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 6a 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.

TrimethylamineN-oxide (TMAO) resists the compression of water structure by magnesium perchlorate: terrestrial kosmotropevs.Martian chaotrope

“…A commonly used osmolyte and powerful protein stabilising agent is trimethylamine N-oxide (TMAO). TMAO has already been shown to protect proteins against denaturation against a range of agents including urea (45,46) and pressure(47,48), as well as enhancing hydrogen bonding in bulk water (49)(50)(51). This motivates us to ask the question: can TMAO help to preserve the hydrogen bond network of water against the pressurising effect of Mg(ClO4)2?…”

Hydration of the Zwitterionic and Protonated Forms of Glycine Betaine Probed by Soft X-ray Emission Spectroscopy Coupled with Chemometrics

“…The experiments were performed at the A3 station on the RIKEN coherent soft X-ray spectroscopy beamline, BL17SU, in the SPring-8 facility, Japan. Details of the experimental setup were given elsewhere, , and the experimental procedure was similar to that described in our previous work . Sample solutions were introduced into a cell equipped with a gold- or platinum-coated silicon nitride membrane (150 nm thickness; NTT Advanced Technology Co., Japan) separating them from the ultrahigh-vacuum chamber.…”

“…This study is intended for investigating the hydration structure of both forms of GB by the application of soft X-ray emission spectroscopy coupled with chemometric analysis, which we proposed in our previous study for the TMAO aqueous solution. 26 The approach is based on the classical least-squares (CLS) regression 27,28 treatment for concentration-dependent emission spectra. The application of the original CLS method leads to the pure solute component having a negative emission region where the emission spectra show apparent inverse dependence on the concentration.…”

“…This study is intended for investigating the hydration structure of both forms of GB by the application of soft X-ray emission spectroscopy coupled with chemometric analysis, which we proposed in our previous study for the TMAO aqueous solution . The approach is based on the classical least-squares (CLS) regression , treatment for concentration-dependent emission spectra.…”

“…Decrease in the emission intensity is rationalized by the loss of bulk solvent molecules. The corrected concentrations are thus termed the effective molar concentrations . With the aid of theoretical calculations on the electric properties of the zwitterionic and protonated forms, the hydration structure is discussed for both forms.…”