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International audience; The Gram-negative bacterium Neisseria meningitidis asymptomatically colonizes the throat of 10 to 30% of the human population, but throat colonization can also act as the port of entry to the blood (septicemia) and then the brain (meningitis). Colonization is mediated by filamentous organelles referred to as type IV pili, which allow the formation of bacterial aggregates associated with host cells. We found that proliferation of N. meningitidis in contact with host cells increased the transcription of a bacterial gene encoding a transferase that adds phosphoglycerol onto type IV pili. This unusual posttranslational modification specifically released type IV pili-dependent contacts between bacteria. In turn, this regulated detachment process allowed propagation of the bacterium to new colonization sites and also migration across the epithelium, a prerequisite for dissemination and invasive disease.

International audience; High-dosage buprenorphine (BUP) consumed concomitantly with benzodiazepines (BZDs) including flunitrazepam (FZ) may cause life-threatening respiratory depression despite a BUP ceiling effect and BZDs' limited effects on ventilation. However, the mechanism of BUP/FZ interaction remains unknown. We hypothesized that BUP may alter the disposition of FZ active metabolites in vivo, contributing to respiratory toxicity. Plasma FZ, desmethylflunitrazepam (DMFZ), and 7-aminoflunitrazepam (7-AFZ) concentrations were measured using gas chromatography-mass spectrometry. Intravenous BUP 30 mg/kg pretreatment did not alter plasma FZ and 7-AFZ kinetics in Sprague-Dawley rats infused with 40 mg/kg FZ over 30 min, whereas resulting in a three-fold increase in the area under the curve (AUC) of DMFZ concentrations compared with control (p < 0.01). In contrast, BUP did not significantly modify plasma DMFZ concentrations after intravenous infusion of 7 mg/kg DMFZ, whereas resulting in a similar peak concentration to that generated from 40 mg/kg FZ administration. Regarding the effects on ventilation, BUP (30 mg/kg) as well as its combination with FZ (0.3 mg/kg) significantly increased PaCO(2), whereas only BUP/FZ combination decreased PaO(2) (p < 0.001). Interestingly, FZ (40 mg/kg) but not DMFZ (40 mg/kg) significantly increased PaCO(2) (p < 0.05), whereas DMFZ but not FZ decreased PaO(2) (p < 0.05). Thus, decrease in PaO(2) appears related to BUP-mediated effects on DMFZ disposition, although increases in PaCO(2) relate to direct BUP/FZ additive or synergistic dynamic interactions. We conclude that combined high-dosage BUP and FZ is responsible for increased respiratory toxicity in which BUP-mediated alteration in DMFZ disposition may play a significant role.

The importance of protein glycosylation in the interaction of pathogenic bacteria with their host is becoming increasingly clear. Neisseria meningitidis , the etiological agent of cerebrospinal meningitis, crosses cellular barriers after adhering to host cells through type IV pili. Pilin glycosylation genes ( pgl ) are responsible for the glycosylation of PilE, the major subunit of type IV pili, with the 2,4-diacetamido-2,4,6-trideoxyhexose residue. Nearly half of the clinical isolates, however, display an insertion in the pglBCD operon, which is anticipated to lead to a different, unidentified glycosylation. Here the structure of pilin glycosylation was determined in such a strain by “top-down” MS approaches. MALDI-TOF, nanoelectrospray ionization Fourier transform ion cyclotron resonance, and nanoelectrospray ionization quadrupole TOF MS analysis of purified pili preparations originating from N. meningitidis strains, either wild type or deficient for pilin glycosylation, revealed a glycan mass inconsistent with 2,4-diacetamido-2,4,6-trideoxyhexose or any sugar in the databases. This unusual modification was determined by in-source dissociation of the sugar from the protein followed by tandem MS analysis with collision-induced fragmentation to be a hexose modified with a glyceramido and an acetamido group. We further show genetically that the nature of the sugar present on the pilin is determined by the carboxyl-terminal region of the pglB gene modified by the insertion in the pglBCD locus. We thus report a previously undiscovered monosaccharide involved in posttranslational modification of type IV pilin subunits by a MS-based approach and determine the molecular basis of its biosynthesis.

BACKGROUND: Selective fetoscopic laser coagulation of the intertwin anastomotic chorionic vessels is the first-line treatment for twin-twin transfusion syndrome. However, in stage 1 twin-twin transfusion syndrome, the risks of intrauterine surgery may be higher than those of the natural progression of the condition. OBJECTIVE: This study aimed to compare immediate surgery and expectant follow-up in stage 1 twin-twin transfusion syndrome. STUDY DESIGN: We conducted a multicentric randomized trial, which recruited from 2011 to 2018 with a 6-month postnatal follow-up. The study was conducted in 9 fetal medicine centers in Europe and the Unites States. Asymptomatic women with stage 1 twin-twin transfusion syndrome between 16 and 26 weeks' gestation, a cervix of >15 mm, and access to a surgical center within 48 hours of diagnosis were randomized between expectant management and immediate surgery. In patients allocated to immediate laser treatment, percutaneous laser coagulation of anastomotic vessels was performed within 72 hours. In patients allocated to expectant management, a weekly ultrasound follow-up was planned. Rescue fetoscopic coagulation of anastomoses was offered if the syndrome worsened as seen during a follow-up, either because of progression to a higher Quintero stage or because of the maternal complications of polyhydramnios. The primary outcome was survival at 6 months without severe neurologic morbidity. Severe complications of prematurity and maternal morbidity were secondary outcomes. RESULTS: The trial was stopped at 117 of 200 planned inclusions for slow accrual rate over 7 years: 58 women were allocated to expectant management and 59 to immediate laser treatment. Intact survival was seen in 84 of 109 (77%) expectant cases and in 89 of 114 (78%) (P=.88) immediate surgery cases, and severe neurologic morbidity occurred in 5 of 109 (4.6%) and 3 of 114 (2.6%) (P=.49) cases in the expectant and immediate surgery groups, respectively. In patients followed expectantly, 24 of 58 (41%) cases remained stable with dual intact survival in 36 of 44 (86%) cases at 6 months. Intact survival was lower following surgery than for the nonprogressive cases, although nonsignificantly (78% and 71% following immediate and rescue surgery, respectively). CONCLUSION: It is unlikely that early fetal surgery is of benefit for stage 1 twin-twin transfusion syndrome in asymptomatic pregnant women with a long cervix. Although expectant management is reasonable for these cases, 60% of the cases will progress and require rapid transfer to a surgical center. ispartof: AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY vol:224 issue:5 ispartof: location:United States status: published

International audience; Ultra-small 1-2 nm gold nanoparticles (NP) were conjugated with a poorly-soluble peptide auto-antigen, associated with type 1 diabetes, to modify the peptide pharmacokinetics, following its intradermal delivery. Peptide distribution was characterized, in vivo, after delivery using either conventional intradermal injection or a hollow microneedle device. The poorly-soluble peptide was effectively presented in distant lymph nodes (LN), spleen and draining LN when conjugated to the nanoparticles, whereas peptide alone was only presented in the draining LN. By contrast, nanoparticle conjugation to a highly-soluble peptide did not enhance in vivo distribution. Transfer of both free peptide and peptide-NPs from the skin to LN was reduced in mice lacking lymphoid homing receptor CCR7, suggesting that both are actively transported by migrating dendritic cells to LN. Collectively, these data demonstrate that intradermally administered ultra-small gold nanoparticles can widen the distribution of poorly-soluble auto-antigenic peptides to multiple lymphoid organs, thus enhancing their use as potential therapeutics.

