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Benzoxazole and 1, 2-benzisoxazole are isomerized in an o-cyanophenol structure before degradation (losses of CO and HCN) as evidenced by analysis of metastable ions abundances and shapes.

The M-HCN+. ion observed in the mass spectrum of benzothiazole is the result of two degradation processes:i) specific fragmentation of the heterocyclic part of the molecule and ii) isomerisation into an o-mercaptobenzonitrile structure which eliminates HCN and CS. This latter process predominates for low-energy molecular ions.

A new route to 2,7-disubstituted pyrene derivatives is described. 2,7-di(ethoxycar-bonyl) pyrene is synthesized in eight steps from pyrene.

The N. M. R. spectra of twelve monosubstituted pyrene derivatives (position 1) have been recorded at 60 Mc. In ten cases, the position of substitution can be deduced by first order analysis of the spectra.

1-acetylimidazole [1] is isomerized into 2- and 4-acetylimidazoles [2] and [3] under flash-vacuum pyrolytic conditions. This has been demonstrated by a real-time analysis of the products using mass and ion kinetic energy spectrometries.

The design of a collision chamber located between the magnetic and electric sectors of a reversed geometry mass spectrometer is described. The analytical and theoretical interests of this arrangement are discussed. La construction d'une chambre de collisions entre les analyseurs magnetique et electrique d'un spectrometre de masse a geometrie inversee est decrite. L'interet d'un tel arrangement tant au point de vue analytique que theorique est discute.

Air introduction in the second field-free region of a reversed geometry mass spectrometer induces an important number of fragment ions which are recorded by scanning the ESA voltage. These C.I.D./M.I.K.E. spectra [collision induced dissociations/mass-analysed ion Kinetic energy spectral are very characteristic of the structure of the stable ions obtained in a normal magnet current scanning and can be used to derive very quickly fragmentation schemes. Application of this technique in the field of heterocyclic compounds (dihydrotetrazines) is discussed.

Electron impact ionization of 1-acryloylpyrazole [1] induces a unimolecular loss of CO forming ionized 1-vinylpyrazole [2] as shown by metastable ion characteristics and neutralization-reionization data. This CO loss implies a rate-determining isomerization process into a pyrazolylmethyl ketene structure 1a+. These ketene ions have been synthetized in the ion source by dissociative ionization of pyrazolylpropionylpyrazoles. Flash-vacuum pyrolysis of these compounds also affords the expected neutral ketenes in the gas phase, which are however readily converted into the acryloyl isomers by an intramolecular nucleophilic process.

Flash-vacuum pyrolysis of 1-benzoylpyrazole 1 at ca 800° under low pressure conditions affords mainly 2-phenylfuran 2 and phenylallene 3 as indicated by a real-time analysis using tandem mass spectrometry and by preparative scale experiments. Although 1-acetylpyrazole [8] loses quasi exclusively ketene, isomerization into (a) C-acylated isomer(s) is also detected by mass spectrometry.

Tandem mass spectrometry (MS/MS) has been applied to investigate the behaviour of 1-(2-nitrophenyl)benzotriazole [8] upon flash-vacuum pyrolysis (FVP) conditions. Above 500°, 8 is pyrolyzed to give a mixture of 1-nitrocarbazole [11], 1-hydroxycarbazole [12] and carbazole [13] Under similar conditions, 2-(2-nitrophenyl) benzotriazole [9] appears to be more stable; it is however partially isomerized into 8 at high temperatures. Aza analogs of 8, like 1-(2-nitro-4-pyridyl) benzotriazole [10] also loose nitrogen above 500° to give a mixture of 1-nitro-3-azacarbazole [19], 1-hydroxy-3-azacarbazole [16] and 3-azacarbazole [17].

The structure of some fragment ions formed in the source and in the first field-free region (FFR) of a triple sector mass spectrometer has been investigated by the collisional activation technique. It is shown that the elucidation of fragmentation pathways by metastable peak analysis may lead to erroneous conclusions. Indeed, high energy (source) fragmentation and the corresponding low energy (FFR) processes produce frequently isobaric or even isomeric ions.

