Hydration structure of trimethylamine N-oxide in aqueous solutions revealed by soft X-ray emission spectroscopy and chemometric analysis

Abstract

resonance 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.