Oxidation
and Nitration of Tyrosine by Ozone and Nitrogen
Dioxide: Reaction Mechanisms and Biological and Atmospheric Implications
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Abstract
The nitration of tyrosine by atmospheric
oxidants, O<sub>3</sub> and NO<sub>2</sub>, is an important cause
for the spread of allergenic
diseases. In the present study, the mechanism and pathways for the
reaction of tyrosine with the atmospheric oxidants O<sub>3</sub> and
NO<sub>2</sub> are studied using DFT-M06-2X, B3LYP, and B3LYP-D methods
with the 6-311+G(d,p) basis set. The energy barrier for the initial
oxidation reactions is also calculated at the CCSD(T)/6-31+G(d,p)
level of theory. The reaction is studied in gas, aqueous, and lipid
media. The initial oxidation of tyrosine by O<sub>3</sub> proceeds
by H atom abstraction and addition reactions and leads to the formation
of six different intermediates. The subsequent nitration reaction
is studied for all the intermediates, and the results show that the
nitration affects both the side chain and the aromatic ring of tyrosine.
The rate constant of the favorable oxidation and nitration reaction
is calculated using variational transition state theory over the temperature
range of 278–350 K. The spectral properties of the oxidation
and nitration products are calculated at the TD-M06-2X/6-311+G(d,p)
level of theory. The fate of the tyrosine radical intermediate is
studied by its reaction with glutathione antioxidant. This study provides
an enhanced understanding of the oxidation and nitration of tyrosine
by O<sub>3</sub> and NO<sub>2</sub> in the context of improving the
air quality and reducing the allergic diseases