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International audience; Two-color air plasma based broadband terahertz (THz) generation and subsequent air biased coherent detection (ABCD) of the THz field are presented. Both source and detection system are characterized experimentally and numerically, yielding excellent agreement of measured and simulated signals. We reveal that it is crucial to model the whole optical setup and include the various pump distortions, like temporal and spatial walk-off as well as ellipticity of polarization, in order to interpret the experimental measurements correctly. Moreover, it turns out that geometrical effects in the ABCD scheme shape the recorded THz spectra and need to be taken into account. We confirm that THz electric fields with peak amplitude in the MV/cm range and large spectral bandwidth are produced, allowing us to demonstrate THz spectroscopy with molecular samples.

Fucose is a ubiquitous monosaccharide linked to the core of major classes of glycans and the identification of fucose location is one critical bottleneck in glycomics. This is due to the remarkable inclination of the fucosyl residue to migrate to neighboring throughout mass spectrometric analysis. Such molecular rearrangements first reported in the 90’s and called “internal residue loss” can be mistaken for diagnostic fragments and lead to false assignment of the position of fucose on the glycan core. While a variety of misleading fucosylated fragments has been observed for glycan standards, the exact molecular structure of fucosylated products after rearrangement remains elusive and their formation unpredictable. This constitutes a major obstacle to the sequencing of fucosylated glycans. Using Infrared ion spectrosopy, we resolve the molecular structure of fucosylated fragments of four Lewis and Blood Group H antigen trisaccharides. Our findings suggest that fucose migration, which was reported decades ago, results in fragment ions, which can be fully characterized. Additionally we report a new type of fucose migration, which does not feature any internal residue loss and therefore had not been previously detected by mass spectrometry: it consists of a local type of migration, where the fucose remains on the initial residue with a change of regiochemistry. Therefore, such glycan fragments previously regarded as diagnostic carry previously undetected molecular rearrangements. Infrared ion spectroscopy enables molecular characterization of glycan fragments and this knowledge is essential to the interpretation of glycomics data, as well as the understanding of the processes underlying Mass Spectrometry analysis.

International audience; O-Acetylations are functional modifications which can be found on different hydroxyl groups of glycans and which contribute to the fine tuning of their biological activity. Localizing the acetyl modifications is notoriously challenging in glycoanalysis, in particular because of their mobility: loss or migration of the acetyl group may occur through the analytical workflow. Whereas migration conditions in the condensed phase have been rationalized, little is known about the suitability of Mass Spectrometry to retain and resolve the structure of O-acetylated glycan isomers. Here we used the resolving power of infrared ion spectroscopy in combination with ab initio calculations to assess the structure of O-acetylated monosaccharide ions in the gaseous environment of a mass analyzer. N-Acetyl glucosamines were synthetized with an O-acetyl group in positions 3 or 6, respectively. The protonated ions produced by electrospray ionization were observed by mass spectrometry and their vibrational fingerprints were recorded in the 3 μm range by IRMPD spectroscopy (InfraRed Multiple Photon Dissociation). Experimentally, the isomers show distinctive IR fingerprints. Additionally, ab initio calculations confirm the position of the O-acetylation and resolve their gas phase conformation. These findings demonstrate that the position of O-acetyl groups is retained through the transfer from solution to the gas phase, and can be identified by IRMPD spectroscopy.

We present a new experimental set-up combining ultrafast XUV technics with electrospray sources. First results of ultrafast dynamics in large molecular ions are shown demonstrating perspectives for applications in attochemistry.

International audience; 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.

Ultrafast charge, energy and structural dynamics in molecules are driven by the topology of the multidimensional potential energy surfaces that determines the coordinated electronic and nuclear motion. These processes are also strongly influenced by the interaction with the molecular environment, making very challenging a general understanding of these dynamics on a microscopic level. Here we use electrospray and mass spectrometry technologies to produce isolated molecular ions with a controlled micro-environment. We measure ultrafast photo-induced ππ*-πσ* dynamics in tryptophan species in the presence of a single, charged adduct. A striking increase of the timescale by more than one order of magnitude is observed when changing the added adduct atom. A model is proposed to rationalize the results, based on the localized and delocalized effects of the adduct on the electronic structure of the molecule. These results offer perspectives to control ultrafast molecular processes by designing the micro-environment on the Angstrom length scale. Pump-probe experiments in the gas phase usually target neutral molecules. Here the authors couple an electron spray source with ultrafast pump-probe UV-Vis spectroscopy, to follow the ππ*-πσ* coupling in tryptophan-based ions.

