Photoexcitation of flavoproteins followed by electron transfer reactions between an amino acid donor and s flavin acceptor generates entangled radical pairs. In the presence of a moderate static magnetic field (~ 10 mT), the singlet-triplet splitting energy of this entangled pair occurs in the microwave (1 GHz) range. The single/triplet states have different downstream fates, one of which results in different fluorescence intensity of the flavin. Other biochemical fates are also known, and many are yet to be discovered.
Soluble organometallic complexes which are capable of delivering the metal atom, or mono-cation through facile, redox-neutral ligand exchange have been well-studied for over half a century. Representative examples of these include: [Rh(cod)2][BF4], [Ni(cod)2], and [Pd2(dba)3].
