Studies in organic mass spectrometry. XXII–Evidence for the existence of cyclic oxonium ions in the gas phase

The electron impact induced loss of a phenoxy radical from the molecular ions of α,ω-bis-aryloxy alkanes ΦO(CH₂)_nOΦ ( 1 _n; n = 2–7) and F-p-C₆H₄(CH₂)_nOΦ(2_n; n = 2?5) is the result of functional group interaction. Labelling data provide conclusive evidence for the O-aryl tetra-hydrofuranium and O-aryl tetrahydropyranium structures of the resulting decomposing species (lifetimes between 10^?6 and 10^?5 s) in the case of n = 4 and 5, respectively. Evidence is presented for the occurrence of phenyl participation in the loss of ΦOH from the molecular ions of the lower homologues of 1 _n and 2_n (n = 2, 3).     

Studies in organic mass spectrometry. XXIII-Evidence for the occurrence of cyclic sulphonium ions in the gas phase

Functional group interaction occurs in the loss of a phenoxy radical from the molecular ions of ω-phenylthio alkylphenylethers ØO(CH₂)_nSØ (n = 2–6). Labelling data provide evidence for the S-phenyl thietanium, S-phenyl tetrahydrothiophenium and S-phenyl tetrahydrothiopyranium structures of the decomposing (lifetimes between 10^?6 and 10^?5 s) [M - ØO]⁺ ions in the case of n = 3, 4 and 5, respectively.     

Complexation of diazaperylene and bisisoquinoline with transition metal ions in the gas phase studied by electrospray ionization mass spectrometry

The complex formation of the ligands 1,12-diazaperylene (dap), 1,1'-bisisoquinoline (bis), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) with transition metal ions (M = Fe, Co, Ni, Cu, Zn, Ru, Os, Re, Pd, Pt, Ag and Cd) in the gas phase has been studied by electrospray ionization mass spectrometry. With the exception of Ru, Os, Fe, Ni and Cu, singly charged complexes [MLn](+) (n = 1,2) were observed. The complexes of dap and bis with Ru, Os, Fe and Ni ions, and the mixed ligand complexes with bpy and phen, are preferably of the doubly charged type [ML3]2+. In addition, collision-induced dissociation (CID) measurements were employed to evaluate the relative stabilities of these complexes. The CID experiments of mixed-ligand complexes which contain both dap and phen or dap and bpy exhibit preferential elimination of bpy, indicating that bpy is a weaker ligand than phen and dap.     

Studies in organic mass spectrometry—XXIV : Evidence for the gas phase occurrence of the O-methyl tetrahydrofuranium ion

The electron impact induced loss of a phenoxy radical from the molecular ions of ω-phenoxyalkyl methylethers φO(CH₂)_nOCH₃ (I_n; n = 2–6) is the result of a functional group interaction. Labeling data provide evidence for the O-methyl tetrahydrofuranium structure of the resulting decomposing species (lifetime between 10^?6 and 10^?5 sec) in the case of n = 4.     

Determination of iron(II) ions in aqueous solutions by secondary-ion mass spectrometry

Model samples of aqueous solutions containing iron(II/III) salts have been studied by secondary-ion mass spectrometry. Mass spectra of the samples containing ferrous and ferric ions have been compared. The possibility of using secondary-ion mass spectrometry for the analysis of rain precipitations and samples of atmospheric aerosols has been considered.     

气相中甲苯离子-分子反应产物的串联质谱研究

应用碰撞诱导解离技术, 研究了甲苯自身化学电离条件下离子-分子反应产物离子m/z 182和184的碰撞诱导解离(CID)反应特性。m/z183和184离子碎裂反应具有多种过渡态结构, 如二苯基甲烷衍生物结构、卓翁离子与甲苯形成的共价键结构、甲苯自由基离子与甲苯分子形成的π-配合物结构和苄基离子与甲苯形成的π-配合物结构。     

Determination of iron(III) ions in aqueous solutions by secondary-emission mass spectrometry

Model aqueous solutions containing micro impurities of iron(III) are studied by secondary-emission mass spectrometry. The possibility of using this method for the analysis of rain deposits and samples of atmospheric aerosols is discussed.     

Applications of laser ionization/fourier-transform mass spectrometry to the study of metal ions and their clusters in the gas phase

Recent software and hardware modifications of the Nicolet FTMS-1000 Fourier-transform mass spectrometer have made it possible to conduct research in what can be termed a “complete gas-phase chemical laboratory”. Selected ions of interest can be mixed with various reagents and their detailed chemistries monitored through a series of as many as eight reaction sequences. At any point in these sequences, ion structures can be elucidated and fundamental kinetic and thermodynamic parameters of the reactions can be determined. These powerful new techniques have been applied to examine the gas-phase chemistry and photochemistry of metal ions, metal ion clusters, and metal ion complexes, all of which have a bearing on the fundamentals of organometallic chemistry and catalysis.     

