Sulfur ylides

The mass spectra of negative ions of keto-stabilized sulfur and phosphorus ylides (obtained from amino acids) and products of their thermal conversion are studied. The most characteristic peaks in the mass spectra of ylides belong to negative molecular ions and to [M−H]⁻ ions. Peaks of fragment ions in the mass spectra of ylides and products of their thermal conversion coincide both in mass numbers and resonance energies. For Part 8, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2100–2103, November, 1999.     

Resonance capture of electrons by cyclopentadienyltricarbonylmanganese and -rhenium derivatives

Negative ion mass spectra of cyclopentadienyltricarbonylmanganese and-rhenium derivatives RC₅H₄M(CO)₃ (R=H, CN, COOH, COMe, COOMe, CH₂OH, CHO; M=Mn, Re) were studied. The subsequent detachment of carbonyl groups is the main process of the fragmentation of these compounds under the conditions of the resonance capture of electrons. On going fron the rhenium complexes to manganese derivatives, the maxima of the yields of the ions [M-nCO]⁻ (n=1–3) shift to the lower energy region indicating that the stability of the Re−CO bond is higher than that of Mn−CO. The average lifetimes of the molecular negative ions relative to the autodetachment of an electron (τ_a) and to dissociation (τ_d) were measured. It was found that electron-accepting substituents increase the τ_a value and decrease τ_d. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1161–1164, June, 1997.     

Mass spectra of new heterocycles: VIII. Fragmentation of 6-alkoxy- and 6-aryl(hetaryl)-3H-azepines under electron impact

The electron impact mass spectra of previously unknown 2-alkyl-6-alkoxy-, 2,3-trimethylene-6-alkoxy- and 2-alkyl-6-aryl(hetaryl)-3H-azepines were studied. All compounds give rise to stable molecular ions (I _rel = 44–100%) whose fragmentation pattern is determined mainly by the substituent on C⁶. Decomposition of the molecular ions derived from 6-alkoxy derivatives (R¹ = MeO, EtO, i-PrO) follows general relations typical of alkyl ethers. The main characteristic peaks in the mass spectra of 2-methyl-6-aryl- and 2-methyl-6-hetaryl-3H-azepines (R¹ = Ph, 1H-pyrrol-1-yl, 5-methylthiophen-2-yl) belong to even-electron rearrangement ions [M − H]⁺ and [M − Me]⁺, which have conjugated bi- and tricyclic structures, and products of their subsequent decomposition. Substituents in positions 2 (R²) and 3 (R⁴) [R⁴ = H, R² = Me, Et; R²R⁴ = (CH₂)₃] bring some specificity to the fragmentation pattern, but their contribution is not crucial. Original Russian Text ? L.V. Klyba, N.A. Nedolya, O.A. Tarasova, E.R. Zhanchipova, O.G. Volostnykh, 2009, published in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 4, pp. 610–621. For communication VII, see [1].     

Positive and negative ion mass spectra of Aryl-ONN-azoxy compounds containing electron withdrawing groups

The positive and negative ion mass spectra, at 70 eV, of p-RC₆H₄N(O)?NCOOCH₃ (R?H, Cl, Br, NO₂), C₆H₅N(O)?NCOOC₂H₅, p-RC₆H₄N(O)?NCONH₂ (R?H, Cl, Br, NO₂) and p-RC₆H₄N(O)?NCOC₆H₅ (R?H, Cl, Br, NO₂) are reported. The azoxyester derivatives show abundant molecular ions and a number of weak fragment and rearrangement ions in the positive ion mass spectra, whereas weak molecular ions and abundant low mass fragment ions are present in the negative ion mass spectra. Similar behaviour is observed in the mass spectra of the azoxyamides. Conversely, for the azoxycarbonyl compounds the positive molecular ion is absent. A ready cleavage of the N? CO bond occurs and only few fragments of low diagnostic value are formed, whereas the negative molecular ion is the base peak for all these compounds with the exception of the p-NO₂ derivative, where [M? O]^?? is the base peak and [M]^?? is the second major ion. The behaviour under electron impact of these classes of compounds is compared with that of azoxycyanides reported previously.     

ESI-MS analyses of lake dissolved organic matter in light of supramolecular assembly

A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV₂₅₄ and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive total ion chromatograms were parallel to the SEC elution profile obtained by UV₂₅₄ detection from DOM-HS solution. The UV₂₅₄ detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and number-weighted average sizes/masses (M _w and M _n) of different SEC fractions was fairly small, in contrast to UV₂₅₄ detection, with increasing elution volume. A reasonable explanation for the great differences between M _w and M _n values, obtained by UV₂₅₄ and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small components through weak dispersive forces. M _n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M _w and M _n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to be unimportant, and the weak ions observed at even m/z values correspond most likely to the ¹³C counterparts of the more abundant ¹²C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing similar structural functionalities.     

