Ligand-engineered metal‒organic frameworks with atomically axial Cu-N₅ sites for controlled nitric oxide delivery and...

Constructing single-site nanozymes with precisely defined coordination environments is essential for achieving high and controllable enzymatic reactivity, yet remains challenging. Herein, we propose a facile ligand-engineering-induced coordination-unsaturation (LEICU) strategy to construct Cu-nitroprusside-based Prussian blue analogues single-site nanozyme (termed as CNPSE). Through rational ligand substitution with nitroprusside, isolated coordination-unsaturated axial Cu-N₅ moieties are generated as dominant enzymatic active centers. The resulting CNPSE exhibits markedly enhanced peroxidase-like and glutathione-depletion activities, while retained Fe-C  N-Fe moieties endow efficient near-infrared photothermal conversion. Density functional theory (DFT) calculations further reveal that Cu active sites significantly lower the energy barrier for H₂O₂ activation, thereby promoting reactive oxygen species (ROS) generation and enhancing peroxidase-like (POD-like) catalytic activity. Upon 808 nm irradiation, the local hyperthermia not only accelerates enzymatic reactions but also triggers nitric oxide release, synergistically amplifying oxidative damage and apoptosis. Both in vitro and in vivo studies demonstrate effective tumor suppression with excellent biosafety, and transcriptomic analyses reveal activation of oxidative stress, immune response, and cyclic guanosine monophosphate (cGMP) signaling pathway. This work demonstrates the potential of ligand engineering to tailor the atomic coordination environment of single-site nanozymes, offering a rational strategy for constructing coordination-unsaturated catalytic sites in multifunctional PBA-based therapeutic platforms.