Background

Isotopologues resulting from the labelling of molecules with deuterium have attracted interest due to the isotope effect observed in chemistry and biosciences. Isotope effect may also play out in noncovalent interactions and mechanisms leading to intermolecular recognition. In chromatography, differences in retention time between isotopologues, as well as between isotopomers have been observed resulting in two different elution sequences (isotope effects): the normal isotope effect when heavier isotopologues retain longer than lighter analogues, and the inverse isotope effect featuring the opposite elution order. Although several cases of deuterium isotope effects have been reported so far, the molecular bases of these phenomena remain unclear.

Results

We report the separation of isotopologues of methamphetamine (N-methyl-1-phenylpropan-2-amine) (MET), featuring different number and location of deuterium substituents, on an achiral column by high-performance liquid chromatography (HPLC), as well as the simultaneous separation of isotopologues and their enantiomers on some polysaccharide-based chiral columns. The effects of the number and location of deuterium substituents introduced in MET's structure, of the surface chemistry of the adsorbent, and the mobile phase composition and pH on the retention and separation of isotopologues and their enantiomers were examined. In several cases, the effect of temperature was also evaluated, and the thermodynamic quantities associated with isotopologue adsorption, separation, and enantioseparation were also calculated. To elucidate the molecular bases of the experimental observations, quantum mechanics calculations were performed focusing on the vibrational degree of freedom calculated for models of isotopologue-selector complexes. On this basis, zero-point vibrational energies were computed as useful descriptors to differentiate computationally between deuterated isotopologues.

Significance

Using HPLC as experimental technique with the following dual function: 1) separation of MET isotopologues and their enantiomers; 2) exploring noncovalent interactions underlying their separation. The degree of deuteration, location of deuterium substituents, and mobile phase pH play key roles in isotopologue separations. By integrating experimental and computational analyses, noncovalent interactions underlying normal and inverse isotope effects were deconvoluted, highlighting the contribution of hydrogen bond, hydrophobic and dispersive forces in isotopologue and enantiomer separation.

中文翻译：

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在高效液相色谱中了解甲基苯丙胺同位素在非手性和多糖基手性柱上的分离、对映体分离和识别机制

 背景

由于在化学和生物科学中观察到的同位素效应，用氘标记分子产生的同位素异构体引起了人们的兴趣。同位素效应也可能在非共价相互作用和导致分子间识别的机制中发挥作用。在色谱分析中，观察到同位素异构体之间以及同位素异构体之间的保留时间差异，导致两种不同的洗脱序列（同位素效应）：当较重的同位素比较轻的类似物保留更长的时间时，正常同位素效应，以及具有相反洗脱顺序的逆同位素效应。尽管迄今为止已经报道了几例氘同位素效应的案例，但这些现象的分子基础仍不清楚。

 结果

我们报道了通过高效液相色谱 （HPLC） 在非手性柱上分离甲基苯丙胺 （N-甲基-1-苯丙-2-胺） （MET） 的同位素体，这些同位素异构体具有不同氘取代基的数量和位置，以及在一些基于多糖的手性柱上同时分离同位素及其对映异构体。研究了 MET 结构中引入的氘取代基的数量和位置、吸附剂的表面化学性质以及流动相组成和 pH 值对同位素异构体及其对映异构体的保留和分离的影响。在一些情况下，还评估了温度的影响，并计算了与同位素吸附、分离和对映体分离相关的热力学量。为了阐明实验观察的分子基础，进行了量子力学计算，重点是为同位素-选择复合物模型计算的振动自由度。在此基础上，零点振动能量被计算为有用的描述符，以便在计算上区分氘代同位素。

 意义

使用 HPLC 作为实验技术，具有以下双重功能：1） 分离 MET 同位素异构体及其对映异构体;2） 探索它们分离背后的非共价相互作用。氘化程度、氘取代基的位置和流动相 pH 值在同位素分离中起着关键作用。通过整合实验和计算分析，消除了正常和逆同位素效应背后的非共价相互作用，突出了氢键、疏水和色散力在同位素和对映异构体分离中的作用。