Kasat Rahul B, Wee Siao Yee, Loh Ji Xian, Wang Nien-Hwa Linda, Franses Elias I
School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907-2100, USA.
J Chromatogr B Analyt Technol Biomed Life Sci. 2008 Nov 1;875(1):81-92. doi: 10.1016/j.jchromb.2008.06.045.
The effects of the molecular structures for 13 structurally similar chiral solutes on their HPLC retention and enantioresolutions on a commercially important polysaccharide-based chiral stationary phase, cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) are studied. Among these 13 solutes, only methyl ephedrine (MEph) shows significant enantioresolution. The retention factors of these chiral solutes vary significantly from 0.7 to 3.2 in n-hexane/2-propanol (90/10, v/v) at 298 K. The retention factors of some simpler non-chiral solutes having similar but fewer functional groups than their chiral counterparts are also studied under the same conditions and are compared to those of the chiral solutes. The H-bonding interactions between the functional groups of the solute and the C=O and NH functional groups of the polymer are probed with attenuated total reflection-infrared spectroscopy (ATR-IR) for the polymer, for binary sorbent-solute systems. The CDMPC IR amide band wavenumbers change significantly, indicating H-bonding interactions of the polymer C=O and NH groups with the solutes. The elution orders predicted for the enantiomers of these chiral solutes using molecular dynamics (MD) simulations of the polymer-solute binary systems are consistent with the HPLC results. The CDMPC cavity nano-structure and the potential interactions with chiral solutes are proposed based on HPLC data, IR data, and the simulations. The results are consistent with the three-point attachment model and support the hypothesis that significant enantioresolution requires at least three different synergistic interactions which can be a combination of steric hindrance, H-bonding, or pi-pi interactions.
研究了13种结构相似的手性溶质的分子结构对其在一种具有重要商业价值的基于多糖的手性固定相——三（3,5-二甲基苯基氨基甲酸酯）纤维素（CDMPC）上的高效液相色谱保留和对映体拆分的影响。在这13种溶质中，只有甲基麻黄碱（MEph）表现出显著的对映体拆分。在298K下，这些手性溶质在正己烷/2-丙醇（90/10，v/v）中的保留因子在0.7至3.2之间有显著差异。还在相同条件下研究了一些比其手性对应物具有相似但更少官能团的简单非手性溶质的保留因子，并与手性溶质的保留因子进行了比较。对于聚合物以及二元吸附剂-溶质体系，用衰减全反射红外光谱（ATR-IR）探测了溶质官能团与聚合物的C=O和NH官能团之间的氢键相互作用。CDMPC红外酰胺带波数发生了显著变化，表明聚合物的C=O和NH基团与溶质之间存在氢键相互作用。使用聚合物-溶质二元体系的分子动力学（MD）模拟预测的这些手性溶质对映体的洗脱顺序与高效液相色谱结果一致。基于高效液相色谱数据、红外数据和模拟结果，提出了CDMPC的空腔纳米结构以及与手性溶质的潜在相互作用。结果与三点结合模型一致，并支持这样的假设，即显著的对映体拆分需要至少三种不同的协同相互作用，这些相互作用可以是空间位阻、氢键或π-π相互作用的组合。
