MODELING THE MAXIMUM CHARGE-STATE OF ARGININE-CONTAINING PEPTIDE IONSFORMED BY ELECTROSPRAY-IONIZATION

A model for the gas-phase proton transfer reactivity of multiply proto nated molecules is used to quantitatively account for the maximum char ge states of a series of arginine-containing peptide ions measured by Downard and Biemann (Int. J. Mass Spectrom. Ion Processes 1995, 148, 1 91-202). We find that our calculations account exactly for the maximum charge state for 7 of the 10 peptides and are off by one charge for t he remaining 3. These calculations clearly predict the trend in maximu m charge states for these peptides and provide further evidence that t he maximum charge state of ions formed by electrospray ionization is d etermined by their gas-phase proton transfer reactivity.