ON THE PH-DEPENDENT YIELD OF HYDROXYL RADICAL PRODUCTS FROM PEROXYNITRITE
ON THE PH-DEPENDENT YIELD OF HYDROXYL RADICAL PRODUCTS FROM PEROXYNITRITE
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DOI：
10.1016/0891-5849(94)90034-5
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发表时间：
1994-03-01
影响因子：
7.4
通讯作者：
BECKMAN, JS
中科院分区：
文献类型：
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作者：
CROW, JP;SPRUELL, C;BECKMAN, JS
一氧化氮与超氧化物快速反应，生成强氧化性过氧亚硝酸根阴离子 (ONOO-)，其在质子化时会发生自发的一级分解。过氧亚硝酸盐 (ONOO-) 的氧化化学性质高度依赖于 pH 值。在酸性 pH 条件下，过亚硝酸 (ONOOH) 将二甲亚砜氧化为甲醛，将 2,2'-偶氮双-(3-乙基-1,2-二氢苯并噻唑啉 6-磺酸盐) (ABTS) 氧化为绿色 ABTS(+) 自由基阳离子。二甲基亚砜和 ARTS 的产物产率在 pH 值偏碱性时降低，表观 pK(a) 分别为 7.9 和 8.2。产率随 pH 值升高而降低不能用过氧亚硝酸盐对甲醛或 ABTS(+) 的氧化来解释。在 50 mM 二甲基亚砜存在下，形成了与另一种反应产物甲醛大约等摩尔量的二氧化氮。二氧化氮的产率也下降，表观 pK(a) 为 8.0。我们提出，过氧亚硝酸盐的复杂氧化化学是由相对稳定的顺式构型（主要在高pH值下）到反式构型的pa依赖性异构化控制的。反式过氧亚硝酸可以形成振动激发的中间体，能够像羟基自由基一样发生反应。振动激发的中间体还可以直接重排成硝酸，将表观羟基自由基产率降低至30%以下。羟基自由基样反应性的丧失可以通过反式过氧亚硝酸电离成伊朗阴离子来解释，伊朗阴离子反过来又经历内部重排形成硝酸盐而不形成强氧化剂。我们提出，通过磷酸盐缓冲液中 302 nm 处的吸光度测得的 pK(a) 为 6.8，对应于顺式过氧亚硝酸根阴离子的质子化，而 pK(a) 为 8 时羟基自由基样反应性的丧失对应于反式过氧亚硝酸根阴离子的质子化。
Nitric oxide reacts rapidly with superoxide to give the strongly oxidizing peroxynitrite anion (ONOO-), which undergoes spontaneous first-order decomposition when protonated. The oxidative chemistry of peroxynitrite (ONOO-) is highly pH-dependent. At acidic pH, peroxynitrous acid (ONOOH) oxidizes dimethylsulfoxide to formaldehyde and 2,2'-azinobis-(3-ethyl-1,2-dihydrobenzothiazoline 6-sulfonate) (ABTS) to the greenish-colored ABTS(+) radical cation. The product yield from dimethylsulfoxide and ARTS decreased at more alkaline pH with apparent pK(a)s of 7.9 and 8.2, respectively. Decreasing yield with increasing pH could not be explained by the oxidation of either formaldehyde or ABTS(+) by peroxynitrite. In the presence of 50 mM dimethylsulfoxide, nitrogen dioxide was formed in approximately equimolar amounts to the other reaction product, formaldehyde. The yield of nitrogen dioxide also decreased with an apparent pK(a) of 8.0. We propose that the complex oxidative chemistry of peroxynitrite is controlled by the pa-dependent isomerization of the relatively stable cis-configuration (predominant at high pH) to the trans-configuration. Trans-peroxynitrous acid can form a vibrationally excited intermediate capable of reacting like hydroxyl radical. The vibrationally excited intermediate can also directly rearrange to nitric acid, reducing the apparent hydroxyl radical yield to less than 30%. The loss of hydroxyl radical-like reactivity can be explained on the basis of ionization of trans-peroxynitrous acid to the Irans-anion, which in turn undergoes internal rearrangement to nitrate without forming a strong oxidant. We propose that the pK(a) of 6.8 measured by absorbance at 302 nm in phosphate buffer corresponds to protonation of cis-peroxynitrite anion, whereas the loss of hydroxyl radical-like reactivity with a pK(a) of 8 corresponds to that of the trans-peroxynitrite anion.