Antimony(III)-D, L-tartrates exhibit proton-assisted enantioselective binding in solution and in the gas phase

The negative ion mode ESI mass spectral analysis of antimony(III)-D- and -L-tartrate ("tartar emetic"), in association with leucine enantiomeric isotopomers, revealed remarkable proton-assisted enantioselective molecular recognition phenomena. The current study infers that recognition of amino acids by antimony(III)-D,L-tartrate complexes requires that the chiral selector associate a proton to become enantioselective. The dianionic selector itself failed to show enantiomeric discrimination capacity. This observation was shown to be consistent both in solution-phase targeting full scan and gas-phase targeting collision threshold dissociation (CTD) experiments. Importantly, this disparity in enantioselective binding capacity between the dianionic and the protonated monoanionic representatives of antimony(III)-D- and -L-tartrates could only be clearly revealed by ESI-MS and tandem mass spectrometry experiments as described herein. This finding urges a more in-depth study of mechanisms associated with exhibited enantiomeric resolving capacity of antimony tartrates in HPLC and CE applications, as well as in former ESI-MS association studies.