Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 145, Issue 18, Pages 10136-10148Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.3c00626
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This study reports a new microenvironment-shielding approach to induce an anodic shift in the redox potentials of hydrazine substrates similar to enzymatic activation. By encapsulating the hydrazines, the catalyst H1 triggers the catalytic reduction N-N bond cleavage when electrons are acquired. The confined microenvironment decreases the Gibbs free energy (up to -70 kJ mol-1) and exhibits a Michaelis-Menten mechanism.
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 NH3 and the product is squeezed. Integrating fluorescein into H1 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.
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