Background Older persons are particularly exposed to adverse events from medication. Among the various strategies to reduce polypharmacy, educational approaches have shown promising results. We aimed to evaluate the impact on medication consumption, of a booklet designed to aid physicians with prescriptions for elderly nursing home residents. Methods Among 519 nursing homes using an electronic pill dispenser, we recorded the daily number of times that a drug was administered for each resident, over a period of 4 years. The intervention group comprised 113 nursing homes belonging to a for-profit geriatric care provider that implemented a booklet delivered to prescribers and pharmacists and specifically designed to aid with prescriptions for elderly nursing home residents. The remaining 406 nursing homes where no such booklet was introduced comprised the control group. Data were derived from electronic pill dispensers. The effect of the intervention on medication consumption was assessed with multilevel regression models, adjusted for nursing home status. The main outcomes were the average daily number of times that a medication was administered and the number of drugs with different presentation identifier codes per resident per month. Results 96,216 residents from 519 nursing homes were included between 1 January 2011 and 31 December 2014. The intervention group and the control group both decreased their average daily use of medication (− 0.05 and − 0.06). The booklet did not have a statistically significant effect (exponentiated difference-in-differences coefficient 1.00, 95% confidence interval 0.99–1.02, P = .45). Conclusion We observed an overall decrease in medication consumption in both the control and intervention groups. Our analysis did not provide any evidence that this reduction was related to the use of the booklet. Other factors, such as national policy or increased physician awareness, may have contributed to our findings.

International audience; The present study aimed to explore the potential antioxidant molecules of the Asian hornet venom (Vespa velutina nigrithorax) responsible for radical scavenging activity and human keratinocyte protection against oxidative stress. We developed a first technical platform that combined a DPPH radical scavenging chemical assay and cytotoxicity and ROS (reactive oxygen species) production in HaCaT keratinocyte cells exposed to UVB to evaluate the antioxidant property of V. velutina venom. We further employed Thin Layer Chromatography (TLC) combined with the DPPH assay as a targeted separation approach to isolate the antioxidant compounds responsible for the free radical scavenging property of V. velutina venom. In parallel, the latter was fractionated by a HPLC-DAD non-targeted separation approach. From this experiment, nine fractions were generated which were again evaluated separately for their antioxidant properties using DPPH assays. Results showed that only one fraction exhibited significant antioxidant activity in which serotonin was identified as the major compound by a UHPLC-ESI-QTOF HRMS/MS approach. We finally demonstrated, using purified serotonin molecule that this bioactive structure is mostly responsible for the free radical scavenging property of the crude venom as evidenced by DPPH and ROS assays in HaCaT cells exposed to UVB.

The present study describes the synthesis of the first phenoxycalix[4]pyrrole-epichlorohydrin based polymer. The advantage of the latter resides in its fast-single step synthesis protocol, low cost, water insolubility and its unexpected anion extraction capacity. The study of this polymer by various solid/liquid extractions with halides in aqueous solutions and quantitative ion chromatography analysis showed that unlike other calix[4]pyrrole-based entities, this polymer extracts iodide rather than bromide and fluoride owing to the presence of large extraction pockets. Evidence of an anion exchange process involving preferably chloride and bromide was also highlighted.

International audience; Experimental infrared multiple-photon dissociation (IRMPD) spectra recorded for a series of deprotonated dicarboxylic acids, HO 2 (CH 2) n CO À 2 (n = 2-4), are interpreted using a variety of computational methods. The broad bands centered near 1600 cm À 1 can be reproduced neither by static vibrational calculations based on quantum chemistry nor by a dynamical description of individual structures using the many-body polar-izable AMOEBA force field, strongly suggesting that these molecules experience dynamical proton sharing between the two carboxylic ends. To confirm this assumption, AMOEBA was combined with a two-state empirical valence-bond (EVB) model to allow for proton transfer in classical molecular dynamics simulations. Upon suitable parametrization based on ab initio reference data, the EVB-AMOEBA model satisfactorily reproduces the experimental infrared spectra, and the finite temperature dynamics reveals a significant amount of proton sharing in such systems.

Liquid chromatography coupled to tandem mass spectrometry-based targeted absolute protein quantification (in fmol of the analyte protein per μg of total protein) is employed for the molecular characterization of the blood-brain barrier using isolated brain microvessels. Nevertheless, the heterogeneity of the sample regarding the levels of different cells co-isolated within the microvessels and bovine serum albumin (BSA) contamination (from buffers) are not always evaluated. We developed an unlabeled targeted liquid chromatography coupled to tandem mass spectrometry method to survey the levels of endothelial cells (ECs), astrocytes, and pericytes, as well as BSA contaminant in rat cortical microvessels. Peptide peak identities were evaluated using a spectral library and chromatographic parameters. Sprague-Dawley rat microvessels obtained on three different days were analyzed with this method complemented by an absolute quantification multiple reaction monitoring method for transporter proteins P-gp, Bcrp, and Na+ /K+ ATPase pump using stable isotope labeled peptides as internal standard. Inter-day differences in the cell markers and BSA contamination were observed. Levels of cell markers correlated positively between each other. Then, the correlation between cell marker proteins and transporter proteins was evaluated to choose the best EC marker protein for protein quantification normalization. The membrane protein Pecam-1 showed a very high correlation with the EC-specific transporter P-gp (Pearson product-moment correlation coefficient (r) > 0.89) and moderate to high with Bcrp (r ≥ 0.77), that can be found also in pericytes and astrocytes. Therefore, Pecam-1 was selected as a marker for the normalization of the quantification of the proteins of endothelial cells.

International audience; Aromatic enynes can be transformed into arylnaphthalenes or benzofulvenes depending on the reaction conditions. Under gold(I) catalysis, exclusive or major 6-endo-dig cyclization took place leading to arylnaphthalenes. However, a catalytic system based on palladium iodide/1,3-Bis(diphenylphosphino)propane, in the presence of cesium carbonate as a base was necessary to furnish exclusively 5-exo-dig cyclization pattern, regardless to the electronic effects of the substituents. In the latter transformation, a mechanistic study (Kinetic Isotopic Effect, Density Functional Theory) involving a C-H activation is suggested for the exclusive benzofulvenes formation.

