Study of structure-activity correlation in LPMO-inspired copper complexes

This work describes a structure-activity study of three bioinspired copper(II) complexes derived from L-proline, focusing on a novel complex (CuAL) compared to CuPol and CuPTB. The new ligand AL was characterized by 1D/2D NMR, HRMS, and IR, while CuAL was comprehensively analyzed via UV-Vis, IR, elemental analysis, XPS, cyclic voltammetry, and EPR spectroscopy. EPR parameters revealed a distorted square-planar geometry with nitrogen donors, mimicking the LPMO active site. Catalytic activity was tested on PNp, filter paper, crystalline cellulose, and carboxymethylcellulose. CuAL outperformed the other complexes, achieving ~1.0 absorbance and 0.14 mg/mL glucose equivalents. It exhibited endoglucanase-like behavior on amorphous cellulose but showed no activity on crystalline regions. Notably, H₂O₂ or ascorbate fully inhibited its activity, indicating a hydrolytic rather than oxidative mechanism, attributed to primary alcohol coordination enhancing water activation. These results demonstrate that subtle coordination changes can dictate catalytic pathways, which offer valuable insights for designing model catalysts.