An in-depth NMR investigation of thermoresponsive unimer micelles loaded with the highly hydrophobic antitumor drug CA-4

Unimer micelles, a special class of single chains nanoparticles (SCNPs), are known to form in water solution by the self-folding of amphiphilic random copolymers via hydrophobic intramolecular interactions. The hydrophobic compartments, derived therefrom, can be usefully exploited for the encapsulation of highly water-insoluble drug for their potential use as drug delivery systems (DDSs). Because the knowledge-base of their self-assembling behaviour in water is of primary importance, in this work, a comprehensive NMR investigation is reported on the self-folding of a fluorinated random copolymer (PEGMA₈₃-co-FA₁₇) with the main aim to highlight the potential of this technique as a complementary tool with respect to the conventionally used DLS and more sophisticated analytical techniques, including SAXS and SANS. In particular, new experimental conformational details were described by using ¹H–¹H, ¹H-¹⁹F and ¹⁹F–¹⁹F 2D NOESY maps. Micelle size determination through DOSY and water solubility enhancement of Combretastatin A-4 (CA-4), a potent highly hydrophobic anticancer drug, were evaluated. Encapsulation efficiency (EE%) was also quantified. Details on PEGMA₈₃-co-FA₁₇/CA-4 molecular interactions were elucidated, and temperature-responsive properties were observed by recording measurements above and below the cloud point temperature typical of the formulation. The obtained results suggest that NMR spectroscopy represents a faceted and powerful analytical tool for the characterization at a molecular level of unimer micelles as innovative materials for the encapsulation of hydrophobic drugs, as CA-4, potentially applicable as drug delivery systems.