Vibrational and electronic spectra of protonated vanillin: exploring protonation sites and isomerisation.

Photofragmentation spectra of protonated vanillin produced under electrospray ionisation (ESI) conditions have been recorded in the 3000-3700 cm-1 (vibrational) and 225-460 nm (electronic) ranges, using room temperature IRMPD (infrared multiphoton dissociation) and cryogenic UVPD (ultraviolet photodissociation) spectroscopies, respectively. The cold (∼50 K) electronic UVPD spectrum exhibits very well resolved vibrational structure for the S1 ← S0 and S3 ← S0 transitions, suggesting long excited state dynamics, similar to its simplest analogue, protonated benzaldehyde. The experimental data were combined with theoretical calculations to determine the protonation site and configurational isomer observed in the experiments.

GlAIcomics: a deep neural network classifier for spectroscopy-augmented mass spectrometric glycans data.

Carbohydrate sequencing is a formidable task identified as a strategic goal in modern biochemistry. It relies on identifying a large number of isomers and their connectivity with high accuracy. Recently, gas phase vibrational laser spectroscopy combined with mass spectrometry tools have been proposed as a very promising sequencing approach. However, its use as a generic analytical tool relies on the development of recognition techniques that can analyse complex vibrational fingerprints for a large number of monomers. In this study, we used a Bayesian deep neural network model to automatically identify and classify vibrational fingerprints of several monosaccharides. We report high performances of the obtained trained algorithm (GlAIcomics), that can be used to discriminate contamination and identify a molecule with a high degree of confidence. It opens the possibility to use artificial intelligence in combination with spectroscopy-augmented mass spectrometry for carbohydrates sequencing and glycomics applications.

Ring-Size Memory of Galactose-Containing MS/MS Fragments: Application to the Detection of Galactofuranose in Oligosaccharides and Their Sequencing.

Analysis of glycans remains a difficult task due to their isomeric complexity. Despite recent progress, determining monosaccharide ring size, a type of isomerism, is still challenging due to the high flexibility of the five-membered ring (also called furanose). Galactose is a monosaccharide that can be naturally found in furanose configuration in plant and bacterial polysaccharides. In this study, we used the coupling of tandem mass spectrometry and infrared ion spectroscopy (MS/MS-IR) to investigate compounds containing galactofuranose and galactopyranose. We report the IR fingerprints of monosaccharide fragments and demonstrate for the first time galactose ring-size memory upon collision-induced dissociation (CID) conditions. The linkage of the galactose unit is further obtained by analyzing disaccharide fragments. These findings enable two possible applications. First, labeled oligosaccharide patterns can be analyzed by MS/MS-IR, yielding full sequence information, including the ring size of the galactose unit; second, MS/MS-IR can be readily applied to unlabeled oligosaccharides to rapidly identify the presence of a galactofuranose unit, as a standalone analysis or prior to further sequencing.

Fucose Migration Pathways Identified Using Infrared Spectroscopy.

Fucose is a ubiquitous monosaccharide associated to major classes of glycans. A main obstacle to the sequencing of fucosylated glycans is the migration of fucose, which leads to misinterpretations in mass spectrometry analysis. Here, using ion vibrational spectroscopy, we resolve the structure of fucosylated fragments of Lewis and blood group H antigen trisaccharides and we unveil the position and linkage of the fucose after migration. Our findings demonstrate that the structure of fragment ions resulting from fucose migration can be characterized. Additionally, we report a new type of fucose migration, which does not feature any change of mass and therefore had not been previously reported: it consists of a local migration where the fucose changes its position remaining on the initial residue. Our approach allows the characterization of glycans, an essential step to interpret glycomics data, as well as to understand underlying processes at play in mass spectrometry.

Rapid IRMPD (InfraRed multiple photon dissociation) analysis for glycomics.

Infrared vibrational spectroscopy in the gas phase has emerged as a powerful tool to determine complex molecular structures with high precision. Among the different approaches IRMPD (InfraRed multiple photon dissociation), which requires the use of an intense pulsed tuneable laser in the InfraRed (IR) domain, has been broadly applied to the study of complex (bio)molecules. Recently, it also emerged as a highly relevant approach for analytical purposes especially in the field of glycomics in which structural analysis is still a tremendous challenge. This opens the perspective to develop new analytical tools allowing for the determination of molecular structures with atomic precision, and to address advanced questions in the field. However, IRMPD experiments require non commercial equipment or/and long acquisition time which limits the data output. Here we show that it is possible to improve the IRMPD performances by optimizing the combination between a linear ion trap mass spectrometer and a high repetition tuneable laser. Two orders of magnitude are gained with this approach compared to the usual experiments ultimately leading to a completely resolved spectrum acquired in less than one minute. These results open the way to many new applications in glycomics with the possibility to include IRMPD in complex analytical workflows.