Structure determination of [C3H3N2]+ ions,formed from monosubstituted pyrazoles C3H3N2R,by collision-induced dissociation mass spectrometry

[C₃H₃N₂]⁺ ions have been generated under electron impact conditions from some monosubstituted pyrazoles C₃H₃N₂R. Collision-induced dissociation (CID) mass spectra of deuterium-labelled precursors suggest that the majority of the [C₃H₃N₂]⁺ ions formed from 1-nitro- and 4-bromo-pyrazole retain their cyclic structure, whereas the ions from 3(5)-bromopyrazole are mainly linear. This is confirmed by the relative values observed for the overall cross-sections for CID and for ion loss. An isotope effect of the order of 1.5–1.9 has been found for the collision-induced loss of H^˙ from [C₃H₃N₂]⁺, generated from 3(5)- and 4-bromopyrazole.     

Unusual behavior of pyrazolo[1,2-a]pyrazoles in fast atom bombardment (fab) and frit-fast atom bombardment (Frit-FAB) mass spectrometry. Influence of the matrix

The nature of the matrix used in Fast Atom Bombardment (FAB) mass spectrometry analyses of pyrazolo[1,2-a]pyrazoles was found to influence significantly their positive and negative ions mass spectra. Indeed the use of glycerol provided an abundant ion corresponding to the protonated molecule (M+H)⁺ whereas the meta-nitrobenzyl alcohol favored the formation of the radical ion M^+°. Such results which are in accordance with the oxidoreduction properties of the matrices studied were also established in Frit-FAB mass spectrometry analyses of pyrazolo[1,2-a]pyrazoles.     

Sonogashira Coupling Offers a New Synthetic Route to Thieno[2,3-c]pyrazoles

Abstract

1,3-Disubstituted-5-chloro-4-iodopyrazoles are selectively coupled with phenylacetylene under typical Sonogashira reaction conditions [PdCl₂(PPh₃)₂, CuI, Et₃N, dimethylformamide (DMF)] to obtain the corresponding 5-chloro-4-(phenylethynyl)pyrazoles in good yield. The latter are smoothly cyclized with Na₂S in DMF into the corresponding thieno[2,3-c]pyrazoles. Detailed spectroscopic investigations (¹H, ¹³C, and ¹⁵N NMR, mass, and infrared) of all compounds are reported.     

Nanoscale imaging of hydrogen and sodium in alteration layers of corroded glass using ToF-SIMS: Is an auxiliary sputtering ion beam necessary?

The hydrogen (H)/sodium (Na) interface is of great interest in glass corrosion research. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is one of the few techniques that can provide nanoscale H and Na imaging simultaneously. However, the optimized condition for ToF-SIMS imaging of H in glass is still unclear. In H depth profiling using ToF-SIMS, H background control is a key, in which an analysis ion beam and a sputtering ion beam work together in an interlaced mode to minimize it. Therefore, it is of great interest to determine if an auxiliary sputtering ion beam is also necessary to control H background in ToF-SIMS imaging of H. In this study, H imaging with and without auxiliary sputtering beams (Cs⁺, O₂⁺, and Ar_n⁺) was compared on a corroded international simple glass (ISG). It was surprising that the H/Na interface could be directly imaged using positive ion imaging without any auxiliary sputtering ion beam under a vacuum of 2 to 3 × 10⁻⁸ mbar. The H⁺ background was about 5% atomic percent on the pristine ISG glass, which was significantly lower than the H concentration in the alteration layer (~15%). Moreover, positive ion imaging could show distributions of other interesting species simultaneously, providing more comprehensive information of the glass corrosion. If an auxiliary O₂⁺ sputtering ion beam was used, the H⁺ background could be reduced but still higher than that in the depth profiling. Besides, this condition could cause significant loss of signal intensities due to strong surface charging.     

