Collisionally activated mass spectra of [M?H] ions of polyhydroxy and hydroxy ether compounds

Collision-induced decomposition/mass-analyzed ion kinetic energy or collisionally activated mass spectra of [M ? H]^? ions of polyhydroxy compounds and other alcohols and ethers are reported. The [M ? H]^? ion of each compound is produced under OH^? negative ion chemical ionization mass spectrometric conditions. Characteristic fragmentations are observed that include production of [M ? H ? 2]^?, [M ? H ? 18]^? and [M ? H ? 32]^? ions. Certain other fragment ions in the collisionally activated mass spectra make it possible to distinguish among structural isomers. In polyhydroxy compounds, fragmentation increases as the number of hydroxyl groups increase, and carbon-carbon bond cleavage becomes favored.     

Anomalies in the molecular ion region in the electron impact mass spectra of α- and β-hydroxyesters

In the electron impact mass spectra of some alkyl α- and β-hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M^+· and the presence of the [M + 1]⁺ ion instead is observed. This phenomenon is especially characteristic of C₃? C₆ glycolates and diethyl malate, and is due to chemical auto-ionization—ion-molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M ? 2]^+·, [M ?1]⁺ and M^+· ions in the mass spectra of other β- and α-hydroxyesters is discussed.     

HPLC Method for the Determination of the Purity of K[Pt(NH3)Cl3], a Precursor of the Platinum Complexes with Cytostatic Activity

K[Pt(NH₃)Cl₃], a valuable precursor for the preparation of platinum complexes with cytostatic activity, e.g. satraplatin, picoplatin, LA-12 and cycloplatam, is currently prepared from cis-[Pt(NH₃)₂Cl₂] or K₂[PtCl₄] and these are the usual impurities in the final product. A simple, selective and sensitive HPLC-UV analytical method for the determination of the purity of K[Pt(NH₃)Cl₃] and the quantification of the impurities has been developed and validated. The platinum complexes present in the final product were separated on a strong base ion exchange column by the gradient elution with detection at 213 nm. Intra-assay precisions for the platinum complexes respective to their ions ([PtCl₄]^2?, [Pt(NH₃)Cl₃]^? and cis-[Pt(NH₃)₂Cl₂]) were between 0.1 and 2.0% (relative standard deviation); intermediate precisions were between 1.4 and 2.0% and accuracies were between 98.6 and 101.4%. Limits of detection of [PtCl₄]^2?, [Pt(NH₃)Cl₃]^? and cis-[Pt(NH₃)₂Cl₂] were 6 µg · ml^?1, 13 mg · ml^?1 and 5 µg · ml^?1 respectively, limits of quantification of [PtCl₄]^2?, [Pt(NH₃)Cl₃]^? and cis-[Pt(NH₃)₂Cl₂] were 51 µg · ml^?1, 55 mg · ml^?1 and 20 µg · ml^?1 respectively.     

Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH₄Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]^? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄]⁺, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^? into a Cl^? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄]⁺ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural correlations with kinetic energy release during loss of chlorine from nineteen selected chlorinated biphenyls

Unimolecular and collision induced decompositions of the major ions of selected polychlorinated biphenyls in the field free region between the magnetic and electric sectors of a reversed Nier-Johnson instrument were studied. Loss of a single chlorine atom is associated with a wide range of kinetic energy releases but still can be correlated by a single reaction mechanism. Loss of two chlorines is interpreted as a rapid sequential loss from isomerized molecular ions for all but one compound. The decompositions which metastable ions undergo are not always the same as those of high energy ions in the source. Correlations between substituent positions and kinetic energy release can be made for the [M]^+·→[M? Cl]⁺ and [M? Cl₂]^+· processes.     

Two hydro­chlorides of 7‐methyl‐3,7,11,17‐tetra­aza­bi­cyclo­[11.3.1]­heptadeca‐1(17),13,15‐triene

The X‐ray structure determinations of the two title com­pounds, namely 7‐methyl‐7,17‐di­aza‐3,11‐diazo­niabi­cyclo[11.3.1]­hep­ta­deca‐1(17),13,15‐triene dichloride monohydrate, C₁₄H₂₆N₄²⁺·2Cl^?·H₂O, (I), and 7‐methyl‐17‐aza‐3,7,11‐triazo­niabi­cyclo­[11.3.1]­heptadeca‐1(17),13,15‐triene 2.826‐chloride 0.174‐nitrate, C₁₄H₂₇N₄³⁺·2.826Cl^?·0.174NO₃^?, (II), are re­ported. Protonation occurs at the secondary amine N atoms in (I) and at all three amine N atoms in (II) to which the Cl^? ions are linked via N—H?Cl hydrogen bonds. The macrocyclic hole is quite different in both structures, as is observed by comparing particularly the N3?N4 distances [2.976 (4) and 4.175 (4) Å for (I) and (II), respectively]. In (II), a Cl^? ion alternates with an NO₃^? ion in a disordered structure.     

