Minimal Model of Intrinsic Chirality to Study the Folding Behavior of Helical Polymers

Abstract

We describe a minimal model of an intrinsically chiral polymer chain, and characterize its equilibrium and transient behavior at different temperatures, and in effective solvent environments by means of Brownian dynamics simulation. By contrast to previous studies, our model transparently includes intrinsic curvature and torsion as a measure of residue-inherent (molecular) chirality to establish a defined handedness, while allowing the observation of a transformation between a high-temperature expanded random coil and a dense helical or globular state at low temperatures. In fair or good solvents, a straightforward denaturation of a folded helix toward a random coil is observed. In poor solvent, this process is superimposed by adoption of a condensed globule in the low-medium temperature range. Under these conditions, we find that helical chains represent metastable states separated from the thermodynamically favored dense globule by an energy barrier. Finally, by combining the observations of structural transformations with the evidence of thermodynamic anomaly in the heat capacity, we suggest that the helix–globule transformation represents a discontinuous phase transition-like process.