1 : 1 Adduct Ion Formation of Permethylated Monosaccharides with Organic Cations in FAB Mass Spectrometry

The 1 : 1 adduct ion formation between a series of permethylated monosaccharides (M; Ia–Ih) and an organic or a metallic cation (A+) has been examined in quantitative FAB mass spectrometry. In a careful comparison under the same FABMS conditions, the relative (M+A)+ peak intensities increase in the following order of the monosaccharides, and further increase at nearly the same extents in spite of using three different cations such as octylammonium, (methoxycarbonyl) methylammonium, and potassium ions: β-Glc<α-Glc<α-Gal<β-Gal≤α-Man<β-Man<α-Tal<β-Tal. The order and cation-independency clearly indicate the OCH3 configurational effects of M on (M+A)+ adduct ion formation. The findings can be interpreted in terms of multisite electrostatic interaction of oxygens with the cation. Coupled with the results of gas-phase behavior by FABMS/MS(CAD), solution behavior by 1H NMR, and model calculations by MNDO, the characteristic structure of the 1 : 1 adduct ion is deduced as host-guest type association between permethylated monosaccharides and cationic species in particular cases, at least β-Tal and α-Tal cases.