Solid-phase microextraction gas chromatography/ion trap mass spectrometry and multistage mass spectrometry experiments in the characterization of germacrene D

Germacrene D is a vegetable pheromone utilized in interactions among organisms belonging to different species. For the first time, using solid-phase microextraction/gas chromatography/ion trap mass spectrometry, the presence of this compound was detected in an in vitro mycorrhizal synthesis system where the mycelium of the ectomycorrhizal fungus Tuber borchii Vittad. interacts with the plant Tilia Americana L. From this symbiosis, a new structure, called ectomycorrhiza, is formed where the two symbionts exchange nutrients and metabolites. It seems that only after this interaction can the mycelium develop the fruitbody, commonly known as truffle. The results obtained allowed us to ascertain that germacrene D was synthesized by the plant exclusively in the presence of T. borchii. The originality of these data prompted us to hypothesize that this compound could be involved in the first step of ectomycorrhiza formation, as it is able to stimulate specific fungi receptors. In fact, plants release hundreds of secondary metabolites that are important in their interactions with other organisms.     

Evolution of instrumentation for the study of gas-phase ion/ion chemistry via mass spectrometry

The scope of gas-phase ion/ion chemistry accessible to mass spectrometry is largely defined by the available tools. Due to the development of novel instrumentation, a wide range of reaction phenomenologies has been noted, many of which have been studied extensively and exploited for analytical applications. This perspective presents the development of mass spectrometry-based instrumentation for the study of the gas-phase ion/ion chemistry in which at least one of the reactants is multiply charged. The instrument evolution is presented within the context of three essential elements required for any ion/ion reaction study: the ionization source(s), the reaction vessel or environment, and the mass analyzer. Ionization source arrangements have included source combinations that allow for reactions between multiply charged ions of one polarity and singly charged ions of opposite polarity, arrangements that enable the study of reactions of multiply charged ions of opposite polarity and, most recently, arrangements that allow for ion formation from more than two ion sources. Gas-phase ion/ion reaction studies have been performed at near atmospheric pressure in flow reactor designs and within electrodynamic ion traps operated in the mTorr range. With ion trap as a reaction vessel, ionization and reaction processes can be independently optimized and ion/ion reactions can be implemented within the context of MSn experiments. Spatial separation of the reaction vessel from the mass analyzer allows for the use of any form of mass analysis in conjunction with ion/ion reactions. Time-of-flight mass analysis, for example, has provided significant improvements in mass analysis figures of merit relative to mass filters and ion traps.     

苯二酚异构体双电荷离子和单电荷离子的动能谱研究

本文利用质量分析离子动能谱(MIKES)、碰撞诱导解离(CID)技术和电子捕获诱导解离(ECID)技术, 研究了邻、间、对苯二酚分子在电子轰击质谱(EIMS)中产生的双电荷离子[C6H6O2]^2^+, [C6H4O]^2^+和单电荷离子[C6H6O2]^+。根据测定的电荷分离反应动能释放值T和由此计算出的两电荷间距R, 推测出过渡态的结构。有趣的是, 可利用单电荷离子[C6H6O2]^+的MIKES/CID谱区分苯二酚异构体。     

Positive ion chemistry of SiH4/GeF4 gaseous mixtures studied by ion trap mass spectrometry and ab initio calculations

The positive ion chemistry occurring in SiH(4)/GeF(4) gaseous mixtures was investigated by ion trap mass spectrometry and ab initio theoretical calculations. The GeF(3)(+) cation, the only fragment obtained from ionized GeF(4), was unreactive towards SiH(4). All the primary ions SiH(n)(+) (n = 0-3) react instead with GeF(4) so to form SiF(+) or SiH(2)F(+). The latter species reacts in turn with SiH(4) and GeF(4) so to form SiH(3)(+) and SiHF(2)(+), respectively. The potential energy profiles conceivably involved in these reactions were investigated by ab initio calculations performed at the MP2 and coupled cluster (CCSD(T)) level of theory.     

Complexes of silver(I) with peptides and proteins as produced in electrospray mass spectrometry

Silver(I) forms aqueous phase complexes with both sulfur and nonsulfur containing peptides and proteins. These complexes were introduced into the gas phase via electrospray, and their structures probed by means of tandem mass spectrometry. Experiments with di-, tri-, and oligopeptides show that the abundance of silver(I)-containing ions increases relative to that of proton-containing ions as peptide length increases. This increase is much more dramatic for methionine-containing peptides. Collision-induced dissociation of silver-peptide complexes yields a multitude of product ions that are silver containing. However, even for methioninecontaining peptides, very few of these product ions contain the methionine residue. The solution-phase structure and the gas-phase structure of the silver/peptide complex are not identical. The methionine sulfur acts as the silver anchoring point in solution. Desolvation in the gas phase leads to a rearrangement of the silver/peptide complex such that the silver ion becomes chelated to the nitrogen and oxygen atom on the peptide backbone in addition to the methionine sulfur. This rearrangement decreases the importance of the silver/sulfur bond to the extent that it is frequently broken upon collision activation and leads to the formation of silver/peptide product ions that are nonsulfur bearing.     

