Synthesis of Hybrid-Polypeptides m-PEO-b-poly(His-co-Gly) and m-PEO-b-poly(His-co-Ala) and Study of Their Structure and Aggregation. Influence of Hydrophobic Copolypeptides on the Properties of Poly(L-histidine)

The highly diverse and sophisticated action of proteins results from their equally diverse primary structure, which along with the nature of interactions between the amino acids, defines the higher self-assembly of proteins. The interactions between amino acids can be very complicated, and their understanding is necessary in order to elucidate the protein structure-properties relationship. A series of well-defined hybrid-polypeptidic diblock copolymers of the type m-PEO-b-poly(His-co-Gly) and m-PEO-b-poly(His-co-Ala) was synthesized through the ring opening polymerization of the N-carboxyanhydrides of the corresponding amino acids, with a molar ratio of the hydrophobic peptide to histidine at 10%, 20% and 40%. The excellent purity of the monomers combined with the high vacuum techniques resulted in controlled polymerization with high molecular and compositional homogeneity. FT-IR, as well as circular dichroism, were employed to investigate the secondary structure of the polymers, while DLS, SLS and ζ-potential were utilized to study the aggregates formed in aqueous solutions, as well as their pH responsiveness. The results revealed that the randomly distributed monomeric units of glycine or alanine significantly influence L-histidine’s structure. Depending on the pH, aggregates with a different structure, different molecular characteristics and a different surface charge are formed, potentially leading to very interesting bioapplications.