{
  "abstract": "When reduced flavin is activated by molecular oxygen it forms a spin-correlated radical pair—a flavin semiquinone and superoxide (O₂•⁻)—born in the triplet manifold, because ground-state O₂ is a triplet. Its singlet/triplet recombination gates the branching of reactive oxygen species, and the pair is realised in the electron-transfer flavoprotein, whose output is field-dependent. Radical-pair theory almost always treats the hyperfine tensor as fixed and the field as the variable. We invert that: with the field held fixed, what upper bound does a time-dependent active-site hyperfine coupling place on the singlet yield? We pose a coefficient inverse problem with the principal-axis components Aₖ,ₐ(t) as the control and solve it for the genuine triplet-born flavin pair (two ¹⁴N at I = 1, three protons; dimension 288) at a 200 ns lifetime. A time-dependent coupling raises the yield to ΦS = 0.290 at 50 µT, against 0.241 for the best constant coupling in the same admissible set (1.20×) and 0.203 for the molecule’s own couplings (1.43×); the reduced models give larger gains, so they overestimate the effect. The optimum places 76% of its modulation in the first 0.5 µs and is smooth and numerically near-singular, unlike the bang–bang optimum of the external-field problem. These are coherent yields obtained over a control set far larger than conformational motion can access—an upper bound on an upper bound—with spin relaxation, the dipolar coupling and the superoxide g-anisotropy left unmodelled. The falsifiable quantity is the dynamic-over-static gain, not the absolute yield.",
  "abstract_shown": true,
  "affiliations": [
    "CONICET",
    "Facultad de Ciencias Exactas y Naturales (FCEN)",
    "Universidad de Belgrano",
    "Departamento de Física Médica",
    "Instituto Balseiro",
    "Johns Hopkins University Applied Physics Laboratory"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 3,
  "authors": [
    {
      "affs": [
        0,
        1,
        2
      ],
      "name": "Pablo R. Castello",
      "orcid": "0000-0002-2983-9294"
    },
    {
      "affs": [
        3,
        4
      ],
      "name": "Pablo Jiménez",
      "orcid": "0000-0001-7368-7753"
    },
    {
      "affs": [
        5
      ],
      "name": "Carlos F. Martino"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/cf5p1ftz2q1kq.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15009742/v1",
  "fulltext_url": null,
  "id": "cf5p1ftz2q1kq",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009742/v1",
  "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",
      "1304|Electron Spin Resonance Studies"
    ]
  ],
  "openalex": "W7215061330",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15009742/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-01",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/cf5p1ftz2q1kq.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:21Z",
      "native_id": "10.26434/chemrxiv.15009742",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009742/v1"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "openalex:1304|Electron Spin Resonance Studies",
      "subfield": "biophysics"
    }
  ],
  "title": "Hyperfine dynamics as an internal control of reactive-oxygen-species output in a triplet-born flavin–superoxide radical pair",
  "title_text": "Hyperfine dynamics as an internal control of reactive-oxygen-species output in a triplet-born flavin–superoxide radical pair",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:21Z",
  "url": "https://research.draconitic.com/paper/cf5p1ftz2q1kq",
  "venue": "ChemRxiv",
  "versions": []
}