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Tandem mass spectrometry was used to explore the trends in the unimolecular fragmentation of the ionized hydroxy-substituted polycyclic aromatic hydrocarbons 1-naphthol, 9-hydroxyphenanthrene, and 1-hydroxypyrene. The main dissociation reactions across all ring systems were CO- and HCO-losses, with ionized 1-naphthol also losing H atoms. Both ionized 1-naphthol and 9-hydroxyphenanthrene displayed the sequential loss of C2H2 and C4H2 from the [M-HCO]+ ions, reminiscent of unsubstituted PAH ions. CO-loss is slightly favored for 1-naphthol and 9-hydroxyphenanthrene, at low collision energy, but less so for 1-hydroxypyrene. Reaction mechanisms for HCO- and CO-losses from 1-hydroxypyrene were derived from CCSD/6-31G(d)//B3-LYP/6-31G(d) calculations. The CO-loss mechanism is dominated by two transition states: TS-A governing a 1,3-H shift in the molecular ion and TS-C which governs a ring-closing step to form a five-member ring in the product ion. HCO-loss occurs over a much flatter potential energy surface with the intermediate being the product ion bound to the carbon atom of HCO. Imaging photoelectron photoion coincidence spectroscopy of 1-hydroxypyrene yielded threshold photon-energy resolved breakdown curves and time-of-flight distributions that were modeled with RRKM theory to give 0 K reaction energies for HCO- and CO-losses of 3.92 ± 0.05 and 2.91 ± 0.05 eV, respectively. The entropies of activation for the two channels were very different, 14 and 95 JK-1 mol-1, respectively, a result consistent with the calculated mechanisms. The threshold photoelectron spectrum yielded an IE value of 7.14 ± 0.01 eV for 1-hydroxypyrene.

Tris(2,2′-bipyridine)ruthenium(II) and similar complexes containing the 1,10-phenanthroline ligand were formed by spraying a ligand solution and a ruthenium trichloride solution through two independent electrospray (ESI) emitters. This was confirmed by comparing ion mobility drift time, mass spectra, and energy-resolved collision-induced dissociation (CID) breakdown curves with the corresponding reference standards. The complexes of 2,2′-bipyridine and 1,10-phenantroline with iron(II), and their mixed-ligand complexes formed by dual-spray exhibited two additional hydrogen atoms. By CID, these unique gas phase complexes showed similar initial ligand loss to the reference standards, however the sequential ligand loss showed unique dissociation channels and energetics. Density functional theory calculations of the [Fe(phen) 3 + 2H] 2+ complex and its fragment ions suggest that, after the initial loss of one ligand, the additional hydrogen atoms transfer to the central iron atom. The relative energy of the dissociation channels showed good agreement with experimental breakdown curves.

Emission spectra from collisions of 8 keV He + and H 2 + with neutral naphthalene, benzene, acetylene and methane were acquired over 190–1020 nm on a modified double-focusing mass spectrometer. The bands, emission intensities and the minimum excitation energy to produce the observed transitions (Emin) were compared for the two projectile ions. Emin values were the same for both projectiles but the emission intensity is greater in the case of He + . This is consistent with calculations at the CISD/6-311+G(2df) level on the excited states of the respective collision complexes which exhibited two distinct state-crossing points for He + collisions but none for H 2 + collisions.

The threshold photoelectron spectra (TPES) and ion dissociation breakdown curves for trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAN) were measured by imaging photoelectron photoion coincidence spectroscopy employing both effusive room-temperature samples and samples introduced in a seeded molecular beam. The fine structure in the breakdown diagram of TFA mirroring the vibrational progression in the TPES suggests that direct ionization to the X+ state leads to parent ions with a lower "effective temperature" than nonresonant ionization in between the vibrational progression. Composite W1U, CBS-QB3, CBS-APNO, G3, and G4 calculations yielded an average ionization energy (IE) of 11.69 ± 0.06 eV, consistent with the experimental value of 11.64 ± 0.01 eV, based on Franck-Condon modeling of the TPES. The measured 0 K appearance energies (AE0K) for the reaction forming CO2H+ + CF3 from TFA were 11.92 for effusive data and 11.94 ± 0.01 eV for molecular beam data, consistent with the calculated composite method 0 K reaction energy of 11.95 ± 0.08 eV. Together with the 0 K heats of formation (ΔfH0K) of CO2H+ and CF3, this yields a ΔfH0K of neutral TFA of -1016.6 ± 1.5 kJ mol-1 (-1028.3 ± 1.5 kJ mol-1 at 298 K). TFAN did not exhibit a molecular ion at room-temperature conditions, but a small signal was observed when rovibrationally cold species were probed in a molecular beam. The two observed dissociation channels were CF3C(O)OC(O)+ + CF3 and the dominant, sequential reaction CF3CO+ + CF3 + CO2. Calculations revealed a low-energy isomer of ionized TFAN, incorporating the three moieties CF3CO+, CF3, and CO2 joined in a noncovalent complex, mediating its unimolecular dissociation.

Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) have been considered as potential carriers of the 11.3 μm band in interstellar observations. To begin to probe their potential contribution to chemistry in the interstellar medium, we report here threshold photoelectron spectra (TPES) for seven oxygen-containing polycyclic aromatic hydrocarbons 2,3-benzofuran (BF), 2,3-dihydrobenzofuran (DHF), phthalan (PH), dibenzofuran (DBF), dibenzo(B,F)oxepine (DBO), benzo[b]naphtho[2,3-d]furan (BNF) and benzo[b]naphtho[1,2-d]furan (cBNF). Vertical ionization energies to the ground and excited ion states were calculated with the outer-valence Green’s function method, and Franck–Condon simulations, based on harmonic (time-dependent) density functional theory results, were used to explore vibrational excitation upon ionization. CBS-QB3 calculations are also reported. Adiabatic ionization energies (IE) could be measured accurately for five of the molecules: BF (8.35 ± 0.01 eV), PH (8.76 ± 0.01 eV), DBF (8.12 ± 0.02 eV), BNF (7.64 ± 0.02 eV), and cBNF (7.62 ± 0.02 eV). For BF and cBNF, excited state optimizations also allowed Franck–Condon simulations of excited-state bands. The TPES of DHF and DBO feature broad ionization onsets due to large geometry changes upon ionization, as both become planar when an electron is removed. The band maxima yield the vertical IE for these two molecules: 8.2 ± 0.2 eV and 8.0 ± 0.2 eV, respectively, while the best estimate of the adiabatic IE for DHF is 7.98 ± 0.05 eV.

Rationale Traditionally, hydrogen/deuterium exchange (HDX) reactions are done in the solution phase. This usually involves incubating the protein with a suitable deuterating agent then acidifying the solution to quench the reaction. A more efficient method may be to conduct the reaction within the ion source of a mass spectrometer and subsequently analyze the products. Methods Using the two electrospray emitters equipped on the Waters Synapt G1 mass spectrometer, HDX reactions were conducted within the ion source region in a controlled fashion (‘dual-spray’). Peptide and protein solutions were electrosprayed through one emitter and the deuterating agent D2O through the secondary electrospray emitter. For the relatively small peptides, Phe-Leu-Glu-Glu-Leu and oxytocin, the yield of products was calculated using deconvolution functions. Electrospray ionization (ESI) charge-state distributions and average number of deuterium exchanges were used to probe secondary and tertiary structures of ubiquitin, lysozyme, and cytochrome c in their native and unfolded states. Results Clear shifts in isotope distributions indicated HDX occurring within the ion source. By ion mobility, simultaneous deuterium exchange for two isobaric species, the oxytocin monomer and dimer, was observed. For denatured ubiquitin, the 12+ and 13+ charge states have a lower average number of exchanges relative to the lower charge states which indicates that these charge states have segments which restrict the access of D2O. Lysozyme has a linear relationship between the charge state and the average number of exchanges, indicating that lysozyme becomes increasingly unfolded as the charge state increases. The dual-spray HDX method was paired to high-performance liquid chromatography (HPLC) to demonstrate the applicability of the technique for probing gas-phase structures in protein mixtures. Conclusions ESI droplets formed from a secondary emitter penetrate primary ESI droplets and change the solvent composition. Dual-spray HDX is demonstrated to be a more efficient method for probing the structure of proteins than solution-phase HDX since the acid quenching step can be surpassed. Copyright © 2016 John Wiley & Sons, Ltd.

Characterizing noncovalent complexes of molecular dimers and higher complexes using tandem mass spectrometry (MS/MS) can be hindered due to spectral overlap in both the MS and the MS/MS. We investigated the structures and dissociation energetics of multimeric β-cyclodextrin (β-CD) complexes alone or with substrates using combinations of ion mobility spectrometry (IMS), MS/MS, and Rice–Ramsperger–Kassel–Marcus (RRKM) unimolecular rate modelling. The doubly charged β-CD dimers ([(β-CD)2 – 2H+]2−) dissociate to two [β-CD – H+]− ions with the same m/z. IMS was used to separate source generated [(β-CD)2 – 2H+]2− from [β-CD – H+]− and the extent of [(β-CD)2 – 2H+]2− dissociation versus collision energy was determined by modelling changes in the ion’s isotopic profile. The RRKM derived critical energy (E0) for dissociation of [(β-CD)2 – H+]− and [(β-CD)2 – 2H+]2− were 1.85 ± 0.11 eV and 1.79 ± 0.09 eV, respectively, corresponding to a slight decrease in complex stability due to increased charge–charge repulsion in the dianion. This approach was extended to include dimeric complexes complexed to 4,4′-(propane-1,3-diyl) dibenzoic acid (PDDA) and ibuprofen (Ibu).

MS/MS of triacylglycerides (TAG) complexed to cations such as NH4+ can allow for the positions of the fatty acids (FA) on the glycerol backbone to be determined. Collision-induced dissociation (CID) of an ammoniated TAG results in the neutral loss of NH3 and a FA. It has been reported that the FA at the central position (sn-2) dissociates less favourably than the terminal fatty acids (sn-1 or sn-3) yet no solid energetic explanation for this has been provided. MS/MS of ammoniated POP, OPO and POL triacylglycerides at multiple collision energies and computational analysis are here used to explain the different dissociation rates of the FAs from the glycerol backbone. The loss of sn-1 and sn-3 FAs are found to have lower activation energies than the loss of the sn-2 position FA, however the loss of the FA from the sn-2 position is more entropically favourable. Theoretical MS/MS breakdown curves were fit to experimental values using RRKM theory to estimate critical energy (E0) of dissociation of FAs from the three positions. The E0 values for cleavage from the sn-1 and sn-3 positions were found to be approximately 1.52 eV, while that for the sn-2 position was highly dependent on the identity of the FA at that position. Computational structures and energy analysis suggest that an important step in the dissociation of [TAG+NH4]+ is the loss of ammonia. In a model system, glyceryl tributyrate, the loss of NH3 produced two distinct [TAG+H]+ product structures sitting 148 kJ and 160 kJ in energy above the ammoniated structure. The [TAG+H]+ structure that leads to the loss of the sn-1(3) is 12 kJ lower than the [TAG+H]+ structure that leads to the loss of the sn-2 FA. From this, the loss of a neutral FA that follows sits only an additional 35–48 kJ above the [TAG+H]+ structures.