International audience; Sequencing glycans is demanding due to their structural diversity. Compared to mammalian glycans, bacterial glycans pose a steeper challenge because they are constructed from a larger pool of monosaccharide building blocks, including pyranose and furanose isomers. Though mammalian glycans incorporate only the pyranose form of galactose (Galp), many pathogens, including Mycobacterium tuberculosis and Klebsiella pneumoniae, contain galactofuranose (Galf) residues in their cell envelope. Thus, glycan sequencing would benefit from methods to distinguish between pyranose and furanose isomers of different anomeric configurations. We used infrared multiple photon dissociation (IRMPD) spectroscopy with mass spectrometry (MS-IR) to differentiate between pyranose- and furanose-linked galactose residues. These targets pose a challenge for MS-IR because the saccharides lack basic groups, and galactofuranose residues are highly flexible. We postulated cationic groups that could complex through hydrogen bonding would offer a solution. Here, we present the first MS-IR analysis of hexose ammonium adducts. We compared their IR fingerprints with those of lithium adducts. We determined the diagnostic MS-IR signatures of the α- and β-anomers of galactose in furanose and pyranose forms. We also showed these signatures could be applied to disaccharides to assign galactose ring size. Our findings highlight the utility of MS-IR for analyzing the unique substructures that occur in bacterial glycans.

The 2'-substituents distinguish DNA from RNA nucleosides. 2'-O-methylation occurs naturally in RNA and plays important roles in biological processes. Such 2'-modifications may alter the hydrogen-bonding interactions of the nucleoside and thus may affect the conformations of the nucleoside in an RNA chain. Structures of the protonated 2'-O-methylated pyrimidine nucleosides were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy, assisted by electronic structure calculations. The glycosidic bond stabilities of the protonated 2'-O-methylated pyrimidine nucleosides, [Nuom+H]+, were also examined and compared to their DNA and RNA nucleoside analogues via energy-resolved collision-induced dissociation (ER-CID). The preferred sites of protonation of the 2'-O-methylated pyrimidine nucleosides parallel their canonical DNA and RNA nucleoside analogues, [dNuo+H]+ and [Nuo+H]+, yet their nucleobase orientation and sugar puckering differ. The glycosidic bond stabilities of the protonated pyrimidine nucleosides follow the order: [dNuo+H]+ < [Nuo+H]+ < [Nuom+H]+. The slightly altered structures help explain the stabilization induced by 2'-O-methylation of the pyrimidine nucleosides.

Nature offers a huge diversity of glycosidic derivatives. Among numerous structural modulations, the nature of the ring size of hexosides may induce significant differences on both biological and physicochemical properties of the glycoconjugate of interest. On this assumption, we expect that small disaccharides bearing either a furanosyl entity or a pyranosyl residue would give a specific signature, even in the gas phase. On the basis of the scope of mass spectrometry, two analytical techniques to register those signatures were considered, i.e., the ion mobility (IM) and the infrared multiple photon dissociation (IRMPD), in order to build up cross-linked databases. d-Galactose occurs in natural products in both tautomeric forms and presents all possible regioisomers when linked to d-mannose. Consequently, the four reducing Gal

International audience; Nature offers a huge diversity of glycosidic derivatives. Among numerous structural modulations, the nature of the ring size of hexosides may induce significant differences on both biological and physicochemical properties of the glycoconjugate of interest. On this assumption, we expect that small disaccharides bearing either a furanosyl entity or a pyranosyl residue would give a specific signature, even in the gas phase. On the basis of the scope of mass spectrometry, two analytical techniques to register those signatures were considered, i.e., the ion mobility (IM) and the infrared multiple photon dissociation (IRMPD), in order to build up cross-linked databases. d-Galactose occurs in natural products in both tautomeric forms and presents all possible regioisomers when linked to d-mannose. Consequently, the four reducing Galf-Manp disaccharides as well as the four Galp-Manp counterparts were first synthesized according to a highly convergent approach, and IM-MS and IRMPD-MS data were second collected. Both techniques used afforded signatures, specific to the nature of the connectivity between the two glycosyl entities.

