Center for Environmental Nanoscience and Risk, Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
Center for Environmental Nanoscience and Risk, Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
Sci Total Environ. 2018 Jun 1;625:1518-1526. doi: 10.1016/j.scitotenv.2017.12.299. Epub 2018 Jan 12.
Interaction of natural organic matter (NOM) with engineered nanoparticles (NPs) determine NP fate, transport, and environmental persistence. However, the effect of NOM chemical composition, structure, and concentration on aggregation kinetics and dissolution behavior of silver nanoparticles (AgNPs) are still poorly understood because of heterogeneity and variability in NOM and AgNP properties. Here, aggregation behavior of citrate-coated silver nanoparticles (cit-AgNPs with a z-average diameter of 18nm) was investigated in the presence of l-cysteine (l-cys) and N-acetyl l-cysteine (NAL-cys) using UV-vis spectroscopy. We also investigated the effect of Suwannee River fulvic acid (SRFA) and a NOM isolated from the Yukon River (YRNOM) on the stability of cit-AgNPs. The dissolution of cit-AgNPs decreased with increased L-cys and NAL-cys concentration from 0 to 10μM. The critical coagulation concentration (CCC) of cit-AgNPs decreased in the presence of l-cys and increased in the presence of NAL-cys. Similarly, l-cys destabilizes cit-AgNPs in the presence of SRFA. The differences in the stability of cit-AgNPs in the presence of l-cys and NAL-cys can be attributed to the differences in the functional groups in these two cysteine molecules. l-cys has both negatively charged carboxylic group and a positively charged amine group, resulting in bridging between different particles. NAL-cys is a derivative of cysteine wherein an acetyl group is attached to the nitrogen atom thus shielding the positive charge on the amine group and therefore eliminating the bridging interaction mechanism. SRFA and YRNOM enhanced the stability of cit-AgNPs and increased the CCC value to higher counter ion concentrations. The concentration of SRFA (1-5mgL) did not affect the CCC, whereas the increased concentration of YRNOM increased the CCC of cit-AgNPs to high Na concentrations likely due to increased sorption of higher molecular weight compounds on the surface of cit-AgNPs. The outcome of this study suggests the importance of understanding the molecular properties of NOM (e.g. functional groups and molecular weight) in determining cit-AgNP environmental behaviors.
天然有机物（NOM）与工程纳米颗粒（NPs）的相互作用决定了 NP 的命运、迁移和环境持久性。然而，由于 NOM 和 AgNP 性质的异质性和可变性，NOM 的化学组成、结构和浓度对银纳米颗粒（AgNPs）聚集动力学和溶解行为的影响仍知之甚少。在这里，使用紫外可见光谱法研究了在半胱氨酸（l-cys）和 N-乙酰基半胱氨酸（NAL-cys）存在下，柠檬酸涂层银纳米颗粒（具有 18nm 的 z 均直径的 cit-AgNPs）的聚集行为。我们还研究了苏万尼河富里酸（SRFA）和育空河分离出的天然有机物（YRNOM）对 cit-AgNPs 稳定性的影响。随着 l-cys 和 NAL-cys 浓度从 0 增加到 10μM，cit-AgNPs 的溶解减少。在 l-cys 和 NAL-cys 的存在下，cit-AgNPs 的临界聚集浓度（CCC）降低。同样，在 SRFA 的存在下，l-cys 使 cit-AgNPs 不稳定。在 l-cys 和 NAL-cys 存在下 cit-AgNPs 的稳定性差异可归因于这两种半胱氨酸分子中官能团的差异。l-cys 既有带负电荷的羧酸基团，又有带正电荷的胺基团，从而导致不同颗粒之间的桥接。NAL-cys 是半胱氨酸的衍生物，其中一个乙酰基连接到氮原子上，从而屏蔽了胺基团上的正电荷，因此消除了桥接相互作用机制。SRFA 和 YRNOM 增强了 cit-AgNPs 的稳定性，并将 CCC 值提高到更高的抗衡离子浓度。SRFA（1-5mgL）的浓度不影响 CCC，而 YRNOM 浓度的增加将 cit-AgNPs 的 CCC 提高到高 Na 浓度，这可能是由于更高分子量化合物在 cit-AgNPs 表面的吸附增加所致。这项研究的结果表明，了解 NOM 的分子特性（例如官能团和分子量）在确定 cit-AgNP 环境行为方面的重要性。
