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Autori: Anna Lisa Maniero, Vasile Chis, Alfonso Zoleo, Marina Brustolon, and Alberto Mezzetti
Editorial: J.Phys. Chem. B, 112, p.3812-3820, 2008.
High-frequency electron paramagnetic resonance (EPR) and X-band electron-nuclear double resonance (ENDOR) spectroscopies were used to investigate the effect of -irradiation on single crystals of L-tyrosine hydrochloride at room temperature. The oxidation product is the tyrosyl radical formed by hydrogen abstraction from the phenolic group; interestingly, on freshly irradiated crystals, two tyrosyl radicals were identified, characterized by slightly different magnetic parameters. In particular, one of the two radicals, with a gxx value of 2.00621, has its phenoxyl oxygen strongly hydrogen-bonded to one or more donors; to our knowledge, this is the lower gxx value reported for tyrosyl radicals. These two oxidation radicals are found to evolve very slowly to a third, single more stable radical conformation. To interpret the experimental data, a possible molecular scenario is presented, where the process of radical formation can be seen as a hydrogen atom transfer or a proton-coupled electron transfer. These processes seem to be controlled by the specific network of hydrogen-bond interactions present in the crystal. The results are discussed in relation to their relevance for the interpretation of EPR spectra of tyrosyl radicals in biological systems.
Cuvinte cheie: tyrosyl, radical, HF-EPR, ENDOR, DFT