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^?).     

Reference standards for negative ion mass spectrometry

The negative ion mass spectra of phosphonitrile chlorides (PNCl₂)_n (n≥3) are studied. Since this series of compounds give very intense negative [M]^? and [M? Cl]^? ions, they can be used as good reference standards for negative ion mass spectrometry.     

A study on mass spectrometry of methylated [60] fullerenes using the “in-beam” electron impact technique

Mass spectra of the methylated [60]fullerenes were obtained by EI mass spectrometry using “desorption” or “in-beam” technique. The mass spectra of the methylated fullerenes, C₆₀Me_n, have the molecular ion peak M⁺ indicating that the product is stable under the MS (EI) conditions. The appearance of an intense peak at m/z 360 was assigned to the formation of fullerene dication C₆₀⁺⁺. The remaining peaks were assigned to successive loss of methyl groups from molecular monocation and dication.     

Determination of steryl sulphates in invertebrate tissue by liquid chromatography–tandem mass spectrometry

A method for the identification and quantification of underivatised steryl sulphates in invertebrates by liquid chromatography (LC) coupled with tandem mass spectrometry (MS) involving a single cleanup step has been developed. Negative electrospray ionisation and positive and negative atmospheric-pressure chemical ionisation (APCI) spectra of steryl sulphate showed pseudomolecular ions ([M+H–H₂SO₄]⁺or [M–H]⁻). Collision-induced dissociation (CID) was efficient only in positive APCI. LC-MS in negative APCI was least susceptible to interference and possible differences in response factors. The detection limits (signal-to-noise ratio of 3) based on cholest-5-enyl-3-sulphate in positive and negative APCI modes are 3.66 and 0.73 pmol μL⁻¹, respectively. Calibration plots and response factors for cholest-5-enyl-3-sulphate relative to the internal standard, cholecalciferyl-3-sulphate, in both positive and negative polarities, were linear in the concentration range from 1.22 to 16.4 pmol μL⁻¹ with good coefficients of determination (R ²>0.98). It is suggested that the structure elucidation of steryl sulphates is best achieved in CID positive APCI mode, whereas their quantification should be carried out using negative APCI.     

Doubly charged ion mass spectra: VI—Amines

Doubly charged ion mass spectra of 22 amines (2–10 carbon atoms) were determined using an Hitachi RMU-7L double focusing mass spectrometer. Molecular ions were not observed in the spectra of aliphatic amines. The most intense product ion peaks in the spectra of lower molecular weight amines resulted from hydrogen elimination from the molecular ion; however, as amine molecular weight increased the largest peaks resulted from both hydrogen and heavy atom elimination from the molecular ion. Dominant ions in the doubly charged ion spectra of lower molecular weight aliphatic amines were from reactions of [C_nH₃N]²⁺ (n:=2, 3, 4) type ions. The spectra of higher molecular weight aliphatic amines spanned a wide mass range. Appearance energies for some of the more prominent ions were measured in the range from 25 to 49 eV. A geometry optimized quantum mechanical self-consistent field molecular orbital treatment was used to compute the energies and structural parameters of prominent ions in the doubly charged ion mass spectra.     

Relationships between cluster secondary ion mass intensities generated by different cluster primary ions

Measurements are described to evaluate the constitution of secondary ion mass spectra for both monatomic and cluster primary ions. Previous work shows that spectra for different primary ions may be accurately described as the product of three material-dependent component spectra, two being raised to increasing powers as the cluster size increases. That work was for an organic material and, here, this is extended to (SiO₂) _t OH⁻ clusters from silicon oxide sputtered by 25 keV Bi _n ⁺ cluster primary ions for n = 1, 3, and 5 and 1 ≤ t ≤ 15. These results are described to a standard deviation of 2.4% over 6 decades of intensity by the product of a constant with a spectrum, H _SiOH/*, and a power law spectrum in t. This evaluation is extended, using published data for Si _t ⁺ sputtered from Si by 9 and 18 keV Au⁻ and Au₃⁻, with confirmation that the spectra are closely described by the product of a constant with a spectrum, H _Si^*, and a simple spectrum that is an exponential dependence on t, both being raised to appropriate powers. This is confirmed with further published data for 6, 9, 12, and 18 keV Al⁻ and Al₂⁻ primary cluster ions. In all cases, the major effect of intensity is then related to the deposited energy of the primary ion at the surface. The constitution of SIMS spectra, for monatomic and cluster primary ion sources, is shown, in all cases, to be consistent with the product of a constant with two component spectra raised to given powers.     

