Arielle Milliet

PAHs analysis of fish whole gall bladders and livers from the Natural Reserve of Camargue by GC/MS

Traces of parent polycyclic aromatic hydrocarbons (PAH) in fish whole gall bladders and livers from the Natural Reserve of Camargue were determined from three different species: cels, goldfishes and catfishes by capillary gas chromatography-mass spectrometry (GC/MS) after Soxhlet extraction and florisil column cleanup. Results have been successfully correlated with biological fish parameters in order to identify adequate biomarkers of PAHs contamination.

Proton affinities of polybenzenoid aromatic hydrocarbons and those with five‐membered rings

Proton affinities of PAHs including one five‐membered ring are calculated by using the AM1 Hamiltonian for the determination of ΔHfo of the neutral and protonated molecules. The calculated PAs are compared to experimental PAs measured by chemical ionization mass spectrometry, using a new method based on competition between charge transfer and proton transfer occurring during the ionization process. A procedure is proposed to validate AM1‐calculated PAs from experimental PAs after rescaling the calculated and measured PA values. The site of protonation is first determined on the criterion of the lowest loss of aromaticity, then on the criterion of the largest HOMO coefficient. For indene, the corrected result is compared to an ab initio calculation at the MP2/6‐31G*//HF/6‐31G* level and to a DFT calculation at the B3LYP/6‐31G* and the B3LYP/6‐311 + G** levels. Five new PAs are thus established and one published experimental PA is revised.

THE DISSOCIATION OF LOW ENERGY 1,2-PROPANEDIOL IONS : AN INTRIGUING MECHANISM REVISITED

Abstract The fascinating unimolecular chemistry of ionized 1,2-propanediol, CH 3 C(H)OHCH 2 OH ·+ , 1 , has been re-examined using computational chemistry (ab initio MO and density functional theories) in conjunction with modern tandem mass spectrometric and 13 C labelling experiments. The calculations allow a considerable simplification of a previously proposed complex mechanism (Org. Mass Spectrom., 23 (1988) 355). Again, the central intermediates are proposed to be stable hydrogen bridged ion—dipole complexes, but our present calculations indicate that the key transformation now is the rearrangement CH 3 C(H)OH + ···O(H)-CH 2 . → CH 3 C(H)OH + ··· . OCH 3 , which can best be viewed as the cation-catalyzed 1,2-hydrogen shift . CH 2 OH → CH 3 O . , a rearrangement which does not occur so easily in the unassisted system. Another important process is the electron transfer CH 3 C(H)O···CH 3 OH ·+ → OCH(CH 3 ) ·+ ···O(H)CH 3 which allows proton transfer to generate CH 3 OH 2 + + CH 3 CO . . Other dissociation processes (loss of CH 3 . , H 2 O, H 2 O + CH 3 . , H 2 O + CH 4 ) are interpreted in terms of Bohmes ‘methyl cation shuttle’ (J. Am. Chem. Soc., 118 (1996) 4500) taking place in ion-dipole complexes. The most stable intermediate is the hydrogen bridged ion-dipole complex CH 2 CHOH .+ ···O(H)CH 3 , which is the reacting configuration for loss of methanol.

Mass Spectrometric Differentiation of Isomeric Polycyclic Aromatic Hydrocarbons by Chemical Ionization with Diethylether, Tetrahydrofuran and Dimethylcarbonate

Chemical ionization of polycyclic aromatic hydrocarbons (PAHs) with three different reactants, diethylether, dimethylcarbonate and tetrahydrofuran, has been used to differentiate PAH isomers. The mechanisms of formation of the molecular ion, the protonated molecular ion and adducts have been elucidated in order to optimize the analytical diagnosis from the measurement of the relative abundances of ions observed on the PAHs chemical ionization mass spectra. As a practical application, chrysene and triphenylene have been determined quantitatively in a diesel exhaust particles sample.

Transposition of linear alkyl-chains into ramificated chains.

