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

Area of Science:

• Supramolecular Chemistry
• Catalysis
• Electrochemistry

Background:

• Supramolecular catalysis typically modifies reaction kinetics via substrate encapsulation.
• Manipulating the thermodynamics of electron-transfer reactions using supramolecular approaches remains largely unexplored.

Purpose of the Study:

• To develop a microenvironment-shielding strategy to alter the redox potentials of hydrazine substrates.
• To mimic enzymatic activation for N-N bond cleavage using a metal-organic capsule.

Main Methods:

• Design and synthesis of a metal-organic capsule (H1) with catalytic cobalt sites and amide groups.
• Encapsulation of hydrazines within H1 to form a clathration intermediate.
• Investigation of catalytic N-N bond cleavage using electron donors and kinetic experiments.
• Integration of fluorescein for photoreduction studies.

Main Results:

• H1 induced an anodic shift in hydrazine redox potentials, decreasing Gibbs free energy for electron transfer (up to -70 kJ mol⁻¹).
• Catalytic reduction of N-N bond cleavage followed a Michaelis-Menten mechanism involving substrate binding and bond cleavage.
• Photoreduction of N2H4 to ammonia achieved rates comparable to natural MoFe proteins (ca. 1530 nmol min⁻¹).

Conclusions:

• The molecular confined microenvironment within H1 effectively modulates reaction thermodynamics.
• This supramolecular approach provides a novel strategy for mimicking enzymatic activation and N-N bond cleavage.