Mass spectrometric study of methyl-substituted 4-azaphenanthrenes and their nitration products

The mass spectral behavior of five derivatives of the 4-azaphenanthrene series — 1,3-dimethyl-(I), 2,3-dimethyl-(II), 1,2,3,-trimethyl-(III), 1,2,3-trimethyl-8-nitro-(IV), and 1,3-dimethyl-6,7-dinitro-4-azaphenanthrene (V) — was studied. The stabilities of the molecular ions with respect to gragmentation (W_M) are higher by a factor of two or more for the methyl-substituted I–III than for nitro derivatives IV and V. The intensity of the [M-H]⁺ ion peak in the mass spectra of I–V does not depend on the number of methyl groups but only on their positions: the presence of a CH₃ group in the 2 position leads to an [M-H]⁺ ion that is 1.5 times more intense than when there is a methyl group in the 1 position. The molecular ions of I–V do not eliminate HCN molecules; this constitutes evidence for the absence of randomization of their methyl groups. The presence of a CH₃ substituent in the 1 or 2 position does not affect the intensity of the [M-CH₃]⁺ ion peaks, while the simultaneous presence of CH₃ groups attached to the C₁ and C₂ atoms increases the intensity of the [M-CH₃]⁺ fragment peak by a factor of two. In the mass spectra of nitro derivatives IV and V, [M-O]⁺, [M-OH]⁺, [M-NO]⁺, and [M-NO₂]⁺ fragments are observed in the first step of the fragmentation of the M⁺ ion, whereas the [M-CO]⁺ ion peak characteristic for the dissociative ionization of 1-nitronaphthalene is also observed for 8-nitro-substituted IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1365–1369, October, 1977.     

Adamantylazoles: IV. Acid-Catalyzed Adamantylation of Pyrazoles

Pyrazoles with pK _{B H} ⁺ no more than 0.8 and having substituents in 3(5) position with effective van der Waals radii not exceeding 2 Å in a mixture of phosphoric and acetic acids at weight ratio 4:1 (H ₀ -1,8) react with 1-adamantanol to afford the corresponding 1-(1-adamantyl)- or 1,4-di(1-adamantyl)pyrazoles.     

High-resolution accurate mass measurements of biomolecules using a new electrospray ionization ion cyclotron resonance mass spectrometer

A novel electrospray ionization/Fourier transform ion cyclotron resonance mass spectrometer based on a 7-T superconducting magnet was developed for high-resolution accurate mass measurements of large biomolecules. Ions formed at atmospheric pressure using electrospray ionization (ESI) were transmitted (through six differential pumping stages) to the trapped ion cell maintained below 10^?9 torr. The increased pumping speed attainable with cryopumping (> 10⁵ L/s) allowed brief pressure excursions to above 10^?4 torr, with greatly enhanced trapping efficiencies and subsequent short pumpdown times, facilitating high-resolution mass measurements. A set of electromechanical shutters were also used to minimize the effect of the directed molecular beam produced by the ES1 source and were open only during ion injection. Coupled with the use of the pulsed-valve gas inlet, the trapped ion cell was generally filled to the space charge limit within 100 ms. The use of 10–25 ms ion injection times allowed mass spectra to be obtained from 4 fmol of bovine insulin (M_r 5734) and ubiquitin (M_r 8565, with resolution sufficient to easily resolve the isotopic envelopes and determine the charge states. The microheterogeneity of the glycoprotein ribonuclease B was examined, giving a measured mass of 14,898.74 Da for the most abundant peak in the isotopic envelope of the normally glycosylated protein (i.e., with five mannose and two N-acetylglucosamine residues (an error of approximately 2 ppm) and an average error of approximately 1 ppm for the higher glycosylated and various H₃PO₄ adducted forms of the protein. Time-domain signals lasting in excess of 80 s were obtained for smaller proteins, producing, for example, a mass resolution of more than 700,000 for the 4⁺ charge state (m/z 1434) of insulin.     

A study of negative ions from substituted benzils

The mass spectra and the appearance potentials for the negative ions from a number of 4-substituted and 4,4′-disubstituted benzils, containing CH₃, CH₃O, CH₃S, (CH₃)₂N and NO₂ substituents have been measured. Molecular anions were observed for all benzils. The negative ion mass spectra of the CH₃O- and CH₃S-substituted compounds also exhibited ions resulting from loss of CH₃ from the parent; Cl^? was observed too in the spectra of the chlorine substituted benzils. Only for the nitrobenzils is more than one fragment ion observed in the spectra. A comparison of the negative ion spectra with the positive ion spectra previously reported is also presented and discussed.     