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) for silver halides

Electrospray droplet imact/secondary ion mass spectrometry (EDI/SIMS) was applied to many materials such as synthetic polymers, metals, semiconductors, and biological tissues. Little surface modification was observed for these samples by in situ XPS analysis. In this work, silver halides AgX (X = F, Cl, Br, and I) were examined by EDI/SIMS. The preferential etching of F for AgF was observed for the first time. This is due to the highly reactive F atoms generated at the colliding interface that are quickly annihilated by the reaction with water molecules. The selective etching of fluorine results in the enrichment of silver on the sample surface leading to the abundant Ag⁺ ion formation. It was suggested that metal fluorides may be useful as the cationization matrices in EDI/SIMS. Copyright © 2014 John Wiley & Sons, Ltd.     

Multiply charged ions of ruthenium(II), rhodium(III) and cobalt(III) complexes in electrospray ionization mass spectrometry

Multiply charged ions from electrospray ionization (ESI) were observed for ruthenium-bidentate ligand complexes, such as [RuL₂B]X₂ and [(RuL₂)₂B]X₄, where L is 2,2′-bipyridine, B are tetradentate ligands of 2,2′-bis(2′-pyridyl)bibenzimidazole and 2,6-bis(2′-pyridyl)benzodiimidazole, bidentate ligand of 2-(2′-pyridyl)benzimidazole and related compounds and X is CIO₄^- or CI^-. ESI mass spectra showed a simple mass pattern for easy structural assignment and detecting impurities. The mass spectra for binuclear complexes provide a charge state distribution ranging from 4+ to 2+ for Ru(II)—Ru(II) compounds and 5+ to 2+ for Ru(II)—Rh(III) compounds. It was found that different multiply charged ions are generated by loss of counterions and by protonation/deprotonation at the proton site of ligands B. The abundances of these ions are qualitatively explained in terms of the acidity of metal complexes depending on the bridging ligand structures and the charge of the metal ions. Ions produced by removal of ligands were hardly observed.     

Determination of thermodynamic parameters of tautomerization in gas phase by mass spectrometry and DFT calculations: Keto-enol versus nitrile-ketenimine equilibria

The study of tautomerics equilibria is really important because the reactivity of each compound with tautomeric capacity can be determined from the proportion of each tautomer. In the present work the tautomeric equilibria in some γ,δ-unsaturated β-hydroxynitriles and γ,δ-unsaturated β-ketonitriles were studied. The first family of compounds presents two possible theoretical tautomers, nitrile and ketenimine, while the second one presents four possible theoretical tautomers, keto-nitrile, enol (E and Z)-nitrile and keto-ketenimine. The equilibrium in gas phase was studied by gas chromatography-mass spectrometry (GC-MS). Tautomerization enthalpies were calculated by this methodology, and results were compared with those obtained by density functional theory (DFT) calculations, observing a good agreement between them. Nitrile tautomers were favored within the first family of compounds, while keto-nitrile tautomers were favored in the second family.     

Electrospray ionization, accurate mass measurements and multistage mass spectrometry experiments in the characterization of stereoisomeric isoquinoline alkaloids

Mass spectrometry has been employed for the characterization of diastereoisomeric isoquinoline alkaloids. Electrospray ionization was used to generate MH(+) ions, and multistage collisionally activated spectra allowed differentiation among the different compounds via specific fragmentation patterns, whose mechanisms have also been elucidated by accurate mass measurements.     

Gas phase prototropic equilibrium studies of 2,4-dihydroxyquinoline by cndo/2 calculations, mass spectrometry and derivatization

The tautomerism of 2,4-dihydroxyquinoline in the gas phase is discussed in terms of its electron impact fragmentation pattern and of quantum chemical calculations by the LCAO-MO method in the CNDO/2 approximation. Dihydroxyquinoline methylated at position 4 can only exist in two tautomeric forms. Thus, comparison of mass spectrometric data of this compound with dihydroxyquinoline provided additional evidence for the gas phase equilibrium of the latter. The equilibria of these compounds in the gas phase were found to be displaced towards the hydroxyl tautomers.     

