Visible-light hematite-supported LPMO oxidation and photo-assisted Fe/H₂O₂ remodeling of chitin substrates.

Abstract

Here, we evaluated two complementary light-responsive routes for chitin conversion: hematite-supported reactions containing chitin-active LPMOs and soluble Fe3+/H₂O₂ oxidative remodeling of colloidal chitin. Among nine materials screened, hematite nanoparticles gave the strongest light-dependent product signals; synthesized Fe₂O₃-Z produced higher chromatographic responses than commercial hematite, with an apparent signal maximum at 5 mg/mL. HPAEC-PAD and MALDI-TOF MS detected oxidized chitooligosaccharides from DP6 and colloidal chitin, with C1-oxidized chitobiose (DP2ox) prominent in the FfAA11 system. In the separate Fe/H₂O₂ treatment, illumination promoted Fe3+ reduction at 0.498 μM/min in the o-phenanthroline assay and increased the operational liquefaction yield of colloidal chitin to 37.31%. FT-IR, XRD, and SEM indicated oxidative surface remodeling while the main α-chitin crystalline reflections were retained. The results extend hematite-assisted photobiocatalysis to chitin-active AA11 and AA10 LPMO systems and characterize a complementary Fe/H₂O₂ route for substrate remodeling. Fe/H₂O₂ pretreatment reduced subsequent chitinase release of DP1/DP2, showing that increased liquefaction did not translate into improved enzymatic digestibility under the tested conditions. This proof-of-concept study does not establish a beneficial one-pot cascade or a specific electron-transfer/ROS mechanism: calibrated spectral irradiance/photon flux and individual ROS species were not measured.

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