Rationale Design of pH-Responsive Core-Shell Nanoparticles: Polyoxometalate-Mediated Structural Reorganization

Herein, we report the rational design of pH-responsive core-shell nanoparticles that incorporate a polyoxometalate (POM) cargo. Cobalt (III)-substituted borotungstate [BIIIW11O39CoIII]6- (POM) was selected due to its stability, low oxidizing power, and the ability to form kinetically inert coordinate bonds with the pyridyl functionality of the hydrophobic core polymer (CP) to yield (POM@CP). Dispersion of the POM-polymer composite in acetone and subsequent nanoprecipitation via the addition of the amphiphilic copolymer (SP) yield the core-shell nanoparticles (SP)(POM@CP). Large-scale structural rearrangement is observed in response to acidification; this is a significantly different response to the POM-free materials, which undergo complete nanoparticle disassembly. The (SP)(POM@CP) assemblies also display host-guest chemistry in addition to structural and compositional changes driven by the pH decrease. Analytical techniques such as nuclear magnetic resonance, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, and cryo-transmission electron microscopy have been utilized to characterize the integrity, structure, and solution-state behavior of the assemblies.