Department of Chemistry, Brown University, 324 Brook Street, Providence, Rhode Island 02912, USA.
Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook Street, Providence, Rhode Island 02912, USA.
J Chromatogr A. 2021 May 24;1645:462122. doi: 10.1016/j.chroma.2021.462122. Epub 2021 Mar 30.
Silver(I)-mercaptopropyl (Ag-MP) functionalized silica gel has demonstrated its effectiveness in separating various unsaturated organic compounds including unsaturated fatty acid ethyl esters (FAEEs), triglycerols (TAGs) and long-chain alkyl ketones (alkenones). While Ag-MP stationary phase displays many advantages over the conventional silver ion-impregnated silica gel (e.g., stability, high recovery, etc.), potential drawbacks of Ag-MP include relatively low retentions for unsaturated molecules, which could limit chromatographic resolutions under certain circumstances. In this study, we evaluate a new silver-thiolate stationary phase: silver(I)-dimercaptotriazine (Ag-DMT) functionalized silica gel targeting the separation of unsaturated compounds. We show Ag-DMT affords substantially higher retention factors, peak resolutions and capacities for TAGs and FAEEs than Ag-MP does. Ag-DMT also yields higher purity eicosapentaenoic acid (EPA) from fish oil FAEE mixtures than Ag-MP. In addition, Ag-DMT resolves double bond positional and cis/trans-isomers of C fatty acid methyl esters (FAMEs) as well as unsaturated methyl/ethyl alkenones with different number of double bonds. Based on van't Hoff plots, enthalpy changes during the adsorption of unsaturated FAEEs onto Ag-DMT are ~2 times higher than those on Ag-MP. Such difference may be attributed to the stronger electron-withdrawing effect of the thiol group on DMT, which results in more positively charged silver ions hence greater interactions with unsaturated molecules. The stronger interaction between double bonds and Ag-DMT is further corroborated by density-functional theory (DFT) calculations. Ag-DMT shows its high stability for repeated uses in the separation of TAGs over 319 runs, with peak resolutions decreasing by < 3%. Collectively, our data demonstrate the exceptionally high efficiency of Ag-DMT column for separating unsaturated molecules.
银（I）-巯丙基（Ag-MP）功能化硅胶已证明其在分离各种不饱和有机化合物方面的有效性，包括不饱和脂肪酸乙酯（FAEEs）、三酰基甘油（TAGs）和长链烷基酮（烯酮）。虽然 Ag-MP 固定相比传统的银离子浸渍硅胶具有许多优势（例如稳定性、高回收率等），但 Ag-MP 的潜在缺点包括对不饱和分子的保留性相对较低，这可能会限制某些情况下的色谱分辨率。在这项研究中，我们评估了一种新的银硫醇固定相：银（I）-二巯基三嗪（Ag-DMT）功能化硅胶，旨在分离不饱和化合物。我们表明，Ag-DMT 为 TAGs 和 FAEEs 提供了大大更高的保留因子、峰分辨率和容量。Ag-DMT 还从鱼油 FAEE 混合物中获得比 Ag-MP 更高纯度的二十碳五烯酸（EPA）。此外，Ag-DMT 还能分辨双键位置和 C 脂肪酸甲酯（FAMEs）的顺/反异构体以及具有不同双键数目的不饱和甲基/乙基烯酮。根据范特霍夫图，不饱和 FAEEs 吸附到 Ag-DMT 上的焓变比吸附到 Ag-MP 上高约 2 倍。这种差异可能归因于 DMT 上的硫醇基团的更强吸电子效应，导致更多带正电荷的银离子，从而与不饱和分子有更大的相互作用。双键与 Ag-DMT 之间的更强相互作用进一步得到了密度泛函理论（DFT）计算的证实。Ag-DMT 在分离 TAGs 方面的 319 次重复使用中表现出高稳定性，峰分辨率下降<3%。总的来说，我们的数据表明 Ag-DMT 柱在分离不饱和分子方面具有极高的效率。
