Lennard-Jones interaction parameters of Mo and W in He and N2 from collision cross-sections of Lindqvist and Keggin polyoxometalate anions.

Drift tube ion mobility spectrometry (DTIMS) coupled with mass spectrometry was used to determine the collision cross-sections (DTCCS) of polyoxometalate anions in helium and nitrogen. As the geometry of the ion, more than its mass, determines the collision cross-section with a given drift gas molecule, we found that both Lindqvist ions Mo6O192- and W6O192- had a DTCCSHe value of 103 ± 2 Å2, and both Keggin ions PMo12O403- and PW12O403- had a DTCCSHe value of 170 ± 2 Å2. Similarly, ion mobility experiments in N2 led to DTCCSN2 values of 223 ± 2 Å2 and 339 ± 4 Å2 for Lindqvist and Keggin anions, respectively. Using optimized structures and partial charges determined from density functional theory calculations, followed by CCS calculations via the trajectory method, we determined Lennard-Jones 6-12 potential parameters ε, σ of 5.60 meV, 3.50 Å and 3.75 meV, 4.40 Å for both Mo and W atoms interacting with He and N2, respectively. These parameters reproduced the CCS of polyoxometalates within 2% accuracy.

Development of a standardized in vitro approach to evaluate microphysical, chemical, and toxicological properties of combustion-derived fine and ultrafine particles.

Ultrafine particles represent a growing concern in the public health community but their precise role in many illnesses is still unknown. This lack of knowledge is related to the experimental difficulty in linking their biological effects to their multiple properties, which are important determinants of toxicity. Our aim is to propose an interdisciplinary approach to study fine (FP) and ultrafine (UFP) particles, generated in a controlled manner using a miniCAST (Combustion Aerosol Standard) soot generator used with two different operating conditions (CAST1 and CAST3). The chemical characterization was performed by an untargeted analysis using ultra-high resolution mass spectrometry. In conjunction with this approach, subsequent analysis by gas chromatography-mass spectrometry (GC-MS) was performed to identify polycyclic aromatic hydrocarbons (PAH). CAST1 enabled the generation of FP with a predominance of small PAH molecules, and CAST3 enabled the generation of UFP, which presented higher numbers of carbon atoms corresponding to larger PAH molecules. Healthy normal human bronchial epithelial (NHBE) cells differentiated at the air-liquid interface (ALI) were directly exposed to these freshly emitted FP and UFP. Expression of MUC5AC, FOXJ1, OCLN and ZOI as well as microscopic observation confirmed the ciliated pseudostratified epithelial phenotype. Study of the mass deposition efficiency revealed a difference between the two operating conditions, probably due to the morphological differences between the two categories of particles. We demonstrated that only NHBE cells exposed to CAST3 particles induced upregulation in the gene expression of IL-8 and NQO1. This approach offers new perspectives to study FP and UFP with stable and controlled properties.

A calibration framework for the determination of accurate collision cross sections of polyanions using polyoxometalate standards.

RATIONALE: Polyoxometalates (POMs) are remarkable oxo-clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N2 with drift tube ion mobility spectrometry (DTIMS). These values were then used to calibrate a traveling wave ion mobility spectrometry (TWIMS) device and the accuracy of the calibration was tested. METHODS: Six POM standards were analyzed by DTIM-MS (Tofwerk, Thun, Switzerland) at different voltages to determine absolute DT CCS (N2 ) values. Five POM compounds (Lindqvist TBA2 Mo6 O19; decatungstate TBA4 W10 O32; Keggin TBA3 PMo12 O40 ; TBA3 PW12 O40 and Dawson TBA6 P2 W18 O62 ) were used for the calibration of the TWIM-MS instrument (Synapt G2 HDMS, Waters, Manchester, UK) and a sixth Dawson POM, TBA9 P2 Nb3 W15 O62 , was used to compare the accuracy of the calibrations with POM or with polyalanine and dextran reference ions. RESULTS: We determined 45 DT CCS (N2 ) values at 30°C or 60°C. Fourteen DT CCS (N2 ) values at 30°C were used to perform calibration of the TWIMS instrument. Better correlations were observed than when DT CCS values in helium from the literature were used. The accuracy tests on six ions of Dawson POM TBA9 P2 Nb3 W15 O62 led to relative errors below 3.1% while relative errors of 3.6% to 10.1% were observed when calibration was performed with polyalanine and dextran reference ions. CONCLUSIONS: Our novel calibration strategy for determination of CCS values of multiply negatively charged ions on TWIM-MS devices based on DT CCS (N2 ) of standard POM structures covered a wider range of CCS and improved the accuracy to 2.1% relative error on average compared with 6.9% using polyalanine and dextran calibration.

