Violette Haldys

Identification of selenocompounds in yeast by electrospray quadrupole-time of flight mass spectrometryElectronic supplementary information (ESI) available: electrospray TOFMS spectra of fractions III and I of the SEC?HPLC, Figs. A?C. See http://www.rsc.org/suppdata/ja/b2/b201015c/

The performance of a quadrupole-time of flight (Q-TOF) tandem mass spectrometer was evaluated for the identification of low-molecular weight selenocompounds in an aqueous yeast extract. The accuracy of mass measurements, evaluated with selenomethionine, selenoethionine and selenocystine standards was found to be between 0.005 and 0.01% (0.01–0.02 u). The low molecular weight fraction was obtained by collecting selenocompounds eluted in the total volume of a G-15 size-exclusion column. The fraction gave three peaks in anion-exchange HPLC of which the identity was investigated by ES-Q-TOFMS/MS. Altogether, eight clusters with the isotopic pattern corresponding to the presence of Se were observed. They were further investigated by collision induced dissociation TOFMS leading to the demonstration of the presence of a series of new selenocompounds, all characterized by the presence of an adenosyl functional group.

Factorial design optimization of experimental variables in preconcentration of carbamates pesticides in water samples using solid phase extraction and liquid chromatography-electrospray-mass spectrometry determination.

An experimental design was applied for the optimization of extraction process of carbamates pesticides from surface water samples. Solid phase extraction (SPE) of carbamates compounds and their determination by liquid chromatography coupled to electrospray mass spectrometry detector were considered. A two level full factorial design 2(k) was used for selecting the variables which affected the extraction procedure. Eluent and sample volumes were statistically the most significant parameters. These significant variables were optimized using Doehlert matrix. The developed SPE method included 200mg of C-18 sorbent, 143.5 mL of water sample and 5.5 mL of acetonitrile in the elution step. For validation of the technique, accuracy, precision, detection and quantification limits, linearity, sensibility and selectivity were evaluated. Extraction recovery percentages of all the carbamates were above 90% with relative standard deviations (R.S.D.) in the range of 3-11%. The extraction method was selective and the detection and quantification limits were between 0.1 and 0.5 µg L(-1), and 1 and 3 µg L(-1), respectively.

Gas-phase reactivity of glycosides and methyl glycosides with Cu + , Ag + and Pb 2+ ions by fast-atom bombardment and tandem mass spectrometry

The analytical potential of the complexation of three isomeric monosaccharides (D-glucose, D-galactose, D-fructose)and two methyl glycosides (O-methyl-α-D-glucose and O-methyl-β-D-glucose)by three metal ions, Ag+, Cu+ and Pb2+, has been investigated by fast-atom bombardment (FAB)ionization and tandem mass spectrometry. Our results have shown that the unimolecular reactivity of Ag+ complexes allows the characterization of the C(4)stereochemistry of the pyranose ring, whereas a distinction between D-glucose and D-fructose is not achieved. On the other hand, each of the three [Cu + monosaccharide]+ complexes exhibits specific dissociation patterns. We have also observed that Pb2+ ions induce the richest reactivity and are of particular interest for the identification of the three isomers. Finally, this study has demonstrated that the stereochemistry of the anomeric center of O-methyl-D-glucose is easily determined by reaction with Ag+ or Pb2+ ions. Several mechanisms are proposed to account for the main fragmentations of cationized glucose.

Gas‐Phase Interactions between Lead(II) Ions and Cytosine: Tandem Mass Spectrometry and Infrared Multiple‐Photon Dissociation Spectroscopy Study

Gas-phase interactions between Pb(2+) ions and cytosine (C) were studied by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory (DFT) calculations. Both singly and doubly charged complexes were generated by electrospray. The [Pb(C)-H](+) complex was extensively studied, and this study shows that two structures, involving the interaction of the metal with the deprotonated canonical keto-amino tautomer of cytosine, are generated in the gas phase; the prominent structure is the bidentate form involving both the N1 and O2 electronegative centers. The DFT study also points out a significant charge transfer from the nucleobase to the low-lying p orbitals of the metal and a strong polarization of the base upon complexation. The various potential energy surfaces explored to account for the fragmentation observed are consistent with the high abundance of the [PbNH2](+) fragment ion.

Structures of [M(Ura‐H)(H2O)n]+ (M = Mg, Ca, Sr, Ba; n = 1–3) complexes in the gas phase by IRMPD spectroscopy and theoretical studies

The structures of singly and doubly (and for Mg, triply) hydrated group 2 metal dications bound to deprotonated uracil were explored in the gas phase using infrared multiple photon dissociation spectroscopy in the mid-infrared region (1000-1900 cm(-1) ) and the O-H/N-H stretching region (2700-3800 cm(-1) ) in a Fourier transform ion cyclotron resonance mass spectrometer. The infrared multiple photon dissociation spectra were then compared with the computed IR spectra for various isomers. Calculations were performed using B3LYP with the 6-31 + G(d,p) basis set for all atoms except Ba(2+) and Sr(2+) , for which the LANL2DZ or the def2-TZVPP basis sets with relativistic core potentials were used. Atoms-in-molecules analysis was conducted for all lowest energy structures. The lowest energy isomers in all cases are those in which the one uracil is deprotonated at the N3 position, and the metal is coordinated to the N3 and O4 of uracil. Regardless of the degree of solvation, all water molecules are bound to the metal ion and participate in a hydrogen bond with a carbonyl of the uracil moiety.