Stability of disubstituted copper complexes in the gas phase analyzed by electrospray ionization mass spectrometry

A series of nitrogen ligand (L)/copper complexes of the type [Cu^IL]⁺, [Cu^IIL(X)]⁺ and [Cu^IL₂]⁺ (X = Cl^–, BF, acac^–, CH₃COO^– and SO₃CF) was studied in the gas phase by electrospray ionization mass spectrometry. The following ligands (L) were employed: 1,12‐diazaperylene (dap), 1,1′‐bisisoquinoline (bis), 2,2′‐bipyridine (bpy), 1,10‐phenanthroline (phen), 2,11‐disubstituted 1,12‐diazaperylenes (dap), 3,3′‐disubstituted 1,1′‐ bisisoquinoline (bis), 5,8‐dimethoxy‐substituted diazaperylene (meodap), 6,6′‐ dimethoxy‐substituted bisisoquinoline (meobis) and 2,9‐dimethyl‐1,10‐phenanthroline (dmphen). Collision‐induced decomposition measurements were applied to evaluate the relative stabilities of the different copper complexes. The influence of the spatial arrangement of the ligands, of the type of substituents and of the counter ion of the copper salts employed for the complexation was examined. Correlations were found between the binding constants of the [ML₂]⁺ complexes in solution and the relative stabilities of the analogous complexes in the gas phase. Furthermore, complexation with the ligands 2,11‐dialkylated 1,12‐diazaperylenes [alkyl = ethyl (dedap) and isopropyl (dipdap)] was studied in the solvents CH₃OH and CH₃CN. Copyright © 2010 John Wiley & Sons, Ltd.     

Composition of thiacalix[4]arene complexes with monovalent metal ions in the gas phase: MALDI mass spectrometry

MALDI-TOF mass spectrometry was used to study the reaction of p-tert-butylthiacalix[4]arene (1) and a number of its derivatives disubstituted at the lower rim (2—9) with monovalent metal salts (Li, Na, K, Cs, Cu, Ag) in the gas phase. It was shown that the thiacalixarenes under study bind the metal ions through the substitution of hydrogen atoms of the hydroxy groups. The reactions of silver and copper salts with the thiacalix[4]arenes were found to form the cluster ions, which represent the macrocycle dimers with several metal ions, while the formation of such clusters is impossible in the case of alkali metal salts. The peak intensities of the cluster ions increase in the weakly basic medium, reaching in some cases 100%.     

Generation and characterization of ionic and neutral P(OH) 2 +/. in the gas phase by tandem mass spectrometry and computational chemistry

The bicoordinated dihydroxyphosphenium ion P(OH)2+ (1+) was generated specifically by charge-exchange dissociative ionization of triethylphosphite and its connectivity was confirmed by collision induced dissociation and neutralization-reionization mass spectra. The major dissociation of 1+ forming PO+ ions at m/z 47 involved another isomer, O=P-OH2+ (2+), for which the optimized geometry showed a long P-OH2 bond. Dissociative 70-eV electron ionization of diethyl phosphite produced mostly 1+ together with a less stable isomer, HP(O)OH+ (3+). Ion 2+ is possibly co-formed with 1+ upon dissociative 70-eV electron ionization of methylphosphonic acid. Neutralization-reionization of 1+ confirmed that P(OH)2* (1) was a stable species. Dissociations of neutral 1, as identified by variable-time measurements, involved rate-determining isomerization to 2 followed by fast loss of water. A competitive loss of H occurs from long-lived excited states of 1 produced by vertical electron transfer. The A and B states undergo rate-determining internal conversion to vibrationally highly excited ground state that loses an H atom via two competing mechanisms. The first of these is the direct cleavage of one of the O-H bonds in 1. The other is an isomerization to 3 followed by cleavage of the P-H bond to form O=P-OH as a stable product. The relative, dissociation, and transition state energies for the ions and neutrals were studied by ab initio and density functional theory calculations up to the QCISD(T)/6-311+G(3df,2p) and CCSD(T)/aug-cc-pVTZ levels of theory. RRKM calculations were performed to investigate unimolecular dissociation kinetics of 1. Excited state geometries and energies were investigated by a combination of configuration interaction singles and time-dependent density functional theory calculations.     

