# Superoxide- and semiquinone-linked activation of molecular hydrogen in metal-catalyst-free solution.
> 金属触媒非存在下におけるスーパーオキシドおよびセミキノンを介した分子状水素の活性化機構


## Abstract

This in vitro study examined the chemical basis by which molecular hydrogen (H2) modulates superoxide (O2•−) kinetics in metal-free, membrane-free aqueous conditions. Using xanthine oxidase/hypoxanthine and potassium superoxide systems alongside the O2•−-specific chemiluminescent probe MPEC, bell-shaped and U-shaped kinetic profiles were recorded as a function of H2 concentration. In the absence of ubiquinone (Q), a bell-shaped profile consistent with tunneling-assisted electron transfer from H2 to O2•− was observed. When Q was included, U-shaped profiles emerged, suggesting semiquinone radical (Q•−)-mediated electron buffering followed by ubiquinol (QH2) formation. ESR radical scavenging experiments and quantitative HPLC analyses corroborated transient semiquinone-driven redox cycling. These findings establish the chemical feasibility of H2 participating in Q redox cycling via a metal-free, tunneling-compatible pathway, with physiological relevance yet to be determined.

### Mechanism

H2 undergoes tunneling-assisted electron transfer to superoxide; in the presence of ubiquinone, semiquinone radicals act as electron buffers, ultimately driving ubiquinol formation through a metal-free redox cycling pathway.

## Bibliographic

- **Authors**: Ishibashi T, Harunari E, Ishihara G, Niiyama T, Noda-Urata M, Komori N
- **Journal**: Front Mol Biosci
- **Year**: 2025
- **PMID**: [41195421](https://pubmed.ncbi.nlm.nih.gov/41195421/)
- **DOI**: [10.3389/fmolb.2025.1680812](https://doi.org/10.3389/fmolb.2025.1680812)
- **PMC**: [PMC12582930](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12582930/)
- **Study type**: in vitro study
- **Delivery route**: in vitro
- **Effect reported**: positive

## Delivery context

This is basic research at the cellular or molecular level. For human application, inhalation is the most promising delivery route, but inhalation carries explosion risk and concentration matters (empirical LFL of 10%; high-concentration devices are not recommended).

## Safety notes

This is basic research at the cellular or molecular level. For human application, inhalation is the most promising delivery route, but inhalation carries explosion risk and concentration matters (empirical LFL of 10%; high-concentration devices are not recommended).

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 41195421. https://h2-papers.org/en/papers/41195421
> **Source**: PubMed PMID [41195421](https://pubmed.ncbi.nlm.nih.gov/41195421/)