University of Pittsburgh, Chevron Science Center, 219 Parkman Avenue, Pittsburgh, PA 15260, United States.
J Chromatogr A. 2019 Apr 26;1591:1-6. doi: 10.1016/j.chroma.2019.01.051. Epub 2019 Jan 21.
In the process of developing a pH-stable, highly crosslinked stationary phase using the thiol-yne reaction, a new charge transfer stationary phase was discovered. The first step in the preparation of the crosslinked phase is to attach 1,4-diethynylbenzene (DEB) to thiol functionalized silica particles using the thiol-yne reaction. Upon preparation of that phase, we noticed that the color of the particles was different when the modified particles were wet with aromatic solvents in comparison to wetting with nonaromatic or aqueous solvents. This color change was still apparent upon crosslinking the DEB with 1,6-hexanedithiol to create the crosslinked stationary phase. The chromatographic selectivity for the flat triphenylene over the bulkier o-terphenyl, α is an indicator of shape selectivity. The crosslinked phase⬢s α is 4.91 ± 0.08, almost twice that of the most shape-selective reversed phase column. The difference of the entropy contributions to retention free energy between the two compounds, ΝTΝS° at 298⬰K, is statistically indistinguishable from zero, (↙0.1⬰±⬰0.9⬰kJ/mol) leading us to believe that the observed shape selectivity is not consistent with the slot model. To test the hypothesis that the DEB-thiol adduct, a 4-ethynyl styryl sulfide (ESS), was responsible for the observed behavior, we prepared a low coverage ESS-containing phase which, unlike higher density, crosslinked, or polymeric phases, should not display shape selectivity based on ⬓slots⬽. With the ESS phase the shape selectivity remained high, with α⬰=⬰3.23⬰±⬰0.01. The ESS ligand has electron donating characteristics based on the selectivity for nitrobenzene compared to benzene: 1.83⬰±⬰0.10 on the ESS phase vs 0.64 ± 0.01 on a commercial C18 stationary phase. This shows that the thiol-yne based ESS stationary phase has electron donating charge transfer characteristics.
在使用硫醇-炔反应开发 pH 稳定的高度交联固定相的过程中，发现了一种新的电荷转移固定相。制备交联相的第一步是使用硫醇-炔反应将 1,4-二乙炔基苯（DEB）连接到巯基功能化的硅胶颗粒上。在制备该相时，我们注意到与非芳香或水溶剂相比，当用芳香族溶剂润湿改性颗粒时，颗粒的颜色会有所不同。在用 1,6-己二硫醇交联 DEB 以形成交联固定相后，这种颜色变化仍然很明显。平面三苯并菲相对于更大的邻三联苯的色谱选择性，α是形状选择性的指标。交联相的α为 4.91±0.08，几乎是最具形状选择性的反相柱的两倍。两种化合物的保留自由能熵贡献之间的差异，在 298 ⁇ K 时为 ΝTΝS°，统计上与零没有区别，（↙0.1 ⁇ ± ⁇ 0.9 ⁇ kJ/mol），这使我们相信观察到的形状选择性与槽模型不一致。为了测试假设，即 DEB-巯基加合物，4-乙炔基苯乙烯基硫醚（ESS），负责观察到的行为，我们制备了一种低覆盖率的 ESS 含有相，与高密度、交联或聚合相不同，它不应该基于 ⬓槽⬽显示形状选择性。使用 ESS 相，形状选择性仍然很高，α ⁇ = ⁇ 3.23 ⁇ ± ⁇ 0.01。与苯相比，根据对硝基苯的选择性，ESS 配体具有供电子特性：在 ESS 相上为 1.83 ⁇ ± ⁇ 0.10，在商业 C18 固定相上为 0.64 ± 0.01。这表明基于硫醇-炔的 ESS 固定相具有供电子电荷转移特性。
