Resonance capture of electrons by substituted pyrazoline molecules

The negative ion mass spectra and photoelectron spectra of substituted pyrazolines were studied. A correlation between the ionization energy of the highest occupied molecular orbital and the yield of [MeNHNH₂ ⁻] ions was found. Isomerization of molecular negative ions was studied by resonance electron capture mass spectrometry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 701–704, April, 2000.     

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.     

Influence of the solvent on the gas chromatographic behaviour of urea herbicides

Summary Degradation products of chlorsulfuron, chlortoluron, diuron, fluometuron, isoproturon, linuron, metabenzthiazuron, metobromuron, and monuron formed in the gas chromatographic injector have been used for identification of the respective herbicides. Mass spectra of the derived compounds were obtained with a quadrupole mass spectrometric detector working in scan mode (20–450 amu). The compounds generated often depended on the solvent used for phenylurea herbicide injection (ethanol, methanol, dichloromethane, and acetonitrile). When methanol and ethanol were used as solvents the major products formed from phenylureas were carbamic acid esters. When acetonitrile or dichloromethane were used the main derivatives were phenylisocyanates. Chlorsulfuron and metabenzthiazuron, however, generated a triazine plus a phenylsulfonamide and a benzothiazolamine, respectively, irrespective of the solvent used. Linuron and diuron behaved similarly and gave degradation products with the same mass spectra. The thermal reactions occurred instantaneously in the injector block and were promoted by the high temperature selected (300°C). Detemination of the compounds derived from urea herbicides, by use of a 30 m BP10 column and a selected ion registering (SIR) program based on two or three ions, can be used for sensitive detection of the presence of urea herbicides in environmental extracts. With standards in methanol instrument detection limits ranged from 0.1 pg for chlorsulfuron (detected as 2-chlorobenzensulfonamide) to 1 pg for monuron and metobromuron (both detected as their carbamic acid methyl esters).RSD were below 9% at the 5 ng L⁻¹ level. The response was linearly dependent on quantily (r>0.9986) in the 5 ng L⁻¹ to 25 μg L⁻¹ range. Unequivocal identification of some phenylurea herbicides was not always possible because some herbicides with similar structures, for example diuron and linuron, gave the same derivative.     

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.     

Identification of Anionic Supramolecular Complexes of Sulfonamide Receptors with Cl<Superscript>−</Superscript>, NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>, Br<Superscript>−</Superscript>, and I<Superscript>−</Superscript> by APCI-MS

As part of a mass spectrometric investigation of the binding properties of sulfonamide anion receptors, an atmospheric pressure chemical ionization mass spectrometric (APCI-MS) method involving direct infusion followed by thermal desorption was employed for identification of anionic supramolecular complexes in dichloromethane (CH₂Cl₂). Specifically, the dansylamide derivative of tris(2-aminoethyl)amine (tren) (1), the chiral 1,3-benzenesulfonamide derivatives of (1R,2S)-(+)-cis-1-amino-2-indanol (2), and (R)-(+)-bornylamine, (3), were shown to bind halide and nitrate ions in the presence of (n−Bu)₄N⁺X⁻ (X⁻ = Cl⁻, NO₃⁻, Br⁻, I⁻). Solutions of receptors and anions in CH₂Cl₂ were combined to form the anionic supramolecular complexes, which were subsequently introduced into the mass spectrometer via direct infusion followed by thermal desorption. The anionic supramolecular complexes [M+X]⁻, (M=1–3, X⁻=Cl⁻, NO₃⁻, Br⁻, I⁻) were observed in negative mode APCI-MS along with the deprotonated receptors [M−H]⁻. Full ionization energy of the APCI corona pin (4.5 kV) was necessary for obtaining mass spectra with the best signal-to-noise ratios.     

Studies on phosphatidylglycerol with triple quadrupole tandem mass spectrometry with electrospray ionization: Fragmentation processes and structural characterization

Negative-ion low-energy collisionally activated dissociation (CAD) tandem mass spectrometry of electrospray-produced ions permits structural characterization of phosphatidylglycerol (PG). The major ions that identify the structures arise from neutral loss of free fatty acid substituents ([M − H − R _x CO₂H]⁻) and neutral loss of the fatty acids as ketenes ([M − H − R′ _x CH = C = O]⁻), followed by consecutive loss of the glycerol head group. The abundances of the ions arising from neutral loss of the sn-2 substutient as a free fatty acid ([M − H − R₂CO₂H]⁻) or as a ketene ([M − H − R′₂CH = C = O]⁻) are greater than those of the product ions from the analogous losses at sn-1. Nucleophilic attack of the anionic phosphate site on the C-1 or the C-2 of the glycerol to which the carboxylates attached expels the sn-1 (R₁CO₂⁻) or the sn-2 (R₂CO₂⁻) carboxylate anion, resulting in a greater abundance of R₂COO⁻ than R₁COO⁻. These features permit assignments of fatty acid substituents and their position in the glycerol backbone. The results are also consistent with our earlier findings that pathways leading to those losses at sn-2 are sterically more favorable than those at sn-1. Fragment ions at m/z 227, 209 and 171 reflect the glycerol polar head group and identify the various PG molecules. Both charge-remote fragmentation (CRF) and charge-drive fragmentation (CDF) processes are the major pathways for the formation of [M − H − R _x COOH]⁻ ions. The CRF process involves participation of the hydrogen atoms on the glycerol backbone, whereas the CDF process involves participation of the exchangeable hydrogen atoms of the glycerol head group. The proposed fragmentation pathways are supported by CAD tandem mass spectrometry of the analogous precursor ions arising from the H-D exchange experiment, and further confirmed by source CAD in combination with tandem mass spectrometry.     

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].     

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.     

