Ligand Radicals Tune LPMO Activity in Model Complex.

Area of Science:

• Bioinorganic Chemistry
• Catalysis
• Organic Chemistry

Background:

• Radicals are crucial for metalloenzyme catalytic chemistry and redox processes.
• Copper-dependent lytic polysaccharide monooxygenases (LPMOs) utilize amino acid radicals for oxidative transformations.
• The role of ligand-centered radicals in synthetic copper models is not well understood.

Purpose of the Study:

• To investigate the generation and function of ligand-centered radicals in synthetic copper complexes.
• To compare the catalytic activity of different copper coordination complexes.
• To establish ligand-centered radicals as functional analogues of enzymatic redox pathways.

Main Methods:

• Synthesis of N,N,O,O- and N,N,N-coordinated copper complexes.
• Characterization of ligand-radical generation and population.
• Catalytic degradation assays using various substrates (4-nitrophenyl-β-d-glucopyranoside, cellobiose, cellulose) with H2O2 or O2.

Main Results:

• An l-proline-based N,N,O,O-coordinated copper complex (4) generated stable carbon-centered ligand-radicals.
• Complex 4 exhibited a higher population of ligand radicals compared to N,N,N-coordinated analogues (1-3).
• Complex 4 demonstrated superior catalytic degradation of substrates, outperforming complexes 1-3.

Conclusions:

• Ligand-centered radicals are key functional analogues of enzymatic redox pathways in copper catalysis.
• Lower steric hindrance in complex 4 contributes to its enhanced catalytic performance, mimicking LPMOs.
• This study provides a blueprint for designing self-protecting copper oxidation catalysts.