Reactivity of anomeric ▫$1\alpha▫$- and ▫$1\beta$▫-pentofuranosyl azide derivatives in ammonia chemical ionization
Kralj, Bogdan ; Kocjan, Darko ; Kobe, Jože, 1942-
Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric1 alpha- and 1 beta- ...azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that beta -anomers have higher affinities for H+ and NH4+ ions than alpha -azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN, giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3](+) ion, a competitive product to the ammonium-attached [SN3NH4](+) ion. The fragmentation pathways of the stable and metastable [MNH4](+), MHC ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4](+) and/or [SNHN2NH3](+) ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3](+), [SNH3](+) and SNH+ insome examples correlates with the exothermicity of the corresponding [MNH4](+) and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high-pressure region of the CI ion source.
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