Specific ion effects on interfacial water structure near macromolecules

Xin Chen, Tinglu Yang, Sho Kataoka, Paul S. Cremer

Research output: Contribution to journalArticle

223 Citations (Scopus)

Abstract

We investigated specific ion effects on interfacial water structure next to macromolecules with vibrational sum frequency spectroscopy (VSFS). Poly-(N-isopropylacrylamide) was adsorbed at the air/water interface for this purpose. It was found that the presence of salt in the subphase could induce the reorganization of water adjacent to the macromolecule and that the changes depended greatly on the specific identity and concentration of the salt employed. Ranked by their propensity to orient interfacial water molecules, sodium salts could be placed in the following order: NaSCN > NaClO 4 > Nal > NaNO3 ≈ NaBr > NaCl > pure water ≈ NaF ≈ Na2SO4. This ordering is a Hofmeister series. On the other hand, varying the identity of the cation exhibited virtually no effect. We also showed that the oscillator strength in the OH stretch region was linearly related to changes in the surface potential caused by anion adsorption. This fact allowed binding isotherms to be abstracted from the VSFS data. Such results offer direct evidence that interfacial water structure can be predominantly the consequence of macromolecule-ion interactions.

Original languageEnglish (US)
Pages (from-to)12272-12279
Number of pages8
JournalJournal of the American Chemical Society
Volume129
Issue number40
DOIs
StatePublished - Oct 10 2007

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Macromolecules
Ions
Water
Salts
Vibrational spectra
Spectrum Analysis
Spectroscopy
Surface potential
Adsorption
Anions
Isotherms
Cations
Negative ions
Positive ions
Sodium
Air
Molecules

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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abstract = "We investigated specific ion effects on interfacial water structure next to macromolecules with vibrational sum frequency spectroscopy (VSFS). Poly-(N-isopropylacrylamide) was adsorbed at the air/water interface for this purpose. It was found that the presence of salt in the subphase could induce the reorganization of water adjacent to the macromolecule and that the changes depended greatly on the specific identity and concentration of the salt employed. Ranked by their propensity to orient interfacial water molecules, sodium salts could be placed in the following order: NaSCN > NaClO 4 > Nal > NaNO3 ≈ NaBr > NaCl > pure water ≈ NaF ≈ Na2SO4. This ordering is a Hofmeister series. On the other hand, varying the identity of the cation exhibited virtually no effect. We also showed that the oscillator strength in the OH stretch region was linearly related to changes in the surface potential caused by anion adsorption. This fact allowed binding isotherms to be abstracted from the VSFS data. Such results offer direct evidence that interfacial water structure can be predominantly the consequence of macromolecule-ion interactions.",
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Specific ion effects on interfacial water structure near macromolecules. / Chen, Xin; Yang, Tinglu; Kataoka, Sho; Cremer, Paul S.

In: Journal of the American Chemical Society, Vol. 129, No. 40, 10.10.2007, p. 12272-12279.

Research output: Contribution to journalArticle

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AU - Cremer, Paul S.

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