Heterocyclic compounds from 2-(alkoxycarbonylcyanomethylene)-1,3-dioxolanes

2-(Alkoxycarbonylcyanomethylene)-1,3-dioxolanes reacted with hydrazines and hydroxylamine to yield 1-substituted 4-alkoxycarbonyl-5-amino-3-(2′-hydroxyethoxy)pyrazoles and 4-alkoxycarbonyl-5-amino-3-(2′-hydroxyethoxy)isoxazoles respectively. With guanidine and benzamidine 2-substituted (R = NH₂, C₆H₅) 5-cyano-6-(2′-hydroxyethoxy)pyrimidin-4-ones were obtained. Reaction of 2-(cyanomethoxycarbonylmethylene)-1,3-dioxolane with 1,3-diaminopropane afforded 2-(cyanomethoxycarbonylmethylene)-1,3-hexahydro-pyrimidine whereas treatment of the same compound with 4,5-dimethyl-1,2-phenylenediamine gave 2-(cyanomethoxycarbonylmethylene)-5,6-benzimidazoline. The structures of pyrazoles and pyrimidones were assigned on the basis of ¹H-{¹H} and ¹³C-{¹H}-nOe experiments.     

Desorption due to charge exchange in low-energy collisions of organofluorine ions at solid surfaces

Collisions of organofluorine ions at a metal surface result in efficient emission of adsorbate species as gas-phase ions. The experiments are done at 120° scattering angle in a hybrid (BQ) mass spectrometer; the primary ions, mass-selected by a magnetic sector (B), are allowed to collide with a target at a selected kinetic energy in the tens of eV range and the emitted ions are mass-analyzed using a quadrupole mass filter (Q). It is proposed that the impinging ions undergo neutralization accompanied by desorption of hydrocarbon ions and that the amount of internal energy deposited in the desorbed ions is strongly dependent on the collision energy and affects their degree of fragmentation. Competing processes include reflection and fragmentation of the colliding particle, along with such ion/adsorbate reactions as hydrogen atom abstraction by the fluorinated ion. Small even-electron ions, such as [CHF₂]⁺ and [C₂H₂F]⁺ are more effective in promoting chemical sputtering of the surface adsorbate as compared to larger ions (e.g. [C₃F₅]⁺) and odd-electron ions (e.g. [C₂F₄]⁺˙ and [C₂HF₂]⁺˙). At low energies some odd-electron fluorinated ions undergo collision without any secondary ions being emitted from the surface. In these cases the parent ions are apparently neutralized, but without sufficient energy transfer to cause hydrocarbon ion desorption. Non-fluorinated organic ions yield fragment ions and ion/surface reaction products under the condition of these experiments, but do not cause significant desorption of hydrocarbon ions.     

Research in the azole series. 103. Synthesis and 13C NMR study of pyrazole-4-carboxaldehydes

Ten new pyrazoles have been prepared and their ¹³C nmr chemical shifts compared with those of twelve other pyrazoles, some of them prepared purposely for this study. The chemical shifts are discussed statistically assuming that they are additive. A formyl group in the position 4 of the pyrazole ring produces a large effect on carbon C₄ (SCS = 17.3 ppm) and medium effects on carbons C₃ (SCS = 1.9 ppm) and C₅ (SCS = 3.8 ppm). The azines derived from pyrazole-4-carboxaldehydes are of the E,E-configuration.     

The [CH2CHOH.+, CH3CHO] solvated enol radical cation

The bimolecular reaction of the CH₂CHOH^.+ enol ion (m/z 44) with acetaldehyde gives a strongly dominant product,m/z 45, formed mainly by proton transfer from the ion to the molecule. The abundance of the product coming from a H^. abstraction reaction from the neutral, albeit more exothermic, is negligible. In order to explain this result, the long lived [CH₂CHOH^.+, CH₃CHO] solvated ion was generated by reaction of the CH₂CHOH^.+ enol ion with (CH₃CHO) _n in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. The structure of this solvated ion was clearly established. Labeling indicates that [CH₂CHOH^.+, CH₃CHO], upon low energy collisions, reacts by H^. abstraction more rapidly than by H⁺ transfer to the neutral moiety. This shows that the entropic factors are determinant when the enol ion reacts directly with acetaldehyde.     