Nature offers a huge diversity of glycosidic derivatives. Amongst numerous structural modulations, the nature of the ring size of hexosides may induce significant differences on both biological and physicochemical properties of the glycoconjugate of interest. On this assumption, we expect that small disaccharides bearing either a furanosyl entity or a pyranosyl residue would give a specific signature, even in the gas phase. On the basis of the scope of mass spectrometry, two analytical techniques to register those signatures were considered, i.e. the ion-mobility (IM) and the infra-red multiple photon dissociation (IRMPD), in order to build up cross-linked databases. D-Galactose occurs in natural products in both tautomeric forms and presents all possible regioisomers when linked to D-mannose. Consequently, the four reducing Galf-Manp disaccharides as well as the four Galp-Manp counterparts were firstly synthesized according to a highly convergent approach, and IM-MS and IRMPD-MS data were secondly collected. Both techniques used afforded signatures, specific to the nature of the connectivity between the two glycosyl entities.

International audience; Precise structural differentiation of often isomeric glycans is important given their roles in numerous biological processes. Mass spectrometry (MS) (and tandem MS) is one of the analytical techniques at the forefront of glycan analysis given its speed, sensitivity in producing structural information as well as the fact it can be coupled to other orthogonal analytical techniques such as liquid chromatography (LC) and ion mobility spectrometry (IMS). This review describes another family of techniques that are more commonly being hybridized to MS(/MS) namely gas-phase infrared (IR) spectroscopy, whose rise is in part due to the development and improved accessibility of tunable IR lasers. Gas-phase IR can often differentiate fine isomeric differences ubiquitous within carbohydrates that MS may be 'blind' to. There are also examples of cryogenic gas-phase IR spectroscopy with much greater spectral resolution as well as hybridizing with separative methods (LC, IMS). Furthermore, collision-induced dissociation (CID) product ions can also be probed by IR, which may be beneficial to deconvolute spectra, aid analysis and build spectral libraries, thus generating novel opportunities for fragment-based approaches to analyze glycans.

International audience; Glycans analysis is challenging due to their immense structural diversity. Isotachophoresis was investigated as separation method for the purification of isobaric sulfated disaccharides prior to their characterization by Mass Spectrometry (MS) and tunable IR multiple photon dissociation (IRMPD). This proof of feasibility study was applied to the separation and characterization of chondroitin sulfate (CS) disaccharides. ITP separation conditions were optimized. Separation starts using a 2.5 mM chloride ions and 10 mM glycine at pH 3.2 solution as leading electrolyte and a terminating electrolyte composed of formic acid 2.5 mM and glycine 10 mM at pH 3.5. The CS disaccharides sample were prepared in the terminating electrolyte. The length of injection was also investigated in order to create longer plateau-like bands of pure solutes. This strategy was helpful for collecting fraction at such microseparation scale. Indeed, capillary ITP affords the injection of few tens of nanoliter of sample. Fractionation of the CS disaccharides mixture in isolated ITP bands and collection of solutes were successfully done using a HPC coated fused silica capillary of 1m-length and 75 µm of internal diameter. Collected fractions in a final of volume 10 µL were analyzed by CZE, tandem MS and IRMPD spectroscopy. The purity of each fraction is higher than 90% and is well-adapted to IRMPD characterization.

International audience; The gas phase IR spectra of α2,3 and α2,6 linkage isomers of sialic acid-containing human milk oligosaccharides and N-glycans epitopes are measured in the 3 µm spectral range using IRMPD spectroscopy in protonated and Na+ charge states. Each linkage isomer has a unique IRMPD fingerprint, providing a convenient diagnostic of the sialic acid position. Finally, a generic trend is observed: 3-linked sialic acid results in a significant broadening of the spectroscopic signature regardless of the glycan core and the charge state which suggests a drastic influence of the sialic acid position on the glycan conformation.

International audience; Positive ions of dimethylnitramine (DMNA), a model system for nitramine energetic molecules, have been produced in the gas phase by electrospray ionization. Protonated dimethylnitramine ion [DMNA+H]+ and its hydrated complex [2DMNA+H2O+2H]2+ have been investigated by both low energy collision induced dissociation (CID) and ab initio MP2 level of theory. Ion structure has been calculated. Fragments have been experimentally determined and dissociation mechanisms have been elucidated. Interestingly, the favored fragmentation pathways depend on the local environment of the ion: the hydrated complex primarily loses NO via nitro nitrite isomerization, while only OH elimination is observed in the case of protonated DMNA.

