CHARACTERIZATION OF CHIRAL HOST-GUEST COMPLEXATION IN FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

Anew method has been developed for the characterization of complexion between host and guest molecules, Adduct formation between chiral crow n ethers 1 and 2 and enantiomeric ammonium ions 4 and 5 was examined, The reference compound 3 (achiral host) was chosen to be similar in st ructure to the chiral crown ethers for quantitative measurements, Our approach is based on a formalism assuming an equilibrium: [chiral host + H](+) + [achiral host + chiral guest](+) reversible arrow [chiral h ost + chiral guest](+) + [achiral host + H](+). The equlibrium constan t for this process was calculated using the relative peak intensities of the corresponding species in the FAB mass spectra, It was found tha t these provide significantly better reproducibility and more reliable results than the relative peak intensity method described before (Saw ada, M.; et al. J. Am. Chem. Soc. 1992, 114, 4405; 1993, 115, 7381; Or g. Mass Spectrom, 1993, 28, 1525).(1-3) In the examples studied, the e quilibrium constants corresponding to the formation of heterochiral ad ducts (S,S-R or R,R-S) were higher than those for the formation of hom ochiral aggregates (S,S-S or R,R-R).