Discontinuous molecular dynamics (DMD) study of heteropolymer collapse in an explicit solvent

In this study, we employ the discontinuous molecular dynamics simulation method to investigate the collapse properties of a single heteropolymer chain in an explicit solvent. Solvent density ρ, fraction of hydrophobic monomers n H (defined as the ratio of the number of hydrophobic monomers to the total number of monomers) and a hydrophobicity parameter λ (which controls the energy mismatch between the monomers and solvent particles) were systematically varied to examine their role in polymer collapse. The average static structure factor of the polymer was used to find the so-called θ-point characterizing the state of an ideal chain. Phase diagrams of ρ versus λ for the coil-globule transition were mapped out for different values of n H. Increasing the fraction of hydrophobic monomers n H, solvent density ρ, and hydrophobicity parameter λ were all shown to aid in stabilizing the globule phase. In an effort to explore scaling behaviour of the coil-globule phase diagram as a function of n H, and to investigate whether the phase boundaries for different n H collapsed on to one universal curve, we rescaled λ by n H (δ) λ; we determined δ = 1.72, in contrast to mean-field predictions of δ = 2.0.