Modifying Enzymatic Substrate Binding within a Metal–Organic Capsule for Supramolecular Catalysis

Abstract

Supramolecular catalysis is established to modify reaction kinetics by substrate encapsulation, but manipulating the thermodynamics of electron-transfer reactions remains unexplored. Herein, we reported a new microenvironment-shielding approach to induce an anodic shift in the redox potentials of hydrazine substrates, reminiscent of the enzymatic activation for N-N bond cleavage within a metal-organic capsule <b>H1</b>. Equipped with the catalytic active cobalt sites and substrate-binding amide groups, <b>H1</b> encapsulated the hydrazines to form the substrate-involving clathration intermediate, triggering the catalytic reduction N-N bond cleavage when electrons were acquired from the electron donors. Compared with the reduction of free hydrazines, the conceptual molecular confined microenvironment decreases the Gibbs free energy (up to -70 kJ mol^-1), which is relevant to the initial electron-transfer reaction. Kinetic experiments demonstrate a Michaelis-Menten mechanism, which involves the formation of the pre-equilibrium of substrate-binding, followed by bond cleavage. Then, the distal N is released as NH₃ and the product is squeezed. Integrating fluorescein into <b>H1</b> enabled the photoreduction of N₂H₄ with an initial rate of ca. 1530 nmol min^-1 into ammonia, comparable to that of natural MoFe proteins; thus, the approach provides an attractive manifold toward mimicking enzymatic activation.