Chiral recognition of amino acids by mass spectrometry with the combinations of two different chiral selectors

Chiral recognition in mass spectrometry typically relies on one chiral selector (CS) to distinguish enantiomers through dissociation of diastereomeric complexes. Here, we report an innovative approach employing two different CSs to form trimeric complexes with analytes in the presence of Cu²⁺. Nineteen proteinogenic chiral amino acids are investigated as both analytes and selectors, and complexes involving proline and aromatic amino acids exhibit superior chiral discrimination. Notably, the two selectors can play distinct roles: one plays an anchoring role, while the other only contributes to the degree of discrimination. Computational modeling reveals that the copper-bound trimers (e.g., [Cu^II(Pro)(Phe)(Tyr) − H]⁺) adopt a pentacoordinated geometry with a square-planar base and an elongated axial bond. Three energetically similar precursor structures co-exist, with dissociation occurring exclusively at the axial position. The strong agreement between experimental and computational results validates this binary CS concept and provides a framework for designing advanced CSs for unknown samples.