Laser desorption mass spectrometry of squaric acid and its salts

The laser desorption mass spectrometry of the oxocarbon squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) and its salts of the form A₂C₄O₄ (A = cation) is described. Both positive and negative ion spectra were obtained. The positive ion spectrum of the acid is characterized by an ion corresponding to loss of CO from [M + H]⁺. The negative ion spectrum shows an intense [M ? H]^? peak in addition to a dimer species. The alkali salt spectra contain [M + A]⁺ in the positive mode and [M ? A]^? and an intense [C₄HO₄]^? in the negative mode. The smaller alkali salts also have an [M + H]⁺ adduct ion. Unlike the alkali squarates, the ammonium salt shows ions corresponding to losses of neutrals from the molecular adduct in the positive ion spectrum and a dimer species in the negative ion spectrum. Molecular weight information was obtained in all cases. A (bis) dicyanomethylene derivative of potassium squarate was also studied. Some field desorption mass spectrometry results are presented for comparison.     

Effect of sequence length, sequence frequency, and data acquisition rate on the performance of a Hadamard transform time-of-flight mass spectrometer

Various factors influencing the performance of a Hadamard transform time-of-flight mass spectrometer (HT-TOFMS) have been investigated. Using a nitrogen corona discharge to produce an ion stream of N ₂ ⁺ , N ₃ ⁺ , and N ₄ ⁺ , it is found for spectra containing only N ₄ ⁺ that the signal-to-noise ratio (SNR) closely approaches the value calculated from the ion background by assuming that the ion background follows a Poisson distribution. In contrast, for a more intense beam containing N ₂ ⁺ , N ₃ ⁺ , and N ₄ ⁺ , the SNR is less than its theoretical value because of the appearance of discrete spikes in the mass spectrum caused by deviations in the actual modulation sequence from the ideal one. These spikes can be reduced, however, by decreasing the modulation voltage. Under these optimized conditions, the pseudo-random sequence length is varied to understand how it alters SNR, mass resolution, and scan speed. When the length of the pseudo-random sequence is doubled, the SNR increases by √2 while the time necessary to record a mass spectrum also doubles. Mass resolution can be varied between 500 and 1200 at m/z = 609 as the sequence length, modulation speed (10 MHz, 25 MHz), and acquisition rate (up to 50 MHz) are changed. Scan speeds of 6000 passes per s can be obtained using a sequence containing 4095 elements modulated at 25 MHz. The capability to tailor the HT-TOFMS to increase the scan speed and resolution with a constant 50% duty cycle makes the technique extremely appealing as a mass analyzer for measuring rapid changes in the composition of an ion stream.     

Stereochemical applications of mass spectrometry: 1—The utility of electron impact and chemical ionization mass spectrometry in the differentiation of stereoisomeric benzoin oximes and phenylhydrazones

A study of the electron impact and chemical ionization (H₂, CH₄, and iso-C₄H₁₀) mass spectra of stereoisomeric benzoin oximes and phenylhydrazones indicates that while the former can be distinguished only by their chemical ionization mass spectra the latter are readily distinguishable by both their electron impact and chemical ionization mass spectra. The electron impact mass spectra of the isomeric oximes are practically identical; however, the chemical ionization spectra show that the E isomer forms more stable [MH]⁺ and [MH? H₂O]⁺ ions than the Z isomer for which both the [MH]⁺ and [MH? H₂O]⁺ ions are relatively unstable. In electron impact the Z-phenylhydrazone shows a lower [M]⁺˙ ion abundance and more facile loss of H₂O than does the E isomer. This more facile H₂O loss also is observed for the [MH]⁺ ion of the Z isomer under chemical ionization conditions.     

Distinction between 17-epimeric hydroxy steroids of the 3,17-dioxygenated androstane series by chemical ionization

The distinction between 17-epimeric 3,17-dioxygenated hydroxyandrostanes has been made by comparison of both their methane or ammonia positive and OH^? negative chemical ionization (CI) mass spectra. In the methane or ammonia positive CI, the 17α-configuration in the eight stereoisomeric 5ξ-androstane-3ξ,17ξ-diols can be determined by the relative abundances of the ion [MH? 2 H₂O]⁺. In the ammonia CI spectra, the ion [M+NH₄? H₂O]⁺ possesses only a low abundance, but a comparison of the relative rates of the loss of water v. the loss of ammonia from [M.NH₄]⁺ in the second field-free region allows a clear distinction to be made between the 17α- and 17β-series. In the OH^? negative CI mass spectra, the 5ξ-androstane-3-one-17ξ-ols produce an intense ion [M? H? H₂O]^? in the 17α-series only.     

