Metastable Ion Spectra Research Articles

Gas-phase generation of dinuclear Au(I)-Au(II) complexes by laser desorption ionization mass spectrometry.

Alkali metal chloroaurates(III) were analysed by laser desorption ionization mass spectrometry. Among a number of generated gas-phase ionic clusters, the unusual ions [MAu2Cl5]- (were M stands for Na, K, Rb, Cs) were detected. The spectra of metastable ions and quantum mechanics calculations show the presence of unprecedented Au(I)-Au(II) interactions in the clusters.

General trends in dissociations of medium-sized hydrocarbon dications

This study aims towards a rationalization and generalization of the fragmentation patterns of medium-sized hydrocarbon dications by tandem mass spectrometry. Phenanthrene (C14H10) serves as a precursor for the generation of CmHn2+ dications with m=9–14 and n=1–10. Four characteristic channels occur in the metastable-ion spectra: loss of a hydrogen atom, elimination of molecular hydrogen, loss of acetylene, and charge-separation fragmentation (Coulomb explosion). The first two channels dominate the spectra and their relative intensities show some regularities for ions with an even number of carbon atoms. Further, parent ions with an odd number of hydrogen atoms exhibit loss of atomic hydrogen, whereas loss of molecular hydrogen is preferred for dications with an even number of hydrogen atoms. The ions with odd number of carbon atoms do not show any evident regularity for the H and H2 losses. The channels involving CC bond cleavages occur for larger dications with m>9, but only for some combinations of m and n without an apparent regularity.

Computational and experimental exploration of the gas-phase chemistry of alkyloxalate ions ROCOCOO − (R = H, CH 3, C 2H 5, i-C 3H 7, and t-C 4H 9)

Alkyloxalate ions ROCOCOO − (R = H, CH 3, C 2H 5, i-C 3H 7, and t-C 4H 9) are investigated by experiment and theory. Computational studies at the MP2/6-311++G(3df,3pd)//MP2/6-311++G(d) level of theory show that the structures vary with changing the size of the alkyl substituent R. Metastable ion and collisional activation mass spectra reveal three decomposition pathways of alkyloxalate ions corresponding to losses of CO and CO 2 as well as a combined expulsion of CO and CO 2. Decarbonylation dominates the spectra by far and leads to the corresponding alkylcarbonate ions ROCOO −. Two mechanisms are envisaged to understand this dissociation, and calculations suggest that the reaction proceeds through the formation of an intermediate ion–neutral complex.

Mass spectrometry of metastable ions from lagochiline-type diterpenoids

Low-and high-resolution mass spectra and spectra of metastable ions were studied using direct analysis of daughter ions (DADI) and metastable defocusing (MD) of lagochiline-type diterpenoids. Patterns in their fragmentation were found.

Discrimination of diastereoisomers by electron ionization mass spectrometry in the 1,3‐dioxane series

AbstractImportant differences in the electron ionization (EI) mass spectra of cis,cis and trans,trans isomers of some 2(r)‐R‐2,4(R),6(S)‐trimethyl‐1,3‐dioxanes are recorded and the significant preference for the fragmentation with the cleavage of the axial substituents at C(2) position is revealed. The fragmentation pattern is elucidated by high‐resolution mass measurements, metastable ion spectra and linked‐scan mass spectrometry. Copyright © 2005 John Wiley & Sons, Ltd.

Mass spectrometric decompositions of copper complexes with esters and amides of nicotinic acid

Mass spectrometric decompositions of complexes of nicotinic acid esters and amides with copper are discussed. Liquid secondary ion mass spectrometry (LSIMS) was used as an ionisation technique and metastable ion spectra were recorded by using B/E linked scans. The fragmentation pathways consist mainly of the loss of one ligand molecule and also the cleavage of amide or ester bonds. It may be possible, on the basis of cleaved neutral fragments, to determine the site of coordination in the gas phase. It was also found that the presence of a chlorine atom affects the fragmentation pathways of complexes.

Fragmentation and skeletal rearrangements of products of the reaction between fluorobenzenes and bicyclic N-bases studied by electron ionization mass spectrometry

The electron ionization (EI) induced mass spectrometric fragmentation pathways of the titled compounds were studied by electron ionization mass spectrometry. It was found that in the case two isomers are formed in one reaction, the substantially different fragmentation patterns enable to discriminate between them. All of the compounds studied have shown simple bond ruptures in the alkyl chain, some of them were accompanied by H-shift. Moreover, complex rearrangements, depending on compound structure, were also observed. In order to better understand the latter processes, mass spectra of isotope-labeled compounds, B/E mass spectra of metastable ions and high resolution mass spectra were recorded.

