Authors: Lianming Wu Andy W Tao R Cooks
Publish Date: 2002/07/05
Volume: 373, Issue: 7, Pages: 618-627
Abstract
Chiral recognition of αhydroxy acids has been achieved and mixtures of enantiomers have been quantified in the gas phase by using the kinetics of competitive unimolecular dissociation of singlycharged transition metal ionbound trimeric complexes MIIAref2–H+ MII=divalent transition metal ion A=αhydroxy acid ref=chiral reference ligand to form the dimeric complexes MIIAref–H+ and MIIref2–H+ Chiral selectivity the ratio of these two fragment ion abundances for the complex containing the analyte in one enantiomeric form expressed relative to that for the fragments of the corresponding complex containing the other enantiomer ranges from 065 to 732 Chiral differentiation is highly dependent on the choice of chiral reference compound and central metal ion The different coordination geometry of complexes resulting from the different dorbital electronic configurations of these transition metal ions plays a role in chiral discrimination Of all the transition metal ions examined chiral recognition is lowest for CuII because of large distortion of the coordination complexes and hence weak metal–ligand interactions and small stereochemical effects It seems that two independent πcation interactions occur when Nacetylsubstituted aromatic amino acids used as the reference ligands and this accounts for improved chiral discrimination If both metal–ligand and ligand–ligand interactions are optimized large chiral selectivity is achieved The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity which are intrinsic to the kinetic method enable mixtures to be analyzed for small enantiomeric excess ee by simply recording the ratios of fragment ion abundances in a tandem mass spectrum
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