International audience; IR spectroscopy of gas-phase ions is proposed to resolve positional isomers of sulfated carbohydrates. Mass spectrometric fingerprints and gas-phase vibrational spectra in the near and mid-IR regions were obtained for sulfated monosaccharides, yielding unambiguous signatures of sulfated isomers. We report the first systematic exploration of the biologically relevant but notoriously challenging deprotonated state in the near IR region. Remarkably, anions displayed very atypical vibrational profiles, which challenge the well-established DFT (Density Functionnal Theory) modeling. The proposed approach was used to elucidate the sulfate patterns in glycosaminoglycans, a ubiquitous class of mammalian carbohydrates, which is regarded as a major challenge in carbohydrate structural analysis. Isomeric glycosaminoglycan disaccharides from heparin and chondroitin sources were resolved, highlighting the potential of infrared multiple photon dissociation spectroscopy as a novel structural tool for carbohydrates.

International audience; Understanding optical properties of molecular dyes is required to drive progress in molecular photonics. This requires a fundamental comprehension of the role of electronic structure, geometry, and interactions with the environment in order to guide molecular engineering strategies. In this context, we studied charged cyanine dye molecules in the gas phase with a controlled microenvironment to unravel the origin of the spectral tuning of this class of molecules. This was performed using a new approach combining femtosecond multiple-photon action spectroscopy of on-the-fly mass-selected molecular ions and high-level quantum calculations. While arguments based on molecular geometry are often used to design new polymethine dyes, we provide experimental evidence that electronic structure is of primary importance and hence the decisive criterion as suggested by recent theoretical investigations.

International audience; Hexoses are mainly found in nature in the pyranose form (6-membered ring). Yet, furanose forms (5-membered ring) are observed in some rare polysaccharides. Using IRMPD spectroscopy (InfraRed Multiple Photon Dissociation), we propose a straightforward diagnostic of the ring-size of N-acetyl galactosamine ions. The furanose form of N-acetyl galactosamine was synthesized and its protonated ion was isolated in an ion trap to measure its gas phase vibrational spectrum by IRMPD. Comparison with the IRMPD spectrum of its pyranose counterpart reveals that they have distinctive optical fingerprints. This new MS-based diagnostic opens the way to facile identification of the ring-size in oligosaccharides. Our experimental data also provide new insights to support the theoretical description of the conformational behavior of the furanose ring, which is notoriously more flexible than the pyranose form but remains difficult to assess.

Synopsis We found that the XUV excited caffeine undergoes nondadabatic cascade via more than 100 shake-up states within the time constant of 40 fs by using femtosecond XUV-NIR pump-probe photo-ion spectroscopy and the SAC-CI level of ab-initio many-body theory. This nonadiabatic cascade results in the photofragmentation to specific large fragments. Furether ionization by NIR probe during the cascade increases the small fragments CH3 +, CO+ etc. This results show that both vibronic coupling and electron correlation are the keys for the femtochemistry in the highly-correlated electronic excited states.

International audience; The gas phase IR spectra of three protonated hexosamines are measured in the 3 μm range using IRMPD spectroscopy and compared with DFT simulation of the IR spectra to identify the ring conformations and the contributions of the α and β anomers to the experimental spectra. We propose an original approach for the deconvolution and quantification of heterogeneous IR spectra based on linear combination of the DFT spectra. The method is applied to the analysis of a two-component anomeric mixture and validated using NMR analysis. Finally, we further estimate the relative populations of a three-component mixture: the anomers and conformers of glucosamine.

International audience; The chemical difference between DNA and RNA nucleosides is their 2′-hydrogen versus 2′-hydroxyl substituents. Modification of the ribosyl moiety at the 2′-position and 2′-O-methylation in particular, is common among natural post-transcriptional modifications of RNA. 2′-Modification may alter the electronic properties and hydrogen-bonding characteristics of the nucleoside and thus may lead to enhanced stabilization or malfunction. The structures and relative glycosidic bond stabilities of the protonated forms of the 2′-O-methylated purine nucleosides, 2′-O-methyladenosine (Adom) and 2′-O-methylguanosine (Guom), were examined using two complementary tandem mass spectrometry approaches, infrared multiple photon dissociation action spectroscopy and energy-resolved collision-induced dissociation. Theoretical calculations were also performed to predict the structures and relative stabilities of stable low-energy conformations of the protonated forms of the 2′-O-methylated purine nucleosides and their infrared spectra in the gas phase. Low-energy conformations highly parallel to those found for the protonated forms of the canonical DNA and RNA purine nucleosides are also found for the protonated 2′-O-methylated purine nucleosides. Importantly, the preferred site of protonation, nucleobase orientation, and sugar puckering are preserved among the DNA, RNA, and 2′-O-methylated variants of the protonated purine nucleosides. The 2′-substituent does however influence hydrogen-bond stabilization as the 2′-O-methyl and 2′-hydroxyl substituents enable a hydrogen-bonding interaction between the 2′- and 3′-substituents, whereas a 2′-hydrogen atom does not. Further, 2′-O-methylation reduces the number of stable low-energy hydrogen-bonded conformations possible and importantly inverts the preferred polarity of this interaction versus that of the RNA analogues. Trends in the CID50% values extracted from survival yield analyses of the 2′-O-methylated and canonical DNA and RNA forms of the protonated purine nucleosides are employed to elucidate their relative glycosidic bond stabilities. The glycosidic bond stability of Adom is found to exceed that of its DNA and RNA analogues. The glycosidic bond stability of Guom is also found to exceed that of its DNA analogue; however, this modification weakens this bond relative to its RNA counterpart. The glycosidic bond stability of the protonated purine nucleosides appears to be correlated with the hydrogen-bond stabilization of the sugar moiety.

