Hofmeister effects in micromolar electrolyte solutions

Shinichi Enami; Himanshu Mishra; Michael R. Hoffmann; Agustn J. Colussi

doi:10.1063/1.4704752

Hofmeister effects in micromolar electrolyte solutions

Shinichi Enami^*, Himanshu Mishra, Michael R. Hoffmann, Agustn J. Colussi

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

44 Scopus citations

Abstract

Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I ^-Br ^-, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH ₄, and N(C ₄H ₉) ₄) and NaY (Y OH, Cl, NO ₃, and ClO ₄) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I ^- and Br ^- are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.

Original language	English (US)
Article number	154707
Journal	JOURNAL OF CHEMICAL PHYSICS
Volume	136
Issue number	15
DOIs	https://doi.org/10.1063/1.4704752
State	Published - Apr 21 2012
Externally published	Yes

Bibliographical note

Funding Information:
This work was financially supported by the Japan Science and Technology Agency (JST) PRESTO program. We are grateful to Dr. Drew Parsons and Professor Barry Ninham for a helpful discussion. S.E. is grateful to Professor K. Takahashi, Professor M. Shiotani, and Ms. A. Hatano of Kyoto University for assisting the startup of a new laboratory. Valuable discussions with Professor William Goddard and Dr. Tod Pascal of California Institute of Technology are also acknowledged.

ASJC Scopus subject areas

General Physics and Astronomy
Physical and Theoretical Chemistry

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10.1063/1.4704752

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title = "Hofmeister effects in micromolar electrolyte solutions",

abstract = "Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I -Br -, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH 4, and N(C 4H 9) 4) and NaY (Y OH, Cl, NO 3, and ClO 4) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I - and Br - are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.",

author = "Shinichi Enami and Himanshu Mishra and Hoffmann, {Michael R.} and Colussi, {Agustn J.}",

note = "Funding Information: This work was financially supported by the Japan Science and Technology Agency (JST) PRESTO program. We are grateful to Dr. Drew Parsons and Professor Barry Ninham for a helpful discussion. S.E. is grateful to Professor K. Takahashi, Professor M. Shiotani, and Ms. A. Hatano of Kyoto University for assisting the startup of a new laboratory. Valuable discussions with Professor William Goddard and Dr. Tod Pascal of California Institute of Technology are also acknowledged.",

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AU - Enami, Shinichi

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AU - Hoffmann, Michael R.

AU - Colussi, Agustn J.

N1 - Funding Information: This work was financially supported by the Japan Science and Technology Agency (JST) PRESTO program. We are grateful to Dr. Drew Parsons and Professor Barry Ninham for a helpful discussion. S.E. is grateful to Professor K. Takahashi, Professor M. Shiotani, and Ms. A. Hatano of Kyoto University for assisting the startup of a new laboratory. Valuable discussions with Professor William Goddard and Dr. Tod Pascal of California Institute of Technology are also acknowledged.

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N2 - Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I -Br -, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH 4, and N(C 4H 9) 4) and NaY (Y OH, Cl, NO 3, and ClO 4) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I - and Br - are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.

AB - Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I -Br -, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH 4, and N(C 4H 9) 4) and NaY (Y OH, Cl, NO 3, and ClO 4) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I - and Br - are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.

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Hofmeister effects in micromolar electrolyte solutions

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