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The peculiarities of dissociative electron capture by 20-hydroxyecdysone molecules with the formation of fragment negative ions were studied. In the region of high electron energies (5–10 eV), processes of skeleton bond rupture are accompanied by the elimination of H₂O and H₂ molecules. In the region of thermal energies of electrons (≈0 eV), the mass spectrum is formed mainly by the [M−nH₂O]^.− (n=1–3) and [M−H₂−nH₂O]^.− (n=0−3) ions that are generated exclusively by the rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–712, April, 2000.     

Stereospecific fragmentation processes in cycloalkane/cycloalkene-fused isomers of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives

Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M^+· ions. The observed 90% stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e. g., in the formation of [M − C₃H₅O]⁺ ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M^+· ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.     

Mass-spectrometric study of the cyclization of diazo compounds. 10. 2-Diazomalonic acid amides. Mass spectra of the negative ions

The mass spectra of the negative ions of the dissociative resonance capture of electrons of diazo amides and the isomeric triazoles were studied. The molecular negative ions of these compounds are unstable and do not undergo interisomerization. The principal fragmentation process involves the elimination of a molecule of nitrogen and transformation of the resulting [M-N₂]^– ions to the heterocyclic form, which is the same for the two isomers.See [1] for communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–944, July, 1987.     

Calculation of spectral characteristics of water clusters upon interaction with oxygen molecules and bromine ions

Interactions of (Br⁻) _i (H₂O)_50−i clusters (0 ≤ i ≤ 6) with molecular oxygen is studied by the molecular dynamics method using flexible molecule model. Values of real and imaginary parts of permittivity decrease in the 0 ≤ ω ≤ 3500 cm⁻¹ frequency range with increasing number of bromine ions in a cluster. The ability of cluster to absorb IR radiation decreases, whereas the reflectance and Raman light scattering remains nearly unchanged. An increase in the content of Br⁻ ions in the cluster lowers the power of emitted IR radiation and decreases the amount of active electrons participating in the interaction with IR radiation. However, when the concentration of Brions becomes substantially higher (at i = 5 and 6), the values of emitted power and the number of active electrons are restored to the values that are typical for water cluster in the absence of Br⁻ ions. At i ≥ 3, repelling Br⁻ ions acquire kinetic energy, which is sufficient to remove molecular oxygen from the system.     

Molecular dynamics calculation of spectral characteristics of water clusters in the presence of ozone molecules and chlorine ions

Simultaneous interaction of the (H₂O)₅₀ cluster with O₃ molecules and Cl⁻ ions was studied by the molecular dynamics method. Six O₃ molecules located near the cluster were absorbed by the aqueous aggregate, and Cl⁻ ions in turn left the zone of the interaction with the cluster. Some of Cl⁻ ions penetrated inside the formed (O₃)₆(H₂O)₅₀ cluster and come into collision with O₃ molecules that split the ozone molecule into atoms. When Cl⁻ ions were removed sufficiently far away from the cluster, the water cluster with absorbed O₃ molecules and O atoms was observed for 15.6 ps. The interaction of water molecules with Cl⁻ ions gives rise to an increase in the integral intensity of absorption and emission IR spectra, and also to an essential decrease in the analogous characteristics of the Raman spectrum in the frequency range of 0 ≤ ω ≤ 1000 cm⁻¹. The presence of Cl⁻ ions did not affect essentially the location of the main band in the IR spectra, but considerably changed the shape of the bands in the Raman spectrum.     

Analysis of a stacked-triangular platinum carbonyl cluster dianion, [Pt3(CO)6] 3 2− by252Cf-Plasma Desorption Mass Spectrometry

²⁵²Cf-Plasma Desorption Mass Spectrometry (²⁵²Cf-PDMS) has been used to investigate the [(Ph₃PCH₂C₅H₄)Fe(C₅H₅)]⁺ salt of the prototype dianionic, platinum carbonyl cluster, [Pt₃(CO)₃(₂-CO)₃] ₃ ^2– . An envelope of singly charged [Pt₉(CO) _x ]^– ions with the principal peak centered atx=8 was observed in the negative ion mass spectrum as a result of successive losses of the carbonyl ligands from the intact platinum core. Another feature of the negative ion spectrum was the prominent occurrence of other envelopes of multiple peaks which conform to Pt₁₂, Pt₁₅, Pt₁₈, Pt₂₁, and Pt₂₄ singly charged metal cores. An unexpected observation was the presence of singly charged positive ions of the dianionic cluster which were formed without incorporation of the counterion. A similar but, largely unresolvable, broad envelope of singly charged ions containing the Pt₉ core resulted with a peak maximum corresponding closely to the completely carbonylated cluster. The peak distribution extended from the fully decarbonylated cluster to well beyond the mass of the fully carbonylated cluster. Analogous peaks attributable to singly charged positive ions of the Pt₁₂, Pt₁₅, and Pt₁₈ clusters were also evident. Very little fragmentation was observed below the molecular ion in either the positive or negative ion mass spectra except for ions associated with the counterion. A detailed analysis of the mass spectra, including the types of ions observed and correlations with the molecular architecture are described.     

