FLASH PHOTOLYSIS OF 3‐IODOTYROSINE IN AQUEOUS SOLUTION AT pH 5

The 3‐tyrosinyl free radicals (3‐Tyr) and iodine atom are formed by flash photolysis of 3‐iodotyrosine (3‐Tyr‐I) in aqueous solutions at pH 5. The presence of iodine atoms in the medium is characterized by the absorption spectrum and the decay kinetics of I formed when KI is added to the system. In the absence of radical scavengers, the 3‐Tyr adds to or reacts with the parent molecule to produce a transient species, probably a radical dimer, which has an absorption maximum at 405 nm. The decay of this transient follows second order kinetics whose rate constant increases with decreasing 3‐iodotyrosine concentration. Measurements of the dependence of the transient yield on the concentration of added ethanol indicate that the 3‐Tyr radical reacts with ethanol by hydrogen abstraction. The rate constants of reaction of the 3‐Tyr radical with 3‐iodotyrosine and ethanol are deduced from results.