MALDI MS In-Source Decay of Glycans Using a Glutathione-Capped Iron Oxide Nanoparticle Matrix

Abstract

A new matrix-assisted laser desorption ionization (MALDI) mass spectrometry matrix is proposed for molecular mass and structural determination of glycans. This matrix contains an iron oxide nanoparticle (NP) core with gluthathione (GSH) molecules covalently bound to the surface. As demonstrated for the monosaccharide glucose and several larger glycans, the mass spectra exhibit good analyte ion intensities and signal-to-noise ratios, as well as an exceptionally clean background in the low mass-to-charge (m/z) region. In addition, abundant in-source decay (ISD) occurs when the laser power is increased above the ionization threshold; this indicates that the matrix provides strong energy transfer to the sample. For five model glycans, ISD produced extensive glycosidic and cross-ring cleavages in the positive ion mode from singly charged precursor ions with bound sodium ions. Linear, branched, and cyclic glycans were employed, and all were found to undergo abundant fragmentation by ISD. (18)O labeling was used to clarify m/z assignment ambiguities and showed that the majority of the fragmentation originates from the nonreducing ends of the glycans. Studies with a peracetylated glycan indicated that abundant ISD fragmentation occurs even in the absence of hydroxyl groups. The ISD product ions generated using this new matrix should prove useful in the sequencing of glycans.

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

“…This ranking differs substantially from the one proposed for matrixes inducing ISD fragmentation of peptides via a hydrogen radical transfer mechanism [27][28][29][30][31]. The fragmentation yield values showed a large variation even for two matrixes, CNA and DCTB, which might be considered to have similar properties (i.e., they are both aprotic and each exhibits low polarity).…”

“…Similarly, dissociations of benzyl-pyridines used as thermometer molecules were explained through two fragmentation mechanisms, one similar to peptide fragmentation [28] and the other by a thermal dissociation route [26]. For the investigation of glycans, ISD produced hydrogen abstraction (still as H • ) [29]. ISD experiments are often successful at producing abundant fragments when DHB, SA or DAN are employed [30,31].…”

Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry

“…29 Some functionalization induces minimal contamination and has been successfully applied for LDI-MS of small molecules. Glutathione-capped iron oxide NPs have been applied for in-source decay of glycans 31 and perfluorinated gold NPs have been shown to softly ionize small molecules for LDI-MS imaging. 32 The LDI efficiency of these NPs, however, has not been systematically studied over a wide range of small metabolite molecules.…”

Citric Acid Capped Iron Oxide Nanoparticles as an Effective MALDI Matrix for Polymers

“…The disadvantage of using organic matrices is that matrix-related ions interfere with the detection of low molecular mass compounds [34]. Similar to other NP matrices such as ZnO [34], graphene [37], halloysite nano-clay [39], and glutathione capped iron oxide nanoparticles [41], NPCA provides a clean spectral background for low molecular mass polymers. This is because NPs are heavy and surface bound during analyte desorption, which eliminates matrix signal from the mass spectra.…”

“…Previously, we have reported glycan characterization with glutathione capped iron oxide nanoparticles as the MALDI matrix [41]. In this study, we will demonstrate for the first time the effectiveness of a citric acid capped iron oxide NP matrix (NPCA) for several distinctively different polymers: PEG, polywax/polyethylene (PE), perfluoropolyether (PFPE), and polydimethylsiloxane (PDMS).…”