International audience; The widespread occurrence of chlorinated herbicides and their degradation products in the aquatic environment raises health and environmental concerns. As a consequence pesticides, and to a lesser degree their degradation products, are monitored by authorities both in surface waters and drinking waters. In this study the formation of degradation products from ultraviolet (UV) treatment of the three chloroacetamide herbicides acetochlor, alachlor and metolachlor and their biological effects were investigated. UV treatment is mainly used for disinfection in water and wastewater treatments. First, the chemical structures of the main UV-degradation products were identified using gas chromatography coupled with mass spectrometry and liquid chromatography-mass spectrometry. The main transformation reactions were dechlorination, mono- and multi-hydroxylation and cyclizations. The ecotoxicity of the mixed photoproducts formed by UV-treatment until 90% of the original pesticide was converted was compared to the toxicity of chloroacetamides using the green alga Pseudokirchneriella subcapitata, the crustacean Daphnia magna and the marine bacteria Vibrio fischeri as test organisms. UV-treatment of alachlor and metolachlor increased the toxicity compared to the parent compounds while an equal toxicity was found for photolysis products of acetochlor. This suggests that toxic photodegradation products are generated from chloroacetamides under UV-treatment. An important perspective of this finding is that the photolysis products are at least as toxic as the parent compounds. © 2013 Elsevier B.V. All rights reserved.

International audience; There is high prospect that derivatives of pentazole can lead to high energy density materials. However these molecules are potentially hazardous because of their high formation enthalpies and weak N-N bonds. In order to devise efficient protocols, possible schemes for the synthesis of nitro and azido derivatives of pentazole, and their mono- and di-oxides, have been explored using quantum chemical methods. Reaction pathways have been investigated in detail, with particular emphasis on locating transition states and on obtaining a reliable treatment of solvent effects. Oxidation by ozone is found to be a favorable process, leading to some regioselectivity in favor of b-mono-oxides. Nitration by NO2+BF4- is also predicted to be favorable. In contrast the electrochemical azidation of N5- and its oxidized derivatives is found to be energetically inaccessible. Combination of the individual addition and oxidation steps leads to recommendations for future synthetic work. Finally the kinetic stability of products with respect to N2 and N2O elimination is assessed.

International audience; Cellulose paper degradation products forming in the “tideline” area at the wet-dry interface of pure cellulose paper were analyzed using gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and high-resolution electrospray ionization-mass spectrometry (ESI-MS, LTQ Orbitrap) techniques. Different extraction protocols were employed in order to solubilize the products of oxidative cellulose decomposition, i.e., a direct solvent extraction or a more laborious chromophore release and identification (CRI) technique aiming to reveal products responsible for paper discoloration in the tideline area. Several groups of low molecular weight compounds were identified, suggesting a complex pathway of cellulose decomposition in the tidelines formed at the cellulose-water-oxygen interface. Our findings, namely the appearance of a wide range of linear saturated carboxylic acids (from formic to nonanoic), support the oxidative autocatalytic mechanism of decomposition. In addition, the identification of several furanic compounds (which can be, in part, responsible for paper discoloration) plus anhydro carbohydrate derivatives sheds more light on the pathways of cellulose decomposition. Most notably, the mechanisms of tideline formation in the presence of molecular oxygen appear surprisingly similar to pathways of pyrolytic cellulose degradation. More complex chromophore compounds were not detected in this study, thereby revealing a difference between this short-term tideline experiment and longer-term cellulose aging.

Amino acid residue-specific backbone and side-chain dissociations of peptide z ions in MS3 spectra were elucidated for over 40 pentapeptides with arginine C-terminated sequences of the AAXAR and AAHXR type, nonapeptides of the AAHAAXX"AR and AAHAXAX"AR type, and AAHAAXX"AAR decapeptides. Peptide z n ions containing amino acid residues with readily transferrable benzylic or tertiary β-hydrogen atoms (Phe, Tyr, His, Trp, Val) underwent facile backbone cleavages to form dominant z n-2 or z n-3 ions. These backbone cleavages are thought to be triggered by a side-chain β-hydrogen atom transfer to the z ion Cα radical site followed by homolytic dissociation of the adjacent Cα–CO bond, forming x n-2 cation-radicals that spontaneously dissociate by loss of HNCO. Amino acid residues that do not have readily transferrable β-hydrogen atoms (Gly, Ala) do not undergo the z n → z n-2 dissociations. The backbone cleavages compete with side-chain dissociations in z ions containing Asp and Asn residues. Side-chain dissociations are thought to be triggered by α-hydrogen atom transfers that activate the Cβ–Cγ or Cβ–heteroatom bonds for dissociations that dominate the MS3 spectra of z ions from peptides containing Leu, Cys, Lys, Met, Ser, Arg, Glu, and Gln residues. The Lys, Arg, Gln, and Glu residues also participate in γ-hydrogen atom transfers that trigger other side-chain dissociations.

International audience; Studies of peptide fragment ion structures are important to aid in the accurate kinetic modeling and prediction of peptide fragmentation pathways for a given sequence. Peptide b(2)(+) ion structures have been of recent interest. While previously studied b(2)(+) ions that contain only aliphatic or simple aromatic residues are oxazolone structures, the HA b(2)(+) ion consists of both oxazolone and diketopiperazine structures. The structures of a series of histidine-analogue-containing Xxx-Ala b(2)(+) ions were studied by using action infrared multiphoton dissociation (IRMPD) spectroscopy, fragment ion hydrogen-deuterium exchange (HDX), and density functional theory (DFT) calculations to systematically probe the influence of different side chain structural elements on the resulting b(2)(+) ion structures formed. The b(2)(+) ions studied include His-Ala (HA), methylated histidine analogues, including π-methyl-HA and τ-methyl-HA, pyridylalanine (pa) analogues, including 2-(pa)A, 3-(pa)A, and 4-(pa)A, and linear analogues, including diaminobutanoic acid-Ala (DabA) and Lys-Ala (KA). The location and accessibility of the histidine π-nitrogen, or an amino nitrogen on an aliphatic side chain, were seen to be essential for diketopiperazine formation in addition to the more typical oxazolone structure formation, while blocking or removal of the τ-nitrogen did not change the b(2)(+) ion structures formed. Linear histidine analogues, DabA and KA, formed only diketopiperazine structures, suggesting that a steric interaction in the HisAla case may interfere with the complete trans-cis isomerization of the first amide bond that is necessary for diketopiperazine formation.