The mass spectra of 1-(3,4-dimethyl-5-isoxazolyl)-3-aryltriazenes may be interpreted on the predominance, in the vapor phase, of the structure A in which the azo group is conjugated with the heterocyclic moiety. This tautomer generates an isoxazolyl diazonium ion b wich rearranged before the loss of nitrogen. Para substituents on the aromatic ring have a weak influence on the displacement of this tautomeric equilibrium. Similarly, the mass spectra of 3-aryl-1-p-tolyl-triazenes show that the equilibrium is only weakly influenced by the position and the nature of the substituent on the aromatic ring.

Ion kinetic energy spectrometry using two triple sector instruments has been used for the study of the fragmentation of ionized 5-nonanone. Mixtures of isomeric [C6H12O]+. ions are formed in the first McLafferty rearrangement whose relative proportions depend on their internal energy.

In a reversed geometry mass spectrometer first field free region fragmentations are usually detected by scanning the accelerating voltage. In some favourable instances, artifacts corresponding to second field free region processes are observed; the influence of a collision gas on their relative intensities is discussed.

Collision-induced dissociations-mass analyzed ion kinetic energy (CID-MIKE) spectrometry has been used to characterize [M-CH3]+ ions from ionized 2-heptanone. Acylium [CH3(CH2)5 C=0] ions are produced at short times (within the source), while protonated cyclohexanone is formed exclusively in the field-free regions.

Electron impact ionization of iodomethane at high pressure (∼ 1 torr) yields high concentrations of dimethyliodonium ions (CH3CH3). Their reactivity towards various functional groups has been studied by mass spectrometry techniques, including in some instances collisional activation. Most of the compounds studied show the methylation process, except aliphatic alcohols and some aromatic compounds like benzene, anisole, furan, thiophene. Nitriles and isonitriles present a very high methyl cation affinity. Other ionization processes have also been observed, e.a. protonation, charge exchange and hydride abstraction. The degree of competition between these processes depends on the nature of the functional groups. Some unusual ion structures have been detected for isonitriles and pyridines.

Collision induced dissociations have been used to characterize the isomeric stable structures of [C2H5N]+. radical cations and the results are in good agreement with previous studies concerning the reactive ions. The competitive fragmentations of [C2H5N]++ cations formed by charge stripping processes have also been observed. The reproducibility of the abundance ratios confirms the usefulness of these metastable fragmentations for the structural investigation of monocharged positive ions via their doubly charged analogs.

Tandem mass spectrometry has been applied to investigate the behaviour of bis-captodative (cd) substituted cyclopropanes NC(SR)CCH2C(SR)CN [1, R=CH3; 2, R=tBu and 3, R=C6H5] upon electron impact (EI) and flash-vacuum pyrolysis (FVP) conditions. Ring-opening of the molecular ions of 1 followed by a 1,2-hydrogen shift preceedes the fragmentation consisting mainly in the competitive losses of CH3S and CH2S. The least energy demanding reaction is however a methyl loss requiring also ring cleavage. The m/z 70 base peak is ascribed to cyanothioacylium ions (N=C-=S) as indicated by the characteristic fragmentations induced by collision. Upon FVP conditions 1decays to the cd olefin 8 and the carbene 9 in competition with the extrusion of CH3S. and CH3. radicals at the highest temperatures. The behaviour of 2 upon both conditions is dominated by the chemistry of the t-butyl substituents. Ring cleavage of the molecular ions of 3 preceedes also the fragmentation and induces rearrangement reactions yielding unexpected cyclohexadiene thione ions and C7H7+ ions. Upon FVP, C-S bond homolysis readily occurs in competition with an elimination of a carbene molecule.

Indole and 2-ethynylaniline behave similarly upon electron impact. Isomerization into a common structure before fragmentation is postulated on the basis of deuterium labeling experiments.

