EPR spectroscopic studies of the reactions of Cr(VI) with L-ascorbic acid, L-dehydroascorbic acid, and 5,6-O-isopropylidene-L-ascorbic acid in water. Implications for chromium(VI) genotoxicity
EPR spectroscopic studies of the reactions of Cr(VI) with L-ascorbic acid, L-dehydroascorbic acid, and 5,6-O-isopropylidene-L-ascorbic acid in water. Implications for chromium(VI) genotoxicity
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DOI：
10.1021/ja961824c
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发表时间：
1996-12-18
影响因子：
15
通讯作者：
Lay, PA
中科院分区：
文献类型：
--
作者：
Zhang, LB;Lay, PA
水溶液中 L-抗坏血酸 (L-AsA) 还原 Cr(VI) 过程中 Cr(V) 中间体的表征被描述为 pH 值和抗坏血酸浓度的函数。在 Cr(V) 与 AsA 的反应中，除了抗坏血酸自由基之外，还存在至少七个 EPR 活性 Cr(V) 信号。 Cr(V)/抗坏血酸络合物 g(iso) = 1.9791 (A(iso) = 16.4 x 10(-4) cm(-1)) 在中等酸性溶液 (pH 3-6) 中比在中性和碱性溶液中稳定得多。该反应受到空中 O-2 的影响，产生 Cr(V)/抗坏血酸/过氧复合物，信号为 g(iso) = 1.9818 (A(iso) = 13.2 x 10(-4) cm(-1)) 和 g(iso) = 1.9812，另一个信号为 g(iso) = 1.9824 (A(iso) = 12.9 x 10(-4)厘米(-1))。这些信号在接近生理 pH 值 (7-8) 时最为突出，而当溶液与过氧化氢酶预孵育时，所有信号均不存在。 Cr(V)/抗坏血酸复合物在 [AsA]:[Cr(VI)] 比例为 1:2 时最稳定，而 Cr(V)/抗坏血酸/过氧复合物在 [AsA]:[Cr(VI)] = 1:1 时达到最大信号强度。这些 Cr(V) 物质在 pH > 10 时都不稳定，并且当 [AsA]:[Cr(VI)] 比率高于 2:1 时，它们会迅速还原为 Cr(III)。这是此类 Cr(V)/抗坏血酸盐/过氧复合物的首次表征。它们是由 AsA 空气氧化过程中 O-2 的还原产生的，并且通过在 H2O2 存在下 AsA 还原 Cr(VI) 的研究证实了它们的身份。它们的存在解释了体外 DNA 损伤的 O-2 敏感性，并考虑了对 Cr(VI) 诱发癌症的影响。还使用 EPR 光谱研究了在存在和不存在 H2O2 的情况下，脱氢抗坏血酸 (DHAA) 和 5,6-O-异亚丙基-L-抗坏血酸 (i-p-AsA) 对 Cr(VI) 的还原作用。从这些研究中，确定了 AsA 还原 Cr(VI) 时形成的 Cr(V) 络合物的可能溶液结构。
The characterization of the Cr(V) intermediates in the reduction of Cr(VI) by L-ascorbic acid (L-AsA) in aqueous solution is described as a function of pH and ascorbate concentration. In the reaction of Cr(V) with AsA at least seven EPR-active Cr(V) signals are present in addition to that of the ascorbate radical. The Cr(V)/ascorbate complex at g(iso) = 1.9791 (A(iso) = 16.4 x 10(-4) cm(-1)) is much more stable in moderately acidic solution (pH 3-6) than in neutral and alkaline solutions. The reaction is affected by aerial O-2 producing Cr(V)/ascorbate/peroxo complexes with signals at g(iso) = 1.9818 (A(iso) = 13.2 x 10(-4) cm(-1)) and g(iso) = 1.9812 and another at g(iso) = 1.9824 (A(iso) = 12.9 x 10(-4) cm(-1)). These signals are most prominent at near physiological pH values (7-8), and all were absent when the solutions were preincubated with catalase. The Cr(V)/ascorbate complex is most stabilized in a [AsA]:[Cr(VI)]ratio of 1:2, while the Cr(V)/ascorbate/peroxo complexes reach their maximum signal intensities at [AsA]:[Cr(VI)] = 1:1. None of these Cr(V) species are stable at pH > 10, and they are reduced rapidly to Cr(III) at [AsA]:[Cr(VI)] ratios above 2:1. This is the first characterization of such Cr(V)/ascorbate/peroxo complexes. They arise from the reduction of O-2 during the aerial oxidation of AsA, and their identities were confirmed by studies on the reductions of Cr(VI) with AsA in the presence of H2O2. Their presence explains the O-2 sensitivity of in vitro DNA damage, and implications for Cr(VI)-induced cancers are considered. The reductions of Cr(VI) by dehydroascorbic acid (DHAA) and 5,6-O-isopropylidene-L-ascorbic acid (i-p-AsA), in the presence and absence of H2O2 were also studied using EPR spectroscopy. From these studies, likely solution structures for the Cr(V) complexes formed in the reduction of Cr(VI) by AsA were assigned.