International audience; The vast array of molecular isomerisms which form the complex molecular structure of carbohydrates is the foundation of their biological versatility but defies the analytical chemist. Hyphenations of mass spectrometry with orthogonal structural characterization, such as ion mobility or ion spectroscopy, have recently shown great promise for distinction between closely related molecular structures. Yet, the lack of analytical strategies for identification of isomers present in mixtures remains a major obstacle to routine carbohydrate sequencing. In this context, an ideal workflow for glycomics would combine isomer separation and individual characterization of the molecular structure with atomistic resolution. Here we report the implementation of such a multidimensional analytical strategy, which consists of the first online coupling of high-performance liquid chromatography (HPLC)-MS and infrared multiple photon dissociation (IRMPD) spectroscopy. The performance of this novel workflow is exemplified in the case of monosaccharides (anomers) and disaccharides (regioisomers) standards. We report that the LC-MS-IRMPD approach offers a robust advanced MS diagnostic of mixtures of isomers, including carbohydrate anomers, which is critical for carbohydrate sequencing. Our results also explain the bimodal character generally observed in LC chromatograms of carbohydrates. More generally, this multidimensional analytical strategy opens the gateway to rapid identification of molecular isoforms with potential application in the "omics" fields.

International audience; We report distinctive spectroscopic fingerprints of the monosaccharide standards GalNAc4S and GalNAc6S by coupling mass spectrometry and ion spectroscopy in the 3-μm range. The disaccharide standards CSA and CSC are used to demonstrate the applicability of a novel approach for the analysis of sulfate position in GalNAc-containing glycosaminoglycans. This approach was then used for the analysis of a sample containing CSA and CSC disaccharides. Finally, we discuss the generalization of the coupling of mass spectrometry with ion spectroscopy for the structural analysis of glycosaminoglycans on a tetrasaccharide from dermatan sulfate source.

International audience; Glycosaminoglycans are biopolymers present in mammalian cells or in the extracellular matrix. To address their structure, the nature of the hexuronic acids and the position of sulfate groups must be determined. Tandem mass spectrometry using collision induced dissociation or electron-based fragmentation techniques, is a well-established approach for the identification of glycans but suffers from the frequent lack of diagnostic fragments in the case of glycosaminoglycans. This review presents alternative fragmentation techniques, namely photofragmentation in the IR and the UV ranges. Alternative approaches based on the direct analysis of the molecular structure, including ion mobility spectrometry and ion spectroscopies are reviewed. The potential of future multidimensional workflows for glycosaminoglycanomics is discussed.

The fragmentation chemistry of protonated sulfoserine was probed using a combination of collision-induced dissociation (CID) mass spectrometry, infrared multiple photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The IRMPD spectra of the dominant fragment ions at m/z 106 and 88 (i.e., loss of SO3 and H2SO4) were obtained and used to determine the corresponding structures. By comparison to a synthetic standard and calculations, it was determined that the m/z 106 ion is structurally identical to protonated serine. The m/z 88 fragment ion was assigned an aziridine structure based on a comparison to theory, analogous to the structure previously proposed by others for phosphoric acid loss from phosphoserine. This work provides the first spectroscopic insights into the dissociation pathways of a sulfated amino acid, laying the groundwork for future studies on related amino acids and peptides with this important, labile post-translational modification.

