Synthetic polymers as biomacromolecular models for studying ligand–protein interactions: A nuclear spin relaxation approach

In this paper, we applied an NMR methodology based on the analysis of selective spin–lattice relaxation rate enhancements of ligand protons induced by interaction processes between prednisolone and a synthetic copolymer, namely poly(N-isopropylacrylamide-co-N-acryloil-l-phenylalanine), in order to investigate this system as a model for studying drug–biomacromolecules interactions. The contribution from the bound ligand fraction to the observed relaxation rate in relation to macromolecule concentration allowed the calculation of the normalized affinity index [AIN]LT, in which the effects of motional anisotropies and different proton densities have been removed. This parameter, which represents the global affinity of the ligand towards the macromolecule, isolates the contribution due to a decrease in the ligand dynamics caused by the binding with the copolymer. The affinity index calculated for prednisolone–copolymer complex compared to that obtained for prednisolone–albumin system, suggested that synthetic polymers as models of biomacromolecules can play an important role in drug–protein interaction studies.