Molecular radical cations of oligopeptides

Abstract

An unprecedented method of producing molecular radical cations of oligopeptides in the gas phase has been discovered. Electrospraying a methanolic mixture of a Cu(II)-amine complex, e.g., CuII(dien)(NO3)2 (where dien = diethylenetriamine), and an oligopeptide (M) yields the [CuII(dien)M]·2+ ion, whose collision-induced dissociation (CID) produces [CuI(dien)]+ and M·+, the molecular cation of the oligopeptide. Abundant M·+ is apparent when the oligopeptide contains both a tyrosyl and a basic residue-arginyl, lysyl, or histidyl. These structural requirements are similar to those in the metalloradical enzyme process in photosystem II. Tandem mass spectrometry of M·+ produces fragment ions that are both common to and also different from [M + H]+. The fragmentation chemistry of M·+ and of its products appear to be radical driven. © 2000 American Chemical Society.