The stability of the B1-ion from glycylglycine dipeptides was studied using collision-induced dissociation experiments and ab initio calculations. This study reveals that the B1-type ion from glycine should be considered as an electrostatically bound ion/moecule complex, which dissociates into a glycine immonium ion (A1) and a carbon monoxide molecule. The stability of this complex has been calculated at various levels of the theory. At the highest level of theory (#RHF/6-311G**) it is found that the energy requirement, including zero-point vibrational energy correction, for dissociation into a glycine immonium A1 ion and a neutral carbon monoxide CO molecule is −4.0 kJ mol−1. Furthermore it could be concluded that B1-ions from glycine are stable if they are present as N-acylated species. The formation of stable B ions requires at least two carbonyl groups in the peptide backbone moiety.
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Dongen et al. (1996) studied this question.