Besides the formation of acylium ions, the molecular ions of 1-acyl-1,2,4-triazoles substituted (R) at position 3 lose competitively ketene and carbon monoxide after electron impact ionization, but the ketene loss dominates largely if R is a strong electron-donating substituent. This supports the occurrence of an ion-molecule complex which incorporates a substituted triazole and ionized ketene before the decarbonylation (methylene transfer) or the ketene elimination (hydrogen transfer). Flash-vacuum pyrolysis (FVP) of these triazolides yields oxazoles with specific substitution at positions 2 (R) and 5 which implies an irreversible sigmatropic [1,5(1,2)] transformation. Oxazole formation dominates largely a competitive ketene loss if the triazolides bear a strong electron-donating substituent like N(CH3)2; this kind of substitution does not however allow the migration of groups like CO2CH3 and CONH2 which have a lower migratory aptitude. The fragmentation of the ionized oxazoles is highly dependent upon the nature of the substituent at position 5 (methyl or phenyl) and is directed by ring cleavages, mainly of the 1,2-bond. Moreover, compounds bearing a N(CH3)2 group undergo a complex rearrangement which eliminates (C, H3, N) from the molecular ions (for the oxazoles) or from the fragment ions [M-C2H2O]−+ (for the azolides).

A conventional double focusing mass spectrometer has been modified in order to obtain mass-analyzed ion kinetic energy spectra.

Collisionally activated dissociations (CAD) spectra have been used to investigate the structures of ions produced by decarbonylation of 1-acetylimidazole [1] and acetylpyrazole [12] ionized by electron impact. The results are best explained by the formation of non classical methylene-azolium ions. The loss of carbon dioxide from l-methoxycarbonylimidazole [7] does not produce these ions but instead leads to ionized C-methyl-2(or 4)H-imidazole. A mixture of structures is produced by electron impact induced fragmentation (loss of C2H4) of 1-(2-hydroxypropyl)imidazole [9]

Mass-analyzed ion kinetic energy spectra of chemically ionized aminotriazoles were used to obtain structural features of protonated molecular ions, differenciation of isomers giving nearly identical c.i. mass spectra and relative basicities of tautomers in the gas phase. Unimolecular fragmentations suggest that the “ethylated dimers” are formed by ethylation with [C2H5]+ followed by solvation of this collision complex with a second molecule.

The study of the mass spectra of six α-diazo-N-cyanoimines and the collision-induced dissociation/mass-analysed ion kinetic energy spectra of their [M-N2]+· fragment ions demonstrate the decay sequence: [α-diazoimine]+· α-iminocarbene]+· [ketenimine]+. This last ion is shown to be structurally identical to the one formed by electron-induced cycloreversion of the ketenimine-benzylideneaniline cycloadduct.

“Collision Induced Dissociation/Mass analyzed Ion Kinetic Energy” (CID/MIKE ) spectrometry is applied to study the structure of cations generated by the chemical ionisation of hydroxypyridines and related compounds. The method described allow, in many cases, the determination of tautomeric structures in the gas phase.

Mass analysed ion kinetic energy and collision induced dissociation spectra show that C-chloro-1, 2, 4-triazole can be generated in three different tautomeric forms by ethylene elimination from the N-ethyl compounds and these ions retain their structure prior to further fragmentation. 5- and predominantly 3-chlorotriazole structures are responsible for the mass spectrum of the parent heterocycle.

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.

Using MS/MS/MS experiments and quantum chemical calculations, it is demonstrated that oxygen (carbonyl) methylated phthalic anhydride cations are produced when metastable dimethyl phthalate molecular ions expel a methoxyl radical. At higher internal energies, isomeric acyl ions are competitively generated.

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.

