Physical Gelation of Polypeptide-Polyelectrolyte-Polypeptide (ABA) Copolymer in Solution

The gelation behavior of polypeptide-polyelectrolyte-polypeptide in solution is investigated by Monte Carlo techniques. It is found that different hydrogen bonding styles, parallel and antiparallel, provide a major influence on the sol-gel transition and the chain conformation. The antiparallel hydrogen bonding style favors the bridge conformation, while loop conformation has less structural limitation with parallel bonding. However, in the parallel style, polyelectrolyte blocks are aligned in the same side of beta-sheets, which induces more steric constrains and the electrostatic repulsion. Consequently, compared with the parallel bonding style, the sol-gel transition of antiparallel style occurs at lower hydrogen bonding energy and the dihedral angle theta of antiparallel beta-sheets is a little higher. The increase of charging fraction of polyelectrolyte blocks prompts the sol-gel transition of both bonding styles but causes an impact on the number of hydrogen bond and the dihedral angle, indicating a decrease in the structure integrity.