ELECTROSPRAY-IONIZATION OF COPPER-GLYCINE SOLUTIONS

We have characterized the electrospray ionization (ESI) spectra of mix tures of the 3d transition metal ion CU2+ with both a model amino acid (glycine) and a simple peptide system (glycylglycine). We found what appear to be two major classes of ions. We suggest that these apparent classes may offer some further insight into the nature of the ion for mation process in ESI. Specifically, we argue that one group of ions i s a consequence of gas-phase reactions of the intramolecular charge tr ansfer type. We also argue that the second group of ions has a close a ssociation with species that have been identified in the bulk phase, a nd which therefore may arise in ESI by a direct desorption process.