Supramolecular Assembly of Charge-Tunable Metal–Phenolic Networks

Controlling the surface charge of nanoassembled structures enables modulation of their physicochemical properties and expands their applications. Metal–phenolic networks (MPNs) typically yield materials with negatively charged surfaces. Herein, MPNs with tunable surface charge were prepared using biscatechol-functionalized poly(2-vinylpyridine) (P2VP) and various metal ions. The first assembly route yielded P2VP–FeIII MPN capsules that displayed pH-dependent surface charge reversal (∼ −10 mV at pH 12 to 20 mV at pH 2) and facilitated the fabrication of hollow superstructures. Besides the catechol–metal interaction, the pyridinyl nitrogen–metal coordination facilitated the continuous assembly of P2VP–CoII MPN capsules (e.g., capsule shell thickness increased from 12 to 26 nm over 24 h). The second assembly route involving concurrent quaternization of P2VP and MPN assembly produced positively charged capsules (i.e., QP2VP/P2VP–FeIII MPN capsules) and provided control of the shell thickness (12–52 nm) and surface charge (6–53 mV) over time (1–8 h) at 70 °C. The positively charged surfaces enabled the fabrication of bioactive and fluorescent capsules and regulation of the cell association properties depending on the degree of positive charge. This work expands the selection of negatively or positively charged MPN building blocks for designing tunable MPN systems.