Photo-oxidation of S-methylglutathione, GS(Me), and S-methylcysteine is studied.
Complementary combination of time-resolved and field dependent CIDNP is utilized.
The structure of the radicals formed during one-electron oxidation is determined.
Cyclization of S-centered cation radical with oxygen atom is proved.
For GS(Me), the radical with three-electron two center SN bond is not found.