Observation of dissipating solvated protons upon hydrogel formation

Area of Science:

• Biophysics
• Materials Science
• Spectroscopy

Background:

• Aqueous hyaluronan solutions exhibit pH-dependent gelation, forming an elastic hydrogel around pH 2.4.
• This pH-induced transition provides a model to study conformational changes in hydrogen bond networks and water solvation.
• Understanding these changes is crucial for biological systems and material science applications.

Purpose of the Study:

• To investigate the role of water solvation and proton behavior during hyaluronan hydrogel formation.
• To correlate macroscopic properties of the hydrogel with molecular-level changes in the water network.
• To explore the influence of additives like urea and glucose on hyaluronan gel elasticity.

Main Methods:

• Terahertz (THz) reflection absorption spectroscopy in attenuated total reflection (ATR) geometry was employed.
• THz spectroscopy was used to probe changes in the hydrogen-bonded water network and hyaluronan solvation.
• Macroscopic elasticity measurements were correlated with spectroscopic data.

Main Results:

• A distinct spectral signature of solvated protons was observed above and below the gelation pH (2.4-2.8).
• This signature was absent within the 2.4-2.8 pH range, coinciding with hydrogel formation.
• Changes in elasticity induced by urea or glucose correlated with the formation and destruction of proposed ion pairs.

Conclusions:

• The absence of solvated protons during gelation suggests their involvement in ion pair formation with hyaluronan.
• This ion pairing mechanism is proposed to be central to hyaluronan hydrogel formation and elasticity.
• THz spectroscopy effectively links macroscopic hydrogel properties to molecular solvation dynamics.