Effect of Encapsulating Arginine Containing Molecules on PLGA: A Solid-State NMR Study

Design of polymer-drug composites based on the lactide/glycolic acid often rely on the chemical complementarity between the polymer and functional groups in a pharmaceutical guest. We previously characterised decapeptide (AZD)/poly(D,L-lactide-co-glycolide) (PLGA) film formulations aiming at localising the interacting groups responsible for the changes in the bulk properties of the polymer matrix and understanding the mechanism of stabilisation of the drug into the polymer matrix. The results suggested interactions to occur between the arginine residue in the peptide and the carbonyl end group of the polymer chains. In order to clarify the role of arginine in directing the drug-polymer interactions, arginine and hexapeptide containing arginine were encapsulated in a PLGA 50/50 polymer. Variable temperature T1ρH measurements and WISE experiments indicated significant changes in the local dynamics of the polymer chains. These effects were enhanced near and above Tg suggesting the presence of guests promote the appearance of backbone motion of the polymer chains. The localisation of the interactions on the carbonyl groups of the polymer was further confirmed by the WISE experiments.