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 H1 . Equipped with the catalytic active cobalt sites and substrate-binding amide groups, H1 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 NH 3 and the product is squeezed. Integrating fluorescein into H1 enabled the photoreduction of N 2 H 4 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.