In a previous study on the pyridine ion (1) and the pyridine-2-ylid isomer (2), we reported that ions 2 readily react with H2O to produce 2-pyridone ions at m/z 95, by O-atom abstraction. The mechanism for this intriguing reaction, however, was not established. This prompted us to use model chemistry calculations (CBS-QB3) to probe various mechanistic scenarios and to perform complementary experiments with the new, more versatile, ion–molecule reaction chamber of the Mons Autospec 6F mass spectrometer. It appears that H2O is not reacting neutral that produces the 2-pyridone ion of the above reaction, but rather O2 from air co-introduced with the water vapour. Theory and experiment agree that the exothermic reaction of O2 with the pyridine-2-ylid ion leads to loss of 3O from a stable peroxide-type adduct ion at m/z 111. Similarly, pyridine-3-ylid ions (3) generate 3-pyridone ions, but the reaction in this case is thermoneutral. The m/z 111:95 peak intensity ratios in the spectra of the ion–molecule products from ions 2 and 3 may serve to differentiate the isomers.

Three carbonyl-containing extracts of essential oils from Eucalyptus citriodora (Myrtaceae), Cymbopogon citratus (Gramineae) and Lippia multiflora (Verbenaceae) were used for the preparation of oximes. The reaction mixtures were analyzed by GC-MS and different compounds were identified on the basis of their retention times and mass spectra. We observed quantitative conversion of aldehydes to their corresponding oximes with a purity of 95 to 99%. E and Z stereoisomers of the oximes were obtained and separated by GC-MS. During GC analysis, the high temperature in the injector was shown to cause partial dehydratation of oximes and the resulting nitriles were readily identified. Based on FT-IR spectroscopy, that revealed the high stability and low volatility of these compounds, the so-obtained oximes could be useful for future biological studies.

Chiral recognition of enantiomers by host compounds is one of the most challenging topics in modern host-guest chemistry. Amongst the well-established methods, mass spectrometry (MS) is increasingly used nowadays, due to its low detection limit, short analysis time, and suitability for analyzing mixtures and for studying chiral effects in the gas phase. The development of electrospray-ionization (ESI) techniques provides an invaluable tool to study, in the gas phase, diastereoisomeric complex ions prepared from enantiomer ions and a chiral selector. This paper reports on an ESIMS and ESIMSMS study of the molecular mechanisms that intervene in the chiral-recognition phenomena observed between amino acids and a chiral crown ether. The modified crown ether, namely (+)-([18]crown-6)-2,3,11,12-tetracarboxylic acid, is used as the chiral selector when covalently bound on a stationary phase in liquid chromatography. This study was stimulated by the fact that, except with threonine and proline, consistent elution orders were observed, which indicates that the D enantiomers interact more strongly with the chiral selector than the L enantiomers. For proline, the lack of a primary amino group is likely to be responsible for the nonresolution of the two forms, whereas the second stereogenic center on threonine could explain the reversed elution order. In light of those observations, we performed mass spectrometry experiments to understand more deeply the enantiomeric recognition phenomena, both in solution by the enantiomer-labeled guest method and in the gas phase by gas-phase ligand-exchange ion/molecule reactions. The results have been further supported by quantum chemical calculations. One of the most interesting features of this work is the identification of a nonspecific interaction between proline and the crown ether upon ESIMS analysis.

The MS/MS spectrum of the metastable molecular ions of dimethyl isophthalate 1 differs from that of the isomeric dimethyl terephthalate 2 by the observation of, inter alia , a quite intense loss of C,H 2 ,O ascribed to formaldehyde. Results obtained using a combination of mass spectrometry techniques suggest that this process could consist of an isomerization reaction of the molecular ion into an ion–neutral complex (INC) linking a benzoyl radical and neutral formaldehyde to a proton [Ar C O⋯H⋯O CH 2 ] + . Within the complex, a proton transfer catalyzed by formaldehyde occurs resulting in the production of an ionized cyclohexadienylidene methanone (ketene) structure.

