Glycan Isomer Identification Using Ultraviolet Photodissociation Initiated Radical Chemistry

Abstract

Glycans are fundamental biological macromolecules, yet despite their prevalence and recognized importance, a number of unique challenges hinder routine characterization. The multiplicity of OH groups in glycan monomers easily afford branched structures and alternate linkage sites, which can result in isomeric structures that differ by minute details. Herein, radical chemistry is employed in conjunction with mass spectrometry to enable rapid, accurate, and high throughput identification of a challenging series of closely related glycan isomers. The results are compared with analysis by collision-induced dissociation, higher-energy collisional dissociation, and ultraviolet photodissociation (UVPD) at 213 nm. In general, collision-based activation struggles to produce characteristic fragmentation patterns, while UVPD and radical-directed dissociation (RDD) can distinguish all isomers. In the case of RDD, structural differentiation derives from radical mobility and subsequent fragmentation. For glycans, the energetic landscape for radical migration is flat, increasing the importance of the three-dimensional structure. RDD is therefore a powerful and straightforward method for characterizing glycan isomers.

Cyclic Ion Mobility Mass Spectrometry Distinguishes Anomers and Open-Ring Forms of Pentasaccharides

“…In their recent study, Schindler et al have utilized vibrational spectroscopy to show that the stereochemistry of the glycosidic bond is retained in the product ions, following dissociation [14]. A related technique of UV photo-dissociation (UVPD) coupled with MS has been shown to yield diagnostic product ions and facilitate structural assignments [15]. Ion mobility spectrometry (IMS) coupled with MS detection (IM-MS) is another attractive approach in deciphering polysaccharide structures.…”

Advanced tandem mass spectrometry in metabolomics and lipidomics—methods and applications

“…But controlled radical delivery via RDD also allows differentiation of oligosaccharides as demonstrated by Riggs et al and shown in Fig. 4 [87]. By irradiating derivatized disaccharides with 213 nm laser light, the authors were able to obtain characteristic UVPD/CID fragmentation patterns.…”

“…4 Selected mass spectrometric signals obtained by RDD of sodiated disaccharide isomers that allow isomer discrimination. Reprinted with permission from [87], copyright 2018 American Chemical Society subsequent processes complicates controlled radical delivery to structural elements of interest, a bottleneck of the method to be addressed in the future.…”

Linkage Memory in Underivatized Protonated Carbohydrates

“…Tools complementary to MS including ion mobility (IM), spectroscopic techniques like cryogenic ion spectroscopy and ultraviolet photodissociation have emerged as powerful gas-phase techniques with potential applications in glycobiology [13][14][15][16][17][18][19][20][21] . Ion mobility with mass spectrometry (IM-MS) separates ions by their charge, size, and shape due to interactions with an inert gas.…”