Charge Effect on the Formation of Polyoxometalate-Based Supramolecular Polygons Driven by Metal Coordination.

The metal-driven self-assembly of a Keggin-based hybrid bearing two remote pyridine units was investigated. The resulting supramolecular species were identified by combination of 2D diffusion NMR spectroscopy (DOSY) and electrospray ionization mass spectrometry (ESI-MS) as a mixture of molecular triangles and squares. This behavior is different from that of the structural analogue Dawson-based hybrid displaying a higher charge, which only led to the formation of molecular triangles. This study highlights the decisive effect of the charge of the POMs in their self-assembly processes that disfavors the formation of large assemblies. An isothermal titration calorimetry (ITC) experiment confirmed the stronger binding in the case of the Keggin hybrids. A correlation between the diffusion coefficient D and the molecular mass M of the POM-based building block and its coordination oligomers was also observed. We show that the diffusion coefficient of these compounds is mainly determined by their occupied volume rather than by their shape.

IRMPD Spectroscopy: Evidence of Hydrogen Bonding in the Gas Phase Conformations of Lasso Peptides and their Branched-Cyclic Topoisomers.

Lasso peptides are natural products characterized by a mechanically interlocked topology. The conformation of lasso peptides has been probed in the gas phase using ion mobility-mass spectrometry (IM-MS) which showed differences in the lasso and their unthreaded branched-cyclic topoisomers depending on the ion charge states. To further characterize the evolution of gas phase conformations as a function of the charge state and to assess associated changes in the hydrogen bond network, infrared multiple photon dissociation (IRMPD) action spectroscopy was carried out on two representative lasso peptides, microcin J25 (MccJ25) and capistruin, and their branched-cyclic topoisomers. For the branched-cyclic topoisomers, spectroscopic evidence of a disruption of neutral hydrogen bonds were found when comparing the 3+ and 4+ charge states. In contrast, for the lasso peptides, the IRMPD spectra were found to be similar for the two charge states, suggesting very little difference in gas phase conformations upon addition of a proton. The IRMPD data were thus found consistent and complementary to IM-MS, confirming the stable and compact structure of lasso peptides in the gas phase.

Ion mobility-mass spectrometry of lasso peptides: signature of a rotaxane topology.

Ion mobility mass spectrometry data were collected on a set of five class II lasso peptides and their branched-cyclic topoisomers prepared in denaturing solvent conditions with and without sulfolane as a supercharging agent. Sulfolane was shown not to affect ion mobility results and to allow the formation of highly charged multiply protonated molecules. Drift time values of low charged multiply protonated molecules were found to be similar for the two peptide topologies, indicating the branched-cyclic peptide to be folded in the gas phase into a conformation as compact as the lasso peptide. Conversely, high charge states enabled a discrimination between lasso and branched-cyclic topoisomers, as the former remained compact in the gas phase while the branched-cyclic topoisomer unfolded. Comparison of the ion mobility mass spectrometry data of the lasso and branched-cyclic peptides for all charge states, including the higher charge states obtained with sulfolane, yielded three trends that allowed differentiation of the lasso form from the branched-cyclic topology: low intensity of highly charged protonated molecules, even with the supercharging agent, low change in collision cross sections with increasing charge state of all multiply protonated molecules, and narrow ion mobility peak widths associated with the coexistence of fewer conformations and possible conformational changes.