Double collision experiments

A variety of double collision experiments, whereby fast species undergo collisional interactions in two distinct regions of a mass spectrometer, are described. These include two-stage charge reversal of negative ions, two-stage double electron transfer from targets to cations, neutralization-reionization experiments as well as delayed analysis of organic cations formed in a one-step charge reversal of anions. Experiments have been performed on a number of systems of current interest in gas-phase ion chemistry. It is concluded that autoelectron detachment of benzyl anions leads to benzyl radicals, whereas the collisionally induced electron detachment produces a mixture of benzyl and tropyl radicals. By contrast, electron detachment from [H₃CNH]^? is not a metastable process and occurs only after excitation to produce H₃CNH˙ radicals, which do not rearrange into the thermodynamically more stable H₂CNH₂˙. It is shown that in the double electron transfer reactions H⁺ + Xe→H˙ + Xe⁺˙ and H˙ + Xe→H^? + Xe⁺˙, excited states are produced. From double collision experiments on methyl formate ions, it is concluded that the non-decomposing ions have undergone rearrangement on the time-scale of 10 μs into the distonic isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} - \mathop {\rm C}\limits^ + ({\rm OH}){\rm O}\mathop {\rm C}\limits^. {\rm H}_2 $\end{document}. Finally, it is shown that short-lived (<0.2 μs) [H₂, C, N]⁺ ions generated by charge-reversal of [H₂CN]^? have the [H₂CN]⁺ structure, whereas most of the long-lived (10 μs) ions have the [HCNH]⁺ structure.     

[C]+· and [CH]+ from doubly charged ions formed from malononitrile

The metastable ions [M]²⁺, [M – H]²⁺· and [M – H₂]²⁺ from malononitrile fragment by loss of [CH]⁺, [C]⁺· and [C]⁺·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M – H]²⁺· involves exclusively the nitrile carbon and that of [M ? H₂]²⁺ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.     

Trinuclear copper(II) complexes of some aza macrocycles

The syntheses of copper(II) complexes with neutral macrocyclic ligands 1,4,7,10,12,- 15,17,20,23,26,27,30-dodecaazadispiro[10·4·10·4]triacontane (DDST), 2,5,7,10,13,15,18,21,-23,26,29,32-dodecaazatricyclo[20·10·0·0^6,17]dotriacontane (DOCD) and 2,5,7,10,13,16,18,-21,23,26,29,32-dodecaaza-1,6,17,22-tetrachlorotricyclo[20·10·0·0^6,17]dotriacontane (DTTD) derived from triethylenetetramine, 1,2-diaminoethane and chlorocarbons (carbon tetrachloride, 1,l,2,2-tetrachloroethane and hexachloroethane, respectively) have been studied. Complexes [Cu₃(DDST)]Cl₆, [Cu₃(DOCD)]Cl₆ and [Cu₃(DTTD)]Cl₆?·?H₂O and the copper ion-free ligand hydrochlorides DDST?·?12HCl and DOCD?·?12HCl are supported by elemental analyses, conductivity measurements and spectroscopic studies. Potentiometric equilibrium studies on DDST and DOCD hydrochlorides and their copper complexes also support the structures.     

Collision-induced oxygen addition to chloroaromatic compounds

The reactions of chloroaromatic radical anions with oxygen were studied with a triple quadrupole mass spectrometer. Two chlorobenzenes and eight polychlorinated biphenyls were analyzed by gas chromatography-tandem mass spectrometry under negative ion chemical ionization. The molecular radical anions were selected with the first quadrupole and reacted with oxygen in the collision cell. Under these conditions, [M+O ? Cl] ions were obtained with intensities similar to those of the transmitted precursor ions. This dechlorination reaction was not affected by a detectable chlorine isotope effect. The intensities of the [M+O ? Cl] ions vary with the nature of the chloroaromatic compounds and with the oxygen pressure and collision energy. Charge transfer reactions are also observed, and the relative amount of O ₂ ^?. produced is controlled by the relative electron affinity of the organochlorine. At high collision energies, collision-induced fragmentation of the molecular ion competes for the production of Cl^?.     

