A computational study on enzymatically driven oxidative coupling of chlorophenols: an indirect dehalogenation...

Area of Science:

• Environmental Chemistry
• Biocatalysis
• Computational Chemistry

Background:

• Peroxidases catalyze dimerization reactions of chlorophenols, potentially forming dimers and polymers.
• Free radicals generated during enzymatic cycles can undergo various coupling reactions.

Purpose of the Study:

• To elucidate the mechanism of peroxidase-catalyzed chlorophenol dimerization.
• To predict chlorine isotopic fractionation during these reactions.
• To investigate four distinct coupling pathways: radical-anion, radical-cation, radical-radical (singlet), and radical-radical (triplet).

Main Methods:

• Density functional theory (DFT) calculations were employed.
• Energetic profiles of different reaction pathways were analyzed.
• Substrates included 2-chlorophenol, 4-chlorophenol, 2,4,6-trichlorophenol, and 4-chloro-2,6-dimethylphenol.

Main Results:

• Radical-cation and radical-radical (singlet) couplings are identified as the most energetically favorable pathways.
• Radical-anion coupling, though energetically demanding, is also considered due to substrate anionic form prevalence.
• Chlorine isotopic fractionation is observed in radical-radical (triplet) coupling and during the intramolecular chlorine transfer in radical-cation and radical-radical (singlet) pathways.

Conclusions:

• The study identifies the most probable mechanisms for chlorophenol dimerization catalyzed by peroxidases.
• Specific reaction pathways, particularly those involving radical-cation and radical-radical (singlet) couplings, are predicted to exhibit significant chlorine isotopic fractionation.
• These findings contribute to understanding the environmental fate of chlorinated pollutants and the mechanisms of enzymatic reactions.