title: Fragmentation processes of hydrogen-deficient peptide radicals in matrix-assisted laser desorption/ionization in-source decay mass spectrometry.
abstract: The mechanism of in-source decay (ISD) in matrix-assisted laser desorption/ionization (MALDI) has been described. The MALDI-ISD with an oxidizing matrix is initiated by hydrogen abstraction from peptides to matrix molecules, leading to hydrogen-deficient peptide radicals. Subsequently, the C(α)-C and C(α)-H bonds are cleaved, forming the a•/x fragment pair and [M-2H], respectively. Those reactions competitively occur during MALDI-ISD processes. Our results suggest that the C(α)-H bond cleavage to form [M-2H] was induced by collisions between hydrogen-deficient peptide radicals and matrix molecules in the MALDI plume. In contrast, the C(α)-C bond cleavages occur via a unimolecular dissociation process and independently of the collision rate in the MALDI plume. The formation mechanism of the a-, b-, and d-series fragments are also described. We report 2,5-bis(2-hydroxyethoxy)-7,7,8,8-tetracyanoquinodimethane (bisHE-TCNQ), being known as an organic semiconductor and an electron acceptor, as a novel suitable matrix for the MALDI-ISD of peptides via hydrogen abstraction.
authors.affiliation: Graduate School in Nanobioscience, Mass Spectrometry Laboratory, Yokohama City University, Kanazawa-ku, Yokohama, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Asakawa
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Takayama
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D005609:Free Radicals; D010455:Peptides; D006859:Hydrogen