RATIONALE There are relatively few cross-section measurements for negatively charged ions. Available calibrants provide sufficient cross-section coverage for the 390 A(2) to 641 A(2) and 1174 A(2) to 3395 A(2) ranges. This is not particularly well suited for determining the collision cross-sections of smaller ions, such as small peptides. METHODS Molecular mechanics/molecular dynamics (MM/MD) simulations, coupled with simulated annealing, were used to find the low-energy molecular conformations of polystyrene (PS) oligomers of length 3-9 (singly deprotonated) and 5-13 (doubly deprotonated). The trajectory method in MOBCAL was employed to derive their respective collision cross-sections, Ω. A calibration plot relating corrected Ω values to drift times in a Waters Synapt G2 mass spectrometer was used to predict the Ω values for the -2 to -6 charge states of dT(10) DNA. RESULTS The in silico design of a reliable negative ion calibration set for ion mobility spectrometry successfully resulted in the use of α,ω-carboxy-terminated PS oligomers to determine the collision cross-sections of negatively charged ions in the range 132-388 A(2). All charge states of dT(10) DNA were predicted to within 3% of the referenced values for these ions. CONCLUSIONS α,ω-Carboxy-terminated PS oligomers were found to be an excellent choice to calibrate ion mobility spectrometers to obtain cross-sections for moderately sized ions. Oligomers with fewer, or weaker, interactions among the internal side chains (like poly(ethylene glycol) oligomers) tend to have a wide range of low-energy molecular conformations resulting in large standard deviations in their theoretically predicted collision cross-sections.

In high-energy (keV) CID experiments, oxygen has the unique ability to enhance specific ion fragmentation pathways that lie within a relatively narrow band of activation energy. It has been previously proposed that this oxygen-enhanced dissociation phenomenon is due to the participation of the \( {{\hbox{O}}_{{2}}}\;{\hbox{B}}{\,^{{3}}}{\Sigma_{\rm{u}}}^{ + } - {\hbox{X}}{\,^{{3}}}{\Sigma_{\rm{g}}}^{ - } \) (Schumann–Runge) system in the collision complex. During the collision, oxygen is first excited to its \( {\hbox{B}}{\,^{{3}}}{\Sigma_{\rm{u}}}^{ + } \) state before it returns this energy to the projectile ion. This energy drives the nonstatistical dissociation of the projectile provided there is an energetically accessible pathway in resonance with the absorbed radiation. To probe the validity of this hypothesis, a modified VG-ZAB mass spectrometer was used to observe the photon emissions from keV collisions of a selection of projectile ions with O2 target gas. By studying the resulting collision-induced emission (CIE) spectra, a second potential mechanism came to light, one that involves the near-isoenergetic O2+. A 2Πu→X 2 Πg state transition.

In the food industry, the use of the oil is determined by the composition of fatty acids, and this is highly dependent on its natural origin. The fatty acid composition of whole corn kernel was determined in three varieties of corn (Astro, GH2547, and Local). Linoleic acid was the predominant fatty acid in the oil of Astro and Local at all collection dates, whereas it was the major fatty acid in the oil of GH2547 only between 40 and 60 days after pollination (DAP). The fatty acid accumulation in the endosperm, pericarp and germ fractions of the corn kernel during maturation was determined. The accumulation pattern of oil content was different in these three kernel fractions. The highest levels of oil content in the endosperm (2.2%), germ (34.3%) and pericarp (10.8%) fractions were detected at 20, 40 and 30 (DAP), respectively. The fatty acid accumulation patterns were different amongst the analysed kernel parts, indicating a numerous differences between the three corn kernel parts. Throughout the sampling periods, the endosperm fraction was distinguished by the highest and the lowest levels of oleic and linoleic acids, respectively. At all stages of kernel development, the pericarp fraction had the highest levels of total polyunsaturated fatty acids, which has numerous healthy applications. These results may be useful in the understanding of the potential source of the beneficial unsaturated fatty acids amongst the different fractions of the corn kernel during maturation.

The threshold photoelectron spectrum (TPES) of tetrahydrofuran (THF) is compared to that of the unsaturated furan molecule. In general, there is a similarity in the orbital ionization profile for the two species, though unlike furan, THF exhibits (modest) vibrational detail only in the (9b)(-1) X (2)B band. An adiabatic ionization energy of 9.445 +/- 0.010 eV has been derived from the onset of the TPES spectrum. Threshold photoelectron photoion coincidence spectroscopy was used to explore the loss of a hydrogen atom from ionized THF over the photon energy range of 9.9-10.4 eV. RRKM fitting of the resulting breakdown curves yields an E(0) of 0.85 +/- 0.03 eV (82 +/- 3 kJ mol(-1)) (AE = 10.30 +/- 0.04 eV). If the G3 IE of 9.48 eV is used to convert the experimental data from photon energy to THF ion internal energy, E(0) = 0.81 +/- 0.01 eV (78 +/- 1 kJ mol(-1)). The latter value is closer to the G3 E(0) of 72 kJ mol(-1) for the formation of the cyclic ion 1. A variety of ring-opening reactions were also probed at the B3-LYP/6-31+G(d) and G3 levels of theory. The distonic isomer (*)CH(2)CH(2)CH(2)OCH(2)(+) lies 70 kJ mol(-1) higher than ionized THF, which places it within 1 kJ mol(-1) of the threshold for the dissociation to 1. All of the probed H-loss products from the distonic isomer (which includes singlet and triplet species) lie significantly higher in energy than ion 1, eliminating the possibility that ionized THF dissociates to m/z 71 via a ring-opening reaction in the present experiment. The derived Delta(double dagger)S value for the dissociation, 8 +/- 5 J K(-1) mol(-1), is also consistent with the formation of 1. The experimentally derived E(0) values can be used to derive the Delta(f)H(o)(0) for ion 1. Together with the Delta(f)H(o)(0) values for the THF ion (752.0 +/- 2 kJ mol(-1), derived from the neutral Delta(f)H(o)(0) of -154.9 +/- 0.7 kJ mol(-1) and experimental IE of 9.445 +/- 0.010 eV) and H atom (218.5 kJ mol(-1)) our E(0) of 82 +/- 3 kJ mol(-1) yields a Delta(f)H(o)(0) for ion 1 of 620 +/- 4 kJ mol(-1) (Delta(f)H(o)(298) = 594 +/- 4 kJ mol(-1)), in good agreement with the G3 Delta(f)H(o)(0) of 621 kJ mol(-1). Appearance energies for all fragment ions up to photon energies of 34 eV are also reported and discussed in comparison with the available literature.

