# Ligand Radicals Tune LPMO Activity in Model Complex

## TL;DR

This study shows how ligand radicals in a copper complex improve catalytic activity, offering a blueprint for designing self-protecting oxidation catalysts.

## Contribution

The study identifies ligand-centered radicals as key functional analogues of enzymatic redox pathways in synthetic copper models.

## Key findings

- Complex 4 generates stable carbon-centered ligand radicals more effectively than N,N,N-coordinated analogues.
- Complex 4 outperforms other complexes in degrading various substrates using H2O2 or O2.
- Lower steric hindrance in complex 4 is linked to its superior catalytic performance.

## Abstract

Radicals are essential to the catalytic chemistry of
metalloenzymes,
enabling reactivity and self-protection through controlled redox processes.
In copper-dependent LPMOs, amino acid radicals mediate oxidative transformations
via hole hopping. However, the generation and role of ligand-centered
radicals in synthetic copper models remain poorly understood. Here
we show that an l-proline–based N,N,O,O-coordinated
copper complex (4) generates stable carbon-centered ligand-radicals.
A markedly higher population of these ligand radicals was observed
in this complex than in the N,N,N-coordinated analogues (complexes 1–3). Catalytically, complex 4 outperforms
complexes 1–3, effectively degrading 4-nitrophenyl-β-d-glucopyranoside, cellobiose, and cellulose using either H2O2 or O2. The superior performance of
complex 4 is linked to its lower steric hindrance, a
key factor in LPMO mimicry. These results establish ligand-centered
radicals as key functional analogues of enzymatic redox pathways and
offer a blueprint for designing self-protecting copper oxidation catalysts.