International audience; Infrared multiphoton dissociation (IRMPD) spectroscopy, using a free-electron laser, and ion mobility measurements, using both drift-cell and traveling-wave instruments, were used to investigate the structure of gas-phase peptide (AAHAL + 2H)(2+) ions produced by electrospray ionization. The experimental data from the IRMPD spectra and collisional cross section (Ω) measurements were consistent with the respective infrared spectra and Ω calculated for the lowest-energy peptide ion conformer obtained by extensive molecular dynamics searches and combined density functional theory and ab initio geometry optimizations and energy calculations. Traveling-wave ion mobility measurements were employed to obtain the Ω of charge-reduced peptide cation-radicals, (AAHAL + 2H)(+●), and the c(3), c(4), z(3), and z(4) fragments from electron-transfer dissociation (ETD) of (AAHAL + 2H)(2+). The experimental Ω for the ETD charge-reduced and fragment ions were consistent with the values calculated for fully optimized ion structures and indicated that the ions retained specific hydrogen bonding motifs from the precursor ion. In particular, the Ω for the doubly protonated ions and charge-reduced cation-radicals were nearly identical, indicating negligible unfolding and small secondary structure changes upon electron transfer. The experimental Ω for the (AAHAL + 2H)(+●) cation-radicals were compatible with both zwitterionic and histidine radical structures formed by electron attachment to different sites in the precursor ion, but did not allow their distinction. The best agreement with the experimental Ω was found for ion structures fully optimized with M06-2X/6-31+G(d,p) and using both projection approximation and trajectory methods to calculate the theoretical Ω values. © 2012 American Chemical Society

International audience; A new synthetic approach to hexahydroisoindol-4-ones is reported, based on the formal [3+2] cyclization reaction between N-arylsulfonylimines and cyclic conjugated dienes, under phosphine catalysis. Key substrates are 3-vinylcyclohex-2-enones with electron-withdrawing substituents (ester, amido, cyano, phosphoryl and keto groups) on the exocyclic double bond, which afford the three atom synthons for the construction of the pyrroline ring. Total syn stereoselectivity is observed in these annulations. The scope of the reaction has been demonstrated and mechanistic issues are considered, based on deuteration experiments and DFT calculations.

International audience; Aromatic substitution reactions of selected ionized benzenes derivatives (chlorobenzene, nitrobenzene, dimethylphtalates) and phenoxy cation using neutral methyl isocyanide as a nucleophile are shown to efficiently occur in the gas phase. Nitrilium ions are produced in high abundance during these processes. These reactions have been performed in the hexapole collision cell of a large-scale hybrid tandem mass spectrometer. Computed 298 K enthalpy diagrams at the B3LYP/6-31+G(d,p) level of theory confirm the exothermic formation of the N-methylbenzonitrilium ions starting with ionized chloro- and nitrobenzene molecular ions. In this last case, two other exothermic processes are also detected: (i) an oxygen atom transfer yielding ionized nitrosobenzene and neutral methyl isocyanate and (ii) a loss of carbon monoxide from the ion/molecule reaction product generated when metastably generated phenoxy cations (produced in the hexapole collision cell) react with methyl isocyanide. Using extended theoretical calculations, several reaction pathways have been derived. The behavior of the three isomeric dimethyl phthalates has been investigated in the same way.

International audience; The electronic structures, as well as spectroscopic and thermodynamic properties of the title Pu@M12 clusters, are considered at the density functional theory level. In both cases, a Pu2+ ion is encapsulated in an icosahedral, stanna-or plumbaspherene M2-12 cage. As suggested before forM= Pb, both systems are reported to follow a 32-electron principle for the central atom. © 2010 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.

International audience; The interaction of Mn2+, being in three possible spin states, with glycine has been studied using quantum chemical calculations in the gas phase. Seven modes of interaction have been considered in all cases. Investigation of manganese complexes having various possible spin state including high, intermediate and low spins shows that the most stable complexes are high spin (total electron spin S = 5/2). Calculations show that the most stable mode of binding involves the simultaneous interaction of Mn2+ with two oxygen atoms of the zwitterionic conformers of glycine (eta(2)-O,O (CO2-)), while the second preferred binding site consists of chelation between the carbonyl oxygen and the amino nitrogen (eta(2)-O,N). These results indicate that the relative affinity of Mn2+ and the glycine zwitterion makes this isomer of glycine more stable than others, even though it is not stable in its isolated form. The results are in accord with those of previous reports for some doubly charged cations and in some cases with monocations. The nature of the interaction between manganese metal cation and glycine is also discussed employing natural population and molecular orbital analyses. It has been found that electrostatics contribution plays a crucial role in this interaction. Complexation energy (D-0) of the low lying energy isomer, for the most stable sextet spin state, has been obtained as about 156 kcal/mol. It has also been shown that the computed vibrational frequencies could aid in identification of the most stable Mn2+-glycine complex.

International audience; The chemistry leading to the competitive eliminations of H, CH(3), and OCOCH(3) from adducts of ionized methyl benzoate and neutral methyl isocyanide has been explored using density functional theory molecular orbital calculations. The energies of the various reactants and transition structures were estimated at the B3LYP/6-31+G(d,p) level of theory. Nucleophilic aromatic substitution is proposed to account for the H and OCOCH(3) eliminations. The corresponding sigma-complex intermediates, B(1ipso) and B(1ortho), are stable species lying in deep energy wells situated 70 and 120 kJ/mol, respectively, below the reactants, ionized methyl benzoate and methyl isocyanide. The latter complex, B(1ortho), may be also at the origin of a multistep rearrangement involving hydrogen migrations and methyl elimination from the original methoxy group of the benzoate moiety.

International audience; Proton affinity, PA(Glu), and protonation entropy (i.e., the difference Delta(p)S(o)(Glu) = S(o)(GluH(+)) - S(o)(Glu)) of glutamic acid have been experimentally determined by the extended kinetic method using electrospray ionization triple quadrupole-time-of-flight (ESI-Q-TOF) tandem mass spectrometry. The values deduced from these experiments are PA(Glu) = 945.3 +/- 2.8(5.8) kJ x mol(-1) and Delta(p)S(o)(Glu) = -28 +/- 4(9) J x mol(-1) x K(-1) thus leading to a gas-phase basicity, GB(Glu), of 904.4 +/- 3.0(6.4) kJ x mol(-1) (uncertainties are standard deviation and, in parentheses, 95% confidence limit). Theoretical calculations performed at the G3MP2B3 level provide information on the structures, conformations, and energetics of the neutral and protonated species. Thermochemical data are calculated at this level and include a correction to the computation of the entropy associated with hindered rotation. When the lowest energy conformers of protonated and neutral glutamic acid are considered the following values are calculated: PA(Glu) = 948.1 kJ x mol(-1) and Delta(p)S(o)(Glu) = -31.3 J x mol(-1) x K(-1). Using G3MP2B3 data to estimate the gas-phase distribution of conformers at 298 K, the averaged molar quantities becomes PA(Glu) = 949.8 kJ x mol(-1) and Delta(p)S(o)(Glu) = -36.0 J x mol(-1) x K(-1). Both computations give comparable GB(Glu) = 906.4-906.7 kJ x mol(-1).