Gas-phase conformations of capistruin - comparison of lasso, branched-cyclic and linear topologies.

RATIONALE: Capistruin is a peptide synthesized by Burkholderia thailandensis E264, which displays a lasso topology. This knot-like structure confers interesting properties to peptides (e.g. antibacterial). Therefore, it is important to evaluate the sensitivity of structural characterization methods to such topological constraints. METHODS: Ion mobility mass spectrometry (IMS-MS) experiments, using both drift tube and travelling wave instruments, were performed on lasso capistruin and on peptides with the same sequence, but displaying a branched-cyclic (un-threaded) or linear topology. Molecular dynamics (MD) simulations were then performed to further interpret the IMS results in terms of conformation. RESULTS: The collision cross sections (CCSs) measured via IMS for the different forms of capistruin were found to be similar, despite their different topologies for the doubly charged species, but significant differences arise as the charge state is increased. MD simulations for the doubly charged linear peptide were consistent with the hypothesis that salt bridges are present in the gas phase. Moreover, through CCS measurements for peptides with site-specific mutations, the arginine residue at position 11 was found to play a major role in the stabilization of compact structures for the linear peptide. CONCLUSIONS: Differences in peptide topologies did not yield marked signatures in their respective IMS spectra. Such signatures were only visible for relatively high charge states, that allow Coulomb repulsion to force unfolding. At low charge states, the topologically unconstrained linear form of capistruin was found to adopt charge solvation-constrained structures, possibly including salt bridges, with CCSs comparable to those measured for the topologically constrained lasso form.

Exploration of polyamide structure-property relationships by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: Polyamides (PA) are among the most used classes of polymers because of their attractive properties. Depending on the nature and proportion of the co-monomers used for their synthesis, they can exhibit a very large range of melting temperatures (Tm ). This study aims at the correlation of data from mass spectrometry (MS) with differential scanning calorimetry (DSC) and X-ray diffraction analyses to relate molecular structure to physical properties such as melting temperature, enthalpy change and crystallinity rate. METHODS: Six different PA copolymers with molecular weights around 3500 g mol(-1) were synthesized with varying proportions of different co-monomers (amino-acid AB/di-amine AA/di-acid BB). Their melting temperature, enthalpy change and crystallinity rate were measured by DSC and X-ray diffraction. Their structural characterization was carried out by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Because of the poor solubility of PA, a solvent-free sample preparation strategy was used with 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix and sodium iodide as the cationizing agent. RESULTS: The different proportions of the repeating unit types led to the formation of PA with melting temperatures ranging from 115°C to 185°C. The structural characterization of these samples by MALDI-TOF-MS revealed a collection of different ion distributions with different sequences of repeating units (AA, BB; AB/AA, BB and AB) in different proportions according to the mixture of monomers used in the synthesis. The relative intensities of these ion distributions were related to sample complexity and structure. They were correlated to DSC and X-ray results, to explain the observed physical properties. CONCLUSIONS: The structural information obtained by MALDI-TOF-MS provided a better understanding of the variation of the PA melting temperature and established a structure-properties relationship. This work will allow future PA designs to be monitored.

PyC2MC: An Open-Source Software Solution for Visualization and Treatment of High-Resolution Mass Spectrometry Data.

