Chemically controlled unfolding of a RNA-like polymer model.

Area of Science:

• Statistical mechanics
• Polymer physics
• Biophysics

Background:

• RNA folding is complex, involving polymer chain interactions.
• A two-tolerant lattice polymer model describes RNA folding, predicting a collapse and a paired state.
• This model lacks the ability to account for external factors influencing folding.

Purpose of the Study:

• To extend the two-tolerant polymer model by incorporating a micromolecular species that inhibits segment pairing.
• To investigate the thermodynamic equilibrium of this extended model under varying micromolecule concentrations.
• To analyze the resulting phase diagram and understand the impact of micromolecules on polymer folding.

Main Methods:

• Utilized a grand-canonical ensemble for thermodynamic investigation.
• Employed the Bethe approximation, a refined mean-field technique.
• Analyzed the model on a random-regular graph, equivalent to the Bethe approximation's exact solution.

Main Results:

• Observed that increasing micromolecule concentration favors polymer unfolding.
• Found that higher micromolecule concentrations decrease the transition temperature.
• The extended model exhibits a remarkably rich and interesting phase diagram.

Conclusions:

• The addition of micromolecules significantly alters the polymer's phase behavior.
• The model provides a framework for understanding how external factors can modulate polymer folding.
• The Bethe approximation offers valuable insights into the complex thermodynamics of such systems.