International audience; The goal of this work was to obtain a detailed insight on the gas-phase protonation energetic of adenosine using both mass spectrometric experiments and quantum chemical calculations. The experimental approach used the extended kinetic method with nanoelectrospray ionization and collision-induced dissociation tandem mass spectrometry. This method provides experimental values for proton affinity, PA(adenosine) = 979 +/- 1 kJ.mol (-1), and for the "protonation entropy", Delta p S degrees (adenosine) = S degrees (adenosineH +) - S degrees (adenosine) = -5 +/- 5 J.mol (-1).K (-1). The corresponding gas-phase basicity is consequently equal to: GB(adenosine) = 945 +/- 2 kJ.mol (-1) at 298K. Theoretical calculations conducted at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level, including 298 K enthalpy correction, predict a proton affinity value of 974 kJ.mol (-1) after consideration of isodesmic proton transfer reactions with pyridine as the reference base. Moreover, computations clearly showed that N3 is the most favorable protonation site for adenosine, due to a strong internal hydrogen bond involving the hydroxyl group at the 2' position of the ribose sugar moiety, unlike observations for adenine and 2'-deoxyadenosine, where protonation occurs on N1. The existence of negligible protonation entropy is confirmed by calculations (theoretical Delta p S degrees (adenosine) approximately -2/-3 J.mol (-1).K (-1)) including conformational analysis and entropy of hindered rotations. Thus, the calculated protonation thermochemical properties are in good agreement with our experimental measurements. It may be noted that the new PA value is approximately 10 kJ.mol (-1) lower than the one reported in the National Institute of Standards and Technology (NIST) database, thus pointing to a correction of the tabulated protonation thermochemistry of adenosine.

International audience; The gas-phase basicity (GB), proton affinity (PA), and protonation entropy (DeltapS degrees (M)=S degrees (MH+)-S degrees (M)) of arginine (Arg) have been experimentally determined by the extended kinetic method using an electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer. This method provides GB(Arg)=1004.3+/-2.2 (4.9) kJ.mol(-1) (indicated errors are standard deviations, and in parentheses, 95% confidence limits are given). Consideration of previous experimental data using a fast atom bombardment ionization tandem sector mass spectrometer slightly modifies these estimates since GB(Arg)=1005.9+/-3.1 (6.6) kJ.mol(-1). Lower limits of the proton affinity, PA(Arg)=1046+/-4 (7) kJ.mol(-1), and of the "protonation entropy", DeltapS degrees (Arg)=S degrees (ArgH+)-S degrees (Arg)=-27+/-7 (15) J.mol(-1).K(-1), are also provided by the experiments. Theoretical calculations conducted at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level, including 298 K enthalpy correction, predict a proton affinity value of ca. 1053 kJ.mol-1 after consideration of isodesmic proton-transfer reactions with guanidine as the reference base. Computations including explicit treatment of hindered rotations and mixing of conformers confirm that a noticeable entropy loss does occur upon protonation, which leads to a theoretical DeltapS degrees (Arg) term of ca. -45 J.mol(-1).K(-1). The following evaluated thermochemical parameter values are proposed: GB(Arg)=1005+/-3 kJ.mol(-1); PA(Arg)=1051+/-5 kJ.mol(-1), and DeltapS degrees (Arg)=-45+/-12 J.mol(-1).K(-1).

International audience; The structures of the sodium complexes of oligoglycines (GG-Na+, GGG-Na+) and oligoalanines (AA-Na+, AAA-Na+) have been studied by infrared spectroscopy in the gas phase. Two different experimental set-ups have been used to generate, trap and analyze the ions. In the first, the complexes were generated by MALDI and analyzed in the cell of a home built FT-ICR mass spectrometer. In the second an external electrospray source was coupled to a Paul type ion trap. Following their trapping, the ions are irradiated in both cases with intense, tunable infrared light in the 1000-2000 cm(-1) range, leading to sodium ion detachment and ion fragmentation via the absorption of multiple photons. The resulting experimental spectra are compared to theoretical linear absorption spectra to assign structures. In agreement with calculations, peptide attachment to Na+ is found to have a strong structuring effect: the lowest energy structures involve binding of all carbonyl oxygens to the cation. Detailed comparison of experimental and computed spectra shows that the IRMPD spectroscopy of such gaseous ions allows the differentiation between structures which do not have the same number of carbonyl oxygens bound to Na+, and structures in which the peptide is either wrapped around the ion or capped by it.

International audience; The sodium ion affinities of the amino acids Asn, Gln, His and Arg have been determined by experimental and computational approaches (for Asn, His and Arg). Ne-bound heterodimers with amino acid and peptide ligands (Pep(1), Pep(2)) were produced by electrospray ionization. From the dissociation kinetics of these Pep(1)-Na+-Pep(2) ions to Pep(1)-Na+ and Pep(2)-Na+, determined by collisionally activated dissociation, a ladder of relative affinities was constructed and subsequently converted to absolute affinities by anchoring the relative values to known Na+ affinities. The Na+ affinities of Asn, His and Arg, were calculated at the MP2(full)/6-311+G(2d,2p)//MP2/6-31G(d) level of ab initio theory. The resulting experimental and computed Na+ affinities are in excellent agreement with one another. These results, combined with those of our previous studies, yield the sodium ion affinities of 18 out of the 20 alpha-amino acids naturally occurring in peptides and proteins of living systems.

Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.

The prion protein (PrP) propensity to adopt different structures is a clue to its biological role. PrP oligomers have been previously reported to bear prion infectivity or toxicity and were also found along the pathway of in vitro amyloid formation. In the present report, kinetic and structural analysis of ovine PrP (OvPrP) oligomerization showed that three distinct oligomeric species were formed in parallel, independent kinetic pathways. Only the largest oligomer gave rise to fibrillar structures at high concentration. The refolding of OvPrP into these different oligomers was investigated by analysis of hydrogen/deuterium exchange and introduction of disulfide bonds. These experiments revealed that, before oligomerization, separation of contacts in the globular part (residues 127–234) occurred between the S1–H1–S2 domain (residues 132–167) and the H2–H3 bundle (residues 174–230), implying a conformational change of the S2–H2 loop (residues 168–173). The type of oligomer to be formed depended on the site where the expansion of the OvPrP monomer was initiated. Our data bring a detailed insight into the earlier conformational changes during PrP oligomerization and account for the diversity of oligomeric entities. The kinetic and structural mechanisms proposed here might constitute a physicochemical basis of prion strain genesis.

International audience; The calculation of infrared spectra by molecular dynamics simulations based on the AMOEBA polarizable force field has recently been demonstrated [Semrouni et al., J. Chem. Theory Comput., 2014, 10, 3190]. While this approach allows access to temperature and anharmonicity effects, band assignment requires additional tools, which we describe in this paper. The Driven Molecular Dynamics approach, originally developed by Bowman, Kaledin et al. [Bowman et al. J. Chem. Phys., 2003, 119, 646, Kaledin et al. J. Chem. Phys., 2004, 121, 5646] has been adapted and associated with AMOEBA. Its advantages and limitations are described. The IR spectrum of the Ac-Phe-Ala-NH 2 model peptide is analyzed in detail. In addition to differentiation of conformations by reproducing frequency shifts due to non-covalent interactions, DMD allows visualizing the temperature-dependent vibrational modes.