Policosanol is a mixture of long-chain primary aliphatic alcohols. The policosanol composition of whole corn kernel was determined in three varieties of corn (Astro, GH2547, Local). The total policosanol content of GH2547 (20.5 mg/kg of dry weight) was higher than those of Local (16.6 mg/kg) and Astro (15.2 mg/kg). The major policosanol components of whole corn kernel were dotriacontanol, triacontanol and tetracosanol. The distribution of policosanol in the germ, endosperm and pericarp of corn kernels was also determined. Corn pericarp had higher contents of policosanols (72.7–110.9 mg/kg) than the endosperm (4.0–16.2 mg/kg) and germ (19.3–37.1 mg/kg) fractions. Corn pericarp policosanol was mainly triacontanol (33.63–46.29 mg/kg), dotriacontanol (22.31–39.46 mg/kg) and octacosanol (8.13–14.0 mg/kg). In contrast, the corn germ fraction contained mostly dotriacontanol (more than 50%) and no triacontanol. The main components of corn endosperm policosanol were triacontanol and hexacosanol. The level of tetracosanol was highest in the germ fraction and lowest in the endosperm fraction. The greatest change in policosanol content (expressed as mg/100 g of oil) occurred during the early stages of corn kernel development. Although the structures of the alcohol constituents of policosanol are similar, their patterns of accumulation were different. The highest levels of octacosanol and dotriacontanol were detected at 20 days after pollination (DAP) followed by a rapid decrease between 20 and 30 DAP. Triacontanol levels decreased rapidly between 10 and 40 DAP, and then remained nearly constant.

The phospholipid composition of corn oil was determined by LC/ESI-MS. The content of phospholipids in the oils varied from 5.2% to 8.7%. The major components in the phospholipids fraction were phosphatidylcholine (57.5–68.1%), phosphatidylinositol (14.5–19.8%), and phosphatidylethanolamine (10.3–13.9%). Phosphatidic acid and phosphatidylglycerol accounted for less than 10% of total phospholipid content. Various molecular species within each class were detected. The phosphatidylcholine class was mainly composed of phosphatidylcholine-C18:2/C18:1 (40–45%) and phosphatidylcholine-18:1/C18:1 (40–51%). Phosphatidylinositol-C16:0/C18:2 (50–69%) was the most abundant phosphatidylinositol. The two phosphatidylethanolamines were phosphatidylethanolamine-C16:0/C18:2 (34–42%) and phosphatidylethanolamine-C18:2/C18:2 (31–36%). Phosphatidylglycerol species were mainly phosphatidylglycerol-C16:0/C18:2 (42–48%) and phosphatidylglycerol-C16:0/C18:1 (36.7–40.3%). Identification of PC molecular species suggests the possibility that corn oil can have therapeutics effects.

This article is a review of the mechanisms responsible for collisional activation of ions in mass spectrometers. Part I gives a general introduction to the processes occurring when a projectile ion and neutral target collide. The theoretical background to the physical phenomena of curve-crossing excitation (for electronic and vibrational excitation), impulsive collisions (for direct translational to vibrational energy transfer), and the formation of long-lived collision intermediates is presented. Part II highlights the experimental and computational investigations that have been made into collisional activation for four experimental conditions: high (>100 eV) and intermediate (1-100 eV) center-of-mass collision energies, slow heating collisions (multiple low-energy collisions) and collisions with surfaces. The emphasis in this section is on the derived post-collision internal energy distributions that have been found to be typical for projectile ions undergoing collisions in these regimes.

Recently, industry has focused attention on plant matrices rich in phytosterols and phytostanols for their ability to reduce serum cholesterol levels. Therefore, the objective of this study was to examine the phytosterols and phytostanols contents of different fractions (endosperm, pericarp, germ) of corn kernel. The germ fraction contained more oil (24.2–30.7%) than endosperm and pericarp fractions (0.4–1.2%). Endosperm oil had the highest levels of phytostanols and 4,4-dimethylsterols, while pericarp oil had the greatest amounts of 4-desmethylsterols and 4-monomethylsterols. In the oil extracted from three corn kernel fractions sitostanol was the predominant phytostanols (77–87%), followed by campestanol (13–23%). The high percentages of 24–methylencycloartanol and cycloartenol were detected in the endosperm and pericarp parts, respectively. Citrostadienol was detected in corn germ oil as the main component of the 4-monomethylsterols fraction. In different parts of corn kernel, β-sitosterol (62–69%) was the major 4-desmethylsterol, followed by campesterol (11–18%) and stigmasterol (5–13%).