Quantum chemical calculations (G3B3 and B3LYP/6-311++G(d,p)) and tandem mass spectrometric experiments demonstrate the higher stability of 1,3-cyclohexadienylidenemethanone radical cation compared to ionized benzaldehyde. Characterized by a heat of formation of 833 kJ mol−1 (at 298 K), this ketene C7H6O + isomer is found 43 kJ mol−1 more stable. It has been generated by ion/molecule reaction between ionized benzaldehyde and neutral methanol, a new example of proton transport catalysis tautomerization. The greater stability of the ketene ion is due to the low IE of the neutral (7.49 eV).

The synthesis of amphiphilic and adaptative block copolymers has been envisioned following a commutative two-step strategy involving atom transfer radical polymerization (ATRP) and the Huisgen-1,3-dipolar cycloaddition techniques. The reliability of this strategy is based on the use of an azido-containing ATRP initiator, the 2-(2-azidoethoxy)ethylbromoisobutyrate (N 3 E i BBr), able to be “clicked” to an alkyne-terminated derivative and to promote the ATRP polymerization from the active site. In the context of this work, an alkyne-terminated poly(e-caprolactone) produced by ring-opening polymerization (ROP) of CL was employed as hydrophobic “clickable” segment. The N 3 E i BBr initiator was obtained by nucleophilic substitution of the chloride atom from 2-(2-chloroethoxy)ethanol by an azide function and followed by the esterification of the hydroxy function by bromoisobutyryl bromide. This initiator was employed in polymerization of N , N -dimethylamino-2-ethyl methacrylate (DMAEMA) monomer by ATRP in THF at 60 °C using CuBr complexed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalytic complex. Low initiation efficiencies were obtained and they were ascribed to intramolecular cyclization during the polymerization as evidenced by ESI-MS and 2D NMR spectroscopy. The “Click” coupling reaction was performed in THF at r.t. and was found to be efficient when using CuBr complexed by 2,2′-bipyridine ligand. To circumvent the low initiation efficiency, the N 3 E i BBr could be “clicked” in a first step to PCL precursors before initiating the polymerization of DMAEMA monomer by ATRP. In this context, various catalytic complexes in different composition ratio were employed to optimize the “click” coupling step. Moreover, this strategy was found to be suitable to produce well-defined PCL-b-PDMAEMA block copolymers, characterized by narrow polydispersity indices. Since ATRP and the Huisgen-1,3-dipolar cycloaddition both require the use of a copper(I)-based catalyst, the two first strategies were merged in a “one-pot” process in order to obtain in one step a well-defined block copolymer characterized by a narrow polydispersity index and predictable composition and block lengths.

Ion/molecule reactions involving toluene and methyl isocyanide have been performed in a new rf-only hexapole collision cell recently installed in a large-scale tandem mass spectrometer. Among the various ionized products identified, indole derivatives have been characterized by collisional activation and result from the intermediacy of hydrogen-bridged radical cations and covalently bound dimers. Quantum theoretical computations support these experimental findings. A covalently bound dimer is also proposed in the ion/molecule reaction between ionized methyl benzoate and methyl isocyanide; such a dimer is nevertheless not detected due to the large exothermicity of the reaction leading to the ultimate products ascribed to N -methyl benzonitrilium ion, carbon dioxide and a methyl radical.

Well-defined amphiphilic PCL-b-PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and "click" chemistry following either a commutative two-step procedure or a straightforward one-pot process using CuBr 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a "one-pot" process allows the preparation of PCL-b-PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.