Mass spectral study on O,O-dialkyl N,N-dialkyl phosphoramidates under electron impact conditions

A series of O,O-dialkyl N,N-dialkyl phosphoramidates ( 1– 25) were analyzed under GC-EIMS conditions. Clear-cut differences are found in the fragmentation of O,O-dialkyl N,N-dimethyl phosphoramidates (Series 1) and O,O-dimethyl N,N-dialkyl phosphoramidates (Series 2). The phosphoramidates comprising of mixed/crossed alkyl groups on nitrogen and oxygen (Series 3) showed mixed fragmentation pattern corresponding to both Series 1 and 2 depending on the nature of alkyl groups. All the possible isomers among the studied compounds showed distinguishable EI mass spectra. Although the major ions in the EI mass spectra for the isomers containing O-n-propyl or O-isopropyl and N,N-diethyl or N-isopropyl N-methyl are similar, the isomers could be distinguished by characteristic ions of low abundance at low mass region. The differences are prominent in the metastable ion spectra of characteristic ions.

Tautomerization and dissociation of ethylene phosphonate ions [OCH 2CH 2O]P(H)O [rad]+: an experimental and CBS-QB3 computational study

The unimolecular gas-phase chemistry of the cyclic title ion, [OCH 2CH 2O]P(H)O +, 1a +, and its tautomer ethylene phosphite, [OCH 2CH 2O]POH +, 1b +, was investigated using mass spectrometry-based experiments in conjunction with isotopic labelling and computational quantum chemistry, at the CBS-QB3 level of theory. A facile tautomerization of the “keto” ion 1a + into its more stable (by 34 kcal/mol) “enol” isomer 1b + is prevented by a substantial 1,2-H shift barrier (14 kcal/mol relative to 1a +). In line with this, the collision-induced dissociation (CID) and neutralization-reionization (NR) spectra of the two isomers are characteristically different. Unlike the corresponding acyclic dimethyl phosphonate/phosphite tautomers, (CH 3O) 2P(H)O +/(CH 3O) 2POH +, where the phosphonate isomer rapidly loses its structure identity by a facile distonicization into CH 2O(CH 3O)P(H)OH +, the barrier for this reaction in 1a + is prohibitively high and the cyclic distonic 1,2-H shift isomer [OCH 2CH 2O(H)]PO +, 1c +, is not directly accessible. The 1,2-H shift barrier separating 1a + and 1b + is calculated to lie close to the thermochemical threshold for the formation of C 2H 4 ++HOP(O) 2. This reaction dominates the closely similar metastable ion (MI) spectra of these tautomers. At these elevated energies, the “enol” ion 1b + can undergo ring-opening by CH 2O or CH 2CH 2 cleavage, yielding ion–dipole complexes of the type [C 2H 4] +/HOP(O) 2, 1e +, and H-bridged radical cations CH 2 O ⋯[ H O P OCH 2] + , 1f +, respectively. Moreover, communication of 1b + with the distonic ion 1c + now also becomes feasible. These computational findings account for the similarity of the MI spectra and provide a rationale for the observation that in the losses of CO, HCO and C 2H 3O from metastable ions [ OCH 2 CH 2 O] P( H) 18 O + and [ OCH 2 CH 2 O] P 18 OH + , the 18 O -atom loses its positional identity. Theory and experiment yield a consistent potential energy profile for the cyclic phosphonate/phosphite system showing that non-dissociating ions 1a + retain their structure identity in the microsecond time-frame. However, the interaction of 1a with a benzonitrile (BN) molecule in a chemical ionization type experiment readily yields the more stable “enol” type ion 1b +. Experiments with benzonitrile-d 5 support the proposal that this interaction does not involve the lowering of the 1,2-H shift barrier between the tautomers, via a proton-transport catalysis type mechanism. Rather, a “quid-pro-quo” mechanism is operative, analogous to that proposed for the benzonitrile-assisted enolization of acetamide [Int. J. Mass Spectrom. 210/211 (2001) 489].

Differentiation of isomeric sulfur heterocycles by electron ionization mass spectrometry: 1,4-dithiins, 1,4-dithiafulvenes and their analogues tetrathianaphthalenes, tetrathiafulvalenes and tetrathiapentalenes.

The electron ionization mass spectra of the title compounds have been studied along with the product ion spectra of their metastable or collisionally activated molecular ions. The relative abundances of ions in the spectra allow unambiguous isomer differentiation. Isomerization of the molecular ions was observed in the metastable ion spectra of tetrathianaphthalenes and tetrathiafulvalenes. This isomerization reaction parallels the electrochemical or base-induced isomerization observed in solution. The studied tetrathiapentalene derivative does not rearrange to the corresponding tetrathiafulvalene or tetrathianaphthalene isomers.

