Laccases as palladium oxidases.

Area of Science:

• Biocatalysis and Organometallic Chemistry
• Enzyme Engineering and Green Chemistry

Background:

• Developing efficient catalytic systems for alcohol oxidation is crucial in green chemistry.
• Enzyme-catalyzed reactions offer mild conditions and high selectivity.
• Palladium catalysts are widely used but often require harsh conditions or are non-renewable.

Purpose of the Study:

• To describe the first coupled catalytic system combining an enzyme and a palladium(II) catalyst for aerobic alcohol oxidation.
• To investigate the interaction between fungal laccase LAC3 and a palladium catalyst under mild conditions.
• To assess the impact of this combined system on catalytic efficiency and enzyme stability.

Main Methods:

• Utilized fungal laccase LAC3 and a water-soluble palladium complex.
• Performed aerobic oxidation of veratryl alcohol in aqueous solution at room temperature and atmospheric pressure.
• Characterized enzyme reduction using UV/VIS and ESR spectroscopy.
• Assessed catalyst regeneration and enzyme activity during the reaction.

Main Results:

• Demonstrated a coupled catalytic system involving laccase LAC3 and a palladium(II) catalyst for aerobic alcohol oxidation.
• Confirmed reduction of LAC3 by a palladium(0) species in the absence of dioxygen.
• Showcased LAC3's ability to regenerate the palladium catalyst and reduce dioxygen to water without activity loss.
• Observed a 7-fold increase in catalytic efficiency for the palladium complex when associated with laccase.

Conclusions:

• The developed enzyme-palladium coupled system enables efficient aerobic alcohol oxidation under mild, environmentally friendly conditions.
• Fungal laccase LAC3 plays a key role in regenerating the palladium catalyst and facilitating oxygen reduction.
• This work represents a significant step towards designing renewable and highly efficient palladium-based oxidation catalysts.