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PreprintCC BYChemRxiv

Water hydrogen bond network elongation below the lower critical solution temperature in aqueous triethylamine solution probed by soft X-ray absorption spectroscopy

  • Masanari Nagasaka1,2
  • Kenji Mochizuki3,4
4 affiliations
  1. 1Institute for Molecular Science, Myodaiji, Okazaki, Japan, 444-8585
  2. 2Graduate Institute for Advanced Studies, SOKENDAI, Myodaiji, Okazaki, Japan, 444-8585
  3. 3Department of Chemistry
  4. 4Zhejiang University
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Abstract

The lower critical solution temperature (LCST) mechanism of aqueous triethylamine (TEA) solution was investigated by the element-specific observation of molecular interactions using soft X-ray absorption spectroscopy (XAS). The H 2 O‒H 2 O hydrogen bonds were probed by O K-edge XAS, and the hydrophobic interactions of TEA and TEA‒H 2 O hydrogen bonds were probed by C and N K-edge XAS. Molecular interactions in aqueous TEA solutions at temperatures below the LCST were analyzed using radial distribution functions obtained from molecular dynamics (MD) simulations. Temperature-dependent changes in the XAS spectra were evaluated by inner-shell calculations using snapshots from MD simulations. These studies revealed that the LCST mechanism of aqueous TEA solution is governed by the balance of H 2 O‒H 2 O hydrogen bonds, hydrophobic interactions of TEA, and TEA‒H 2 O hydrogen bonds. Aqueous TEA solution is miscible below the LCST, where the H 2 O‒H 2 O hydrogen bonds elongate owing to the TEA‒H 2 O hydrogen bonds and hydrophobic interactions of TEA. The H 2 O‒H 2 O hydrogen bonds near the LCST are closer to those of liquid water owing to the weakening of the TEA‒H 2 O hydrogen bonds. The hydrophobic interactions of TEA are also enhanced owing to the strong H 2 O‒H 2 O hydrogen bonds, resulting in liquid‒liquid phase separation above the LCST. These three factors provide a framework for interpreting the LCST mechanisms of amphiphilic molecules, polymers, and soft matter related to protein folding and DNA packing.

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Cite

BibTeXRIS
BibTeX
@misc{nagasaka2026water,
  title = {{Water hydrogen bond network elongation below the lower critical solution temperature in aqueous triethylamine solution probed by soft X-ray absorption spectroscopy}},
  author = {Masanari Nagasaka and Kenji Mochizuki},
  howpublished = {ChemRxiv},
  year = {2026},
  month = sep,
  doi = {10.26434/chemrxiv.15009325/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009325/v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Water hydrogen bond network elongation below the lower critical solution temperature in aqueous triethylamine solution probed by soft X-ray absorption spectroscopy
AU  - Masanari Nagasaka
AU  - Kenji Mochizuki
PY  - 2026
DA  - 2026/09/22
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15009325/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009325/v1
AB  - The lower critical solution temperature (LCST) mechanism of aqueous triethylamine (TEA) solution was investigated by the element-specific observation of molecular interactions using soft X-ray absorption spectroscopy (XAS). The H 2 O‒H 2 O hydrogen bonds were probed by O K-edge XAS, and the hydrophobic interactions of TEA and TEA‒H 2 O hydrogen bonds were probed by C and N K-edge XAS. Molecular interactions in aqueous TEA solutions at temperatures below the LCST were analyzed using radial distribution functions obtained from molecular dynamics (MD) simulations. Temperature-dependent changes in the XAS spectra were evaluated by inner-shell calculations using snapshots from MD simulations. These studies revealed that the LCST mechanism of aqueous TEA solution is governed by the balance of H 2 O‒H 2 O hydrogen bonds, hydrophobic interactions of TEA, and TEA‒H 2 O hydrogen bonds. Aqueous TEA solution is miscible below the LCST, where the H 2 O‒H 2 O hydrogen bonds elongate owing to the TEA‒H 2 O hydrogen bonds and hydrophobic interactions of TEA. The H 2 O‒H 2 O hydrogen bonds near the LCST are closer to those of liquid water owing to the weakening of the TEA‒H 2 O hydrogen bonds. The hydrophobic interactions of TEA are also enhanced owing to the strong H 2 O‒H 2 O hydrogen bonds, resulting in liquid‒liquid phase separation above the LCST. These three factors provide a framework for interpreting the LCST mechanisms of amphiphilic molecules, polymers, and soft matter related to protein folding and DNA packing.
ER  -