The Inorganic Origins of Biocatalysis: Electron Logic in Iron-Based Nanomaterials

Iron oxide nanomaterials are widely studied as artificial enzymes (nanozymes), yet their catalytic activity emerges not from intentional design but from intrinsic solid-state properties. These nanostructures function as inorganic enzymes, with redox activity governed by the d-electron configurations of transition metal centers. Catalysis arises from directional electron and proton transfer between Fe²⁺ and Fe³⁺ across Fe–O–Fe motifs, activated by water sorption and facilitated by the binding of target compounds such as hydrogen peroxide or phosphate esters, with activity shaped by lattice geometry and surface asymmetry. We propose a unifying model—an electron ratchet—in which substrate sorption induces rectified charge flow, enabling redox or hydrolytic catalysis in the absence of proteins or genetic encoding. This framework reframes nanozymes not as enzyme mimics but as mineral-based precursors to biological catalysis. By linking transition metal chemistry, structural asymmetry, and water-mediated electron dynamics, this work highlights the role of iron-based nanomaterials as mechanistic and evolutionary antecedents to modern biocatalysts.