Chemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901, USA.
Environ Sci Technol. 2013 May 7;47(9):4572-80. doi: 10.1021/es305283k. Epub 2013 Apr 11.
Kinetics of the oxidation of tryptophan (Trp) and kynurenine (Kyn), precursors of nitrogenous disinfection byproducts (N-DBP), by ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) were investigated over the acidic to basic pH range. The second-order rate constants decreased with increase in pH, which could be described by the speciation of Fe(VI) and Trp (or Kyn). The trend of pH dependence of rates for Trp (i.e., aromatic α-amino acid) differs from that for glycine (i.e., aliphatic α-amino acid). A nonlinear relationship between transformation of Trp and the added amount of Fe(VI) was found. This suggests that the formed intermediate oxidized products (OPs), identified by LC-PDA and LC-MS techniques, could possibly compete with Trp to react with Fe(VI). N-Formylkynurenine (NFK) at pH 7.0 and 4-hydroxyquinoline (4-OH Q) and kynurenic acid (Kyn-A) at pH 9.0 were the major OPs. Tryptophan radical formation during the reaction was confirmed by the rapid-freeze quench EPR experiments. The oxygen atom transfer from Fe(VI) to NFK was demonstrated by reacting Fe(18)O4(2-) ion with Trp. A proposed mechanism explains the identified OPs at both neutral and alkaline pH. Kinetics and OPs by Fe(VI) were compared with other oxidants (chlorine, ClO2(•), O3, and (•)OH).
高铁酸盐（Fe(VI)O4(2-), Fe(VI)）氧化色氨酸（Trp）和犬尿氨酸（Kyn）（氮消毒副产物（N-DBP）的前体）的反应动力学在酸性到碱性 pH 范围内进行了研究。随着 pH 的增加，二阶速率常数降低，这可以用 Fe(VI)和 Trp（或 Kyn）的形态来描述。Trp（即芳香族α-氨基酸）的速率对 pH 的依赖性趋势与甘氨酸（即脂肪族α-氨基酸）不同。发现 Trp 转化与添加的 Fe(VI)之间存在非线性关系。这表明形成的中间氧化产物（OPs），通过 LC-PDA 和 LC-MS 技术鉴定，可能与 Trp 竞争与 Fe(VI)反应。在 pH 7.0 时主要的 OPs 为 N-甲酰犬尿氨酸（NFK），在 pH 9.0 时主要的 OPs 为 4-羟基喹啉（4-OH Q）和犬尿氨酸（Kyn-A）。通过快速冷冻猝灭 EPR 实验证实了反应过程中色氨酸自由基的形成。通过用 Fe(18)O4(2-)离子与 Trp 反应，证明了 Fe(VI)向 NFK 的氧原子转移。提出的机制解释了在中性和碱性 pH 下鉴定出的 OPs。Fe(VI)的动力学和 OPs 与其他氧化剂（氯、ClO2(•)、O3 和 (•)OH）进行了比较。