Ni+ Reactions with Aminoacrylonitrile, A Species of Potential Astrochemical Relevance

The reaction of aminoacrylonitrile, a species of astrochemical interest, with Ni(+)((2)D(5/2)) was investigated by means of mass spectrometry techniques and density functional theory calculations. The dominant fragmentations in the MIKE spectrum correspond to the loss of [C2,N,H3], HCN, and NH3, the loss of H2 being very minor. The structure and bonding of the different aminoacrylonitrile-Ni(+) complexes were investigated at the B3LYP/6-311G(d,p) level of theory. The same approach was employed in our survey of the corresponding potential energy surface. This survey indicates that the [C2,N,H3] neutral product can be formed either as ketenimine (CH2CNH) or acetonitrile. The formation of the latter is significantly more exothermic but involves slightly higher activation barriers; so very likely, both isomers are produced along the reaction process. The lost of HNC is not competitive with the loss of HCN, because when the former is formed the products lie higher in energy and the corresponding mechanisms involve energy barriers above the entrance channel. The loss of NH3 is associated with the formation of a complex between cyanoacetylene, HCCCN, which is very abundant in the interstellar media, and Ni(+).

Characterization of Protonated Model Disaccharides from Tandem Mass Spectrometry and Chemical Dynamics Simulations

The fragmentation mechanisms of prototypical disaccharides have been studied herein by coupling tandem mass spectrometry (MS) with collisional chemical dynamics simulations. These calculations were performed by explicitly considering the collisions between the protonated sugar and the neutral target gas, which led to an ensemble of trajectories for each system, from which it was possible to obtain reaction products and mechanisms without pre-imposing them. The β-aminoethyl and aminopropyl derivatives of cellobiose, maltose, and gentiobiose were studied to observe differences in both the stereochemistry and the location of the glycosidic linkage. Chemical dynamics simulations of MS/MS and MS/MS/MS were used to suggest some primary and secondary fragmentation mechanisms for some experimentally observed product ions. These simulations provided some new insights into the fundamentals of the unimolecular dissociation of protonated sugars under collisional induced dissociation conditions.

Gas-phase interactions of organotin compounds with glycine: Gas-phase interactions of organotins with glycine

Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H](+) and [(R)3Sn(Gly)](+) ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)](+) ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn](+) carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H](+) complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH](+) (-57 u),[(R)2SnNH2](+) (-58 u) and [(R)2SnH](+) (-73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH](+) and [(R2)SnNH2](+) ions. Interestingly, formation [(R)2SnH](+) ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H](+) complexes, a preferable bidentate interaction of the type η(2)-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn](+) ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes.

Specific reactivity of 1-alkenes with transition metal cations: 1-Pentene– and 1-octene–Cu+ reactions in the gas phase

Abstract The topology of the potential energy surface associated with 1-pentene–Cu + and 1-octene–Cu + was investigated through the use of high-level density functional theory calculations. This theoretical survey, together with a combination of tandem mass spectrometry and isotopic labeling experiments carried out for 1-octene, confirm that the pseudo-insertion mechanism tentatively proposed by Fordham et al. [J. Mass Spectrom. 34 (1999) 1007], is the most favorable one. In this mechanism, attachment of the metal cation to the π-system forces a folding of the alkyl chain which favors the formation of an hexa-coordinated intermediate much more stable than the complexes formed along a typical dissociative attachment process. We have also shown that the main features of the pseudo-insertion mechanism do not change when the alkyl chain attached to the CC double bond is much longer. Hence, we can safely conclude from our calculations and the experimental results obtained for 1-octene deuterated derivatives, that this mechanism would explain, in general, the specific reactivity of Cu + with alkenes. We have also shown that the minor loss of H 2 systematically observed in these gas-phase processes, would be related with the ability of Cu + to yield strong agostic interactions either with the methylene groups or with the terminal methyl group of the alkyl chain.

Gas-phase reactivity of copper cations with ketones

Gas-phase ion–molecule reactions between copper ions and ketones were investigated. Organometallic adducts were prepared using a chemical ionisation/fast-atom bombardment source. Abundant pseudo-molecular ion adducts were observed in the Cu+-chemical ionisation mass spectra and their unimolecular decompositions were studied by tandem mass spectrometry. Mass-analysed ion kinetic energy spectroscopy revealed diagnostic fragmentation patterns. Losses of alkenes, losses of alkanes and dehydrogenation and dehydration reactions were observed, as well as eliminations of CuR (R = C n H2n + 1). The rich reaction chemistry of the cationised ketones enabled differentiation of the majority of the linear and branched ketone isomers studied. Isotope-labelled derivatives were employed to elucidate fragmentation mechanisms.