Collision-induced photon emissions (CIE) were observed for keV CO 2 +· /He collisions from 190 to 1020 nm. The emissions were assigned to the Δν=0 band of the CO 2 +· B 2Σ u + → X 2Πg electronic transition and the Δν = +3, +2, +1, 0, −1, −2, −3 vibrational transition progression in the CO 2 +· A 2Πu → X 2Πg electronic transition. The other peaks arise from the emissions of excited O· fragment atoms and the target gas. The relative intensities of the CO 2 +· and O· emissions are independent of the ion translational energy above 3 keV, supporting the curve-crossing mechanism for collisional excitation. Investigation of the relative intensities within the A 2Πu → X 2Πg emission of CO 2 +· indicates that the vibrational distribution is well described by the Franck-Condon principle at high collision energy, a consequence of short collision time but not necessarily an indication of vertical transitions. Below 3 keV ion translational energy, vibrational excitation in the A 2Πu electronic state was observed. The observation is consistent with the explanation that the reaction occurs at small impact parameters, in which short-range, repulsive interactions between the projectile and the target result in direct translational-vibrational excitation.

The unimolecular dissociation of the pyrene radical cation, C16H10(+•), has been explored using a combination of computational techniques and experimental approaches, such as multiple photon absorption in the cold ion trap Piege a Ions pour la Recherche et l'Etude de Nouvelles Especes Astrochimiques (PIRENEA) and imaging photoelectron photoion coincidence spectrometry (iPEPICO). In total, 22 reactions, involving the fragmentation cascade (H, C2H2, and C4H2 loss) from the pyrene radical cation down to the C14(+•) fragment ion, have been studied using PIRENEA. Branching ratios have been measured for reactions from C16H10(+•), C16H8(+•), and C16H5(+). Density functional theory calculations of the fragmentation pathways observed experimentally and postulated theoretically lead to 17 unique structures. One important prediction is the opening of the pyrene ring system starting from the C16H4(+•) radical. In the iPEPICO experiments, only two reactions could be studied, namely, R1 C16H10(+•) → C16H9(+) + H (m/z = 201) and R2 C16H9(+) → C16H8(+•) + H (m/z = 200). The activation energies for these reactions were determined to be 5.4 ± 1.2 and 3.3 ± 1.1 eV, respectively.

This study has determined oil, fatty acid (FA) and phytosterols content during the ripening of the Tunisian Onopordum acanthium L. seeds. In total, nine FAs and six phytosterols were identified. The main FAs were linoleic acid (0.18–8.06 mg/g of seed) followed by oleic acid (0.051–2.45 mg/g of seed), palmitic acid and stearic acid. Pentadecanoic acid was detected, for the first time, in unripe fruits and the two last stages of development were characterised by a relative abundance of erucic acid. Overall, β-sitosterol (34.5–77.79% of total sterols) was the major 4-desmethylsterols during maturation. The first episodes of growth were characterised by the best amounts of stigmasterol and campesterol, while stigmastanol and Δ7 sitosterol had quoted the semi-ripe and fully ripe fruits; however, cholesterol was absent. These findings are useful in understanding a potential new source of important natural compounds (Phytosterols and USFA) found in this fruit and when harvest should be undertaken to optimise desired FA and phytosterols content.

A Finnigan GCQ ion trap mass spectrometer has been modified for the measurement of ion/molecule reaction rate constants. The rate constants for the reactions between CH3OH2+ and methanol, CH3CH2OH2+ with methanol and ethanol, CH3CH2CH2OH2+ with methanol, ethanol, and n-propanol and protonated isopropanol with neutral isopropanol, all leading to products consisting of a protonated ether and neutral water, have been determined. All of the values, except that for the reaction involving isopropanol, are significantly lower than that predicted by the collision capture theory of Su and Chesnavich. Common to all the systems studied is an isomerization reaction that takes place in the proton-bound dimer that is initially formed in the reaction. This isomerization, which takes place via an internal SN2-type mechanism, leads to the formation of the protonated ether. The rate constants, in combination with Rice-Rampsberger-Kassel-Marcus modeling, allow the isomerization activation energies, Eiso, for the proton-bound dimers to be estimated. The Eiso values were found to decrease as the size of the alcohols increased, an observation consistent with the SN2-type rearrangement that has been predicted for these systems.

An ion trap mass spectrometer has been used to measure the ion/molecule reaction rate constants for three reactions involving acetonitrile and primary alcohols. The values obtained for the reaction between CH 3 CNH + and CH 3 OH leading to the products CH 3 CNCH 3 + was 4.6 ± 0.2 × 10 −11 cm 3 molecule −1 s −1 . The reaction between CH 3 CNH + and CH 3 CH 2 OH (to give CH 3 CNCH 2 CH 3 + + H 2 O) proceeds with a rate constant of 3.9 ± 0.4 × 10 −10 cm 3 molecule −1 s −1 , and that between CH 3 CH 2 CH 2 OH 2 + + CH 3 CN has a value of 2.1 ± 0.4 × 10 −10 cm 3 molecule −1 s −1 . These values for the rate constants have been used to extract the activation energy for isomerization of the initially formed proton-bound dimer in each case.

