Salt-modulated structure of polyelectrolyte-macroion complex fibers

Area of Science:

• Polymer physics
• Soft matter physics
• Biophysics

Background:

• Complex fibers form from polyelectrolyte chains and macroions.
• Understanding their structure and stability is crucial for various applications.

Purpose of the Study:

• Investigate the structure and stability of strongly charged complex fibers.
• Explore the influence of electrostatic interactions and chain elasticity.

Main Methods:

• Numerical investigation at the ground-state level.
• Utilized a chain-sphere cell model with periodic boundary conditions.
• Employed a numerical optimization method to find minimum energy configurations.

Main Results:

• Observed diverse helical arrangements of macroions: zig-zag, solenoidal, and beads-on-a-string.
• Identified a competition between attractive and repulsive forces governing structures.
• Found dense zig-zag patterns most stable at physiological salt concentrations, resembling chromatin fiber.
• Predicted a fiber diameter of approximately 30 nm and macroion density of 5-6 per 11nm.

Conclusions:

• The generic chain-sphere model accurately predicts complex fiber structures, including those relevant to chromatin.
• Similar structures are expected for DNA and synthetic nano-colloid complexes.
• Phase separation into dense and dilute phases is predicted at intermediate salt concentrations.