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.     

Desorption chemical ionization tandem mass spectrometry of polyprenyl and dolichyl phosphates

Negative-ion desorption chemical ionization (DCI) tandem mass spectrometry was applied to the analysis of nanomole quantities of semisynthetic polyisoprenyl phosphates, the chain length of which ranged from 7 to 20 isoprene units. The DCI spectrum of all the compounds tested show the presence of independently generated ions [M-HPO₃-H]^?, [M-H₃PO₂-H]^? and [M-H₃PO₄-H]^? resulting from the loss of a part of or the entire phosphate group of a polyisoprenyl-P. In tandem mass spectrometry, the [M-H₃PO₄-H]^? fragment produces series of ions 68 mass units apart, indicative of the polyisoprenoid nature of a compound. Studies with deuterated and α-saturated polyisoprenyl phosphates demonstrated that fragmentations of the [M-H₃PO₄-H]^? ion proceed from both ends (α and ω) of a polyisoprenoid chain and may occur at either allylic (A) or vinylic (V) sites. Fragments of masses equal to [n×68 ? 1] and [n×68 ? 13] (where n is the number of isoprene units and 3≤n is less than the total number of isoprene residues within a polyisoprenoid chain) comprise the αA and ωV series, respectively, and represent the most abundant ions in tandem mass spectra of the [M-H₃PO₄-H]^? fragment of polyprenyl phosphates, α-Saturated dolichyl phosphates can be distinguished easily from corresponding polyprenyl phosphates not only on the basis of a 2-u shift of the [M-H₃PO₄-H]^? ion and the α series of fragments, but also because of the presence of an additional (A+14) series of ions 14 u heavier than fragments resulting from the allylic cleavages of an α-saturated polyisoprenoid chain. Possible mechanisms of the collision-induced dissociation reactions of polyprenyl phosphates are discussed.     

Losses of ions during forward and reverse scans in a quadrupole ion trap mass spectrometer and how to reduce them

The higher order fields present in the quadrupole ion trap may have beneficial effects such as increases in mass resolution in the mass-selective instability or resonance ejection modes of operation, but may also result in losses of ions due to nonlinear resonances. In this work, the reduction in ion intensities observed in the mass spectra of polyethylene glycol (PEG 1000) has been utilized to monitor the ion losses resulting from these higher order fields during the rf voltage scans in both the forward and reverse directions. Extensive ion losses were observed in reverse rf voltage scans at q _z=0.64 (a _z=0), which corresponds to octopole resonance at β _z=1/2. The losses depended upon rf voltage scan rate and ion mass being greater for lower scan rates and lower masses. For ions of m/z 877, losses of up to 60% of the stored ions were observed at low scan rates (<1×10⁴ Da/s), but were minimal at higher scan rates. Thus, it is possible to avoid such losses during reverse scans by scanning the region q _z=0.64 at rates in excess of 4×10⁴ Da/s. In forward rf voltage scans, ion storage was considerably more reliable, with significant losses observed only at very high scan rates near the region q _z=0.78 (hexapole resonance at β _z=2/3).     

The negative ion mass spectra of mixtures of sulphur and organic compounds. I—The formation of [M+Sn]− from the mixture of sulphur and dinitriles

The negative ion mass spectra of sulphur, dinitriles and their mixtures were studied. The abundance of negative ions of sulphur was almost comparable to that of positive ions. In the negative ion mass spectrum of a mixture of sulphur and dinitrile, intense and characteristic peaks of [M + S_n]^? (n = 2, 3, 4, etc.) were observed resulting from ion–molecule association of dinitrile with the S_n^? anions. As a standard sample of a negative ion mass spectrum, sulphur itself has proved useful in the lower mass region (below m/e 256: S₈^?).