Water hydrogen bond network elongation below the lower critical solution temperature in aqueous triethylamine solution probed by soft X-ray absorption spectroscopy
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Authors: Masanari Nagasaka, Kenji Mochizuki
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214077924