International audience; In this paper we describe femtosecond photoionization and the imaging photoelectron photoion coincidence spectroscopy of tetrathiafulvene, TTF. Femtosecond photoionization of TTF results in the absorption of up to twelve 808 nm photons leading to ion internal energies up to 12.1 eV as deduced from the photoelectron spectrum. Within this internal energy a variety of dissociation channels are accessible. In order to disentangle the complex ionic dissociation, we utilized the imaging photoelectron photoion coincidence (iPEPICO) technique. Above the dissociation threshold, iPEPICO results show that the molecular ion (m/z = 204) dissociates into seven product ions, six of which compete in a 1.0 eV internal energy window and are formed with the same appearance energy. Ab initio calculations are reported on the possible fragment ion structures of five dissociation channels as well as trajectories showing the loss of C2H2 and C2H2S from high internal energy TTF cations. A three-channel dissociation model is used to fit the PEPICO data in which two dissociation channels are treated as simple dissociations (one with a reverse barrier), while the rest involve a shared barrier. The two lower energy dissociation channels, m/z = 146 and the channel leading to m/z = 178, 171, 159, 140, and 127, have E0 values of 2.77 ± 0.10 and 2.38 ± 0.10 eV, respectively, and are characterized by ΔS(‡)(600 K) values of -9 ± 6 and 1 ± 6 J K(-1) mol(-1), respectively. Competing with them at higher internal energy is the cleavage of the central bond to form the m/z = 102 fragment ion, with an E0 value of 3.65 ± 0.10 eV and ΔS(‡)(600 K) = 83 ± 10 J K(-1) mol(-1).

The heat of formation of CISO + , 802 ± 1 kJ mol −1 at 0 K, has been obtained by the dissociative photoionization of supersonically cooled thionyl chloride, Cl 2 SO. Threshold photoelectron photoion coincidence spectroscopy was used to obtain the appearance energy from the cross-over point in the breakdown diagram for the dissociation. Also measured was the adiabatic ionization energy of thionyl chloride, 10.85 ± 0.05 eV. The experimentally measured kinetic energy release was found to agree with that calculated by statistical theory confirming that there is no reverse energy barrier to the Cl loss reaction. The interpretation was aided by ab initio MO calculations.

The optical emission spectra between 190 and 680 nm of 8 keV O 2 +. and CO 2 +. collisions with He and N 2 target gases were obtained and analyzed on a modified commercial VG ZAB-2F mass spectrometer. Emissions observed were from O, O + , He, N 2 +. (B 2 Σ u +→X 2 Σ g + ) and N 2 (C 3 Π u →B 3 Π g ) in the case of O 2 +. projectiles and C, CO 2 +. (B 2 Σ u + , A 2 Π u →X 2 Π g ), CO +. (B 2 Σ + →X 2 Σ + ), N 2 +. (B 2 Σ g +X 2 Σ g ) and 2N (C 3 Π u →B 3 Π g ) in the case of CO 2 +. projectiles. The results are discussed in relation to previous reports on N 2 +. -target collisions and the collision-induced dissociation mass spectral characteristics of O 2 +. and CO 2 +.

International audience; The dissociation of the naphthalene radical cation has been reinvestigated here by a combination of tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C(10)H(8)(*+) → C(10)H(7)(+) + H (m/z = 127); (R2) C(10)H(8)(*+) → C(8)H(6)(*+) + C(2)H(2) (m/z = 102); (R3) C(10)H(8)(*+) → C(6)H(6)(*+) + C(4)H(2) (m/z = 78); (R4) C(10)H(8)(*+) → C(10)H(6)(*+) + H(2) (m/z = 126); (R5) C(10)H(7)(+) → C(6)H(5)(+) + C(4)H(2) (m/z = 77); (R6) C(10)H(7)(+) → C(10)H(6)(*+) + H (m/z = 126). The E(0) activation energies for the reactions deduced from the present measurements are (in eV) 4.20 ± 0.04 (R1), 4.12 ± 0.05 (R2), 4.27 ± 0.07 (R3), 4.72 ± 0.06 (R4), 3.69 ± 0.26 (R5), and 3.20 ± 0.13 (R6). The corresponding entropies of activation, ΔS(‡)(1000K), derived in the present study are (in J K(-1) mol(-1)) 2 ± 2 (R1), 0 ± 2 (R2), 4 ± 4 (R3), 11 ± 4 (R4), 5 ± 15 (R5), and -19 ± 11 (R6). The derived E(0) value, combined with the previously reported IE of naphthalene (8.1442 eV) results in an enthalpy of formation for the naphthyl cation, Δ(f)H°(0K) = 1148 ± 14 kJ mol(-1)/Δ(f)H°(298K) = 1123 ± 14 kJ mol(-1) (site of dehydrogenation unspecified), slightly lower than the previous estimate by Gotkis and co-workers. The derived E(0) for the second H-loss leads to a Δ(f)H° for ion 7, the cycloprop[a]indene radical cation, of Δ(f)H°(0K) =1457 ± 27 kJ mol(-1)/Δ(f)H°(298K)(C(10)H(6)(+)) = 1432 ± 27 kJ mol(-1). Detailed comparisons are provided with values (experimental and theoretical) available in the literature.

This research has determined oil, fatty acid and sterol contents of the Tunisian Pistacia lentiscus (Lentisc) fruits during maturation. Low oil accumulation was observed during the first 35 days after the fruiting (DAF) date (from 1.83% to 2.57%). After that, two phases were distinguished (35th until the 60th and 105th to the 145th DAF), where the rate of oil accumulation increased significantly. At the last stage of maturation, the lentisc fruits had the highest percentage of lipid content, 42.54%. The changing profile of fatty acids during maturation had been marked mainly by an increase in oleic acid content (from 19.49% to 50.72%) paralleling a decrease in linoleic acid content (from 42.5% to 21.75%). At the 15th DAF, the alpha-linolenic acid was found with a maximum of 13.81%. At full maturity, the main fatty acids were oleic acid, followed by palmitic and linoleic acid. Other fatty acids were present in trace proportions, such as palmitoleic, stearic, linolenic, gadoleic and arachidic acid. In all stages of ripening only four sterols were identified and quantified. β-Sitosterol was the major 4-desmethylsterol in samples tested, followed by campesterol. Cholesterol and stigmasterol were detected in trace amounts. During the first stage of ripening, the amount of total sterols was about 5.19/100 g of oil. It decreased to 0.43/100 g in the last stage. Sitosterol and campesterol showed nearly the same profile during the ripening of P. lentiscus fruit which could be linked to the relation between these compounds during their biosynthesis.