International audience; Pyrolysis experiments were conducted to elucidate the effects of metal chlorides on the thermal degradation of low-density polyethylene on a continuous pyrolysis temperature range of 600 degrees C to 1100 degrees C. The present work focusses on the ratio of aromatics generated on increasing the pyrolysis temperature in the presence of metal salts, iron(II), iron(III) and copper(II) chlorides. It was observed that beside alpha,omega-dienes, alpha-olefins and n-alkanes which are usually observed during the thermal decomposition of polyethylene, the level of aromatics noticeably increases with the addition of metal salts. At high temperatures, the formation of these aromatics took place in such a way that they become the major products when polyethylene is pyrolyzed in presence of FeCl(3) and CuCl(2). Quantification of the effect of metal salts has been tempted comparing the variation of the ratio of aromatics with pyrolysis temperatures. Mechanisms responsible for the formation of these aromatics in presence of metal salts have been tentatively investigated. They are proposed to result from cyclization/dehydrogenation reactions similar to those observed during the thermal decomposition of polyethylene, but with an increased efficiency due to the metal salts.

A method to separate specific and nonspecific noncovalent interactions observed in ESI mass spectra between a protein and its ligands is presented. Assuming noncooperative binding, the specific ligand binding is modeled as a statistical distribution on identical binding sites. For the nonspecific fraction we assume a statistical distribution on a large number of "nonspecific" interacting sites. The model was successfully applied to the noncovalent interaction between the protein creatine kinase (CK) and its ligands adenosine diphosphate (ADP) and adenosine triphosphate (ATP) that both exhibit nonspecific binding in the mass spectrum. The two sequential dissociation constants obtained by applying our method are K(1,diss) = 11.8 +/- 1.5 microM and K(2,diss) = 48 +/- 6 microM for ADP. For ATP, the constants are K(1,diss) = 27 +/- 7 microM and K(2,diss) = 114 +/- 27 microM. All constants are in good correlation with reported literature values. The model should be valuable for systems with a large dissociation constant that require high ligand concentrations and thus have increased potential of forming nonspecific adducts.

International audience; The thermochemical properties of some small clusters such as the (H2O)2*+ dimer have already been investigated by both experimental and theoretical methods. The recent method to selectively prepare the ammonia-water ionized dimer [NH3, H2O]*+ (and not its proton transfer isomer [NH4+, OH*]) allowed us to study its chemical reactivity. This study focuses on the charge and proton transfer pathways: Ion-molecule reactions in the cell of an FT-ICR mass spectrometer were carried out with a range of organic compounds. Examination of the reactivity of the [NH3, H2O]*+ ionized dimer versus ionization energy and proton affinity of the neutral reagents shows a threshold in the reactivity in both instances. This leads to a bracketing of thermochemical properties related to the dimer. From these experiments and in agreement with ab initio calculations, the adiabatic recombination energy of the [NH3, H2O]*+ dimer was evaluated at -9.38 +/- 0.04 eV. The proton affinity bracketing required the reevaluation of two reference gas-phase basicity values. The results, in good agreement with the calculation, lead to an evaluation of the proton affinity of the [NH2*, H2O] dimer at 204.4 +/- 0.9 kcal mol(-1). These two experimental values are respectively related to the ionization energy of NH3*+ and to the proton affinity of NH2* by the difference in single water molecule solvation energies of ionized ammonia, of neutral ammonia, and of the NH2* radical.

The thermokinetic method is applied to a set of six amino acids (glycine, alanine, proline, serine, lysine, histidine) and 30 of their di-and tri-peptides for which experimental proton transfer rate constants were available. The comparison between the presently determined gas-phase basicities, GBs, of the amino acids with values obtained from equilibrium constant determination is generally good (a mean deviation of ∼3 kJ mol−1 is observed). Derived proton affinities values are discussed. The gas-phase basicities of peptides provided by the present study correct several previously estimated values thus offering a more firm basis for structural discussion. Composite reaction efficiency curves indicate the existence, for several peptides, of at least two non-interconverting populations of protonated forms.

International audience; Na+-bound heterodimers of amino acids (AA) are produced in the gas phase by electrospray ionization (ESI). The dissociation kinetics of these AA1Na+AA2 ions are determined by collisionally activated dissociation (CAD) and converted to a ladder of relative Na+ affinities via the Cooks kinetic method. The affinities derived follow the order (kJ mol−1, relative to Gly): Gly (0), Ala (6), Val (12), Leu (13), Cys (14), Ile (15), Ser (31), Pro (35), Thr (36), Phe (37), Tyr (40), Asp (42), Glu (43), Asn (45), Trp (49), Gln (51), His (57). Absolute Na+ binding energies are estimated by anchoring the relative values to the Na+ affinity of Ala (167 kJ mol−1), measured by the same approach using Na+-bound dimers of Ala and a series of acetamide derivatives. The Na+ binding energies of the acetamide reference bases and of representative aliphatic and side-chain functionalized amino acids (Gly, Ala, Pro, Cys and Ser) are determined by ab initio theory. Experimental and ab initio affinities agree very well. The combined data show that functional side chains increase the AANa+ bond strength by providing an extra ligand to the metal ion. Aromatic and carbonyl substituents in the side chain bring about substantial increases in the Na+ binding energy, with particularly large increments observed for amide and electron-rich (N-containing) aromatic groups. A poor correlation is found between sodium ion and proton affinities, strongly suggesting that the Na+ complexes do not have salt-bridge structures involving zwitterionic amino acids (in which the most basic site is protonated). (C) 2003 Elsevier Science B.V. All rights reserved.

MH + ions from sec -alkyl m -dimethylamino ethers have been studied by MS/MS using chemical ionization (CI) and electrospray ionization (ESI). Collisionally activated dissociation (CAD) of MH + from the vicinally perdeuterated 3-hexyl ether, CH 3 CD 2 CHOArCD 2 CH 2 CH 3 , shows that alkene expulsion is >96% regioselective, yielding m / z 139 and m / z 124 fragment ions. The fact that alkene elimination is not 100% regioselective (but gives about 3% m / z 138) is attributed to a small amount of ion–neutral complex formation. CAD of MH + ions from vicinally monodeuterated ethers (the 3-hexyl-4- d 1 ether ( 1 ) and the sec -butyl-3- d 1 ether ( 2 )) demonstrates that the erythro and threo diastereomers give significantly different m / z 139: m / z 138 fragment ion intensity ratios. These intensity ratios are sufficiently reproducible that they can be used to quantitate the proportions of erythro and threo in mixtures. DFT calculations show substantial differences between the 4-center transition states for charge-remote elimination vs. alkene elimination from a neutral precursor.

International audience; The gas phase reactions of five ionized carbenes, HC-OH*+ 1, HC-NH2*+ 2, CH3-C-OH*+ 3, HO-C-OH*+ 4 and HO-C-NH2*+ 5 with different molecules are studied by FT-ICR mass spectrometry. Interaction between an ionized carbene and a molecule can yield two kinds of stable adducts, as expected from the electronic structure of the carbene radical cations, explaining the ambident reactivity of these ions. The first kind of adduct corresponds to H-bonded species (hydrogen-bridged radical cations), the second to covalent structures. Since interconversion between these adducts is generally slow, each kind of adduct leads to a particular set of reactions. The H-bonded species can be involved in the protonation of the neutral as well as in the catalyzed interconversion between the carbene and its conventional radical cation counterpart. The covalent adducts, formed by reaction of ionized carbenes with methanal and alkenes, are ß-distonic ions. Reactions with labeled propene show that the so formed distonic ions either dissociate by simple cleavage or undergo rearrangements and H-exchange after isomerization into conventional ions by 1,4-H transfers. Cyclopropane gives a characteristic reaction of the carbene structure: addition yields a ?-distonic ion which loses ethylene. Finally, H*, I* and *SCH3 abstraction from appropriate neutrals confirms a radical reactivity of the carbenic carbon. © 2003 Published by Elsevier Science B.V.

