Comparing the gas-phase fragmentation reactions of protonated and radical cations of the tripeptides GXR

Abstract

Electrospray ionization (ESI) mass spectrometry of methanolic solutions of mixtures of the copper salt (2,2′:6′,2″-terpyridine)copper(II) nitrate monohydrate ([Cu(II)(tpy)(NO3)2]·H 2O) and a tripeptide GXR (where X = 1 of the 20 naturally occurring amino acids) yielded [Cu(II)(tpy)(GXR)]·2+ ions, which were then subjected to collision induced dissociation (CID). In all but one case (GRR), these [Cu(II)(tpy)(GXR)]·2+ ions fragment to form odd electron GXR·+ radical cations with sufficient abundance to examine their gas-phase fragmentation reactions. The GXR·+ radical cations undergo a diverse range of fragmentation reactions which depend on the nature of the side chain of X. Many of these rea..