Attempts have been made to characterize ionic and neutral C2H2S +/o isomers, viz., thioketene (1 +), ethynylthiol (2 +), and thiirene (3 +) using various tandem mass spectrometric methodologies. Dissociative electron ionization of thiophene, 1-propane thiol and thiirane were used to produce the C2H2S + (m/z 58) ions. The collisional activation (CA) mass spectrum of m/z 58 ions from thiophene is highly compatible with thioketene ions which has been supported by the CA mass spectrum of metastably generated m/z 58 ions and by comparison with the previously reported CA mass spectrum of thioketene ions. Theoretical calculations at the B3LYP/6-311G(d,p), and G2/G2(MP2) levels predict that low energy thioketene ions equilibrate with other isomeric ions viz., ethynylthiol and thiirene prior to dissociation by loss of H (m/z 57) and CH (m/z 45). The CA spectra of C2H2S + ions from 1-propane thiol and thiirane are nearly identical indicating a facile isomerization of the initial structures at energies lower than the dissociative threshold. The low energy CID spectra of the m/z 58 ions from three precursors are found to be similar. However, significant differences are noticed in the relative abundances of product ions in the NR spectra of m/z 58 ions from the three precursors. While the NR mass spectra of m/z 58 ions from thiophene and thiirane confirms the stability of thioketene neutrals, the NR spectra of m/z 58 ions from 1-propane thiol suggests formation of a mixture of ethynylthiol and thioketene ions. Calculations predict a different thermo-chemistry for 1 +–3 +, but, due to a mixture of reacting isomeric ions whatever the precursor molecule is, similar results were obtained for the associative ion/molecule reactions between the C2H2S + ions with methylisocyanide.

The MS/MS spectrum of the metastable molecular ions of dimethyl terephthalate 1 features an unexpected, quite intense, loss of a methyl radical. Using a combination of mass spectrometry techniques, it is shown that this process consists of a pseudo simple cleavage reaction isomerizing, in the first step, one of the two methoxycarbonyl substituents into a distonic ArC+(–OH)–OCH2 (Ar = CH3O2C–C6H4–) connectivity. The final product is established to be protonated 5-carboxyphthalide. The overall mechanism of the methyl loss includes a sequence of five steps as supported by quantum chemical (DFT) calculations.

New 4-hydroxy-1,3-oxazin-6-ones 8 and 16 were prepared from chlorocarbonyl(phenyl)ketene and amides. The flash vacuum thermolysis (FVT) reactions of these compounds and the 4-methoxy derivative 17 were investigated by Ar matrix isolation IR spectroscopy and online mass spectrometry including MS/MS analysis. Carboxy(phenyl)ketene 10 is formed as the major product by thermal fragmentation of 4-hydroxy-1,3-oxazin-6-one 8. This takes place via the unstable 6-hydroxy tautomer 9. Another tautomer, the 5H-isomer 12, leads to the formation of benzoyl isocyanate 13 as a minor product together with phenylketene 14. Carboxy(phenyl)ketene 10 remains detectable at high FVT temperatures but undergoes thermal decarboxylation to phenylketene 14. The same carboxy(phenyl)ketene 10 is also produced in significant amounts by FVT of 5-phenyl-Meldrum's acid 18 via the unstable enol tautomer 19. A small amount of the unsubstituted carboxyketene 20 is observable on FVT of Meldrum's acid 1 itself.

The C 6 H 5 C + (OH)OCH 2 radical cation, formally a distonic isomer of ionized methyl benzoate, has been prepared by dissociative ionization of neopentyl benzoate, as earlier suggested by Audier et al. [H.E. Audier, A. Milliet, G. Sozzi, S. Hammerum, Org. Mass. Spectrom. 25 (1990) 44]. Its distonic character has now been firmly established by its high reactivity towards neutral methyl isocyanide (ionized methylene transfer) producing N -methyl ketenimine ions. Other mass spectrometric experiments and ab initio quantum chemical calculations also concur with each other pointing toward the existence of a stable distonic radical cation.

Sea stars (Asterias rubens L.) were collected in different stations distributed in the Southern Bight of the North Sea. Concentrations of four heavy metals and six PCB congeners were measured in two body compartments (body wall and pyloric caeca). In order to assess the potential harm of these contaminants, two biochemical parameters were measured in sea stars, viz. reactive oxygen species (ROS) production by amoebocytes and cytochrome P450 immunopositive protein (CYP1A IPP) induction in pyloric caeca. Sea stars from stations located in the plume of the Scheldt river showed the highest contamination levels. Other stations, similarly located, displayed lower levels. No simple relationship could be established between ROS production by sea star amoebocytes and contaminant levels measured in sea star tissues. CYP1A IPP induction displayed more contrasted responses, and highly significant regressions were found between PCB concentrations measured in pyloric caeca and CYP1A IPP. Both biological parameters were found to vary significantly over the study area. On the whole, data indicated that contamination levels and subsequent effects in sea stars were comparable to those described in previous large-scale studies, but that working at a smaller scale highlighted the existence of patterns of contamination which can blur general trends due to major contamination sources like contaminated rivers.