Ion-selective carbon-paste electrodes for halides and silver(I) ions

The behaviour of a simple type of ion-selective electrode for halogens and silver has been studied. The electrode consists of a plastic body filled with carbon paste, the surface of which can be easily renewed. The paste composition is based on carbon-nujol (5:1, w/v) or carbon-paraffin wax (3:1,w/w) containing a prepared mixture of silver halide-silver sulphide (1–30%). The electrodes have low ohmic resistance and show a rapid Nernstian response (within 2–5 mV) for halide and silver ions down to 5·10^-5M chloride, 1·10^-5M bromide and 5·10^-7M iodide with the respective electrodes. Ions forming very stable complexes with halide or silver and those having strong oxidizing or reducing action interfere.     

Gas phase attachment of water and methanol to Ag(I) complexes with alpha-amino acids in an ion trap mass spectrometer

Electrospray ionization was used to generate gas phase complexes of Ag+ with selected alpha-amino acids. Following storage (isolation without collisional activation) in an ion trap mass spectrometer, the mass spectra produced from the complexes of Ag+ with alpha-amino acids such as alanine, valine and tert-leucine contained peaks consistent with the formation of water or methanol molecule adduct ions. The same adduct ions were not present, however, in the mass spectra generated from the Ag+ complexes with phenylalanine, tyrosine and tryptophan following isolation and storage under similar conditions. For those complexes that showed reactivity, the uptake of water and methanol increased with longer storage times in the ion trap. A preliminary molecular modeling study using phenylalanine demonstrated that the aromatic ring coordinates the Ag+ ion, and the interaction between the metal ion and pi-system, in part, is assumed to prohibit the binding of water or methanol during isolation in the gas phase. This conclusion is supported by a comparison of the adduct formation by the Ag+ complexes with phenylalanine, 4-fluorophenylalanine and alpha-aminocyclohexanepropionic acid. In addition, collision induced dissociation experiments involving the Ag+ complexes of phenylalanine, tyrosine and tryptophan suggest that limiting the coordination of the Ag ion by the complexing molecule (i.e. by loss of a coordinating functional group and/or change in structure due to dissociation) results in the binding of a water or methanol molecule during storage in the ion trap. Surprisingly, the bare Ag+ ion, when trapped and stored under identical experimental conditions, formed neither adduct species, suggesting that the attachment of water or methanol may be due to interactions with a molecular orbital within the Ag+/molecule complex.     

Coordination chemistry of the cyclo-(P(5)tBu(4))(-) ion: monomeric and oligomeric copper(I), silver(I) and gold(I) complexes

[Na{cyclo-(P(5)tBu(4))}] (1) reacts with [CuCl(PCyp(3))(2)] (Cyp=cyclo-C(5)H(9)) and [CuCl(PPh(3))(3)] (1:1) to give the corresponding copper(I) complexes with a tetra-tert-butylcyclopentaphosphanide ligand, [Cu{cyclo- (P(5)tBu(4))}(PCyp(3))(2)] (2) and [Cu{cyclo-(P(5)tBu(4))}(PPh(3))(2)] (3). The CuCl adduct of 2, [Cu(2)(mu-Cl){cyclo-(P(5)tBu(4))}(PCyp(3))(2)] (4), was obtained from the reaction of 1 with [CuCl(PCyp(3))(2)] (1:2). Compounds 2 and 3 rearrange, even at -27 degrees C, to give [Cu(4){cyclo- (P(4)tBu(3))PtBu}(4)] (5), in which ring contraction of the [cyclo-(P(5)tBu(4))](-) anion has occurred. The reaction of 1 with [AgCl(PCyp(3))](4) or [AgCl(PPh(3))(2)] (1:1) leads to the formation of [Ag(4){cyclo-(P(4)tBu(3))PtBu}(4)] (6). Intermediates, which are most probably mononuclear, "[Ag{cyclo-(P(5)tBu(4))}(PR(3))(2)]" (R=Cyp, Ph) could be detected in the reaction mixtures, but not isolated. Finally, the reaction of 1 with [AuCl(PCyp(3))] (1:1) yielded [Au{cyclo-(P(5)tBu(4))}(PCyp(3))] (7), whereas an inseparable mixture of [Au(3){cyclo-(P(5)tBu(4))}(3)] (8) and [Au(4){cyclo-(P(4)tBu(3))PtBu}(4)] (9) was obtained from the analogous reaction with [AuCl(PPh(3))]. Complexes 3-7 were characterised by (31)P NMR spectroscopy, and X-ray crystal structures were determined for 3-9.     

