Fig. 3.
Heat and cold polymer unfolding. (a) Contours of equal Rg(T, P) for M = 44 in the P–T plane, showing polymer collapse in the central region of P and T, and reflecting regions of good and poor solvent behavior; the numbers denote the value of Rg(T, P). The large filled circles C1 and C2 indicate the liquid–gas and liquid–liquid critical points, respectively. Note that at low P, on decreasing T along a constant P trajectory (dashed line), one passes from a region of good solvent behavior (swollen “denatured” polymers) to a region of poor solvent behavior (collapsed polymers) and finally again to a region of swollen polymer (“cold denaturation”). (b) Schematic illustration of the closed loop region encompassing the domain of hydrophobic collapse for a polymer chain such as studied here, and mimicking the stability regime of native protein folding. In comparison with a, the regions of high-T swelling (“heat denaturation”) and low-T swelling (“cold denaturation”), and the distinct pressure dependence of the polymer melting point are evident in the Jagla solvent model.