title: Hydration structure of trimethylamine N-oxide in aqueous solutions revealed by soft X-ray emission spectroscopy and chemometric analysis.
abstract: The hydration structure of trimethylamine N-oxide (TMAO) in aqueous solutions has been investigated by means of soft X-ray spectroscopy and chemometric analysis. Soft X-ray absorption spectra in the O 1s region have a concentration-dependent shoulder at 533 eV, which is assigned to the 6a1resonance of TMAO. Soft X-ray emission spectra acquired at this resonance comprise both TMAO and water components, with a prominent peak at 525.6 eV which is assigned to the emission caused by the 5e to O 1s transition. An apparent inverse concentration dependence of around 523 eV suggests that the electronic structure of water is modified by the strong interaction with TMAO. Such an effect has been included in the quantitative spectral analysis, called the classical least squares regression method, to obtain information on the hydration structure of the system. The analysis indicates that nine or more water molecules interact with a TMAO molecule. The present method offers a useful technique for probing the solvation structure around the solute which interacts strongly with the solvent.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. okadak@sci.hiroshima-u.ac.jp and RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
authors.forename: Yuu
authors.initials: Y
authors.lastname: Sasaki
authors.affiliation: RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan and Department of Physics and Information Science, Faculty of Science, Yamaguchi University, Yamaguchi, Yamaguchi 753-8511, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Horikawa
authors.affiliation: RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
authors.forename: Takashi
authors.identifier: http://orcid.org/0000-0003-2586-0712
authors.initials: T
authors.lastname: Tokushima
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. okadak@sci.hiroshima-u.ac.jp and RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
authors.forename: Kazumasa
authors.identifier: http://orcid.org/0000-0002-4274-2438
authors.initials: K
authors.lastname: Okada
authors.affiliation: RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Oura
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. okadak@sci.hiroshima-u.ac.jp and Center for Quantum Life Sciences (QuLiS), Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Misako
authors.initials: M
authors.lastname: Aida