Cluster mechanism of the atmosphere ozone destruction by bromine ions

Interaction of bromine ions absorbed by water cluster with adsorbed oxygen and ozone molecules has been investigated by the molecular dynamics method. It was shown that the part of O₂ molecules was removed from the system by evaporating Br⁻ ions, while all O₃ molecules and Br ions were kept in the system during 25 ps. The increase the concentration of the Br⁻ ions in the clusters resulted in a reduction of the absorption intensity and emission in IR spectra at the presence of oxygen, whereas the absorption intensity in the appropriate IR spectra of ozone-containing systems increased with the growth of a number of the Br⁻ ions. Raman spectra of oxygen-containing systems were poorly sensitive to the concentration of the Br⁻ ions but the absorption intensity of Raman spectra for systems with ozone considerably decreased with the growth of a number of bromine ions.     

Mass spectrometry of rhenium complexes: a comparative study by using LDI‐MS,MALDI‐MS,PESI‐MS and ESI‐MS

A group of rhenium (I) complexes including in their structure ligands such as CF₃SO₃‐, CH₃CO₂‐, CO, 2,2′‐bipyridine, dipyridil[3,2‐a:2′3′‐c]phenazine, naphthalene‐2‐carboxylate, anthracene‐9‐carboxylate, pyrene‐1‐carboxylate and 1,10‐phenanthroline have been studied for the first time by mass spectrometry. The probe electrospray ionization (PESI) is a technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid metal needle. In this work, mass spectra for organometallic complexes obtained by PESI were compared with those obtained by classical ESI and high flow rate electrospray ionization assisted by corona discharge (HF‐ESI‐CD), an ideal method to avoid decomposition of the complexes and to induce their oxidation to yield intact molecular cation radicals in gas state [M]^+. and to produce their reduction yielding the gas species [M]^–.. It was found that both techniques showed in general the intact molecular ions of the organometallics studied and provided additional structure characteristic diagnostic fragments. As the rhenium complexes studied in the present work showed strong absorption in the UV–visible region, particularly at 355 nm, laser desorption ionization (LDI) mass spectrometry experiments could be conducted. Although intact molecular ions could be detected in a few cases, LDI mass spectra showed diagnostic fragments for characterization of the complexes structure. Furthermore, matrix‐assisted laser desorption ionization (MALDI) mass spectra were obtained. Nor‐harmane, a compound with basic character, was used as matrix, and the intact molecular ions were detected in two examples, in negative ion mode as the [M]^–. species. Results obtained with 2‐[(2E)‐3‐(4‐tert‐buthylphenyl)‐2‐methylprop‐2‐enylidene] malononitrile (DCTB) as matrix are also described. LDI experiments provided more information about the rhenium complex structures than did the MALDI ones. Copyright © 2012 John Wiley & Sons, Ltd.     

Laser desorption/ionization fourier transform mass spectrometry of thin films deposited on silicon by plasma polymerization of acetylene

Thin films deposited on silicon substrate by three different methods of plasma polymerization of acetylene were analyzed by direct laser desorption/ionization Fourier transform mass spectrometry. High-resolution mass spectra showed the presence of carbon clusters and hydrocarbon oligomers in different relative abundances. During unipolar and continuous discharge polymerization of acetylene-hydrogen gas mixtures, quadrupole mass spectra of the plasma constituents showed the presence of molecular species with m/z lower than 100 — mainly peaks of C₄H₂ and C₆H₂. Films produced had smooth surfaces and the corresponding LDI-FTMS spectra displayed only carbon cluster signals in the positive ion mode and both hydrocarbon and carbon cluster signals (with much higher relative abundance of carbon cluster signals) in the negative ion mode. Alternatively, during bipolar discharge with either higher acetylene gas flux (>40 cm³/min) or longer deposition times (>10 min), quadrupole mass spectra of the plasma constituents showed signals corresponding to polycyclic aromatic hydrocarbons (PAH) with m/z higher than 100. SEM pictures of the bipolar thin films demonstrated the presence of “flower” structures and nanoparticles developed on the surface. LDI-FTMS spectra of such thin films showed either total absence or lower relative abundance of carbon cluster signals, compared with hydrocarbon signals.