Introduction of cationizing agents in soft ionization processes of short-chain peptides: laser desorption and electrospraying

A mass spectrometric study of ionization processes of short peptides of triglycine, alanylglutamine, and prolylleucine by electrospray ionization (ESI) and surface-activated laser desorption/ionization (SALDI) methods in the presence of copper sulfate crystalline hydrate is performed. It is shown that during ESI ionization, the presence of copper ions in the solution initiates the aggregation of peptide molecules with the formation of large associates of up to 7-8 peptide molecules. The influence of the nature of peptides on the nature of ionization processes is studied. At the same time, competitive cationization of peptide molecules by copper ions with the formation of an M+Cu+ ion occurs during ionization by SALDI method. Peptide fragmentation and copper cationization of decarboxylation products are also typical.