THE B-1-FRAGMENT ION FROM PROTONATED GLYCINE IS AN ELECTROSTATICALLY-BOUND ION MOLECULE COMPLEX OF CH2=NH2+ AND CO/

The stability of the B-1-ion from glycylglycine dipeptides was studied using collision-induced dissociation experiments and ab initio calcul ations. This study reveals that the B-1-type ion from glycine should b e considered as an electrostatically bound ion/moecule complex, which dissociates into a glycine immonium ion (A(1)) and a carbon monoxide m olecule. The stability of this complex has been calculated at various levels of the theory. At the highest level of theory (#RHF/6-311G*) i t is found that the energy requirement, including zero-point vibration al energy correction, for dissociation into a glycine immonium A(1) io n acid a neutral carbon monoxide CO molecule is -4.0 kJ mol(-1). Furth ermore it could be concluded that B-1-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.