Department of Environmental Health and Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Environ Sci Process Impacts. 2019 Jun 19;21(6):1038-1051. doi: 10.1039/c9em00128j.
At pH 4.0, hydrous manganese oxide (HMO) oxidizes mandelic acid by two mole-equivalents of electrons, yielding phenylglyoxylic acid and benzaldehyde. These intermediates, in turn, are oxidized by two mole-equivalents of electrons to the same ultimate oxidation product, benzoic acid. The four compounds of the "reaction set" just described are conveniently monitored using capillary electrophoresis (CE) and HPLC. Extents of adsorption are negligible and their sum exhibits mass balance. Concentrations of phenylglyoxylic acid, benzaldehyde, and benzoic acid can therefore be used to calculate mole-equivalents delivered to HMO for comparison with experimentally-determined dissolved MnII concentrations. Semi-log plots (ln[substrate] versus time) and numerical analysis can also be used to explore rates of oxidation of the functional groups represented, i.e. an α-hydroxycarboxylic acid, an α-ketocarboxylic acid, and an aldehyde. Inserting a -CH2- group between the benzene ring and the functional groups just described yields a new reaction set comprised of phenyllactic acid, phenylpyruvic acid, and phenylacetaldehyde, plus the C-1 ultimate oxidation product, phenylacetic acid. At pH 4, mass balance for phenyllactic acid oxidation fell short by ∼9%. Phenyllactic acid was oxidized 2.7-times more slowly than mandelic acid, while phenylpyruvic acid was oxidized 12.7-times faster than phenylglyoxylic acid. Unlike benzaldehyde, oxidation rates for phenylacetaldehyde were too fast to measure. Under pH 4.0 conditions, this reaction set approach was used to explore the acceleratory effects of increases in HMO loading and inhibitory effects of 500 μM phosphate and pyrophosphate additions. Mandelic acid and phenyllactic acid were oxidized by HMO far more slowly at pH 7.0 than at pH 4.0. At pH 7.0, 2 mM MOPS and phosphate buffers did not yield appreciable dissolved MnII, despite oxidation of organic substrate. 2 mM pyrophosphate, in contrast, solubilized HMO-bound MnII and MnIII.
在 pH 值为 4.0 时，水合氧化锰 (HMO) 通过两个电子摩尔当量氧化扁桃酸，生成苯乙醛酸和苯甲醛。这些中间体继而又通过两个电子摩尔当量氧化为相同的最终氧化产物苯甲酸。上述“反应体系”中的四个化合物可通过毛细管电泳 (CE) 和高效液相色谱 (HPLC) 方便地监测。吸附程度可以忽略不计，它们的总和表现出质量平衡。因此，苯乙醛酸、苯甲醛和苯甲酸的浓度可用于计算传递给 HMO 的电子摩尔当量，以便与实验测定的溶解 MnII 浓度进行比较。半对数图（ln[substrate] 与时间）和数值分析也可用于探索所代表的官能团的氧化速率，即α-羟基羧酸、α-酮羧酸和醛。在苯环和上述官能团之间插入一个-CH2-基团，生成一个新的反应体系，包括苯乳酸、苯丙酮酸和苯乙醛，以及 C-1 最终氧化产物苯乙酸。在 pH 值为 4 时，苯乳酸氧化的质量平衡差约为 9%。苯乳酸的氧化速度比扁桃酸慢 2.7 倍，而苯丙酮酸的氧化速度比苯乙醛酸快 12.7 倍。与苯甲醛不同，苯乙醛的氧化速度太快，无法测量。在 pH 值为 4.0 时，该反应体系方法用于探索 HMO 负载增加的加速作用以及 500 μM 磷酸盐和焦磷酸盐添加的抑制作用。在 pH 值为 7.0 时，HMO 对扁桃酸和苯乳酸的氧化速度远低于 pH 值为 4.0 时。在 pH 值为 7.0 时，尽管有机底物被氧化，但 2 mM MOPS 和磷酸盐缓冲液并未产生可观的溶解 MnII。相比之下，2 mM 焦磷酸盐可溶解 HMO 结合的 MnII 和 MnIII。
Zotero 插件