Matrix-Assisted Laser Desorption/Ionisation Time-of-Flight Mass Spectrometry. A Comparison of Fragmentation Patterns of Linear Dextran Obtained by In-Source Decay, Post-Source Decay and Collision-Induced Dissociation and the Stability of Linear and Cyclic Glucans Studied by In-Source Decay

Abstract

In the first part of this study fragmentation patterns from a range of dextran oligomers (containing 4-20 anhydroglucose units) were compared in three different methods of analysis coupled with matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry. Collision-induced-dissociation (CID), prompt in-source decay (ISD) and post-source decay (PSD) all caused cleavage of the glycosidic bonds. Both CID and to a lesser extent ISD caused further cleavage of pyranose rings of the individual sugar residues. There was very little cleavage of pyranose rings detected in the PSD spectrum. Derivatisation of the reducing end-groups of the oligodextrans with 1-phenyl-3-methyl-5-pyrazolone (PMP) restricted cleavage in the MALDI mass spectrometer to the non-reducing end, and further it enabled the saccharides to be separated by HPLC so that a single chain length could be examined as a standard. Maltoheptaose was also used as a standard. In the second part of the study prompt ISD-MALDI mass spectrometry was used to compare the fragmentation of three oligoglucans, dextran, maltodextrin and gamma cyclodextrin, that have different linkages and different secondary structure. The results showed that the degree of fragmentation correlated with the degree of freedom in the saccharide chains in solution determined by NMR. Dextran the most random conformation was fragmented most whereas there was little evidence of any fragments, not even glycosidic bond breakage from cyclodextrin, even when the laser power was increased considerably. The fragmentation pattern of maltodextrin was intermediate. The patterns of fragmentation produced by MALDI mass spectrometry, particularly where standards are available to calibrate the spectrum and the energy of the laser is controlled, can be used to predict the type of linkage present.

Structural Characterization of Neutral Oligosaccharides by Laser-Enhanced In-Source Decay of MALDI-FTICR MS

“…The results from LEISD of oligosaccharides obtained using laser of mJ level in this study were much distinct from those from traditional ISD reported [16][17][18][19][20][21]. Abundant fragmentation ions were obtained in this work, where laser power played an essential role.…”

“…The fragmentations could be dynamically controlled; therefore, the intensities of ions could be described by Arrhenius equation, in which the front exponential factor A reflects the structural characteristics. There are some striking advantages of the LEISD method over the previously reported ISD methods [16][17][18][19][20][21], such as better S/N, more extensive fragmentation, and no interference from matrix ions. Better results obtained in positive-ion mode with continuous extraction in our experiments were probably because the laser energy (50 mJ per pulse) used here was much higher than that used in any previously reported ISD method.…”

“…There are several previous publications on the analysis of carbohydrates involving MALDI-ISD method [16][17][18][19][20][21]. Harvey et al observed weak fragment ions in the ISD spectra of N-linked oligosaccharides with a magnetic sector instrument operated at full-power laser (180 μJ/pulse) [16].…”

MALDI In-Source Decay, from Sequencing to Imaging

“…As glycans can be easily isolated and purified, the ISD and pMS 3 -sequencing approaches were also employed to characterize thoroughly the structures of both native [43,[54][55][56][57][58][59][60] and permethylated glycans [61][62][63][64][65][66], allowing unambiguous discrimination of isobaric species. In ref.…”

2-Aminobenzamide and 2-Aminobenzoic Acid as New MALDI Matrices Inducing Radical Mediated In-Source Decay of Peptides and Proteins

“…M ALDI in-source decay (or MALDI ISD) has been observed for various kinds of analytes such as peptides and proteins [1][2][3][4][5][6], carbohydrates [7][8][9][10][11][12] oligonucleotides [13], and is currently used for top-down protein sequencing [14]. Concerning peptides and proteins, two main activation modes, thermal and radical-mediated, were described in literature to explain the in-source fragmentation pathways.…”