Study of the characteristic fragmentation behavior of hydroquinone glycosides by electrospray ionization tandem mass spectrometry with optimization of collision energy

The fragmentation behavior of hydroquinone glycosides involving one or two sugar groups from Fraxinus sieboldiana and their analogue arbutin was investigated systematically by electrospray ionization tandem mass spectrometry in negative ion mode. The characteristic fragmentation reaction of these compounds was through the homolytic and heterolytic cleavage of the O‐glycosidic bond to produce radical aglycone ion ([Y₀ ? H]^??) and aglycone ion (Y₀^?), respectively. Unambiguous differentiation between the mono‐O‐glycoside isomers which differ in glycosylation position was achieved by comparing the relative abundance of [Y₀ ? H]^?? and Y₀^? ions with the optimized collision energy. In the fragmentation of 1, 4‐di‐O‐glycosides, only the Y₀^? ion was produced when the first glucosyl residue was expelled. However, both the [Y₀ ? H]^?? and Y₀^? ions were present when the second glucosyl residue was eliminated. In addition, an interesting [Y₀‐2H]^? ion was present in the product ion spectra of hydroquinone glycosides with methoxy group(s) substituted at C‐3 or/and C‐5 positions of the benzene ring. The results of this study can facilitate the rapid determination of hydroquinone glycosides in crude plant extracts and also reveal that the systematic investigation and optimization of collision energy play an important role in the differentiation of isomers which have subtle differences in structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Ion-molecule reactions observed for nitroaromatic compounds in negative ion fast atom bombardment mass spectrometry

Analyses of a series of nitroaromatic compounds using fast atom bombardment (FAB) mass spectrometry are discussed. An interesting ion-molecule reaction leading to [M + O ? H]^? ions is observed in the negative ion FAB spectra. Evidence from linked-scan and collision-induced dissociation spectra proved that [M + O ? H]^? ions are produced by the following reaction: M + NO₂^? → [M + NO₂]^? → [M + O ? H]^?. These experiments also showed that M^?˙ ions are produced in part by the exchange of an electron between M and NO₂^? species. All samples showed M^?˙, [M ? H]^? or both ions in their negative ion FAB spectra. Not all analytes studied showed either [M + H]⁺ and/or M⁺˙ in the positive ion FAB spectra. No M⁺˙ ions were observed for ions having ionization energies above ～9 eV.     

A relation between ion structures and experimental overall cross-sections for collisionally activated decomposition

Collisionally activated dissociation (CAD) mass spectra sometimes appear to be identical in spite of the fact that the precursor ion structures are known to differ. It is shown that determination of the experimental overall cross-section for collisionally activated decomposition yields valuable extra information. After applying it to examples of known structure, [C₄H₅N]^+·, [C₅H₅N]^+· and [C₅H₅O]⁺, it is used to study a more complex problem, that of [C₆H₆]^+· ions from four isomeric precursors.     

Structural identification of fatty acid methyl esters by collision spectra of their [M ? H]− species

Negative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass-analysed ion kinetic energy spectra of [M ? H]^? species, obtained by OH^? reaction with a selection of six C₁₈ fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.     

Negative- and positive-ion chemical ionization mass spectra of aromatic amines: Surface-assisted reactions involving oxygen

The O₂–N₂ and O₂–Ar negative-ion chemical ionization mass spectra of aromatic amines show a series of unusual ions dominated by an addition appearing at [M + 14]^?˙. Other ions are observed at [M – 12]^?˙, [M + 5]^?˙, [M + 12]^?˙, [M + 28]^?˙ and [M + 30]^?˙. Ion formation was studied using a quadrupole instrument equipped with a conventional chemical ionization source and a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. These studies, which included the examination of ion chromatograms, measurement of positive-ion chemical ionization mass spectra, variation of ion source temperature and pressure and experiments with ¹⁸O₂, indicate that the [M + 14]^?˙ ion is formed by the electron-capture ionization of analytes altered by surfaceassisted reactions involving oxygen. This conversion is also observed under low-pressure conditions following source pretreatment with O₂. Experiments with [¹⁵N]aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆]aniline show that the [M + 14]^?˙ ion corresponds to [M + O ? 2H]^?˙, resulting from conversion of the amino group to a nitroso group. Additional ions in the spectra of aromatic amines also result from surface-assisted oxidation reactions, including oxidation of the amino group to a nitro group, oxidation and cleavage of the aromatic ring and, at higher analyte concentrations, intermolecular oxidation reactions.     