Complex molecular mixtures are encountered in almost all research disciplines, such as biomedical 'omics, petroleomics, and environmental sciences. State-of-the-art characterization of sample materials related to these fields, deploying high-end instrumentation, allows for gathering large quantities of molecular composition data. One established technological platform is ultrahigh-resolution mass spectrometry, e.g., Fourier-transform mass spectrometry (FT-MS). However, the huge amounts of data acquired in FT-MS often result in tedious data treatment and visualization. FT-MS analysis of complex matrices can easily lead to single mass spectra with more than 10,000 attributed unique molecular formulas. Sophisticated software solutions to conduct these treatment and visualization attempts from commercial and noncommercial origins exist. However, existing applications have distinct drawbacks, such as focusing on only one type of graphic representation, being unable to handle large data sets, or not being publicly available. In this respect, we developed a software, within the international complex matrices molecular characterization joint lab (IC2MC), named "python tools for complex matrices molecular characterization" (PyC2MC). This piece of software will be open-source and free to use. PyC2MC is written under python 3.9.7 and relies on well-known libraries such as pandas, NumPy, or SciPy. It is provided with a graphical user interface developed under PyQt5. The two options for execution, (1) a user-friendly route with a prepacked executable file or (2) running the main python script through a Python interpreter, ensure a high applicability but also an open characteristic for further development by the community. Both are available on the GitHub platform (https://github.com/iC2MC/PyC2MC_viewer).

Use of procaine and procainamide as derivatizing co-matrices for the analysis of oligosaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: Analysis of oligosaccharides by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry often yields only alkali metal cation adducts, which results in lower fragmentation yields and difficulty to retrieve sequence information. Derivatization by reductive amination may be used to promote Y-type glycosidic cleavages. However, this involves time-consuming preparations and purifications with sample loss. Here, procaine and procainamide were used directly as co-matrices with 2,5-dihydroxybenzoic acid (DHB). METHODS: Acidified 10 g/L procaine hydrochloride or procainamide hydrochloride solutions in water/acetonitrile were added to the oligosaccharide solution one minute before preparing our MALDI targets using DHB with the dried-droplet method. This simple protocol resulted in deposits of very fine homogeneous crystals. RESULTS: Positive ion mass spectra, easily acquired in an automated mode, presented a high percentage of oligosaccharides derivatized as Schiff base or glycosylamine notably detected as protonated molecules [M + H](+). The high abundance of procaine or procainamide on the target did not impede the ionization process, improved the signal-to-noise ratio and eliminated the need to search for 'sweet spots'. Fragmentation of the protonated precursor ions of the derivatives largely favored Y-type glycosidic cleavages. CONCLUSIONS: This easy and fast sample preparation, involving low toxicity and easily accessible chemicals, allowed the selection of protonated molecules as precursor ions for post-source decay analyses. This opened the possibility of simplifying sequence retrieval in routine oligosaccharide analyses.

Ultrafine Particles Issued from Gasoline-Fuels and Biofuel Surrogates Combustion: A Comparative Study of the Physicochemical and In Vitro Toxicological Effects.

Gasoline emissions contain high levels of pollutants, including particulate matter (PM), which are associated with several health outcomes. Moreover, due to the depletion of fossil fuels, biofuels represent an attractive alternative, particularly second-generation biofuels (B2G) derived from lignocellulosic biomass. Unfortunately, compared to the abundant literature on diesel and gasoline emissions, relatively few studies are devoted to alternative fuels and their health effects. This study aimed to compare the adverse effects of gasoline and B2G emissions on human bronchial epithelial cells. We characterized the emissions generated by propane combustion (CAST1), gasoline Surrogate, and B2G consisting of Surrogate blended with anisole (10%) (S+10A) or ethanol (10%) (S+10E). To study the cellular effects, BEAS-2B cells were cultured at air-liquid interface for seven days and exposed to different emissions. Cell viability, oxidative stress, inflammation, and xenobiotic metabolism were measured. mRNA expression analysis was significantly modified by the Surrogate S+10A and S+10E emissions, especially CYP1A1 and CYP1B1. Inflammation markers, IL-6 and IL-8, were mainly downregulated doubtless due to the PAHs content on PM. Overall, these results demonstrated that ultrafine particles generated from biofuels Surrogates had a toxic effect at least similar to that observed with a gasoline substitute (Surrogate), involving probably different toxicity pathways.

Collision Cross Sections of Phosphoric Acid Cluster Anions in Helium Measured by Drift Tube Ion Mobility Mass Spectrometry.

