{
  "abstract": "Flavin-dependent halogenases (FDHs) catalyze site-selective C–H halogenation of electron-rich aromatic compounds but rely on multienzyme cofactor-recycling systems to continuously supply reduced flavin (FADH 2 ). Here, we establish an overpotential-driven, mediator-assisted bioelectrocatalytic strategy for FADH 2 regeneration that eliminates auxiliary reductases, nicotinamide cofactors, and enzyme immobilization. Cyclic voltammetry confirmed the proton-dependent FAD/FADH 2 redox couple (-0.42 V vs Ag/AgCl, 3.5 M KCl) and the competing oxygen reduction reaction (ORR). Bulk electrolysis involving the FDH RebH revealed that L-ascorbic acid suppresses ORR-derived species more effectively than conventional catalase/glutathione/superoxide-dismutase systems, increasing conversion of tryptophan to 7-bromotryptophan from 20% to 46% after 24 h at -0.7 V. Increasing the cathodic potential to -1.1 V improved yields to 64% without substantially improving the faradaic efficiency (FE~ 5%). Introducing redox mediators such as 2-hydroxy-1,4-naphthoquinone (HNQ) and methyl viologen (MV 2+ ) enabled the HNQ/FAD pair to achieve quantitative halogenation within 10 h (FE ~ 14%) and the MV 2+ /FAD pair within 12 h (FE ~ 9%), enabling production of 8.8 mg of 7-bromotryptophan in a scale-up reactor. Moreover, the HNQ/FAD system exhibited a kinetic isotope effect (KIE) of ( k H / k D = 1.8) for product formation in H 2 O versus D 2 O, supporting proton involvement in productive FAD regeneration and potentially reflecting cooperation between mediator-assisted electron transfer and surface-adsorbed hydrogen (H ads ) produced during the hydrogen evolution reaction in accelerating FADH 2 formation. Extending this method to engineered RebH variant 4-V enabled halogenation of larger substrates, establishing a scalable electrochemical platform for FDH catalysis. These results establish how electron delivery, proton availability, and competing oxygen reduction govern productive electrochemical flavin regeneration and provide a scalable platform for FDH catalysis.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Chemistry",
    "Indiana University"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 6,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Batul Shakir"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Xuzhong Shen"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Conor Wallace"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Declan B. Mackey"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Jared. C. Lewis"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Ricardo Javier Vázquez",
      "orcid": "0000-0003-3245-8123"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/21zxx0wf90cfv.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15002776/v2",
  "fulltext_url": null,
  "id": "21zxx0wf90cfv",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15002776/v2",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "1312|Enzyme Catalysis and Immobilization"
    ]
  ],
  "openalex": "W7221627897",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15002776/v2",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-12",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/21zxx0wf90cfv.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:22Z",
      "native_id": "10.26434/chemrxiv.15002776",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15002776/v2"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "openalex:1312|Enzyme Catalysis and Immobilization",
      "subfield": "molecular-biology"
    }
  ],
  "title": "Site-selective Halogenation of Aromatic C-H Bonds via Electrocatalytic Flavin Adenine Dinucleotide Cofactor Regeneration",
  "title_text": "Site-selective Halogenation of Aromatic C-H Bonds via Electrocatalytic Flavin Adenine Dinucleotide Cofactor Regeneration",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:22Z",
  "url": "https://research.draconitic.com/paper/21zxx0wf90cfv",
  "venue": "ChemRxiv",
  "versions": []
}