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

Abstract

Herein, we report the rational design of pH-responsive core−shell nanoparticles that incorporate a polyoxometalate (POM) cargo. Cobalt (III)-substituted borotungstate [B III W 11 O 39 Co III ] 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.

Polymeric Nanoparticles for Drug Delivery

“…Cryo-EM was conducted on the hybrid nanoparticles at pH 8, 7, and 6 to observe the distribution of [B III W 11 O 39 Co III ] 6− as well as the particle's structural rearrangement in response to acidification. 554 Generally, pre-modification is a feasible strategy to improve the loading efficiency and overall stability of hybrid assemblies. Although it provides a more controlled means of loading and release, more research is needed in terms of better characterization techniques and the incorporation of cleavable bonds between polymer chains and inorganic cargo.…”

Polyoxometalates as chemically and structurally versatile components in self-assembled materials

“…Based on the data from all analytical techniques, we have attributed this structural rearrangement to the increase in inter-and intra-polymer hydrogen bonding with the polyanion surface and stronger point charge interactions, which ultimately prevents particle disassembly. 94 The development of research on organic modification of POM clusters as well as the design and control of molecular weight and morphology have become the key factors affecting the application performance of the POM-polymer hybrids. Thus, the synthetic methodology of polymer hybrids with POM as the pendant sidechain has evolved from free radical polymerization to more controlled polymerization methods, such as RAFT and ROMP.…”

“…Based on the data from all analytical techniques, we have attributed this structural rearrangement to the increase in inter- and intra-polymer hydrogen bonding with the polyanion surface and stronger point charge interactions, which ultimately prevents particle disassembly. 94 …”

Intelligent Polymers, Fibers and Applications

“…olymers 2021, 13,1427 12 of 20 their surroundings changes, these polymers change their conformation, surface behavior and solubility by acquiring or losing ionizable basic groups or acid groups, therefore tuning the solubility of the polymeric nanoparticles [129], fabricating ion-stabilized membranes [130] or designing core-shell nanoparticles [131]. Such characteristics are the origin of how the pH-sensitive release of drug-delivery carriers works.…”

“…Some polymers can react to environmental pH fluctuations to protonate or deprotonate correspondingly [ 123 , 127 , 128 ] as Figure 6 c shows. When the pH condition of their surroundings changes, these polymers change their conformation, surface behavior and solubility by acquiring or losing ionizable basic groups or acid groups, therefore tuning the solubility of the polymeric nanoparticles [ 129 ], fabricating ion-stabilized membranes [ 130 ] or designing core-shell nanoparticles [ 131 ].…”