In order to obtain experimental data on the question of compensation of positive charges by anionic groups in multiply charged ions of polyfunctional molecules in electrospray MS, several pairs of peptides with the same basic structure but differentiated by one or two strongly acidic groups (phosphate or sulfonate) were investigated. It was found that depending on the density of basic centers and the strength of acidic groups present, the observed changes upon introduction of acidic groups ranged from complete elimination of the most highly charged state to absence of any difference.
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