Ramezanian M S, Padmaja S, Koppenol W H
Department of Chemistry, Louisiana State University, Baton Rouge 70803, USA.
Chem Res Toxicol. 1996 Jan-Feb;9(1):232-40. doi: 10.1021/tx950135w.
The kinetics and products of the reaction of peroxynitrite with the phenolic compounds phenol, tyrosine, and salicylate were studied as a function of pH. All reactions are first-order in peroxynitrite and zero-order in the phenolic compound. Relative to the hydroxyl group, electrophilic substitution in the 2- and 4-positions (if available) leads to hydroxylated and nitrated products. The total yield of the products is proportional to the concentration of peroxynitrite. The sum of the rates of hydroxylation and nitration of phenol, determined by the stopped-flow technique, is approximately equal to the rate constant for the isomerization of peroxynitrite to nitrate. The rate vs pH profiles of the nitration and hydroxylation reactions parallel the yield vs pH profile with nitration maxima at pH 1.8 and 6.8, while hydroxylation is dominant between these two pH values. The activation energies for both hydroxylation and nitration are 18.8 +/- 0.3 kcal mol-1, identical to that of the isomerization of peroxynitrite to nitrate. Ethanol decreases the yield of hydroxylation, but has less effect on the nitration. The rate of reaction in the presence of metal complexes is first-order in metal complex and peroxynitrite and zero-order in the phenolic compound. The enhancement of the nitration of phenol by Fe(III)-edta and -nta is pH-dependent, with a maximum near pH 7, while Fe(III)-citrate, Cu(II)-edta, and CuSO4 affect the nitration much less. The second-order rate constants for Fe(III)-edta at pH 4.8 and 7.2 are 1.4 x 10(3) and 5.5 x 10(3) M-1 s-1, respectively, at 25 degrees C. The activation energies for the nitration reaction in the presence of Fe(III)-edta are 11.5 and 12.2 kcal mol-1 at pH 4.8 and 7.2, respectively. The nitration of tyrosine and salicylate by peroxynitrite is maximally enhanced by Fe(III)-edta.
研究了过氧亚硝酸根与酚类化合物苯酚、酪氨酸和水杨酸盐反应的动力学及产物随pH的变化情况。所有反应对过氧亚硝酸根为一级反应，对酚类化合物为零级反应。相对于羟基而言，在2位和4位（若有）的亲电取代会生成羟基化和硝化产物。产物的总产率与过氧亚硝酸根的浓度成正比。用停流技术测定的苯酚羟基化和硝化速率之和近似等于过氧亚硝酸根异构化为硝酸根的速率常数。硝化和羟基化反应的速率与pH关系曲线与产率与pH关系曲线相似，硝化在pH 1.8和6.8时出现最大值，而在这两个pH值之间羟基化占主导。羟基化和硝化的活化能均为18.8±0.3 kcal mol⁻¹，与过氧亚硝酸根异构化为硝酸根的活化能相同。乙醇会降低羟基化产率，但对硝化的影响较小。在金属配合物存在下的反应速率对金属配合物和过氧亚硝酸根为一级反应，对酚类化合物为零级反应。Fe(III)-edta和Fe(III)-nta对苯酚硝化的促进作用与pH有关，在pH 7附近达到最大值，而Fe(III)-柠檬酸盐、Cu(II)-edta和CuSO₄对硝化的影响要小得多。在25℃时，Fe(III)-edta在pH 4.8和7.2时的二级速率常数分别为1.4×10³和5.5×10³ M⁻¹ s⁻¹。在Fe(III)-edta存在下，硝化反应在pH 4.8和7.2时的活化能分别为11.5和12.2 kcal mol⁻¹。过氧亚硝酸根对酪氨酸和水杨酸盐的硝化作用在Fe(III)-edta存在时得到最大增强。
