensures that the physical properties of all but the most dilute electrolyte solutions exhibit pronounced deviations from ideal behavior. These deviations primarily arise from the steric "crowding" of ions and the electrostatic correlation of ions, for example the formation of neutral ion pairs, both of which increase the range of electrostatic interactions, compared with ideal solutions (1). As a result, the development of a general conceptual picture of concentrated electrolyte solutions remains challenging. Nevertheless, electrolytes with high ionic concentrations are prevalent in biological systems (2) and technological applications, such as energy storage devices (3-5), so overcoming this challenge remains an important task.In this work, we study room-temperature ionic liquids (RTILs), ...

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Section: Discussionmentioning

confidence: 91%

“…As a result, the development of a general conceptual picture of concentrated electrolyte solutions remains challenging. Nevertheless, electrolytes with high ionic concentrations are prevalent in biological systems (2) and technological applications, such as energy storage devices (3)(4)(5), so overcoming this challenge remains an important task.…”

mentioning

confidence: 99%

Long-range electrostatic screening in ionic liquids

Gebbie

Dobbs

Valtiner

et al. 2015

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

242

302

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“…Thus a single model with almost unchanging parameters can account for the valence selectivity features of both sodium and calcium channels (reviewed in Refs. [38,39]). An analytic treatment of such a model [35,40,41] showed that transport of Ca 2+ ions through a negatively doped channel exhibited several ionexchange phase transitions as functions of bulk concentration and Q f , with a near-zero transport barrier at the transition points [41].…”

Section: Introductionmentioning

confidence: 94%

Energetics of discrete selectivity bands and mutation-induced transitions in the calcium-sodium ion channels family

et al. 2013

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We use Brownian dynamics (BD) simulations to study the ionic conduction and valence selectivity of a generic electrostatic model of a biological ion channel as functions of the fixed charge Q(f) at its selectivity filter. We are thus able to reconcile the discrete calcium conduction bands recently revealed in our BD simulations, M0 (Q(f)=1e), M1 (3e), M2 (5e), with a set of sodium conduction bands L0 (0.5e), L1 (1.5e), thereby obtaining a completed pattern of conduction and selectivity bands vs Q(f) for the sodium-calcium channels family. An increase of Q(f) leads to an increase of calcium selectivity: L0 (sodium-selective, nonblocking channel) → M0 (nonselective channel) → L1 (sodium-selective channel with divalent block) → M1 (calcium-selective channel exhibiting the anomalous mole fraction effect). We create a consistent identification scheme where the L0 band is putatively identified with the eukaryotic sodium channel The scheme created is able to account for the experimentally observed mutation-induced transformations between nonselective channels, sodium-selective channels, and calcium-selective channels, which we interpret as transitions between different rows of the identification table. By considering the potential energy changes during permeation, we show explicitly that the multi-ion conduction bands of calcium and sodium channels arise as the result of resonant barrierless conduction. The pattern of periodic conduction bands is explained on the basis of sequential neutralization taking account of self-energy, as Q(f)(z,i)=ze(1/2+i), where i is the order of the band and z is the valence of the ion. Our results confirm the crucial influence of electrostatic interactions on conduction and on the Ca(2+)/Na(+) valence selectivity of calcium and sodium ion channels. The model and results could be also applicable to biomimetic nanopores with charged walls.

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“…However, numerous studies have established that accounting for finite ion size is essential in order to accurately simulate electrical double layers for large electric potentials and/or large electrolyte concentrations typical of EDLCs. [93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] Among the models accounting for the finite size of ions, the modified Poisson-Boltzmann (MPB) models are based on the local-density and mean-field approximations and are relatively convenient both mathematically and numerically.…”

Section: Equilibrium Modelingmentioning

confidence: 99%

Recent Advances in Continuum Modeling of Interfacial and Transport Phenomena in Electric Double Layer Capacitors

Pilon

Wang

d’Entremont

2015

J. Electrochem. Soc.

119

105

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This paper reviews recent advances in physical modeling of interfacial and transport phenomena in electric double layer capacitors (EDLCs) under both equilibrium and dynamic cycling. The models are based on continuum theory and account for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion sizes, (iii) steric repulsions, (iv) asymmetric electrolytes featuring ions with different valencies, effective diameters, or diffusion coefficients, (v) electric-field-dependent dielectric permittivity of the electrolyte, and/or (vi) porous three-dimensional morphology of the electrodes. Typical characterization methods such as electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic cycling were reproduced numerically to identify the dominant physical phenomena and to gain insight into experimental observations. In addition, recent thermal models derived from first principles for EDLCs under constant-current cycling accounting for irreversible Joule heating and reversible heat generation rates due to ion diffusion, steric effects, and changes in entropy are discussed. Scaling analyses of both equilibrium and dynamic models are also presented as a way to identify self-similar and asymptotic behaviors as well as to develop design rules for electrodes and electrolytes of next generation EDLCs. Electrical double layer capacitors (EDLCs) store energy by ion adsorption in the electrical double layer (EDL) forming at the electrode/electrolyte interfaces.1,2 This process is highly reversible and the cycle life of EDLCs exceeds 100,000 cycles.2,3 EDLCs can operate in a wide range of specific energy and power densities. This versatility is a key feature for electrical energy storage, energy harvesting, and energy regeneration applications. 2The performance of EDLCs is determined by the combination of the electrode material and morphology and of the electrolyte. In general, the key attributes of a good electrode include 1,3-7 (i) large surface area accessible to ions to maximize charge storage, (ii) optimum pore size, short pore length, and good pore connectivity to facilitate ion transport, (iii) large electrical conductivity to enable fast charging and discharging and low ohmic resistance, (iv) thin electrodes and current collectors to reduce the total resistance of the device, (v) small leakage current, (vi) small self-discharge, (vii) environmentally friendly materials, and (viii) low price. However, satisfying all these criteria simultaneously is challenging. For example, increasing surface area often results in larger electrode electrical resistivity.1 Micropores with diameter less than 2 nm contribute greatly to EDLCs capacitance.2 But pores smaller than the ion size are typically inactive and do not contribute to charge storage. 1,8 Porous electrodes must also be electrochemically accessible to ions. Then, interconnected mesopores with diameter ranging from 2 to 50 nm are necessary for fast charging thanks to their easier accessibility to ions. 1,6,[9][10][11] In practice, electrode...

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Interacting Ions in Biophysics: Real is not Ideal

Cited by 57 publications

References 291 publications

Long-range electrostatic screening in ionic liquids

Long-range electrostatic screening in ionic liquids

Energetics of discrete selectivity bands and mutation-induced transitions in the calcium-sodium ion channels family

Recent Advances in Continuum Modeling of Interfacial and Transport Phenomena in Electric Double Layer Capacitors

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