International audience; Processes in atoms or molecules on the attosecond timescale have been measured using XUV attosecond and IR femtosecond pulses overlapping in time and controlled with attosecond accuracy. Within this general framework, many strategies have been developed using the harmonics of the fundamental pulse. In this paper, we focus on a specific configuration where the attosecond pulse train is composed by odd harmonics and is dressed by the second harmonic of the fundamental light. Measuring the angularly resolved photoelectron spectrum as a function of the delay between the pulses, a clear oscillation of the anisotropy parameters appears revealing attosecond controlled interferences. This process, is assigned to interferences between two quantum paths involving one XUV photon, on one path, and a XUV+UV photons on the other path. The XUV-UV delay dependent up–down asymmetry can be interpreted following the usual RABBITT formalism, where the dressing photon energy corresponds to the energy separation between the XUV photons of the attosecond pulse train. This approach allows an intuitive analysis of the interference and provides a well suited method for the study of complex valence band systems thanks to the limited congestion of the resulting spectrum.

The gas phase IR spectra of three protonated N -acetyl hexosamines and their methyl-blocked α and β anomers are measured in the 3 μm spectral range using IRMPD spectroscopy. Using molecular dynamics exploration of the conformational space followed by MP2 energy calculations and DFT simulation of the IR spectra, we propose energetic and spectroscopic arguments to elucidate (i) the site of protonation, (ii) the conformational preference of the carbohydrate ring, and (iii) the contributions of the α and β anomers to the experimental spectra. We report that protonation occurs on the carbonyl group. All isomers of N -acetyl hexosamines are observed in a 4 C 1 chair conformation regardless of the methylation at the reducing end. Subtle structural variations of this common conformation are described. Finally, anomer-diagnostic spectroscopic features are proposed for GlcNAc and ManNAc.

We propose a novel, bi-dimensional analysis of partially N-acetylated chitosan oligosaccharides based on gas phase Infra-Red spectroscopy integrated to mass spectrometry (MS). By providing simultaneously MS and IR fingerprints, this approach combines the advantages of MS with the refined structural detail offered by gas phase spectroscopy and provides robust signatures for the rapid discrimination of the patterns of N-acetylation. Four mono-N-deacetylated and two doubly-N-deacetylated chitosan tetramer standards with well-defined patterns of acetylation were produced and analyzed by IR integrated to MS. We show that each sequence displays a unique combination of MS and IR fingerprints, thus offering a rapid diagnostic for the pattern of acetylation without the need for reducing end labeling.

We report an original MS-based hyphenated method for the elucidation of the epimerization in GAG fragments. It consists of measuring simultaneously the MS/MS spectrum and the gas phase IR spectrum to gain direct structural information. This is possible using a customized MS instrument, modified to allow injection of a tunable IR laser inside of the instrument for in situ spectroscopy of trapped ions. The proof of principle of this approach is performed in the case of a hyaluronic acid tetrasaccharide standard. In addition, we provide the reference IR fingerprint of glucuronic and Iduronic monosaccharide standards. Remarkably, we show that the gas phase IR fingerprint of reference hexuronic acid monosaccharides proves to be transposable to oligosaccharides. Therefore, the method presented here is predictive and allows structural elucidation of unknown GAG fragments, even in the absence of referenced standards.

International audience; The lack of robust, high-throughput, and sensitive analytical strategies that can conclusively map the structure of glycans has significantly hampered progress in fundamental and applied aspects of glycoscience. Resolution of the anomeric α/β glycan linkage within oligosaccharides remains a particular challenge. Here, we show that “memory” of anomeric configuration is retained following gas-phase glycosidic bond fragmentation during tandem mass spectrometry (MS2). These findings allow for integration of MS2 with ion mobility spectrometry (IM-MS2) and lead to a strategy to distinguish α- and β-linkages within natural underivatized carbohydrates. We have applied this fragment-based hyphenated MS technology to oligosaccharide standards and to de novo sequencing of purified plant metabolite glycoconjugates, showing that the anomeric signature is also observable in fragments derived from larger glycans. The discovery of the unexpected anomeric memory effect is further supported by IR-MS action spectroscopy and ab initio calculations. Quantum mechanical calculations provide candidate geometries for the distinct anomeric fragment ions, in turn shedding light on gas-phase dissociation mechanisms of glycosidic linkages.