The water-solvated methanol ion and its isomers: experiment and theory

Tandem mass spectrometry combined with ab initio calculations was used to explore the chemistry of the water-solvated methanol cation and its isomers, including the distonic methanol ion solvated by water, CH 2OH 2 +/H 2O ( I), the methanol molecular ion associated with water, CH 3OH +/H 2O ( II), and protonated methanol bound with a hydroxyl radical, CH 3OH 2 +/HO ( IV). Another ion, [H 2O⋯HCH 2OH +] ( III), where the water molecule is attached to a methyl H of the methanol cation, proved inaccessible experimentally although it was predicted to be stable in a shallow potential well by theoretical calculations. The ions were generated by collision-induced loss of a radical or atom from appropriate proton bound molecular pairs. The heats of formation of ions ( I) to ( IV) were calculated to be 448, 482, 486 and 538 kJ/mol, respectively. Ions ( I), ( II) and ( IV) can be identified by their metastable ion and collision-induced dissociation mass spectra. A partial potential energy surface linking the isomers is used to discuss the experimental data obtained with deuterium-labeled species.

Determination of the Structure of Batumic Acid by Mass Spectrometry

Using various mass spectrometric methods (electron ionization, field desorption, high-resolution operation and metastable-ion spectra), specific chemical reactions and derivatization, the structure of batumic acid was established as 3,5,15-trimethyl-7-methylene-17-oxooctadeca-2,10,12-trienoic acid.

Loss of isocyanic acid from the internal oxadiazole ring of protonated molecules of some 2,5-diaryl-1,3,4-oxadiazoles.

The fragmentation pattern of some protonated 2,5-diaryl-1,3,4-oxadiazoles is discussed. An unusual decomposition consisting of elimination of the isocyanic acid molecule from the internal oxadiazole ring was found. This fragmentation pathway was deduced on the basis of B/E linked scan mass spectra of metastable ions with liquid secondary ion mass spectrometry as the ionization method and also of low-energy CID mass spectra where electrospray was used as the ionization technique. High resolution measurements were also performed.

Dissociation behavior of ionized valeramide: Part III. An unprecedented temperature effect on the C 3/C 2 branching ratio and its implications for metastable ion dissociations

The competing formations of C 2- and C 3-fragments in the unimolecular decay of mass-selected valeramide cation-radicals are analyzed in detail. It turns out that the different branching ratios observed in the various experiments are due not only to the internal energy of the ions but also to that of the neutral precursors. The latter is manifested by a pronounced effect of the temperature of the ion source on the C 3/C 2 branching ratios in the metastable ion spectra of ionized valeramide. Exploratory studies indicate that the effect is not limited to valeramide in that similar temperature phenomena are observed for the metastable molecular ions of hexanoic acid and its amide.

Application of Mass Spectrometry and Chromatography–Mass Spectrometry in Drug Analysis

The review is devoted to the use of mass spectrometry and chromatography–mass spectrometry in various areas of pharmaceutical chemistry. The role of the above techniques in the structural identification of impurities in drug preparations and in the determination of the biotransformation behavior of pharmaceuticals in human and animal bodies is shown. The inactivation of drugs under the action of external factors (oxidation by atmospheric oxygen and the effects of moisture, heat, and light) is illustrated. The use of various ionization techniques and the spectra of metastable ions for determining the structures of components of biologically active substances are exemplified.

The chemistry of some low energy C 5H 9O + oxonium ions

The reactions of the low energy oxonium ions CH 3CHCHC +(H)OCH 3, b 1 + , CH 2CHC +(CH 3)OCH 3, b 2 + , and CH 2C(CH 3)C +(H)OCH 3, b 3 + , are reported and compared with those of their 1,3-H shift isomers CH 3CHCHCH 2OCH 2 +, b 4 + , CH 2CHCH(CH 3)OCH 2 +, b 5 + , and CH 2C(CH 3)CH 2OCH 2 +, b 6 + . The metastable ion (MI) spectrum of the C 4H 6OCH 3 + ions b 1 + – b 3 + is dominated by loss of CH 2O. Elimination of C 3H 6, which is associated with a composite metastable peak, is also significant from b 2 + and b 3 + . From (multiple) collision experiments and analysis of D- and 13C-labeled isotopologues, it follows that b 1 + – b 3 + do not readily interconvert. Loss of CH 2O is proposed to involve a 1,5-H shift followed by a (dipole-assisted) 1,3-H shift into an energy-rich ion-neutral complex (INC) [C 4H 7 +/CH 2O]. Loss of CH 2O from b 4 + – b 6 + may also occur via an INC. This reaction is associated with a very small kinetic energy release, indicating that it generates the most stable C 4H 7 + ion, CH 2CHC +(H)CH 3, at the thermochemical threshold. However, this process is only prominent for ions b 5 + , which also undergo a facile loss of H 2O, via rearrangement in the INC [C 4H 7 +/CH 2O], to yield C 5H 7 + (most probably the cyclopentenyl cation). Loss of C 3H 6 and CO dominates the MI spectra of b 4 + and b 6 + and these reactions, which also occur from b 5 + , are proposed to take place from 1,2-H shift isomers of the cyclic counterparts of b 4 + – b 6 + . The behavior of b 1 + – b 3 + and b 4 + – b 6 + differs considerably from their C 4H 7O + homologues, CH 2CHC +(H)OCH 3, a 1 + , and CH 2CHCH 2OCH 2 +, a 2 + . Differences in the dissociation characteristics of the C nH 2n−2OCH 3 + species (n = 3–5) are discussed in terms of the energetics of the products that may be formed. ΔH f (298 K) values for the key ions in this study were obtained from CBS-QB3 calculations and thermochemical estimates.

