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In [[quantum biology]], the '''[[Radical (chemistry)|radical]]-pair mechanism''' is a proposed [[Spin chemistry|spin-chemistry]] explanation for [[magnetoreception]], the ability for an organism to sense weak magnetic fields. It has been significantly studied in the context of [[bird migration]].<ref name=":1">{{Cite journal |last=Zadeh-Haghighi |first=Hadi |last2=Simon |first2=Christoph |date=2022-08-01 |title=Magnetic field effects in biology from the perspective of the radical pair mechanism |url=https://doi.org/10.1098/rsif.2022.0325 |journal=Journal of The Royal Society Interface |volume=19 |issue=193 |pages= |doi=10.1098/rsif.2022.0325 |issn=1742-5689}}</ref>

== Mechanism ==
A [[Radical (chemistry)|radical]] is a molecule with an unpaired [[valence electron]]; thus, a pair of radicals is a radical pair. In the radical-pair mechanism, the unpaired electrons of the radical pair are [[Spin (physics)|spin]]-correlated, oscillating between a [[singlet state]] and a [[triplet state]]. Importantly, the radical pair spin state can interact with its environment, particularly with external magnetic fields, which influences which state it will be in.<ref name=":1" />

== Biological impacts ==
<ref name=":1" /><ref name=":2">{{Cite journal |last=Adams |first=Betony |last2=Sinayskiy |first2=Ilya |last3=Petruccione |first3=Francesco |date=2018-10-24 |title=An open quantum system approach to the radical pair mechanism |url=https://www.nature.com/articles/s41598-018-34007-4 |journal=Scientific Reports |language=en |publisher=Nature Publishing Group |volume=8 |issue=1 |pages=15719 |doi=10.1038/s41598-018-34007-4 |issn=2045-2322|doi-access=free}}</ref><ref name=":3">{{Cite web |title=The radical-pair mechanism as a paradigm for the emerging science of quantum biology |url=https://arxiv.org/html/1512.00450v2 |access-date=2026-09-23 |website=arxiv.org|date=2016|last=Kominis|first=Iannis K.}}</ref>

== Discovery ==
The radical-pair mechanism was first described in the late 1960s to explain the phenomena of [[chemically-induced dynamic electron polarization]] (CIDEP) and [[Chemically induced dynamic nuclear polarization|chemically-induced dynamic nuclear polarization]] (CIDNP): that is, anomalously large [[electron spin resonance]] and [[nuclear magnetic resonance]] signal values in organic-molecule chemical reactions, respectively.<ref name=":3" /> It was first applied to a theory of [[avian magnetoreception]] in the 1970s by Schulten et al.<ref name=":2" />

== See also ==

* [[Chemically induced dynamic nuclear polarization|Chemically-induced dynamic nuclear polarization]]

== References ==