International audience; Threshold photoelectron spectra (TPESs) were obtained for naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene using imaging photoelectron photoion coincidence spectroscopy, from threshold to a photon energy of ∼20 eV. Outer valence Green's function calculations at the OVGF∕cc-pVTZ level of theory were used to assign molecular orbitals to the observed TPES features. There is generally good agreement between the predicted and observed bands. Threshold regions for each molecule exhibit vibrational structure which is readily assigned based on previous PES studies. While the measured adiabatic ionization energies (IE(a)) for naphthalene, anthracene, and pyrene are in good agreement with previous works, new values are reported for the two dihydro species (1,2-dihydronaphthalene, 8.010 ± 0.010 eV and 9,10-dihydroanthracene, 8.335 ± 0.010 eV). A comparison is also made with the G3∕∕B3LYP composite method, which consistently overestimates the IE values by 0.06-0.09 eV. The double ionization energies for anthracene and pyrene have been measured to be 19.3 ± 0.2 and 19.8 ± 0.2 eV, respectively.

Neutral hydroxymethylene HCOH is an important intermediate in several chemical reactions; however, it is difficult to observe due to its high reactivity. In this work, neutral hydroxymethylene and formaldehyde were generated by charge exchange neutralization of their respective ionic counterparts and then were reionized and detected as positive-ion recovery signals in neutralization-reionization mass spectrometry in a magnetic sector instrument of BEE geometry. The reionized species were characterized by their subsequent collision-induced dissociation mass spectra. The transient hydroxymethylene neutral was observed to isomerize to formaldehyde with an experimental time span exceeding 13.9 µs. The vertical neutralization energy of the HCOH(+•) ion has also been assayed using charge transfer reactions between the fast ions and stationary target gases of differing ionization energy. The measured values match the result of ab initio calculations at the QCISD/6-311 + G(d,p) and CCSD(T)/6-311 + + G(3df,2p) levels of theory. Neutral hydroxymethylene was also produced by proton transfer from CH(2) OH(+) to a strong base such as pyridine, confirmed by appropriate isotopic labeling. There is a kinetic isotope effect (KIE) for H(+) versus D(+) transfer from the C atom of the hydroxymethyl cation of ∼3, consistent with a primary KIE of a nearly thermoneutral reaction.

The unimolecular dissociation reactions of the methylhydrazine (MH) and tetramethylhydrazine (TMH) radical cations have been investigated using tandem mass spectrometry and threshold photoelectron photoion coincidence spectroscopy in the photon energy ranges 9.60-31.95 eV (for the MH ion) and 7.74-29.94 eV (for the TMH ion). Methylhydrazine ions (CH3NHNH2(+*)) have three low-energy dissociation channels: hydrogen atom loss to form CH2NHNH2(+) (m/z 45), loss of a methyl radical to form NHNH2(+) (m/z 31), and loss of methane to form the fragment ion m/z 30, N2H2(+*). Tetramethylhydrazine ions only exhibit two dissociation reactions near threshold: that of methyl radical loss to form (CH3)2NNCH3(+) (m/z 73) and of methane loss to form the fragment ion m/z 72 with the empirical formula C3H8N2(+*). The experimental breakdown curves were modeled with Rice-Ramsperger-Kassel-Marcus theory, and it was found that, particularly for methyl radical loss, variational transition state theory was needed to obtain satisfactory fits to the data. The 0 K enthalpies of formation (delta(f)H0) for all fragment ions (m/z 73, m/z 72, m/z 45, m/z 31, and m/z 30) have been determined from the 0 K activation energies (E0) obtained from the fitting procedure: delta(f)H0[(CH3)2NNCH3(+)] = 833 +/- 5 kJ mol(-1), delta(f)H0 [C3H8N2(+*)] = 1064 +/- 5 kJ mol(-1), delta(f)H0[CH2NHNH2(+)] = 862 +/- 5 kJ mol(-1), delta(f)H0[NHNH2(+)] = 959 +/- 5 kJ mol(-1), and delta(f)H0[N2H2(+*)] = 1155 +/- 5 kJ mol(-1). The breakdown curves have been measured from threshold up to h nu approximately 32 eV for both hydrazine ions. As the photon energy increases, other dissociation products are observed and their appearance energies are reported.

Electrospray ionization (ESI-MS) and matrix-assisted laser desorption/ionization (MALDI-MS) were used to determine the composition (monomer ratios) and structure (end group analysis) relative to 1H nuclear magnetic resonance (NMR) spectroscopy and theoretical predictions for three different co-polymers: poly(butyl acrylate/vinyl acetate) (PBA/PVAc), poly(methyl methacrylate/vinyl acetate) (PMMA/PVAc) and poly (butyl acrylate/methyl methacrylate) (PBA/PMMA). We found that the ESI results were in excellent agreement with 1H NMR spectroscopy for PBA/PVAc and PBA/PMMA co-polymers, whereas there was more divergence in the case of PMMA/PVAc. In the case of PBA/PMMA co-polymers, a similar distribution of products was observed by ESI-MS and MALDI-MS with the two major product classes differing by their end-groups. One class has hydrogen and dodecylthio end groups while, in the other, the dodecylthio has been replaced by α-cyanoisopropyl from the initiator. The relative abundance of these distributions as a function of co-polymer conversion for a series of reaction conditions was investigated by both ESI and MALDI. MALDI results consistently underestimated (relative to ESI) the butylacrylate monomer ratio in PBA/PMMA and the abundance of co-polymer oligomers terminated by a dodecylthio group from the chain transfer agent.