Tandem mass spectrometry of poly(ethylene glycol) lithium-attachment ions

A study of the fast-atom bombardment tandem mass spectrometry behavior of a number of ethylene glycol polymers (PEGs) has been carried out. Both linear (hydroxyl, amino, and/or alkyl end groups) and cyclic (crown ether) polymers were studied. One of the materials is a block copolymer of ethylene and propylene oxides. Collisional activation was carried out in the collision octapole of a BEoQ hybrid mass spectrometer at a translational energy of 50 eV, with collision gas air. For the linear polymers, the most intense product ions are lithiated, linear polyglycol oligomers. These ions are formed via internal hydrogen transfer reactions that are facilitated (charge-induced) by lithium. This series of product ions allows for the observation of consecutive losses of monomer units from the chain end; this is useful to determine the sequence of monomers in a copolymer. The most abundant product ions from cyclic PEGs are lithiated radical cations. An especially interesting finding in this work is the preferential loss of two internal ethylene oxide (EO) units (dioxane, 88 u) from some [M + Li]⁺ precursors. Factors that influence this loss include (a) the sequence length of EO repeat units in the oligomer and (b) the identity of the end group(s) on the oligomer. It is proposed that this elimination of dioxane involves a six-membered ring intermediate; this decomposition reaction is believed to be a lithium-mediated (charge-induced) rearrangement. (J Am Soc Mass Spectrom 1994, 5, 1072-1080)     

Radical-induced aromatic substitution between benzoyl peroxide and benzenediols in the gas phase characterized by mass spectrometry

A radical-induced aromatic substitution mechanism for the reaction between benzoyl peroxide and benzenediols in the gas phase was characterized by mass spectrometry. The benzoyloxy radical produced from the homolysis of benzoyl peroxide associates at its carbonyl group with the phenolic hydroxyl group. The pairing tendency of the unpaired electron on the oxygen of the radical induces electron transfer along the hydrogen bond, which results in the rupture of the O? H bond of the phenol and aromatic substitution at the ortho position of the benzoyloxy radical. Supporting evidence for the mechanism was obtained by isotope labelling.     

Influence of weakly bound adduct ions on breath trace gas analysis by selected ion flow tube mass spectrometry (SIFT-MS)

This paper describes how weakly bound adduct ions form when the precursor ions used in selected ion flow mass spectrometry, SIFT-MS, analyses, viz. H₃O⁺, NO⁺ and O₂⁺, associate with the major components of air and exhaled breath, N₂, O₂ and CO₂. These adduct ions, which include H₃O⁺N₂, H₃O⁺CO₂, NO⁺CO₂, O₂⁺O₂ and O₂⁺CO₂, are clearly seen when dry air containing 5% CO₂ (typical of that in exhaled breath) is analysed using SIFT-MS. These adduct ions must not be misinterpreted as characteristic product ions of trace gases; if so, serious analytical errors can result. However, when exhaled breath is analysed these adduct ions are partly removed by ligand switching reactions with the abundant water molecules and the problems they represent are alleviated. But the small fractions of the adduct ions that remain in the SIFT-MS spectra, and especially when they are isobaric with genuine characteristic product ion of breath trace gases, can result in erroneous quantifications; such is the case for H₃O⁺N₂ interfering with breath ethanol analysis and H₃O⁺CO₂ with breath acetaldehyde analysis. However, these difficulties can be overcome when the isobaric adduct ions are properly recognised and excluded from the analyses; then these two important compounds can be properly quantified in breath. The presence of O₂⁺CO₂ in the product ion spectra interferes with the analysis of CS₂ present at low levels in exhaled breath. It is likely that similar problems will occur as other trace compounds are detected in exhaled breath when consideration will have to be given to the possibility of overlapping between their characteristic product ions and ions produced by hitherto unknown reactions. Similar problems are evident in other systems; for example, H₃O⁺CH₄ adduct ions are observed in both SIFT-MS analyses of methane rich mixtures like biologically generated waste gases and in model planetary atmospheres.     

Sulphonylium ions in the gas phase

Electron impact mass spectrometry was used to investigate the fragmentation of a series of arenesulphonyl chlorides. Sequential losses of a chlorine atom and sulphur dioxide from the molecular ions occurred and the reverse of these reactions had small critical energies that were generally unaffected by the ring substituent. However, an interesting intramolecular cyclization reaction occurring on the ortho-nitro derivative is discussed with the aid of kinetic energy release measurements on this derivative and on a model compound. Appearance energy measure ments combined with multiple scattering Xα calculations led to an estimate of the sulphur-chlorine bond strength in benzenesulphonyl chloride.