Aquatic indirect photochemical transformations of natural peptidic thiols: impact of thiol properties, solution pH, solution salinity and metal ions,Environmental Science: Processes & Impacts

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Aquatic indirect photochemical transformations of natural peptidic thiols: impact of thiol properties, solution pH, solution salinity and metal ions
Environmental Science: Processes & Impacts ( IF 4.3 ) Pub Date : 2017-10-19 00:00:00 , DOI: 10.1039/c7em00324b
Chiheng Chu _{1,

2,

3,

4} , Dimitrios Stamatelatos _{1,

2,

3,

4} , Kristopher McNeill _{1,

2,

3,

4}

Affiliation

Natural peptidic thiols play numerous important roles in aquatic systems. While thiols are known to be susceptible to sensitized photoreaction, the photochemical transformation of thiols in surface waters remains largely unknown. This study systematically assessed the photochemical transformation of naturally occurring thiols, including arginylcysteine (RC), γ-glutamylcysteine (γEC), glutathione (GSH), and phytochelatin (PC) in solutions containing dissolved organic matter (DOM). The results show that all thiols underwent rapid indirect photochemical transformation. The transformation rates of thiols were highly pH-dependent and increased with increasing solution pH. γEC and GSH show lower transformation rates than free Cys, which was ascribed to their higher thiol pK_a values. In comparison, PC and RC show much higher transformation rates than γEC and GSH, due to more reactive thiol groups contained in the PC molecule and sorption of RC to DOM macromolecules, respectively. While all investigated pathways contributed to thiol transformation, hydroxyl radical-mediated oxidation dominated at low solution pH and singlet oxygen-mediated oxidation dominated at high solution pH in the DOM-sensitized phototransformations of γEC, GSH, and PC. Furthermore, the effects of metal complexation and solution salinity on thiol transformation rates were examined. Thiol reactivity was not affected by Fe³⁺ and Ag⁺, slightly enhanced in the presence of Zn²⁺, Cd²⁺ and Hg²⁺, and significantly enhanced by Cu²⁺. Additionally, enhanced thiol transformation rates were observed in solutions with high salinity.

中文翻译：

天然肽硫醇的水生间接光化学转化：硫醇性质，溶液pH，溶液盐度和金属离子的影响

天然肽硫醇在水生系统中起着许多重要的作用。虽然已知硫醇易受敏化光反应的影响，但在地表水中硫醇的光化学转化仍然非常未知。这项研究系统地评估了在含有溶解性有机物（DOM）的溶液中，天然存在的硫醇（包括精氨酸半胱氨酸（RC），γ-谷氨酰半胱氨酸（γEC），谷胱甘肽（GSH）和植物螯合素（PC））的光化学转化。结果表明，所有硫醇都经历了快速的间接光化学转化。硫醇的转化率高度依赖于pH值，并随着溶液pH值的增加而增加。γEC和GSH的转化率低于游离Cys，这归因于其较高的硫醇p K _a价值观。相比之下，PC和RC的转化率要比γEC和GSH高得多，这分别是由于PC分子中含有更多的反应性硫醇基以及RC对DOM大分子的吸附。尽管所有研究的途径都有助于硫醇的转化，但在γ-γ，GSH和PC的DOM敏化光转化中，在低溶液pH下羟基自由基介导的氧化占主导，而在高溶液pH下单线态氧介导的氧化占主导。此外，检查了金属络合和溶液盐度对硫醇转化率的影响。硫醇的反应性不受Fe ³⁺和Ag ^+的影响，在Zn 2 ⁺，Cd ²⁺和Hg ²⁺的存在下略有增强，并被Cu ²⁺显着增强。另外，在高盐度溶液中观察到硫醇转化率提高。

更新日期：2017-11-01

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