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Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics

Werner, Josephina; Wernersson, Erik; Ekholm, Victor; Ottosson, Niklas; Öhrwall, Gunnar LU ; Heyda, Jan; Persson, Ingmar; Soderstrom, Johan; Jungwirth, Pavel and Bjorneholm, Olle (2014) In The Journal of Physical Chemistry Part B 118(25). p.7119-7127
Abstract
Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N Is binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed... (More)
Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N Is binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting-out effect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well. The simulations suggest that the relatively higher surface propensity of guanidinium compared with ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
118
issue
25
pages
7119 - 7127
publisher
The American Chemical Society
external identifiers
  • wos:000338184400014
  • scopus:84903466740
ISSN
1520-5207
DOI
10.1021/jp500867w
language
English
LU publication?
yes
id
80d37214-1732-4206-9c55-b72f2aca0b16 (old id 4602845)
date added to LUP
2014-09-04 12:50:38
date last changed
2017-11-12 03:38:13
@article{80d37214-1732-4206-9c55-b72f2aca0b16,
  abstract     = {Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N Is binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting-out effect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well. The simulations suggest that the relatively higher surface propensity of guanidinium compared with ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it.},
  author       = {Werner, Josephina and Wernersson, Erik and Ekholm, Victor and Ottosson, Niklas and Öhrwall, Gunnar and Heyda, Jan and Persson, Ingmar and Soderstrom, Johan and Jungwirth, Pavel and Bjorneholm, Olle},
  issn         = {1520-5207},
  language     = {eng},
  number       = {25},
  pages        = {7119--7127},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics},
  url          = {http://dx.doi.org/10.1021/jp500867w},
  volume       = {118},
  year         = {2014},
}