Synthesis, Molecular Docking Simulation, and Enzymatic Degradation of AB-Type Indole-Based Polyesters with Improved Thermal Properties

We report the facile synthesis of a series of indole-based hydroxyl-carboxylate (AB-type) monomers by a one-step procedure. These monomers were successfully polymerized by melt polycondensation to yield AB-type polyesters with a varied number of flexible methylene units in the backbones. These indole-based AB-polyesters showed decent thermal stability according to the TGA results (onset thermal degradation temperature of >330 °C), and their glass transition temperatures are dependent on the length of the methylene bridge (Tg ≈ 62-102 °C) according to the DSC results. Furthermore, DSC and WAXD measurements revealed that these polymers did not crystallize from melt, but the ones with flexible structures could crystallize from solution. Molecular docking simulations showed favorable interactions between indole-based polyesters and polyethylene terephthalate hydrolase (PETase) from Ideonella sakaiensis. This was corroborated by the experimental results, which indicated that the PETase enzyme has degrading activity on the indole-based AB polyesters except for the one with the highest degree of crystallinity.