The chirality determination of amino acids by forming complexes with cyclodextrins and metal ions using ion mobility spectrometry, and a DFT calculation

Chiral recognition is of highly interest in the areas of chemistry, pharmaceuticals, and bioscience. An effective strategy of enantiomeric determination of amino acids (AAs) was developed in this work. All 19 natural AAs enantiomers can be easily distinguished by ion mobility-mass spectrometry of the non-covalent complexes of AAs with cyclodextrins (α-CD, β-CD and γ-CD) and Mg2+ without any chemical derivatization. Differences of the mobilities between the enantiomers' complexes is from 0.006 to 0.058 V s/cm2. In addition, the complex of [β-CD + Phe + Mg]2+ was selected as an example to study the relative quantification by measuring L/D-Phe at different molar ratio of 10:1 to 1:10 in the μM range, resulting in a good linearity (R2 > 0.99) and high sensitivity at 2 μM. A DFT calculation was also performed to illustrate the detailed molecular structure of the complexes of CDs, Mg2+ and D- or L-Phe. Both experiment and theoretical calculation showed that Mg2+ plays an important role in host/guest interactions, which changed the molecular conformations by non-covalent interaction between Mg2+ and CDs, and resulted in the different collision cross-sections of the complex ions of CDs, Mg2+ and D- or L-AAs in the gas phase. This effective and convenient strategy could potentially be utilized in scientific research and industry for routine enantiomeric determination of natural AAs, peptides and some other small chiral biomolecules such as non-natural AAs and carboxylic acid-containing drugs.