Abstract It is shown by the study of alkyl ethers and benzoates, that formation of [C n H 2n ] + ions is preceded by an isomerisation of the alkyl-chains leading to a substituted ethylenic ion. A mechanism of isomerisation is proposed for the respective intensities of peaks and the values of appearance energies in the spectra of labelled compounds. The fragmentation is initiated by the shift of one H at position 3 leading to an intermediary complex in which a neutral molecule interacts with a [C n H 2n ] + ion.

Contrasting behavior of tetracene and perylene in collision-induced dissociation: a theoretical interpretation

Dimethyl ether chemical ionization mass spectrometry of polycyclic aromatic hydrocarbons (PAHs) leads to [M + 13](+) and [M + 45](+) ions. The process leading to these ions is sensitive to the proton affinity of the PAH. Collision-induced dissociation observations on [M + 45](+) ion also show that tetracene has a peculiar reactivity in comparison with perylene, despite the similar physico-chemical properties of these two molecules. Ab initio calculations were used to establish a potential energy profile for the mechanistic pathway of [M + 13](+) and [M + 45](+) formation. [M + 45](+) ions result from the addition of CH(3)-O-CH(2)(+) to PAHs. A 1,2-hydride transfer followed by a 1,4-proton transfer and a loss of methanol subsequently lead to the formation of [M + 13](+) ions. For tetracene, the 1,2-hydride transfer does not occur, as it would lead to a thermodynamically unstable non-planar ion.

HYDRIDE AND PROTON TRANSFER REACTIONS IN GASEOUS ION-MOLECULE COMPLEXES PHCH2+ HOCH2CH2OH

Benzyl cations and ethylene glycol react in the gas phase and form covalently bound adducts, as shown by slow and site-selective proton exchange, but also undergo irreversible hydride transfer giving two ion–neutral complexes, [PhCH 3 HOCH 2 CHOH + ] and [PhHCH 3 + HOCH 2 CHO], which interconvert by a rapid and non-selective proton exchange.

Mechanisms of ring opening of indanols

Abstract Substituted and unsubstituted 1 and 2-indanols have been studied. The experimental results show that two isomerisation reactions occur before rupture. The first one begin by the cleavage between the aromatic ring and the position 3 carbon, concerted with the transfer of an hydrogen of the position 1. The second one is a cleavage of the benzylic bond followed by the hydroxylic H transfer.

Rearrangement and dissociation of ionized 1,2-diaminoethane ☆

Abstract The chemistry of ionized 1,2-diaminoethane, [NH 2 CH 2 CH 2 NH 2 ] ·+ , 1 ·+ is studied by means of tandem mass spectrometry techniques and molecular orbital calculations at the QCISD(T)/6-31 G∗//UMP2(full)/6-31G∗ + ZPE level. At low internal energy 1 ·+ isomerizes into the distonic ion, [NH 2 CHCH 2 NH 3 ] ·+ , 2 ·+ which, further, dissociates by ammonia loss. The 1,3-hydrogen migration, 1 ·+ → 2 ·+ , is the energy determining step of the fragmentation. Ions of higher internal energy rapidly dissociate by a simple C–C bond cleavage. As confirmed by RRKM statistical calculations, this system provides a clear example of the influence of the internal energy on the competition between rearrangement and simple bond rupture.

Formation of stable “Proton-bridged dimers” by decomposition of α,β-diether radical cations. Part II: Two populations with different energy content are evidenced in the case of 1,2-diethoxycyclohexane +•

The mass analyzed ion kinetic energy (MIKE) spectrum of the 1,2-diethoxycyclohexane radical cation 1 exhibits fragment ions generated from two molecular ion populations with different energy contents. An ethanol··H+··acetaldehyde proton-bridged dimer originates from molecular ions of low internal energy, whereas cyclohexene radical cation formation results from more energetic ions. This statement is based on the comparison of the kinetic energy released for each fragmentation and on the extent of H/D exchange preceding the formation of fragment ions from (C2D5O)2–cycloC6H10 (1a).