How could plain hydrogen gas do anything inside mitochondria? A quantum calculation maps a narrow doorway — in computer models
Edited by Samael A. Tejada, Founder & Editor-in-Chief
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Quantum-chemical calculations suggest molecular hydrogen could be split inside mitochondria only in a narrow setting: by a neutral semiquinone radical at Complex I or III, under strongly reductive conditions (Physical Chemistry Chemical Physics, October 28, 2026). The anionic form showed no pathway at all. It is a modelled mechanism — computational evidence only, with no biological experiment in this study.
Hydrogen therapy's hardest question is not whether H2 is safe — it is how such an inert molecule could do anything at all. This study takes the question seriously, at the level of electrons.
What did the calculation test?
Whether semiquinone can directly dissociate H2 in the low-dielectric interior of the respiratory chain. The team built active-site cluster models from the Q-chamber of Complex I (structure PDB 7QSK) and the Qo site of Complex III (PDB 1PP9), optimised geometries with one quantum-chemical method and evaluated energies with a higher-level one — the standard first-principles approach for asking whether a reaction is physically possible, and by what route.
What did it find?
A sharp either/or. The anionic semiquinone, Q-, had no pathway for cleaving the H-H bond at either site. The neutral radical, QH, protonated by nearby residues, did open a pathway: a true homolytic hydrogen-atom transfer, confirmed at the electronic level by the transferring hydrogen's spin density shifting from nearly 0 to +0.99 — ruling out proton or hydride transfer. Reaction energies ran +21 to +26 kcal/mol, consistent with the bond-energy arithmetic of breaking H-H versus forming the O-H bond of ubiquinol. The barrier is thin enough to bring the temperature at which quantum tunnelling takes over (the crossover temperature) to 293.9 K for Complex I — within about 16 K of body temperature.
What does this change — and what does it not?
If the model is right, it reframes hydrogen's mechanism: not the classical picture of H2 wandering the cell scavenging radicals, but a conditional, enzyme-site chemistry — the authors describe 'quantum-tunnelling-assisted conditional hydrogenase activity conditioned by reductive pressure'. The same conditionality is the caution: the doorway exists only where the protonated semiquinone environment and hyper-reductive pressure coincide, which the study does not show happening in any living system. A calculation can prove a mechanism is physically possible; it cannot prove it occurs in a patient, at a dose, with an effect.
Frequently asked questions
What is a semiquinone?
A halfway state of ubiquinone (coenzyme Q) — the electron carrier of the respiratory chain — carrying one electron and, in its neutral form, one hydrogen. Radicals like this are reactive enough to do chemistry inert molecules cannot.
What is quantum tunnelling here?
At low enough barriers, a hydrogen atom can pass through an energy barrier rather than over it. The study's crossover temperatures mark where that tunnelling route begins to dominate — near body temperature for Complex I.
Does this prove hydrogen therapy works?
No. It proposes a physically possible activation mechanism in modelled enzyme sites, under conditions not yet shown in living systems.
Where the evidence stands
- Established: Ameliorative effects of molecular hydrogen have been reported across many pathological conditions, while the molecular mechanism by which animal cells — which lack metal hydrogenases — could activate H2 has remained unresolved.
- Preliminary: The semiquinone mechanism itself: one first-principles computational study (Physical Chemistry Chemical Physics, 2026) on modelled enzyme clusters; no experimental system was tested.
- Absent: Direct evidence that this H2 activation happens in cells, animals or people, and any link from this mechanism to a clinical effect of hydrogen therapy.
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