Location of Cholic Acid Sequestered by Core−Shell Nanoparticles Using REDOR NMR

Solid-state 13C{19F} rotational-echo double-resonance (REDOR) NMR was used to locate [24-13C]cholic acid that had been absorbed by nanoparticles with a core−shell morphology. The nanoparticles were composed of poly(4-fluorostyrene)-block-poly(acrylic acid) copolymers in which 15% of the poly(acrylic acid) shell functionality had been cross-linked with 2,2‘-(ethylenedioxy)bis(ethylamine). The REDOR data were consistent with no cholic acid in the core, approximately 28% located at or near the core−shell interface, and the remaining 72% of the cholic acid farther than 25 Å from the interface.