MS/MS/MS experiments were carried out using a large-scale tandem mass spectrometer featuring a sector-quadrupole-sector geometry to probe the C 7 H 8 + and C 5 H 6 + radical cations. These ions ( m / z 92 and 66) were produced from metastable ionized precursors or charge exchange reactions in the quadrupole cell; subsequent fragmentations and double ionization were performed after mass-selection and collisional activation with oxygen. Charge stripping spectra show significant variations in the relative intensities of the same doubly charged species generated in different ways. These variations are likely to be associated with the inherent differences in internal energy content.

The synthesis of novel amphiphilic graft copolyesters based on hydrophobic poly(e-caprolactone) (PCL) segments grafted all along a hydrophilic poly((R,S)-β-malic acid) (PMLA) backbone is proposed. ...

The formation of alkoxy isothiocyanates from N-alkoxy-substituted thioureas and alkoxy cyanates from N-alkoxy-substituted ureas by flash vacuum pyrolysis has been shown by combined Fourier Transform Infra Red (FTIR)-matrix isolation spectroscopy and online collisional activation mass spectrometry.

Ion–molecule reactions between ionized carbonyl compounds or ionized enols with t-butyl nitrite allow a clear-cut distinction to be made between both these isomeric structures. The most relevant difference between the observed reactions is the formal substitution of a hydrogen atom by nitric oxide in the enol ions. Collisional activation experiments on the product ions are interpreted in terms of α-nitroso carbonyl structures. However, a quantum chemical investigation at the B3LYP/6-311++G(d,p) level of theory shows that ionized α-nitroso carbonyl and vinyl nitrite structures may isomerize provided they contain ca 60 kJ mol−1 of internal energy. It is, therefore, possible that both structures are generated in the substitution reaction.

The protonation and methylation of thiophenol (C6H5SH), thioanisole (C6H5SCH3) and 4-bromo derivatives have been studied using both tandem mass spectrometric techniques and ab initio quantum chemical calculations. Protonated 4-bromo thio-compounds produced by chemical ionization (CI) are found to be collisionally dehalogenated in an rf-only quadrupole collision cell in the low (20–30 eV) kinetic energy regime giving essentially thiophenol or thioanisole radical cations. This is indicated by MS/MS/MS experiments performed in an hybrid sector-quadrupole-sector mass spectrometer. B3LYP and CCSD(T) calculations using the 6-311++G(d,p) basis set consistently confirm that protonation of either (bromo)thiophenol or thioanisole takes place on the ring; the C 4-protonated thiophenol lies about 13 kJ mol −1 below the S-protonated isomer. However, under similar conditions, protonated thioanisole is also readily demethylated generating thiophenol radical cation, but no isomer has been detected. On the other hand, experimental and theoretical results reveal a regiospecific cationization (methylation) at the sulfur atom of the title compounds. The proton and methyl cation affinities are estimated as follows: PA (thiophenol) = 812 ± 10 kJ mol −1 , MCA (thiophenol) = 397 ± 10 kJ mol −1 , PA (thioanisole) = 839 ± 10 kJ mol −1 , and MCA (thioanisole) = 454 ± 10 kJ mol −1 . The available experimental value of 873 kJ mol −1 for PA (thioanisole) appears to be overestimated. Calculated PAs at various sites of halogeno (F, Cl and Br) thiophenols (o, m, p) are also reported. © 2003 Elsevier Science B.V. All rights reserved.