An original workflow allowing inline FAIMS separation, electrospray ionization, mass analysis and ion spectroscopy (IRMPD: InfraRed Multiple Photon Dissociation) is presented for multidimensional molecular analysis. This new instrument consists of an ultraFAIMS (Owlstone) device interfaced to a linear ion trap (LTQ XL Thermo Scientific) which was modified for IRMPD spectroscopy. Two modes of operation are demonstrated on an isomeric mixture of paracetamol and 2-phenylglycine. In the first mode a FAIMS (high-Field Asymmetric waveform Ion Mobility Spectrometry) separation of the isomers is performed with a static compensation field for mass- and isomer- selective ion spectroscopy. In the second mode, the compensation field is scanned while the ions are irradiated at a fixed wavenumber. The advantages of this workflow as compared to traditional FAIMS-MS and IRMPD spectroscopy are described. The potential of the two modes for molecular spectroscopy and analytical applications, in particular the new “omics” are discussed.

The standard velocity-map imaging (VMI) analysis relies on the simple approximation that the residual Coulomb field experienced by the photoelectron ejected from a neutral or ion system may be neglected. Under this almost universal approximation, the photoelectrons follow ballistic (parabolic) trajectories in the externally applied electric field, and the recorded image may be considered as a 2D projection of the initial photoelectron velocity distribution. There are, however, several circumstances where this approximation is not justified and the influence of long-range forces must absolutely be taken into account for the interpretation and analysis of the recorded images. The aim of this paper is to illustrate this influence by discussing two different situations involving isolated atoms or molecules where the analysis of experimental images cannot be performed without considering long-range Coulomb interactions. The first situation occurs when slow (meV) photoelectrons are photoionized from a neutral system and strongly interact with the attractive Coulomb potential of the residual ion. The result of this interaction is the formation of a more complex structure in the image, as well as the appearance of an intense glory at the center of the image. The second situation, observed also at low energy, occurs in the photodetachment from a multiply charged anion and it is characterized by the presence of a long-range repulsive potential. Then, while the standard VMI approximation is still valid, the very specific features exhibited by the recorded images can be explained only by taking into consideration tunnel detachment through the repulsive Coulomb barrier.

We have developed and tested a new time-effective and accurate hybrid QM//MM generalized second-order vibrational perturbation theory (GVPT2) approach. In this approach, two different levels of theory were used, a high level one (DFT) for computing the harmonic spectrum and a lower fast one (Molecular Mechanic) for the anharmonic corrections. To validate our approach, we used B2PLYP/def2-TZVPP as the high-level method, and the MMFF94 method for the anharmonic corrections as the low-level method. The calculations were carried out on 28 molecules (containing from 2 to 47 atoms) covering a broad range of vibrational modes present in organic molecules. We find that this fast hybrid method reproduces the experimental frequencies with a very good accuracy for organic and bio-molecules. The root-mean-square deviation (RMSD) is about 27 cm -1 while the full B3LYP/SNSD simulation reproduces the experimental values with a RMSD of about 41 cm -1. Concerning the computational time, the hybrid B2PLYP//MMFF94 approach considerably outperforms the full B3LYP/SNSD: for the larger molecule of our set (a dipeptide containing 47 atoms), the anharmonic corrections are 2300 times faster using hybrid MMFF94 rather than full B3LYP, which represents an additional computation time to the harmonic calculation of merely 9 %, instead of 32100 % with the full B3LYP approach. This time-effective and accurate alternative to the traditional GVPT2 approach will allow the spectroscopy community to explore anharmonic effects in larger biomolecules, which are generally unaffordable.

Gold(I)– and silver(I)–thiolate oligomers generated under nanoparticle growth conditions have been suggested to play an important role in the growth mechanism of thiolate-protected noble metal clusters. In this work, we explore the formation of isolated noble metal–glutathione complexes by complementing electrospray mass spectrometry and optical action spectroscopy with TDDFT calculations. We have isolated and recorded action spectra of [Au+GSH–2H]−, [Ag+GSH–2H]−, and [3Ag+2GSH–4H]− complexes. Competition between photofragmentation and photodetachment channels related to electron binding energies was observed. Our findings show that, although structural properties of silver and gold metal–glutathione oligomers are similar, their optical properties in the UV range differ substantially. The experimental spectra were interpreted and assigned by comparison with TDDFT simulations, which allowed us to identify the key role of O–metal–S subunits and characterize their optical properties depending on the choice o...

