Photosensitized Dimerization of Tyrosine: The Oxygen Paradox

DANTOLA, MARIA LAURA; NEYRA RECKY, JAEL R.; LORENTE, CAROLINA; THOMAS, ANDRÉS HÉCTOR

PHOTOCHEMISTRY AND PHOTOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021

0031-8655

In electron-transfer initiated photosensitization processes,molecular oxygen (O2) is not involved in the first bimolecularevent, but almost always participates in subsequent steps givingrise to oxygenated products. An exception to this generalbehavior is the photosensitized dimerization of tyrosine (Tyr),where O2 does not participate as a reactant in any step ofthe pathway yielding Tyr dimers (Tyr2). In the pterin (Ptr)photosensitized oxidation of Tyr, O2 does not directly participatein the formation of Tyr2 and quenches the triplet excitedstate of Ptr, the reactive species that initiates the process.However, O2 is necessary for the dimerization, phenomenonthat we have named as the oxygen paradox. Here, we reviewthe literature on the photosensitized formation of Tyr2 andpresent results of steady-state and time resolved experiments,in search of a mechanistic model to explain the contradictoryrole of O2 in this photochemical reaction system.