Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science Chinese Academy of Sciences, Nanjing, 210008, China.
Water Res. 2020 May 1;174:115631. doi: 10.1016/j.watres.2020.115631. Epub 2020 Feb 20.
Low-molecular-weight thiols (LMWTs) are widely occurring in waters and soils, which can act as electron shuttles in biogeochemical cycles. It is interesting to study the interactions between LMWTs and clay minerals, which would produce free radicals on clay surfaces and influence As(III) transformation. Batch experiments and spectroscopic analysis in combined with computational modeling were conducted with three Fe-bearing clay minerals (Na-NAu-1, Na-NAu-2 and Na-SAz-2) and four LMWTs (l-cysteine, cysteamine, homocysteine, and glutathione) to investigate the reaction mechanisms of LMWTs with Fe-bearing clay minerals and influences of clay types and LMWT structures on the interactions. The results showed that Fe-bearing clay minerals can improve 2.4-3.7 times of •OH formation in 96-h LMWTs oxidation. Quenching experiments confirmed surface-Fenton-like reactions were the main pathways of •OH formation in the presence of Fe-bearing smectite clay minerals. The most possible hypothesis is that structural Fe (III) can accept electrons from LMWTs through proton-coupled transfer from -SH functional group, which was supported by FTIR, XRD and Mössbauer spectroscopies. The results of DFT calculations suggested that clay surfaces could accelerate RS• formation and stabilize the radicals. The addition of Na-NAu-2 in the cystein solution could increase As(III) oxidation to As(V) from 16.3% to 42.0%. The results imply that in-situ •OH formation in the presence of LMWTs and smectite clays may be an important geochemical process for the transformation of environmental contaminants.
低分子巯基化合物（LMWTs）广泛存在于水和土壤中，它们可以作为生物地球化学循环中的电子穿梭体。研究 LMWTs 与粘土矿物之间的相互作用很有趣，因为这会在粘土表面产生自由基并影响 As(III)的转化。本研究通过批实验和光谱分析，结合计算模拟，使用三种含 Fe 粘土矿物（Na-NAu-1、Na-NAu-2 和 Na-SAz-2）和四种 LMWTs（l-半胱氨酸、半胱胺、同型半胱氨酸和谷胱甘肽）来研究 LMWTs 与含 Fe 粘土矿物的反应机制，以及粘土类型和 LMWT 结构对相互作用的影响。结果表明，含 Fe 粘土矿物可以将 LMWTs 氧化 96 小时内的 •OH 生成量提高 2.4-3.7 倍。猝灭实验证实，在含 Fe 蒙脱石粘土矿物存在下，表面类芬顿反应是 •OH 生成的主要途径。最有可能的假设是结构 Fe(III)可以通过 -SH 官能团的质子偶联转移从 LMWTs 中接受电子，这得到了 FTIR、XRD 和 Mössbauer 光谱的支持。DFT 计算结果表明，粘土表面可以加速 RS•的形成并稳定自由基。在半胱氨酸溶液中添加 Na-NAu-2 可以将 As(III)氧化为 As(V)的比例从 16.3%提高到 42.0%。结果表明，在 LMWTs 和蒙脱石粘土存在下原位形成的 •OH 可能是环境污染物转化的一个重要地球化学过程。
