Characterization of variant soft nanoparticle structure and morphology in solution by NMR spectroscopy

The physicochemical properties of soft nanoparticles, most notably size, morphology, and ligand interactions, typically depend upon the solution environment in which they are suspended. Comprehensive characterization in a given environment is therefore essential. We have employed high resolution solution nuclear magnetic resonance (NMR) spectroscopy, nuclear spin relaxation measurements, and diffusion ordered NMR spectroscopy (DOSY) techniques to thoroughly characterize polymeric nanoparticles formed by salt induced collapse of a methacrylic acid ethyl acrylate copolymer stabilized by ultraviolet (UV) irradiation. UV dose dependent production of new chemical species is apparent from ¹H and ¹³C chemical shift patterns. ¹H ¹³C correlation spectroscopy reveals that cross linking is likely responsible for nanoparticle structural integrity. Paramagnetic relaxation enhancement (PRE) unambiguously shows protection of photochemically derived moieties from solvent, with a UV dose dependent decrease in particle size. Temperature dependent swelling and solvent induced contraction demonstrate that increased UV dose leads to an increase in the proportion of compact, solvent protected particle core relative to more dynamic, solvent accessible shell. Correlation of disparate solution state NMR observables allowed for these conclusions and is readily generalizable to the in situ characterization of the exact state of a wide variety of soft nanoparticles as a function of environment.