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Three Different Tyrosyl Radicals Identified in L-tyrosine HCl Crystals Upon Gamma-Irradiation: Magnetic Characterization and Temporal Evolution

Three Different Tyrosyl Radicals Identified in L-tyrosine HCl Crystals Upon Gamma-Irradiation: Magnetic Characterization and Temporal Evolution

Anna Lisa Maniero, Vasile Chis, Alfonso Zoleo, Marina Brustolon, Alberto Mezzetti

J Phys Chem B. 2008 Mar 27;112(12):3812-20.

PMID: 18318523

Abstract:

High-frequency electron paramagnetic resonance (EPR) and X-band electron-nuclear double resonance (ENDOR) spectroscopies were used to investigate the effect of gamma-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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP16870432	L-Tyrosine hydrochloride		16870-43-2	Price

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