The valence shell photoelectron spectrum, threshold photoelectron spectrum, and threshold photoelectron photoion coincidence (TPEPICO) mass spectra of acetone have been measured using synchrotron radiation. New vibrational progressions have been observed and assigned in the X 2 8 2 state photoelectron bands of acetone-h 6 and acetone-d 6 , and the influence of resonant autoionization on the threshold electron yield has been investigated. The dissociation thresholds for fragment ions up to 31 eV have been measured and compared to previous values. In addition, kinetic modeling of the threshold region for CH 3 · and CH 4 loss leads to new values of 78 ± 2 kJ mol -1 and 75 ± 2 kJ mol -1 , respectively, for the 0 K activation energies for these two processes. The result for the methyl loss channel is in reasonable agreement with, but slightly lower than, that of 83 ± 1 kJ mol -1 derived in a recent TPEPICO study by Fogleman et al. The modeling accounts for both low-energy dissociation channels at two different ion residence times in the mass spectrometer. Moreover, the effects of the ro-vibrational population distribution, the electron transmission efficiency, and the monochromator band-pass are included. The present activation energies yield a Δ f H 298 for CH 3 CO + of 655 ± 3 kJ mol -1 , which is 4 kJ mol -1 lower than that reported by Fogleman et al. The present Δ f H 298 for CH 3 CO + can be combined with the Δ f H 298 for CH 2 CO (-47.5 ± 1.6 kJ mol -1 ) and H + (1530 kJ mol -1 ) to yield a 298 K proton affinity for ketene of 828 ± 4 kJ mol -1 , in good agreement with the value (825 kJ mol -1 ) calculated at the G2 level of theory. The measured activation energy for CH 4 loss leads to a Δ f H 298 (CH 2 CO + ·) of 873 ± 3 kJ mol -1 .

Methods for the analysis of fungal biomass in contaminated building materials have been limited to methods that use viable propagules as well as indicators of total biomass such as fungal glucan and ergosterol. Because of large differences in the survival times of spores, and limitations imposed by the use of agar media to assess fungal cells for the former approach, no quantitative information and poor qualitative information is obtained. The use of the biochemical indicators provides reliable quantitative information but no qualitative data. Analysis of phospholipids of various bacteria and, recently, of fungi common in outdoor air has provided both qualitative and quantitative data on their distributions in various substrates including in outdoor air samples. In this report, we provide new data on the signature lipids of some fungi common on moldy building materials. Using the LC/MS/MS analysis described, an estimate can be made of the fresh weight of fungal cells and the relative abundance of the common genera of fungi typically found on moldy materials.

A highly selective molecularly imprinted solid phase extraction (MISPE)-pulsed elution (PE) method coupled with electrospray mass spectrometry (MS) was developed for the rapid screening and determination of cephalexin in alpha-aminocephalosporin antibiotics. This method involved the solid phase extraction of cephalexin using a molecularly imprinted polymer micro-column, and pulsed elution with 1% trifluoroacetic acid in methanol, which contains sulindac as an internal standard for enhanced precision in MS detection. An LC/MS spectrometer was operated in the positive electrospray mode, and the selected-ion-recording (SIR) function was employed to detect the molecular ions of cephalexin, cefradine, cefadroxil and sulindac at m/z 348, 350, 363 and 357. Linearity was achieved in the cephalexin concentration range from 0.3 to 25microg/ml (or 5-500ng) (R(2) = 0.998). The detection limit was estimated at 0.04microg/ml (or 0.8ng) of cephalexin. Advantages of the newly developed MISPE-PE-MS, over the previously reported MISPE-DPE-FPE-UV, were evidenced in terms of detection limit, analysis time, solvent consumption, and simplicity of method development.

In Issue 5 of Volume 12, Figure 7 (see opposite) was omitted from the paper by Alhazmi et al. (page 309). [Figure: see text]

Photon emissions following 8 keV ion beam–target gas collisions of the polyatomic cations of composition C2,H4,O and C2,H5,Cl were measured and interpreted in conjunction with their collision-induced dissociation (CID) mass spectra. The experiments were performed in a modified analytical VG ZAB-2F mass spectrometer of magnetic sector/electric sector/electric sector (BEE) geometry. The identification of the emission bands in the collision-induced emission (CIE) spectra of oxirane+• , acetaldehyde and vinyl alcohol with helium and argon target gases was assisted by obtaining the CIE spectra of CO , HCO and CH3. Distinct emission bands due to the HC (A,B → X), HC (B → A and A → X) and HO (A → X) transitions, as well as atomic C, O and H lines, were observed. The emission spectra of 8 keV CH3CH2Cl +• and CH3ClCH2 –helium and argon target gas collisions were obtained and analyzed with the aid of the CIE spectra for CCl and CH2Cl . Many of the same bands appeared as for the C2,H4,O isomers, with the addition of bands due to the CCl (A → X) transition and Cl atomic lines.

International audience; Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7-20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below similar to 13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies all species behave similarly; the ionization yield gradually increases, leveling off between 0.8 and 0.9 at similar to 18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them; all are in good agreement with theoretical ones, confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.