Dynamic heterogeneity controls diffusion and viscosity near biological interfaces.

Area of Science:

• Physical Chemistry
• Nanoscale Science
• Fluid Dynamics

Background:

• Biological fluid behavior at the nanoscale is governed by interfacial physical chemistry.
• This can lead to anomalous diffusion, where particle movement deviates from bulk predictions.
• Existing models often require empirical corrections for solute size, like the hydrodynamic radius.

Purpose of the Study:

• To quantitatively measure interfacial effects on water dynamics using methods from glassy systems.
• To explain the slowed diffusion of large solutes near surfaces.
• To develop a method for calculating diffusion constants from molecular details, removing empirical factors.

Main Methods:

• Applied measures developed for studying glassy systems.
• Quantitatively measured interfacial effects on water dynamics.
• Analyzed correlated particle motions near surfaces.

Main Results:

• Correlated particle motions near surfaces result in higher effective viscosity than predicted by individual motions.
• This increased interfacial viscosity explains the slower diffusion of large solutes (e.g., proteins).
• A new method allows diffusion constant calculation from molecular details alone.

Conclusions:

• Spatial heterogeneity on nanometre scales fundamentally increases interfacial viscosity for any fluid near any surface.
• The empirical hydrodynamic radius correction for large solutes is unnecessary when using this new molecular-level approach.
• This work provides a more accurate, physics-based understanding of diffusion in confined systems.