A colloidal solution of Au25(SG)18-protected metal gold clusters was electrosprayed. [Au25(SG)18-6H]7− was selected, stored in a quadrupole ion trap, and irradiated with a UV−vis tunable laser. The excess charges are due to the deprotonation of six COOH moieties and a net charge of −1 on the Au core. Photoexcitation of this species results in electron detachment. The action spectrum obtained by recording the electron detachment yield as a function of the laser wavelength displays a strong decrease as the photon energy decreases and the onset of a band at around 650 nm. This spectrum is compared with the absorption spectrum recorded for Au25(SG)18 in solution. We also show that electron detachment is a one-photon process and likely involves, at low photon energy, ionization by tunneling through a repulsive coulomb barrier.

International audience; We present a simple upgrade of a time-resolved attosecond extreme ultraviolet and infrared (XUV-IR) setup designed to perform time-resolved or spectrally resolved studies of a target under similar experimental conditions. A flat XUV grating inserted in the path of an attosecond pulse train obtained via high order harmonic generation in gases is used either in the zeroth order of diffraction to follow attosecond dynamics or in the first order of diffraction to study the target spectral response with a temporally stretched single harmonic. Electron momentum measurement is performed with a velocity map imaging spectrometer, and the 10 W femtosecond laser system operating at 5 kHz provides an XUV photon flux compatible with rapid acquisition in both the monochromatic and broadband configurations. The change of experimental configuration between broadband and monochro-matic sources is rapid and performed in situ. We present the experimental implementation applied to krypton atoms and detail the capabilities and limits of this approach when an XUV grating with constant groove density is used with a converging XUV beam.

International audience

We present the mid-IR (400-1800 cm(-1)) spectra of 9-ethyl guanine, guanosine, and 2-deoxyguanosine measured by IR-UV double-resonance spectroscopy. We compare the recorded mid-IR spectra with the spectra of the most stable structures obtained from RI-MP2 and RI-DFT-D calculations. The results confirm the enol form for all structures and demonstrate the efficacy of a new approach to DFT calculations that includes dispersion interactions.

We present a joint experimental and theoretical gas phase study of photoabsorption and photofragmentation of silver cluster-biomolecule complexes. We demonstrate on the example of [ Trp.Ag3] + that binding of the metal cluster to a biomolecule leads to a significant enhancement of the photoabsorption in comparison with [Trp.H]+ and [Trp.Ag]+. This enhancement arises due to the coupling between the excitations in the metallic subunit with charge transfer excitations between silver cluster and tryptophan. Our experimental studies show that silver clusters up to eleven atoms can be bound to tryptophan and we present first results on the photofragmentation of the Trp.Ag11 + complex cation, in which properties of cluster subunit remain preserved.

International audience; XUV induced dynamics in molecules is still largely unexplored while experimental and theoretical tools are becoming available in several labs. In this work, we present a compact XUV beamline designed to induce and probe femtosecond and attosecond dynamics in gas samples (from atoms to complex molecular species). The induced processes are studied with time-resolved photoelectron or/and photoion imaging. The characterization of the performances of the experimental setup is presented. We show experimental results obtained in naphthalene molecule showing femtosecond and attosecond time-resolved photoelectron imaging experiments allowing electron wavepacket phase measurements.

International audience; Mid-infrared spectroscopy coupled with mass spectrometry is an appealing tool for the sequencing and structural elucidation of functional modifications in biopolymers, as it offers direct spectroscopic identification of the functionality where the traditional mass spectrometric approach is insufficient. Whereas the gas phase vibrational spectroscopy of peptides (and to a lesser extent saccharides) has been widely investigated, sulfation has attracted much less attention, despite its prevalence in natural polymers. The simulation of the vibrational spectra of such functionalized compounds is however notoriously challenging, which impairs the interpretation of spectroscopic data in terms of structure. Driven by a striking case of such a failure for a sulfated glycosaminoglycan fragment, we elaborate on an original hybrid GVPT2 anharmonic approach. This strategy offers a significantly improved accuracy in the description of the sulfate modes, without the recourse to empirical scaling factors, and with a greatly reduced computational cost which is otherwise prohibitive for molecules of this size. Alternatively, we propose a selection of reasonably accurate harmonic methods with adequate scaling factors optimized on a set of benchmark compounds.

The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide-water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules.

By coupling a matrix-assisted laser desorption source to an electric beam deflection setup, we have measured the permanent electric dipole moment of the isolated p-amino benzoic acid (PABA) molecule in the ground state along its principal axis. This is the first measurement of the electric dipole of an isolated push−pull molecule. The experimental value is compared to different calculations, and the accuracy of Hartree−Fock and density functional approaches to predict the electronic properties of π-conjugated systems is discussed.