The halonium metathesis reaction of ketones and aldehydes, C=O + XF + → C=F + + X=O is difficult to harness for three reasons: (1) the interchange of F + for O is so exothermic that the C=F + product ion often decomposes further; (2) the adduct of XF + to the carbonyl oxygen frequently undergoes side reactions to the virtual exclusion of metathesis; and (3) the metathesis ion is liable to rearrange to a mixture of isomers. Several approaches have been explored to make this reaction a useful source of gaseous fluoroalkyl cations. DFT calculations reinforce the intuition that cyclopentenone should give a good yield of metathesis ions in its ion–molecule reaction with CF3 + , an expectation that is borne out by experiment. Other approaches have met with less dramatic success. Variation of XF + gives a number of interesting results, but little improvement over CF3 + . Deuterium substitution at the carbon adjacent to the carbonyl (-position) does not restrain further decomposition, but deuteration of the next carbon (-position) does appear to do so. The isotopic labeling experiments indicate that the prevalent mode of decomposition requires hydrogen shift followed by a 1,3-elimination of HF. Observed side reactions of adduct ions include alkene expulsion to yield CF3-containing products (such as m/z 125 from the reaction of cycloalkanones with CF3 + ) and direct elimination of HF (as conjectured for the reaction of CFO + with diethyl ketone, with concurrent loss of CO2). Structures of ion–molecule reaction products can be reliably inferred only when the expected mechanism yields the minimum energy structure for that molecular formula. (Int J Mass Spectrom 222 (2003) 451–463) © 2002 Published by Elsevier Science B.V.

In the cell of an FT-ICR spectrometer, (CH3)(X)C(OCR)( + OHR ′ ) and (CH3)(X)Si(OCR) + OHR ′ (R and R′=H, CH3 or C2H5; X=H or CH3) covalent ions were generated by reaction of the (CH3)(X)+SiOCR′ cations with water or alcohols. In the so-formed covalent ions, experiment shows that 1,3-H+ transfers from oxygen to oxygen are often easy in silicon containing ions while they are not observed in the corresponding ions containing only carbon. Calculations indicate that the energy required for a 1,3-H+ transfer from oxygen to oxygen is almost identical whether the transition state contains a silicon atom or not. The greater strength of the SiO bond in cations, compared to that of the CO bond or, in other words, the great electrophilic character of cations possessing a Si+, is the main factor explaining the difference in the behavior of the studied silicon containing ions and ions containing exclusively carbon.

International audience; The first part of this work was devoted to the determination of the most sensitive GC-MS2 method for LSD detection on the ion trap apparatus. On neat samples, it has been shown that trimethylsilylation of LSD decreases the detection threshold by a factor 10 and that chemical ionization using acetonitrile as the reagent gas provides a method seven times more sensitive than electron ionization. The decomposition pathways of protonated trimethylsilylated LSD were determined owing to isotopic labeling and MSn experiments with n up to 4. The ion trap analyzer allowed the observation of intermediate ions that are not observed in triple quadrupole analysis. The resort to MS3 and MS4 experiments also permitted to show evidence of isobaric daughter ions and to attribute the corresponding structures. © 2002 Elsevier Science B.V. All rights reserved.

International audience; Competitive deamination and dehydration of protonated alpha,omega-antmoalcohols (1,2-aminoethanol (1), 1,3-aminopropanol (2), 1,4-aminobutanol (3) and 1,5-aminopentanol (4)) in the gas-phase has been examined by both tandem mass spectrometry experiments including metastable ions decompositions and collisional activation (CA) techniques and molecular orbital calculations. For all the precursor molecules 1-4, CA experiments demonstrate that the low energy product ions are either a protonated cyclic amine or a protonated cyclic ether. The mechanisms of the internal nucleophilic substitution reactions leading to these products have been detailed at the MP2/6-31G* level of theory. The thermochemistry associated with the initial protonation process of 1-4 has been examined up to the G2(MP2,SVP) level. (C) 2002 Elsevier Science B.V All rights reserved.

International audience; The thermochemical properties of seven UV-MALDI matrices and two IR-MALDI matrices were evaluated by means of ab initio molecular orbital calculations using the B3LYP functional density approach with 6-31+G(d,p) and 6-311+G(2d,2p) basis sets. These thermochemical properties include ionization energy, proton and electron affinities of neutral molecules and proton affinity of deprotonated molecules. The choosen UV-MALDI matrices are: 2,5-dihydroxybenzoic acid (2,5DHB), nicotinic acid (NA) and 2-aminonicotinic acid (2ANA), picolinic acid (PA) and 3-hydroxypicolinic acid (3HPA), 2-aminobenzoic acid (2ABA) and 4-nitroaniline (4NiAn) while the studied IR-MALDI matrices are urea (U) and glycerol (G). The proton affinities of neutral and deprotonated molecules are in very good agreement with the available experimental values (the differences between experimental and calculated values are smaller than the precision on the experimental measurements); the calculated ionization energies are close to the experimental values of adiabatic electronic transitions; the calculated electron affinities are new and cannot be compared with corresponding experimental values since they are not available. (C) 2002 Elsevier Science B.V. All rights reserved.

International audience; The presence of trace levels of organic contaminants in the environment is currently an environmental concern. When these contaminants are subjected to environmental transformations, environmental transformation products (ETPs) are obtained, whose structures often remain unknown. The absence of information concerning these new compounds makes them unavailable and consequently makes their environmental detection as well as their (eco)toxicological study impossible. This report describes a multidisciplinary approach that seeks to both anticipate the fate and evaluate the impact of organic environmental contaminants. Our approach consists of three steps. First, isolated and fully characterized transformation products (TPs) of the parent molecule are obtained. In the second step, the parent molecule is subjected to environmentally relevant transformations to identify plausible ETPs. The detection of previously characterized TPs allows the concomitant identification of plausible ETPs. The third step is devoted to the toxicological evaluation of the identified plausible ETPs. Such an approach has recently been applied to furosemide and has allowed the identification of its main TPs. This report now seeks to identify and evaluate toxicologically plausible ETPs of this drug, which is also known as an environmental contaminant.

