Kröger Sabrina, Wong Yong Foo, Chin Sung-Tong, Grant Jacob, Lupton David, Marriott Philip J
Institute for Inorganic and Analytical Chemistry, University of Münster, Münster, Germany.
Australian Centre for Research on Separation Science, School of Chemistry, Monash University, Wellington Road, 3800 Victoria, Australia.
J Chromatogr A. 2015 Jul 24;1404:104-14. doi: 10.1016/j.chroma.2015.05.049. Epub 2015 May 28.
The reversible molecular interconversion behaviour of a synthesised oxime (2-phenylpropanaldehyde oxime; (C6H5)CH(CH3)CHN(OH)) was investigated by both, single dimensional gas chromatography (1D GC) and comprehensive two-dimensional gas chromatography (GC×GC). Previous studies on small molecular weight oximes were extended to this larger aromatic oxime (molar mass 149.19gmol(-1)) with interest in the extent of interconversion, enantioselective resolution, and retention time. On a polyethylene glycol (PEG; wax-type) column, a characteristic interconversion zone between two antipodes of E and Z isomers was formed by molecules which have undergone isomerisation on the column (E⇌Z). The extent of interconversion was investigated by varying chromatographic conditions (oven temperature and carrier flow rate) to understand the nature of the behaviour observed. The extent of interconversion was negligible in both enantioselective and methyl-phenylpolysiloxane phase-columns, correlating with the low polarity of the stationary phase. In order to obtain isomerisation along with enantio-resolution, a wax-type and an enantioselective column were coupled in either enantioselective-wax or wax-enantioselective order. The most appropriate column arrangement was selected for study by using a GC×GC experiment with either a wax-phase or phenyl-methylpolysiloxane phase as (2)D column. In addition to evaluation of these fast elution columns, a long narrow-bore enantioselective column (10m) was introduced as (2)D, providing an enantioselective-PEG (coupled-column ensemble: (1)D1+(1)D2)×enantioselective ((2)D) column combination. In this instance, the (1)D1 enantioselective column provides enantiomeric separation of the corresponding enantiomers ((R) and (S)) of (E)- and (Z)-2-phenylpropanaldehyde oxime, followed by E/Z isomerisation in the coupled (1)D2 PEG (reactor) column. The resulting chromatographic interconversion region was modulated and separated into either E/Z isomers (achiral (2)D column) or into the respective (R) and (S) enantiomers of the E/Z isomers when using a (2)D enantioselective column. With this arrangement, the isomers underneath the broad interconversion plateau in 1D elution profiles, including the enantiomers, could be resolved, illuminating salient features and understanding of the molecular reversible process of the interconverting molecules during the chromatographic elution. The two-dimensional patterns (contour plots), resulting from the combination of interconversion process and chiral separation, are discussed phenomenologically.
通过一维气相色谱法（1D GC）和全二维气相色谱法（GC×GC）研究了合成肟（2-苯基丙醛肟；(C6H5)CH(CH3)CHN(OH)）的可逆分子互变行为。先前对小分子量肟的研究扩展到了这种更大的芳香族肟（摩尔质量149.19gmol(-1)），研究内容包括互变程度、对映体选择性拆分和保留时间。在聚乙二醇（PEG；蜡型）柱上，在柱上发生异构化的分子（E⇌Z）形成了E和Z异构体两种对映体之间的特征性互变区。通过改变色谱条件（柱温箱温度和载气流速）来研究互变程度，以了解所观察到的行为的本质。在对映体选择性柱和甲基苯基聚硅氧烷相柱中，互变程度都可以忽略不计，这与固定相的低极性相关。为了实现异构化以及对映体拆分，将一根蜡型柱和一根对映体选择性柱以对映体选择性-蜡型或蜡型-对映体选择性的顺序连接。通过使用以蜡相或苯基甲基聚硅氧烷相作为二维柱的GC×GC实验，选择了最合适的柱排列方式进行研究。除了评估这些快速洗脱柱外，还引入了一根长的窄口径对映体选择性柱（10m）作为二维柱，提供了一种对映体选择性-PEG（联用柱组合：(1)D1+(1)D2）×对映体选择性（(2)D）柱组合。在这种情况下，(1)D1对映体选择性柱对(E)-和(Z)-2-苯基丙醛肟的相应对映体（(R)和(S)）进行对映体分离，随后在联用的(1)D2 PEG（反应器）柱中发生E/Z异构化。当使用二维对映体选择性柱时，所得的色谱互变区被调制并分离为E/Z异构体（非手性二维柱）或E/Z异构体各自的(R)和(S)对映体。通过这种排列方式，可以分辨出一维洗脱曲线中宽互变平台下方的异构体，包括对映体，从而揭示互变分子在色谱洗脱过程中分子可逆过程的显著特征并加深理解。对由互变过程和手性分离相结合产生的二维图谱（等高线图）进行了现象学讨论。
