An Ab initio MO Study of the Fragmentation Mechanism of the Cycloglycylglycine Ion in Mass Spectrometry

Abstract

The unimolecular dissociation of the cycloglycylglycine ion has been investigated using the ab initio MO method. The optimized geometries of possible molecular ion conformers, reaction intermediates and fragments have been calculated at the HF/6-31G//3-21G and HF/3-21G//3-21G levels. The potential energy curves for CO and NHCO eliminations from cycloglycylglycine ions have been calculated at low energy. The present study indicates that [M-CO]^+· and [M-NHCO]^+· are produced via proton transfers, which result in stable intermediates with a three-membered ring and a five-membered ring, respectively.