Abstract
This paper reports the investigation of the chiral interaction between 3,4-methylenedioxy-methamphetamine (MDMA) enantiomers and an immobilized polysaccharide-based chiral phase. For that, suspended-state high-resolution magic angle spinning nuclear magnetic resonance spectroscopy (1H HR-MAS NMR) was used. 1H HR-MAS longitudinal relaxation time and Saturation Transfer Difference (STD NMR) titration experiments were carried out yielding information at the molecular level of the transient diastereoisomeric complexes of MDMA enantiomers and the chiral stationary phase. The interaction of the enantiomers takes place through the aromatic moiety of MDMA and the aromatic group of the chiral selector by π-π stacking for both enantiomers; however, a stronger interaction was observed for the (R)-enantiomer, which is the second one to elute at the chromatographic conditions.
Highlights
Separation mechanisms are based on the solvated structure of the analyte and of the stationary phase and on their tridimensional structure; enantiorecognition is a result of the sum of all these different interactions
Saturation transfer difference nuclear magnetic resonance (STD NMR) spectroscopy has been successfully employed as a key technique to differentiate interactions at the supramolecular level [1]
For 1H HR-MAS NMR experiments, first it is necessary to obtain the enantiomers in a high degree of enantiomeric purity
Summary
Separation mechanisms are based on the solvated structure of the analyte and of the stationary phase and on their tridimensional structure; enantiorecognition is a result of the sum of all these different interactions. Pinpointing these interactions at the molecular level is, an analytical challenge. In this context, saturation transfer difference nuclear magnetic resonance (STD NMR) spectroscopy has been successfully employed as a key technique to differentiate interactions at the supramolecular level [1]. The first spectrum corresponds to the ‘saturation on-resonance’ (STDon), in which the chiral stationary phase (CSP) 1H signals are selectively excited using a narrow NMR pulse that does not excite the enantiomer under
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