Characterization of the Site‐Specific Acid‐Base Equilibria of 3‐Nitrotyrosine

Pálla, Tamás and Fogarasi, Erzsébet and Noszál, Béla and Tóth, Gergő (2019) Characterization of the Site‐Specific Acid‐Base Equilibria of 3‐Nitrotyrosine. CHEMISTRY & BIODIVERSITY, 16 (9). ISSN 1612-1872

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Abstract

The complete macro- and microequilibrium analyses of 3-nitrotyrosine, a biomarker of oxidative stressdamage, are presented for the first time. The protonation macroconstants were determined by1H-NMR-pHtitration, while microconstants were elucidated by a combination of deductive and NMR methods, in whichproperties of the methyl ester derivative as an auxiliary compound were also studied. Combination of the NMR-pH characterization of the title and auxiliary compounds and the pair-interactivity parameters of 3-iodotyrosineprovided the sufficient system to evaluate all the microconstants. NMR-pH profiles, macroscopic and microscopicprotonation schemes, and species-specific distribution diagrams are included. The phenolate basicity of 3-nitrotyrosine is 500 times below that of tyrosine, and it is even lower than that of 3-iodotyrosine. Thisphenomenon can be explained by the stronger electron withdrawing and the negative mesomeric effect of thenitro group. Based on our results, 89 % of the phenolic OH groups are deprotonated in 3-NT molecules at the pHof the blood plasma.

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