Complex Dynamics of Water in Protein Confinement

Area of Science:

• Physical Chemistry
• Biophysics
• Materials Science

Background:

• Water dynamics are crucial for biological and material processes.
• Understanding molecular behavior in confined environments is key to many applications.
• Protein powders represent a complex biological matrix where water exhibits unique properties.

Purpose of the Study:

• To investigate the single-molecule and collective dynamics of water confined within protein powders.
• To elucidate the influence of protein-water interactions on water's dynamic behavior.
• To compare confined water dynamics with bulk water properties.

Main Methods:

• Molecular dynamics simulations were employed to model water confined in protein powders.
• Analysis of single-particle dynamics and collective dipole dynamics.
• Examination of dielectric spectra and comparison with neutron scattering data.

Main Results:

• Single-molecule water dynamics showed modest retardation and significant stretching (exponent ~0.2) in protein powders.
• Collective water dipole dynamics were influenced by water-water and water-protein correlations.
• Dielectric spectra revealed two peaks: a Debye peak (~16 ps) and a highly stretched peak (~13 ns, exponent ~0.12), attributed to protein motion.
• Neutron scattering data confirmed highly stretched dynamics, with translational motion overshadowed by rotational loss.

Conclusions:

• Water dynamics in protein powders are significantly altered, exhibiting slower and more stretched relaxation compared to bulk water.
• Protein elastic motions play a critical role in the collective dynamics of confined water.
• The findings provide insights into water's behavior in biological and complex material systems.