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Molecular Sinkers: X-ray Photoemission and Atomistic Simulations of Benzoic Acid and Benzoate at the Aqueous Solution/Vapor Interface

Ottosson, Niklas; Romanova, Anastasia O.; Soderstrom, Johan; Bjorneholm, Olle; Öhrwall, Gunnar LU and Fedorov, Maxim V. (2012) In The Journal of Physical Chemistry Part B 116(43). p.13017-13023
Abstract
In this work, we provide a detailed microscopic picture of the behavior of benzoic acid at the aqueous solution/vapor interface in its neutral as well as in its dissociated form (benzoate). This is achieved through a combination of highly surface-sensitive X-ray photoelectron spectroscopy experiments and fully atomistic molecular simulations. We show that significant changes occur in the interface behavior of the neutral acid upon release of the proton. The benzoic acid molecules are found to be strongly adsorbed at the interface layer with the planes of the aromatic rings oriented almost parallel to the water surface. In contrast, in the benzoate form, the carboxylate group shows a sinker-like behavior while the aromatic ring acts as a... (More)
In this work, we provide a detailed microscopic picture of the behavior of benzoic acid at the aqueous solution/vapor interface in its neutral as well as in its dissociated form (benzoate). This is achieved through a combination of highly surface-sensitive X-ray photoelectron spectroscopy experiments and fully atomistic molecular simulations. We show that significant changes occur in the interface behavior of the neutral acid upon release of the proton. The benzoic acid molecules are found to be strongly adsorbed at the interface layer with the planes of the aromatic rings oriented almost parallel to the water surface. In contrast, in the benzoate form, the carboxylate group shows a sinker-like behavior while the aromatic ring acts as a buoy, oriented nearly perpendicular to the surface. Furthermore, a significant fraction of the molecular ions move from the interface layer into the bulk of the solution. We rationalize these findings in terms of the very different hydration properties of the carboxylic group in the two charge states. The molecule has an amphiphilic nature, and the deprotonation thus changes the hydrophobic/hydrophilic balance between the nonpolar aromatic and the polar carboxylic parts of the molecule. That, consequently, leads to a pronounced reorientation and depletion of the molecules at the interface. (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
116
issue
43
pages
13017 - 13023
publisher
The American Chemical Society
external identifiers
  • wos:000310482800014
  • scopus:84868249974
ISSN
1520-5207
DOI
10.1021/jp300956j
language
English
LU publication?
yes
id
2ab8a517-af5d-4eb6-a8dd-e89cccc526f6 (old id 3388389)
date added to LUP
2013-01-30 14:10:34
date last changed
2017-08-13 03:58:08
@article{2ab8a517-af5d-4eb6-a8dd-e89cccc526f6,
  abstract     = {In this work, we provide a detailed microscopic picture of the behavior of benzoic acid at the aqueous solution/vapor interface in its neutral as well as in its dissociated form (benzoate). This is achieved through a combination of highly surface-sensitive X-ray photoelectron spectroscopy experiments and fully atomistic molecular simulations. We show that significant changes occur in the interface behavior of the neutral acid upon release of the proton. The benzoic acid molecules are found to be strongly adsorbed at the interface layer with the planes of the aromatic rings oriented almost parallel to the water surface. In contrast, in the benzoate form, the carboxylate group shows a sinker-like behavior while the aromatic ring acts as a buoy, oriented nearly perpendicular to the surface. Furthermore, a significant fraction of the molecular ions move from the interface layer into the bulk of the solution. We rationalize these findings in terms of the very different hydration properties of the carboxylic group in the two charge states. The molecule has an amphiphilic nature, and the deprotonation thus changes the hydrophobic/hydrophilic balance between the nonpolar aromatic and the polar carboxylic parts of the molecule. That, consequently, leads to a pronounced reorientation and depletion of the molecules at the interface.},
  author       = {Ottosson, Niklas and Romanova, Anastasia O. and Soderstrom, Johan and Bjorneholm, Olle and Öhrwall, Gunnar and Fedorov, Maxim V.},
  issn         = {1520-5207},
  language     = {eng},
  number       = {43},
  pages        = {13017--13023},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Molecular Sinkers: X-ray Photoemission and Atomistic Simulations of Benzoic Acid and Benzoate at the Aqueous Solution/Vapor Interface},
  url          = {http://dx.doi.org/10.1021/jp300956j},
  volume       = {116},
  year         = {2012},
}