Molecular characterization of l-phenylalanine terminated poly(l-lactide) conjugates

Peptide-polymer conjugates made of poly(l-lactide) and l-phenylalanine or l,l-diphenylalanine (F-PLA and FF-PLA, respectively) have been synthesized by the ring-opening polymerization of l-lactide using the peptide fragment as an initiator. The structure of the conjugates was confirmed by ¹H NMR, FT-IR, GPC, UV-Vis and CD. Molecular dynamics simulations have been used to identify both the conformational preferences of the FF-PLA conjugate in solution and the potential intramolecular interactions between the peptide and polymer blocks, while TD-DFT calculations have been applied to model the electronic transitions observed by the UV-Vis absorption spectroscopy. Results show that the polymer fragment prefers a random coil or a mix of helix/strand while the peptide fragment tends to have folded and helical conformations. Although the degree of interaction between the two fragments is slightly higher than that reported for other peptide-polymer conjugates, it is small enough to suggest that FF-PLA is a potential candidate to aggregate forming peptide-guided organizations via self-assembly. On the other hand, quantum mechanical calculations have allowed us to identify the π → π* transition, which is typically observed in helical peptides and proteins, as well as the n → π* transition along the N-C-O backbone.