Hyperfine dynamics as an internal control of reactive-oxygen-species output in a triplet-born flavin–superoxide radical pair
6 affiliations
- 1CONICET
- 2Facultad de Ciencias Exactas y Naturales (FCEN)
- 3Universidad de Belgrano
- 4Departamento de Física Médica
- 5Instituto Balseiro
- 6Johns Hopkins University Applied Physics Laboratory
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.
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BibTeX
@misc{castello2026hyperfine,
title = {{Hyperfine dynamics as an internal control of reactive-oxygen-species output in a triplet-born flavin–superoxide radical pair}},
author = {Pablo R. Castello and Pablo Jiménez and Carlos F. Martino},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009742/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009742/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Hyperfine dynamics as an internal control of reactive-oxygen-species output in a triplet-born flavin–superoxide radical pair
AU - Pablo R. Castello
AU - Pablo Jiménez
AU - Carlos F. Martino
PY - 2026
DA - 2026/10/01
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009742/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009742/v1
AB - 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.
ER -