Napolitano Michael J, Stewart David J, Margerum Dale W
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA.
Chem Res Toxicol. 2006 Nov;19(11):1451-8. doi: 10.1021/tx060124a.
The reactions between aqueous ClO2 and guanosine 5'-monophosphate (5'-GMP) are investigated from pH 5.96 to 8.30. The decay of ClO2 follows mixed first-order and second-order kinetics. The addition of chlorite (0.01-0.05 M) to the reaction mixture suppresses the reaction rate and changes the observed decay of ClO2 to second-order. The reaction rates increase greatly with pH to give oxidized products. The second-order rate constant for the guanosine anion is 4.7 x 10(5 )M-1 s-1 and comprises a mixture of rate constants, k1k2/k-1. The ratio k1/k-1, with a calculated value of 2.4 x 10(-4), corresponds to the reversible reaction between ClO2 and the guanosine anion to generate ClO2- and the guanosyl radical. To determine k1/k-1 and k2, E values for guanosine and ClO2 are used as well as acid dissociation constants for guanosine and its radical. The value of k1 (1.1 x 10(5) M-1 s-1) represents the reaction between ClO2 and the guanosine anion as determined by initial rates. The second-order rate constant k2, with a value of 1.8 x 10(9 )M-1 s-1, represents the reaction between the guanosyl radical with a second molecule of ClO2 to generate a guanosyl-OClO adduct. The consumption of two mol of ClO2 per mol of 5'-GMP corresponds to a four-electron oxidation that gives ClO(2- )in the first step and HOCl in the second step. The 2',3',5'-tri-O-acetylated derivative of guanosine is used to more easily separate guanosine from its ClO2 oxidation products. Imidazolone and monochlorinated imidazolone are identified as products of the reaction between ClO2 and guanosine.
研究了在pH值为5.96至8.30的条件下，二氧化氯水溶液与5'-鸟苷单磷酸（5'-GMP）之间的反应。二氧化氯的衰减遵循一级和二级混合动力学。向反应混合物中加入亚氯酸盐（0.01 - 0.05 M）会抑制反应速率，并将观察到的二氧化氯衰减转变为二级反应。反应速率随pH值大幅增加，生成氧化产物。鸟苷阴离子的二级反应速率常数为4.7×10⁵ M⁻¹ s⁻¹，它由速率常数k₁k₂/k⁻¹的混合物组成。k₁/k⁻¹的比值计算值为2.4×10⁻⁴，对应于二氧化氯与鸟苷阴离子之间的可逆反应，生成ClO₂⁻和鸟苷基自由基。为了确定k₁/k⁻¹和k₂，使用了鸟苷和二氧化氯的E值以及鸟苷及其自由基的酸解离常数。k₁的值（1.1×10⁵ M⁻¹ s⁻¹）代表了通过初始速率确定的二氧化氯与鸟苷阴离子之间的反应。二级反应速率常数k₂的值为1.8×10⁹ M⁻¹ s⁻¹，代表鸟苷基自由基与第二个二氧化氯分子反应生成鸟苷基 - OClO加合物。每摩尔5'-GMP消耗两摩尔二氧化氯对应于四电子氧化，第一步生成ClO₂⁻，第二步生成HOCl。鸟苷的2',3',5'-三 - O - 乙酰化衍生物用于更轻松地将鸟苷与其二氧化氯氧化产物分离。咪唑酮和一氯代咪唑酮被鉴定为二氧化氯与鸟苷反应的产物。
