Phase transition of a single protein-like copolymer chain

Abstract

Protein-like copolymers (PLCs) are a kind of artificial macromolecule owning protein characteristics. We investigate the general phase transition of a single PLC chain with uniform block structure using a parallel Wang–Landau sampling method. Two typical PLC models, i.e. HP and AB models, are employed to reveal the hydrophobic effect and the phase separation effect for a PLC chain folding in aqueous environments. It is found that the block length m greatly influences the phase transition of PLC. With increasing m, the low energy stable structures for the HP model change from a tube-like aggregation to a tadpole-shape structure, and for the AB model they evolve from a multilayer structure to two separated spheres. When m is very small, the liquid–crystal transition disappears. When m is larger, the AB-PLC shows two first order transitions corresponding to the A and B phase separation transition and the liquid–crystal transition, respectively, while the HP model only shows one first order liquid–crystal transition. We further found that during the freezing of the AB-PLC, the whole chain experiences a special intermediate state where one component is embedded by another component. The result is valuable to design the functional single-molecule devices and next generation nano building blocks using PLCs.