Gas-phase basicity and enantiodiscrimination of some phosphorous-containing α-amino acid mimics

Abstract

The kinetic method has been used for enantiodiscriminating important chiral residues from post-translationally modified proteins, i.e., the O-phospho α-amino acids, and some chiral α-amino acid mimics, i.e., the α-aminophosphonic acids. Their proton affinities (PA) have been evaluated using the same method in its extended form which allows the estimate of the entropy contributions on the kinetic measurements. The kinetic approach is based on the competing collision-induced decomposition (CID) of suitable proton-bound complexes between the P-containing molecules and suitable reference compounds, e.g., α-amino acids. The investigation was carried out in a QqQ instrument as a function of the collision energy (4–14 eV). The proton-bound complexes were generated in an electrospray ionization (ESI) source from calibrated water/methanol solutions of the two components. The experimental results have been discussed and compared with theoretical calculations.