In the last years, ion mobility mass spectrometry (IMS-MS) has improved structural analysis and compound identification by giving access to the collision cross section (CCS). An increasingly wide and accurate database of CCS values is now available but often without assessment of the influence of different instrumental settings on CCS values. Here, we present 75 CCS values in helium (DTCCSHe) for phosphoric acid cluster anions [(H3PO4)n - zH]z- with charge state (z) up to 4-. The CCS values, noted DTCCSHe, were obtained with a commercial drift tube ion mobility mass spectrometer, in helium, by applying a classic multifield approach. Phosphoric acid clusters are fragile structures that allow to evaluate the effect of different experimental conditions on the retention of weak bonds and their effect on CCS values. We probed harsh and soft voltage gradients in the electrospray (ESI) source before the IMS and two different voltage gradients in the post-IMS region. The variations in the ion mobility and mass spectra consisted in a change in the distribution of the cluster anions aggregation numbers (n) and charge states (z), with a higher amount of multiply charged species for the soft pre-IMS voltage gradient and a lower proportion of cluster dissociation for soft post-IMS conditions. However, the CCS values did not change with experimental conditions for a given cluster, as long as it stays intact from the IMS to the mass analyzer. The DTCCSHe were found in good agreement among 3 to 10 replicated values, with a relative standard deviation between 0.1 and 1.7%.

Direct Inlet Probe Atmospheric Pressure Photo and Chemical Ionization Coupled to Ultrahigh Resolution Mass Spectrometry for the Description of Lignocellulosic Biomass.

Lignocellulosic biomass, in particular wood, is a complex mixture containing cellulose, hemicellulose, lignin, and other trace compounds. Chemical analysis of these biomasses, especially lignin components, is a challenge. Lignin is a highly reticulated polymer that is poorly soluble and usually requires chemical, enzymatic, or thermal degradation for its analysis. Here, we studied the thermal degradation of lignocellulosic biomass using a direct insertion probe (DIP). The DIP was used with two ionization sources: atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) coupled to ultrahigh-resolution mass spectrometry. Beech lignocellulosic biomass samples were used to develop the DIP-APCI/APPI methodology. Two other wood species (maple and oak) were analyzed after optimization of DIP parameters. The two ionization sources were compared at first and showed different responses toward beech samples, according to the source specificity. APPI was more specific to lignin degradation compounds, whereas APCI covered a larger variety of oxygenated compounds, e.g., fatty acids and polyphenolics compounds, in addition to lignin degradation products. The study of the thermodesorption profile gave information on the different steps of lignocellulosic biomass pyrolysis. The comparison of the three feed sample types (oak, maple, and beech), using principal component analysis (PCA) with DIP-APCI experiments, showed molecular level differences between beech wood pellets and the two other wood species (maple and oak).

Particulate inorganic salts and trace element emissions of a domestic boiler fed with five commercial brands of wood pellets.

Pellet stoves arouse a real interest from consumers because they are perceived as a renewable and carbon neutral energy. However, wood combustion can contribute significantly to air pollution, in particular through the emission of particulate matter (PM). In this article, five brands of wood pellets were burnt under optimal combustion conditions and trace element and inorganic salt emission factors (EFs) in PM were determined. Results show that a significant proportion of metals such as lead, zinc, cadmium, and copper initially present in pellets were emitted into the air during combustion with 20 ± 6%, 31 ± 12%, and 19 ± 6% of the initial content respectively for Zn, Pb, and Cd. The median emission factors for Pb, Cu, Cd, As, Zn, and Ni were respectively 188, 86, 9.3, 8.7, 2177, and 3.5 µg kg-1. The inorganic fraction of the PM emissions was dominated by K+, SO42-, and Cl- with respective EFs of 33, 28.7, and 11.2 mg kg-1. Even taking into account a consumption of 40.1 million tons by 2030 in the EU, the resulting pollution in terms of heavy metal emissions remains minimal in comparison with global emissions in the EU.

