Residue-specific radical-driven dissociation of peptides using matrix-assisted laser desorption/ionization in-source decay with C hydrogen-donating and -abstracting matrices

摘要

Radical-driven dissociation (RDD) of peptides was examined by MALDI-ISD with hydrogen-donating and - abstracting matrices. The observed fragment ions could be explained by the RDD of carbonyl-carbon (C-co)-centered hydrogen-excess radical ions [M + H-co + H](+) and beta-carbon (C beta)-centered hydrogen-deficient radical ions [M - H beta + H](+). The ISD spectra with hydrogen-abstracting and -donating matrices yielded C-terminal [x](+), [y](+)and [z](+) ions and C-terminal [x +2H](+), [y + 2H](+) and [z + 2H](+) ions, respectively, indicating the formation of MALDI plume devoid or rich in hydrogen radicals H. The residue-specific cleavages of the hydrogen-deficient radical ions [M-H +H](+) gave [d](+) ions for Asp and Met, [b](+), [y](+) and [w](+) ions for Pro, and relatively intense [a](+) ions for aromatic residues (Tyr and Phe). We suggest that [y + 2 H](+) ions are produced from transient radical ions [z(m)(+1) + H](+). (C) 2018 Elsevier B.V. All rights reserved.