In biological systems, copper ions often serve as redox-active enzyme centers by transferring electrons and driving oxidation-reduction reactions. Outside enzymes, copper(II) typically adopts a square-planar geometry due to the Jahn–Teller effect, a configuration that reduces its oxidation power when cycling between copper(II) and copper(I). Many copper-dependent enzymes circumvent this limitation by distorting the metal center toward a distorted tetrahedral arrangement, which promotes efficient electron transfer and substrate oxidation. Inspired by these enzymes, we aimed to achieve fully tetrahedrally coordinated copper(II) within zeolitic imidazole frameworks (ZIFs).
In this study, zinc(II) or cobalt(II) in ZIF-8 and ZIF-67 was substituted with copper(II), yielding a unique class of Cu-substituted ZIFs. Structural analyses confirmed that copper(II) occupies tetrahedral sites—an arrangement traditionally challenging to realize. Remarkably, these Cu-substituted ZIF-8 displayed high oxidative activity, outperforming natural CuZn-superoxide dismutase (SOD) in superoxide dismutation assays.1 Mechanistic investigations revealed that these materials rely on a distinct pathway compared to enzymes, maintaining activity even under conditions that inhibit native SOD.
Building on these findings, we designed Cu-doped ZIF-67 particles to emulate the oxygen-reducing function of laccase.2 These catalysts efficiently oxidized phenolic substrates in aqueous media using molecular oxygen, showing excellent selectivity and reusability over multiple cycles. Hence, our approach demonstrates that engineering SOD-like and laccase-like functionalities into a single class of materials can expand the frontiers of biomimetic catalysis.