Signatures of Mechanically Interlocked Topology of Lasso Peptides by Ion Mobility-Mass Spectrometry: Lessons from a Collection of Representatives.

Lasso peptides are characterized by a mechanically interlocked structure, where the C-terminal tail of the peptide is threaded and trapped within an N-terminal macrolactam ring. Their compact and stable structures have a significant impact on their biological and physical properties and make them highly interesting for drug development. Ion mobility - mass spectrometry (IM-MS) has shown to be effective to discriminate the lasso topology from their corresponding branched-cyclic topoisomers in which the C-terminal tail is unthreaded. In fact, previous comparison of the IM-MS data of the two topologies has yielded three trends that allow differentiation of the lasso fold from the branched-cyclic structure: (1) the low abundance of highly charged ions, (2) the low change in collision cross sections (CCS) with increasing charge state and (3) a narrow ion mobility peak width. In this study, a three-dimensional plot was generated using three indicators based on these three trends: (1) mean charge divided by mass (ζ), (2) relative range of CCS covered by all protonated molecules (ΔΩ/Ω) and (3) mean ion mobility peak width (δΩ). The data were first collected on a set of twenty one lasso peptides and eight branched-cyclic peptides. The indicators were obtained also for eight variants of the well-known lasso peptide MccJ25 obtained by site-directed mutagenesis and further extended to five linear peptides, two macrocyclic peptides and one disulfide constrained peptide. In all cases, a clear clustering was observed between constrained and unconstrained structures, thus providing a new strategy to discriminate mechanically interlocked topologies. Graphical Abstract ᅟ.

Toward a Rational Design of Highly Folded Peptide Cation Conformations. 3D Gas-Phase Ion Structures and Ion Mobility Characterization.

Heptapeptide ions containing combinations of polar Lys, Arg, and Asp residues with non-polar Leu, Pro, Ala, and Gly residues were designed to study polar effects on gas-phase ion conformations. Doubly and triply charged ions were studied by ion mobility mass spectrometry and electron structure theory using correlated ab initio and density functional theory methods and found to exhibit tightly folded 3D structures in the gas phase. Manipulation of the basic residue positions in LKGPADR, LRGPADK, KLGPADR, and RLGPADK resulted in only minor changes in the ion collision cross sections in helium. Replacement of the Pro residue with Leu resulted in only marginally larger collision cross sections for the doubly and triply charged ions. Disruption of zwitterionic interactions in doubly charged ions was performed by converting the C-terminal and Asp carboxyl groups to methyl esters. This resulted in very minor changes in the collision cross sections of doubly charged ions and even slightly diminished collision cross sections in most triply charged ions. The experimental collision cross sections were related to those calculated for structures of lowest free energy ion conformers that were obtained by extensive search of the conformational space and fully optimized by density functional theory calculations. The predominant factors that affected ion structures and collision cross sections were due to attractive hydrogen bonding interactions and internal solvation of the charged groups that overcompensated their Coulomb repulsion. Structure features typically assigned to the Pro residue and zwitterionic COO-charged group interactions were only secondary in affecting the structures and collision cross sections of these gas-phase peptide ions. Graphical Abstract ᅟ.

Traveling wave ion mobility mass spectrometry and ab initio calculations of phosphoric acid clusters.

Positive and negative ion electrospray mass spectra obtained from 50 mM phosphoric acid solutions presented a large number of phosphoric acid clusters: [(H3PO4)n + zH](z+) or [(H3PO4)n - zH](z-), with n up to 200 and z up to 4 for positively charged clusters, and n up to 270 and z up to 7 for negatively charged cluster ions. Ion mobility experiments allowed very explicit separation of the different charge states. Because of the increased pressures involved in ion mobility experiments, dissociation to smaller clusters was observed both in the trap and transfer areas. Voltages along the ion path could be optimized so as to minimize this effect, which can be directly associated with the cleavage of hydrogen bonds. Having excluded the ion mobility times that resulted from dissociated ions, each cluster ion appeared at a single drift time. These drift times showed a linear progression with the number of phosphoric atoms for cluster ions of the same charge state. Cross section calculations were carried out with MOBCAL on DFT optimized geometries with different hydrogen locations and with three types of atomic charges. DFT geometry optimizations yielded roughly spherical structures. Our results for nitrogen gas interaction cross sections showed that values were dependent on the atomic charges definition used in the MOBCAL calculation. This pinpointed the necessity to define a clear theoretical framework before any comparative interpretations can be attempted with uncharacterized compounds.

