Does hydrated glycine act as solidification nucleus at multi-kilobar conditions?

Area of Science:

• Biophysics
• Physical Chemistry
• Biochemistry

Background:

• Understanding biological processes requires studying biomolecules in aqueous solutions under varying thermodynamic conditions.
• Pressure is a critical thermodynamic parameter influencing biomolecular behavior and biological functions, especially under extreme environmental conditions.

Purpose of the Study:

• To investigate the low-frequency spectra of aqueous glycine solutions under high pressure.
• To understand the pressure-dependent compression of solvated glycine and its effect on the hydration water network.

Main Methods:

• Acquired low-frequency Raman spectra of 1.5 M aqueous glycine from ambient pressure to 8 kbar.
• Analyzed spectral shifts of specific modes related to glycine structure and water hydration.

Main Results:

• Observed a linear blue shift in the N-C-C-O open/close mode (~320 cm⁻¹) with increasing pressure, indicating glycine compression.
• Noted a non-linear, slower blue shift in the hydration water network peak (~184 cm⁻¹) compared to the intramolecular glycine mode.
• Found that hydrated glycine acts as the solidification nucleus for the liquid-solid phase transition above 8 kbar.

Conclusions:

• High pressure significantly alters the structure and compression of aqueous glycine.
• The behavior of the hydration water network under pressure is distinct from that of glycine itself.
• Hydrated glycine plays a critical role in initiating phase transitions in aqueous solutions at high pressures.