Synthesis,crystal structure,and magnetic properties of a salt containing [Cu2Cl7]3− and 4-nitrobenzyl-4′-dimethylaminopyridinium

A new salt, [NO₂BzDMAP]₃[Cu₂Cl₇]?·?H₂O (1), has been synthesized, where [NO₂BzDMAP]⁺ is 1-(4′-nitrobenzyl)-4-dimethylaminopyridinium. Herein, the synthesis, spectral and structural characterization, and magnetic behavior of 1 are reported. It is orthorhombic, with space group Pca2₁, and a?=?26.639(2)?Å, b?=?9.638(1)?Å, and c?=?20.011(2)?Å with V?=?5137.5(7)?ų for Z?=?4. The anion shows a chloride-bridged binuclear structure with Cu?···?Cu distance of 3.872?Å; the two Cu(II) ions have a tetrahedral geometry. The cations stack through p?···?π and π?···?π interactions, and a complicated hydrogen-bonding network structure is formed through C–H?···?Cl and C–H?···?O hydrogen bonds. The variable temperature magnetic susceptibility measurements reveal that 1 exhibits strong antiferromagnetic interaction with J?=??193.0?cm^?1.     

Molecular fragmentation on collision with protons for freon and propane molecules

In ab initio calculations, we determined the most probable routes of decomposition of the [CF₃Cl]⁺, [CF₂Cl₂]⁺, [CFCl₃]⁺, [CCl₄]⁺ molecular ions of freons and [C₃H₈]⁺ ions of hydrocarbons formed by collision of neutral molecules with protons with energies of the order of 10 keV. The calculated potential surface sections are compared on a qualitative level with the probability of various ion fragments in experiments on fragmentation. The role of the charge transfer dynamics between the proton and the molecule is discussed.     

Energy dependence of rearrangements of an N-terminal protecting group in tandem mass spectrometry of protonated tripeptides containing C-terminal arginine

The types and intensities of tandem mass spectrometric products of side-chain interactions were investigated with a hybrid tandem instrument. Positive-ion unimolecular decomposition and collisionally activated decomposition studies were conducted on the [M + H]⁺ ions of two N-benzyloxycarbonyl (Cbz or Z)-protected tripeptides, Cbz-Gly-Leu-Arg-NH₂ and Cbz-Gly-Pro-Arg-NH₂. The loss of benzyl alcohol (108 u) and the formation of other significant product ions and their dependence on collision energy and gas pressure suggest reaction between both ends of the molecule. Replacement of leucine with proline at the second position in the tripeptide produces a very intense [M + H ? 108]⁺ ion and fewer lower mass fragment ions in the tandem mass spectra for Cbz-Gly-Pro-Arg-NH₂ than in those for Cbz-Gly-Leu-Arg-NH₂.     

Ring expansion and hydrogen scrambling in the molecular ion of 3-methylthiophene

The ratio [M ? D]/{[M-D] + [M ? H]} in the 70 eV mass spectra of six deuterated 3-methylthiophenes has been determined. From these values the mole fractions of the molecular ions that lose hydrogen atoms specifically from the various positions of the molecule were calculated, as well as the mole fraction in which the hydrogen atoms are fully scrambled before hydrogen elimination. It appears that hydrogen atoms are mainly lost from a fully scrambled [C₅H₆S]⁺· ion and from the α-position of the original molecular ion. A deuterium isotope effect of 1·60 to 1·72 was calculated for the hydrogen elimination. The reaction was also studied at low electron energies. In order to determine the degree of scrambling in the [C₅H₅S]⁺ ions, some decomposition reactions of this ion were investigated.     

Mass spectral fragmentation pattern of 3-(2′-hydroxyethyl)quinolin-2(1H)-one and its derivatives

Fragmentation patterns resulting from electron impact ionization of 3-(2′-hydroxyethyl)quinolin-2(1H)-one, three of its monosubstituted derivatives and four of its disubstituted derivatives were studied. The molecular ion of quinolinone-2-etbanol undergoes initial fragmentation with the loss of OH^·, H₂O, CO, ^·CHO, CH₂O, CH₂OH^·, CH₂?CHOH and HCNO species. The [M – CHO]⁺ ion is tentatively suggested to have been formed by the expulsion of H^· from the [M – CO]^+· ion and the [M - CHO]⁺ peak may be considered as diagnostic of a 2-quinolone-3-ethanol.