Identification of isobaric product ions in electrospray ionization mass spectra of fentanyl using multistage mass spectrometry and deuterium labeling

Isobaric product ions cannot be differentiated by exact mass determinations, although in some cases deuterium labeling can provide useful structural information for identifying isobaric ions. Proposed fragmentation pathways of fentanyl were investigated by electrospray ionization ion trap mass spectrometry coupled with deuterium labeling experiments and spectra of regiospecific deuterium labeled analogs. The major product ion of fentanyl under tandem mass spectrometry (MS/MS) conditions (m/z 188) was accounted for by a neutral loss of N‐phenylpropanamide. 1‐(2‐Phenylethyl)‐1,2,3,6‐tetrahydropyridine (1) was proposed as the structure of the product ion. However, further fragmentation (MS³) of the fentanyl m/z 188 ion gave product ions that were different from the product ion in the MS/MS fragmentation of synthesized 1, suggesting that the m/z 188 product ion from fentanyl includes an isobaric structure different from the structure of 1. MS/MS fragmentation of fentanyl in deuterium oxide moved one of the isobars to 1 Da higher mass, and left the other isobar unchanged in mass. Multistage mass spectral data from deuterium‐labeled proposed isobaric structures provided support for two fragmentation pathways. The results illustrate the utility of multistage mass spectrometry and deuterium labeling in structural assignment of isobaric product ions. Copyright © 2010 John Wiley & Sons, Ltd.     

1D silver(I) complex of nitronyl nitroxide with strong spin-spin interaction through silver(I) ion

A 1D silver(I) complex of nitronyl nitroxide was prepared and its structure was determined by X-ray diffraction analysis; magnetic studies indicate that the spin-spin interaction of nitronyl nitroxides through silver(I) ions along the chain are fairly strong (J/kb = -84 K).     

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of polyisoprenes

Polyisoprenes (PIPs) with average molecular weights from 650 to 800,000 Da have been studied by time-of-flight secondary ion mass Spectrometry (TOF-SIMS) in the static mode. Polymer samples were bombarded by argon primary ions, and positive SIMS spectra were collected. Effects of branching and unsaturation in the polymer structure on ion formation were studied. The pendant methyl group showed little tendency to fracture as a cation. In the low mass region, C_nH _2n–1 ⁺ appeared to be more intense than C_nH _2n+1 ⁺ , attributed to the double bond structure of polyisoprene. Additionally, ion formation varied as a function of polymer molecular weight. Cationized intact oligomers and fragments dominate the high mass region. Oligomer distributions were used to calculate average molecular weights for polyisoprenes. A statistical chain scission mechanism was used to qualitatively explain the formation of five clusters within a unique fragmentation pattern. Detailed studies of the cluster structure pointed out that each cluster contained several species having varied degrees of unsaturation. It is believed that double bond rearrangements occur.     

Elucidation of a Sc(I) complex by DFT calculations and reactivity studies

Sc(BrMgL)(2)Br (L = (R(2)NCH(2)CH(2)NCMe)(2)CH, R = H) was studied by DFT methods leading to the conclusion that this diamagnetic formal scandium(I) system enjoys stabilization of its Sc-based filled d(yz)() orbital by a delta-acceptor linear combination of BrMgL ring orbitals. Investigation of the reactivity of Sc(BrMgL)(2)Br (L = (R(2)NCH(2)CH(2)NCMe)(2)CH, R = Et) with H(2)O.B(C(6)F(5))(3) and (HOCH(2))(2)CMe(2), respectively, led to decomposition, with LMgBr being isolated in the latter case.     

Observation of doubly charged mercury cluster ions Hg n 2+, n=1-10 using secondary ion mass spectrometry

Mass spectra of doubly charged mercury clusters (m/z=30-1065) were investigated by secondary ion mass spectrometry. Positively charged ions were generated from an amalgam of mercury and silver by bombardment with a xenon ion beam and mass analysis by a grand-scale sector type mass spectrometer. Hg _n ²⁺, n=1-10 and Hg _n +, n =1- 5 were observed. Some doubly charged mercury clusters, (Hg _n ²⁺) survived at least for 0.1 ms.     

Negative ion electrospray mass spectrometry of aminomethylphosphonic acid and glyphosate: elucidation of fragmentation mechanisms by multistage mass spectrometry incorporating in-source deuterium labelling

Glyphosate and its main metabolite, aminomethylphosphonic acid, introduced by direct infusion in (2)H(2)O, appear in negative ion electrospray mass spectrometry (ES-MS) as triply deuteriated [M[bond]H](-) ions. Sites of deuterium residence and loss were established using the multistage (MS(n)) capabilities of an ion trap mass spectrometer to assist in the determination of fragmentation mechanisms. The study reveals specific mechanisms, common to each analyte, such as those involving a five-membered transition state between the amine and phosphonate group, as well as analyte specific transitions.