Sodium-tolerant matrix for matrix-assisted laser desorption/ionization mass spectrometry and post-source decay of oligonucleotides.

A mixture of 2',4',6'-trihydroxyacetophenone in acetonitrile and aqueous triammonium citrate solution in a 1:1 molar proportion (0.2 M concentration) was found to be a good matrix for the detection of synthetic oligodeoxynucleotide samples. A high proportion of volatile solvent as well as the high salt content ensure fast co-crystallization of the matrix, co-matrix and analyte molecules. Matrix-assisted laser desorption/ionization (MALDI) mass spectra obtained in negative ion reflectron mode from samples prepared with this protocol show deprotonated molecules [M - H](-), rather than sodium adducts, as the most abundant ions even when up to 50 mM of sodium chloride is present in the sample. The matrix is shown to be effective for low mass modified single nucleotides as well as for longer oligodeoxynucleotides (up to 18mer). Post-source decay (PSD) mass spectra can also be obtained by increasing the laser fluence. Simple sequence information such as the identity and localization of a deleted base or the 5'/3' orientation can then easily be obtained. The calibration method and mass accuracy required are discussed depending on the type of information required.

Novel Mo(V)-dithiolene compounds: characterization of nonsymmetric dithiolene complexes by electrospray ionization mass spectrometry.

Three new Mo(V) dithiolene compounds have been synthesized by addition of alkynes ((Me(3)Si)(2)C(2) (TMSA), (Me(3)Si)(2)C(4), and (Ph)(2)C(4) to MoO(2)S(2)(2-) in a MeOH/NH(3) mixture: [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(2))](2)(-) 1, [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(C(2)Ph))](2-) 2 (X = O or S), and [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(C(2)H))](2-) 3. The structure of 1 as determined by single-crystal X-ray diffraction study (space group Pbca, a = 13.3148(1) A, b = 15.7467(4) A, c = 28.4108(7) A, V = 5956.7(2) A(3)) is discussed. 2 and 3 have been identified by ESMS (electrospray mass spectrometry), (1)H NMR, (13)C NMR, and infrared spectroscopies. This investigation completes our previous study devoted to the addition of DPA (C(2)Ph(2)) to MoO(2)S(2)(2-) which led to [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(2))](2-) 4 (X = O or S). A reaction scheme is proposed to explain the formation of the different species present in solution. The reactivity of the remaining nucleophilic site of these complexes (eta(2)-S(2)) toward dicarbomethoxyacetylene (DMA) is also discussed.

New organosilyl derivatives of the Dawson polyoxometalate [alpha2-P2W17O61(RSi)2O]6-: synthesis and mass spectrometric investigation.

In the field of functionalized polyoxometalates, organosilyl derivatives of polyoxotungstate constitute a special class of hybrid organic-inorganic system. The first organosilyl derivative of the monovacant Dawson heteropolyoxotungstate [alpha2-P2W17O61]10- was obtained by three different methods. The use of two organosilanes as reagents enabled the preparation of the functionalized polyoxometalate [alpha2-P2W17O61(RSi)2O]6- in good yield. Electrospray (ESI-MS) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and 183W, 31P, and 29Si NMR spectroscopy were used to characterize the composite systems. In several cases, ESI-MS analyses generated reduction processes which were compared to those related to [PMo11VO40]4-, the highly reducible Keggin polyoxometalate.