Electron impact mass spectral interpretation for some thiophosphoryl‐p‐acetylaminobenzenesulfonamides

This work discusses the synthesis and the fragmentation patterns for 2-(p-acetylaminosulfonamido)-2-thiono-(5,5-dimethyl-1,3,2-dioxaphosphorinane)(1) and for the p-acetylaminosulfonylamides of O,O-diethylthiophosphoric acid (2), O,O-diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic-thiolimidic structure was attributed to compounds 1-5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions.

Fragmentation behavior of Si2Cln+ cations (n = 1—6)

Sector-field mass spectrometry was used to probe the fragmentation patterns of the cationic silicon chlorides Si2Cln+ (n = 1—6). For almost all Si2Cln+ ions, Si—Si fragmentation predominates the Si—Cl bond cleavage both in the metastable ion and collisional activation mass spectra. Analysis of the fragmentation patterns indicates that the long-lived radical cation Si2Cl6·+ corresponds to a complex [SiCl2·SiCl4]·+ rather than the intact molecular ion of hexachlorodisilane. The behavior of Si2Cl5+ is consistent with the formation of the (trichlorosilyl)dichlorosilyl cation Cl3SiSICl2+. Structural aspects are also discussed for the other Si2Cln+ species. A semi-quantitative analysis of the fragmentation patterns in conjunction with the literature thermochemistry data was used to estimate some thermochemical properties of the Si2Cln+ cations.

Tautomerization and Dissociation of Dimethyl Phosphonate Ions(CH3O)2P(H)=O•+:Theory and Experiment in Concert

The unimolecular gas phase chemistry of the title ion,(CHThe identity of the ions was probed by tandem mass spectrometry methods. These include MI (metastable ion) or CID (collision induced dissociation) spectra, consecutive MI/CID and CID/CID spectra, NRMS (neutralization-reionization mass spectra), NR/CID and CIDI (collision induced dissociative ionization) spectra, time-resolved CID spectra and deuterium labelling. The energetics of the CHTheory and experiment yield a consistent potential energy profile that describes the isomerization and low energy dissociation chemistry of ions

Metastable and collision-induced fragmentation studies and thermochemistry of isomeric C4H11Si+ ions and their adducts with C4H12Si silanes

Metastable Ion (MI) and collision-induced dissociation (CID) mass spectra for all isomeric even-electron [C(4)H(12)Si - H](+) ions were recorded and compared. Deuterium labeling experiments indicated that most precursors give rise to silylium ions. Silylium ions with two or more methyl groups are found to lose C(2)H(4) after isomerization via a straightforward hydrogen transfer to the appropriate ethylsilylium ion. Similarly, all isomeric propyl- and butyl-containing silylium ions are found to lose C(2)H(4) by rearrangement preceding dissociation. In the CI source of the mass spectrometer many of the silylium ions are found to cluster with the parent neutral silane present in the source to give stable [M - H](+)+M adduct ions. The MI and CID spectra of these adduct ions were also obtained. In the MI spectra of all adducts, except i-BuSiH(3), only the starting silylium ion is observed. Under CID conditions generation of silylium ions dominates. Deuterium labeling studies show that this dissociation may be accompanied by some rearrangement, in particular for the adducts from i-BuSiH(3). High-pressure mass spectrometric clustering equilibrium measurements were also carried out to determine the enthalpies and entropies of binding of the silylium ions to the neutral silanes. These measurements yield insight into the effects of various alkyl group substitutions on the association thermochemistry in these adducts. Copyright 2000 John Wiley & Sons, Ltd.