In-source decay characteristics of peptides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

In-source decay (ISD) of peptides, coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, has been examined to determine the influence of the matrix, the susceptibility of amino-acid residues to ISD, and the effect of extraction delay times. Out of nine di- and tri-hydroxybenzoic acids and three cinnamic derivatives tested, the most suitable matrix for ISD was 2,5-dihydroxybenzoic acid. The amine bond at Xxx-Gly and Xxx-Val residues was less susceptible than other amino-acid residues to ISD; however, the more sensitive residue(s) were not as clear. Using a peptide that gave the y(n)- and (z(n) + 2)-series product ions, it was confirmed that amide-bond cleavage (formation of the y(n)-series ions) accompanied metastable peaks, whereas metastable peaks were never observed with amine-bond cleavage [formation of the (z(n) + 2)-series ions]. Furthermore, abundant c(n)-series ions, which originate from amine-bond cleavage on the peptide backbone, were observed whenever a minimum delay time of 38 ns or continuous extraction was used to obtain spectra. These data indicate that amine-bond cleavage in ISD takes place on the ionization time scale before the energy randomization is completed.

MALDI In-Source Decay, from Sequencing to Imaging

“…Hydrogen radicals formed by the matrix are at the origin of the formation of the c-and z-fragments [25][26][27], as depicted in a mechanism proposed by Takayama [25]. In the matrix crystals, hydrogen bonds are formed between the matrix and the analytes.…”

Fragmentation of leucine enkephalin as a function of laser fluence in a MALDI TOF-TOF

“…Without ramping the laser fluence, one would not be able to distinguish whether these features resulted from chemicals present in the sample or fragmentation resulting from the process of ionization. This mechanism of fragment formation is traditionally termed in source decay (ISD) [42,43]. It should also be noted that ions that fragment after acceleration, but before the detector, have an energy defined by E frag ϭ E prec ϫ (m frag /m prec ) and would thus appear as unfocused metastable features in the spectrum.…”

“…Thus, such studies ignore fragmentation post ionization. The experimental examination of the effect of laser fluence on ion fragmentation has also been investigated in dinucleotides [29], in protein complexes [41], and peptides [42,43]. This paper presents the results of our preliminary investigations of peptide fragmentation and sets the stage for a systematic investigation of peptide fragmentations in MALDI.…”

Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation

“…Typically, a laser power of approximately 1.5 times the laser threshold value was used for each matrix to obtain in-source decay (ISD). No other parameters were modified because the optimum delay time observed for ISD fragments seems to be in agreement with standard MALDI-TOF/MS experiments [22].…”