Dynamics of Single-Chain Nanoparticles under Crowding: A Neutron Spin Echo Study

Area of Science:

• Polymer Physics
• Biomolecular Dynamics
• Soft Matter Science

Background:

• Single-chain nanoparticles (SCNPs) are synthetic models for flexible biomacromolecules like intrinsically disordered proteins (IDPs).
• Macromolecular crowding significantly influences the dynamics and behavior of biological molecules.

Purpose of the Study:

• To investigate the impact of macromolecular crowding on the internal and center-of-mass dynamics of SCNPs.
• To compare SCNP dynamics under crowding to behaviors observed in IDPs.
• To determine how crowder size affects SCNP dynamics.

Main Methods:

• Neutron spin echo (NSE) spectroscopy was employed to probe SCNP dynamics.
• Poly(methyl methacrylate) (PMMA)-based SCNPs (33 kDa) were studied in solutions with varying molecular weight PMMA linear crowders (10 kDa and 100 kDa).
• Analysis utilized the Zimm model to interpret dynamic structure factors.

Main Results:

• SCNPs in dilute solution exhibit internal dynamics but possess high internal friction, leading to effective chain stiffening, similar to IDPs.
• Under crowding conditions, SCNP internal dynamics remained largely unchanged.
• Center-of-mass diffusion of SCNPs slowed down in the presence of crowders.
• The effective viscosity experienced by SCNPs was lower than the solution's macroscopic viscosity and independent of crowder molecular weight.

Conclusions:

• Macromolecular crowding primarily affects the translational diffusion of SCNPs, not their internal dynamics.
• SCNPs serve as valid models for understanding crowding effects on flexible biomacromolecules like IDPs.
• The observed dynamics suggest a decoupling between internal chain motion and overall diffusion under crowding.