Characterization of the Site‐Specific Acid‐Base Equilibria of 3‐Nitrotyrosine |
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Authors: | Tams Plla Erzsbet Fogarasi Bla Noszl Gerg Tth |
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Institution: | Tamás Pálla,Erzsébet Fogarasi,Béla Noszál,Gergő Tóth |
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Abstract: | The complete macro‐ and microequilibrium analyses of 3‐nitrotyrosine, a biomarker of oxidative stress damage, are presented for the first time. The protonation macroconstants were determined by 1H‐NMR‐pH titration, while microconstants were elucidated by a combination of deductive and NMR methods, in which properties 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‐iodotyrosine provided the sufficient system to evaluate all the microconstants. NMR‐pH profiles, macroscopic and microscopic protonation 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. This phenomenon can be explained by the stronger electron withdrawing and the negative mesomeric effect of the nitro group. Based on our results, 89 % of the phenolic OH groups are deprotonated in 3‐NT molecules at the pH of the blood plasma. |
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Keywords: | nitrotyrosine microspeciation oxidative stress NMR pKa |
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