International audience; Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) has become an important method to study protein dynamics in solution. Recently, electron-based fragmentation methods (ECD and ETD) have been utilized in HDX-MS/MS experiments as experimental tools to increase the spatial resolution (the ability to obtain deuterium levels of individual residues). An essential prerequisite for this approach is that the level of hydrogen scrambling is negligible. The occurrence of hydrogen scrambling depends critically on the extent of vibrational excitation in the mass spectrometer. In particular, the desolvation process in the electrospray ion source is likely to induce scrambling at standard operating conditions. Consequently, finding experimental conditions that minimize hydrogen scrambling to a negligible level is thus pivotal for the application of electron-based fragmentation in HDX-MS/MS experiments. In the present work, we investigate the occurrence of scrambling in the Apollo I electrospray ion source using ECD of selectively deuterium labeled peptides. The electrospray ion source settings leading to minimal scrambling were identified. Furthermore, an energy dependent loss of deuterium occurring in the ion source was also observed. This loss was critically dependent on the occurrence of scrambling.

In pathogenic bacteria post-translationally modified proteins have been found to promote bacterial survival, replication and evasion from the host immune system. In the human pathogen Neisseria meningitidis, the protein PilE (15–18 kDa) is the major building block of type IV pili, extracellular filamentous organelles that play a major role in mediating pathogenesis. Previous reports have shown that PilE can be expressed as a number of different proteoforms, each harbouring its own set of post-translational modifications (PTMs) and that specific proteoforms are key in promoting bacterial virulence. Efficient tools that allow complete PTM mapping of proteins involved in bacterial infection are therefore strongly needed. As we show in this study, a simple combination of mass profiling and bottom-up proteomics is fundamentally unable to achieve this goal when more than two proteoforms are present simultaneously. In a N. meningitidis strain isolated from a patient with meningitis, mass profiling revealed the presence of four major proteoforms of PilE, in a 1:1:1:1 ratio. Due to the complexity of the sample, a top-down approach was required to achieve complete PTM mapping for all four proteoforms, highlighting an unprecedented extent of glycosylation. Top-down mass spectrometry therefore appears to be a promising tool for the analysis of highly post-translationally modified proteins involved in bacterial virulence.

The grey mouse lemur (Microcebus murinus) is a non-human primate used to study the ageing process. Resveratrol is a polyphenol that may increase lifespan by delaying age-associated pathologies. However, no information about resveratrol absorption and metabolism is available for this primate. Resveratrol and its metabolites were qualitatively and quantitatively analyzed in male mouse-lemur plasma (after 200 mg.kg−1 of oral resveratrol) by ultra-high performance liquid chromatography (UHPLC), coupled to a quadrupole-time-of-flight (Q-TOF) mass spectrometer used in full-scan mode. Data analyses showed, in MSE mode, an ion common to resveratrol and all its metabolites: m/z 227.072, and an ion common to dihydro-resveratrol metabolites: m/z 229.08. A semi-targeted study enabled us to identify six hydrophilic resveratrol metabolites (one diglucurono-conjugated, two monoglucurono-conjugated, one monosulfo-conjugated and two both sulfo- and glucurono-conjugated derivatives) and three hydrophilic metabolites of dihydro-resveratrol (one monoglucurono-conjugated, one monosulfo-conjugated, and one both sulfo- and glucurono-conjugated derivatives). The presence of such metabolites has been already detected in the mouse, rat, pig, and humans. Free resveratrol was measurable for several hours in mouse-lemur plasma, and its two main metabolites were trans-resveratrol-3-O-glucuronide and trans-resveratrol-3-sulfate. Free dihydro-resveratrol was not measurable whatever the time of plasma collection, while its hydrophilic metabolites were present at 24 h after intake. These data will help us interpret the effect of resveratrol in mouse lemurs and provide further information on the inter-species characteristics of resveratrol metabolism.

International audience; The potential energy profile associated with CH3 and OH losses from the dimethyl sulfoxide radical cation, CH3SOCH3*+, 1, has been examined at the G2(MP2,SVP) level. Isomerization of 1 into its aci-tautomer, CH3S(OH)CH2*+, 2, by a 1,3-hydrogen migration constitutes the initial and energy-determining step of both dissociations. This explains the observation of identical appearance energies for the corresponding fragment ions. Heats of formation values of 702, 794, and 795 kJ/mol are obtained from atomization energies at the G2(MP2,SVP) level for CH2SOH+, CH3SO+, and CH2SCH3+, respectively. The kinetics of the reactions 2 CH2SCH3+ + *OH and 2 ? CH2SOH+ + *CH3 have been examined by using a RRKM-type orbiting transition state theory. Explicit consideration of the rotational effect is crucial, inducing the latter process to be dominant at a high internal energy of the precursor ions 2. This offers the reason for why the m/z 63 (CH2SOH+) ions are more abundant than the m/z 61 (CH2SCH3+) in the mass spectrum of dimethyl sulfoxide even though the OH loss represents the less energy demanding reaction.

International audience; Unimolecular deamination of protonated a,?-alkanediamines (1,2-ethanediamine (1), 1,3-propanediamine (2), 1,4-butanediamine (3), and 1,5-pentanediamine (4)) in the gas phase has been examined by tandem mass spectrometry experiments including metastable ions decompositions and collisional activation techniques and molecular orbital calculations up to the G2(MP2,SVP) level. For all the protonated molecules, only one unimolecular dissociation channel, leading to the formation of a protonated cyclic amine via an internal nucleophilic substitution, was detected. The hydride ion transfer from the a carbon to the ? position is not competitive with the internal nucleophilic substitution. This has been found to be the result of a large critical energy for this latter reaction.

International audience; The bimolecular reaction of the CH2CHOH*+ enol ion (m/z 44) with acetaldehyde gives a strongly dominant product, m/z 45, formed mainly by proton transfer from the ion to the molecule. The abundance of the product coming from a H* abstraction reaction from the neutral, albeit more exothermic, is negligible. In order to explain this result, the long lived [CH2CHOH*+, CH3CHO] solvated ion was generated by reaction of the CH2CHOH*+ enol ion with (CH3CHO)n in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. The structure of this solvated ion was clearly established. Labeling indicates that [CH2CHOH*+, CH3CHO], upon low energy collisions, reacts by H* abstraction more rapidly than by H+ transfer to the neutral moiety. This shows that the entropic factors are determinant when the enol ion reacts directly with acetaldehyde. Copyright © 2000 Elsevier

Molecular orbital calculations at the unified G2(MP2, SVP) level of theory have been used to examine the energy barrier for 1,n-hydrogen atom migrations in ionized aliphatic alcohols [H(CH2)n−1OH]·+ → [(CH2)n−1OH2]·+ (n = 2–5). A complementary set of experimental and theoretical data confirm that this approach leads to results accurate to within a few kJ mol−1. The better stability of distonic ions [(CH2)n−1OH2]·+ with respect to their classical homologs [H(CH2)n−1OH]·+ is clearly demonstrated by the calculations; it amounts to ∼30 kJ mol−1. Critical energies of 106, 90, 76, and 19 kJ mol−1 are calculated for n = 2, 3, 4, and 5, respectively. A lowering of the barrier height is observed when considering the energy barrier for 1,5 hydrogen atom migrations in ionized systems with respect to the neutral equivalent, i.e. the Barton rearrangement. Keywords: Ionized alcohols; Hydrogen migrations; Distonic ions; α2(MP2,SVP) molecular orbital calculations.