Mass spectra of the negative ions of some dioxanes

It was established by mass spectrometry of negative ions that fragmentation of some 1,3- and 1,4-dioxanes proceeds through intermediate [M-H]⁻ ions. The fragmentation pathway depends on the site of negative charge localization in these ions. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2199–2201, November, 1999.     

Electron capture negative ion (ECNI) mass spectrometry of complex mixtures of chlorinated decanes and dodecanes: An approach to ECNI mass spectra of chlorinated paraffins in technical mixtures

The electron capture negative ion (ECNI) mass spectra of two complex mixtures of polychlorinated decanes (PCDe) and polychlorinated dodecanes (PCDo) are presented. The number of isomers in these mixtures is still high but is drastically reduced in comparison to technical products of chlorinated paraffins (CP), due to their fixed chain length. As a result, the mass spectra are simplified and less complex. Different modes of negative ion formation were observed in the spectra of the PCDe and PCDo. [M+Cl]^– adduct ions were the most abundant ions in the spectra of lower chlorinated molecules. Higher chlorinated isomers formed prominently [M-Cl]^– and [M-HCl]^– fragments besides [M+Cl]^–. Possible consequences for the determination of chlorinated paraffins by ECNI-MS that result from the variation in ion formation are addressed. Received: 18 August 1997 / Revised: 26 January 1998 / Accepted: 31 January 1998     

Analysis of Cyclic Peptides in Pseudostellaria heterophylla (Miq.) Pax by HPLC–APCI–MS

A new method for the analysis of cyclic peptides (Pseudostellarins) in traditional Chinese medicine, Pseudostellaria heterophylla (Miq.) Pax, was established by high performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (HPLC–APCI–MS). The real samples were separated by a reversed-phase C₁₈ column using a binary eluent under gradient conditions. Six cyclic peptides were isolated and detected with a DAD detector. The Pseudostellarins components were identified by APCI–MS in a negative mode. In the negative ion APCI mode, the best sensitivity and the lowest detection limit for Pseudostellarins were obtained by using a mobile phase consisting of acetonitrile and pure water. The APCI spectra were characterized by [M-H]⁻ peak. The parent ions [M-H]⁻ with highest intensity was used for quantification of one cyclic peptide-Pseudostellarin B.     

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.     

Resonant dissociative electron capture by the simplest amino acids and dipeptides

The formation of ions from amino acids (glycine and alanine) and dipeptides (glycylglycine, alanylalanine, and glycylalanine) under the resonant electron capture conditions was studied by negative ion resonant electron capture mass spectrometry. The isobaric ions were found, their effective yield curves were experimentally separated, and the elemental composition was determined. The thermochemical aspect of ion formation was considered, and probable dissociative channels of fragmentation ion formation and their structures were established on the basis of this aspect. Bond cleavage reactions only and H-shift processes were revealed. The rearrangements occur presumably through the stage of formation of intramolecular hydrogen bonds. The cross-sections of formation of ions [M − H]⁻ were measured in the energy range 1.1–1.3 eV. The metastable decay channels of ions [M − H]⁻ and [M − COOH]⁻ were found in the energy range 4.5–7.5 eV for dipeptides, which enabled establishing the genetic relationship between the parental and daughter ions and revealing hidden fragmentation pathways.     

Structure and properties of μ<Subscript>2</Subscript>-<Emphasis Type="Italic">S</Emphasis>-[bis(benzenethiolato)tetranitrosyldiiron] in solution

Dinuclear iron tetranitrosyl complex with the composition [Fe₂(SPh)₂(NO)₄] (1) was synthesized and its single crystals and polycrystals were studied by X-ray diffraction, IR spectroscopy, and elemental analysis. The decomposition products of complex 1 were investigated by electrochemical method and mass spectrometry. The mass spectrum of a solution of complex 1 shows two groups of ions: the primary decomposition products of 1 in solution (the complex ions [Fe(SPh)(NO)₂(NO₂)]⁻, [Fe(SPh)₂(NO)]⁻, and [Fe(SPh)₂(NO)₂]⁻) and a series of the ions [FeO₂ + n(NO)]⁻ and [FeO₃ + n(NO)]⁻ (n = 0–4), which are formed in secondary reactions. The structures of the complexes, which were formed through the Fe-NO bond dissociation and the replacement of the NO ligand by aqua and oxygen ligands in complex 1, and the structure of the complex [FeO₃]⁻ were studied by quantum chemical modeling.     

On the Chemistry of the Resveratrol Diastereomers

Summary.  The (E)- and (Z)-diastereomers of resveratrol were investigated with respect to their photochemical and thermal diastereomerization reactions. The free enthalpy difference between the two diastereomers was estimated to be in the order of common stilbenes, with the (E)-diastereomer more stable by about 11–14 kJ mol⁻¹. The Arrhenius activation barrier of about 280 kJ mol⁻¹ was found to be quite high and implies that thermal equilibration cannot account for the (Z)-diastereomer found in nature. A preparative access to the (Z)-diastereomer by photodiastereomerization is described. The ¹H and ¹³C NMR spectra of the two diastereomers were assigned and their absorption spectra and fluorescence quantum yields of the neutral and monodeprotonated species were determined. Corresponding author. E-mail: heinz.falk@jku.at Received October 15, 2002; accepted November 7, 2002 Published online February 20, 2003     

The Thermal Decomposition of Magnesium(II) Complexes with Acetic and Halogenacetic Acids

Thermogravimetry (TG), differential thermal analysis (DTA) and other analytical methods have been applied to the investigation of the thermal behaviour and structure of the compounds Mg(Ac)₂ × 2H₂ O(I), Mg(ClAc)₂ ×2H₂ O(II) and Mg(Cl₂ Ac)₂ ×H₂ O(III) (Ac =CH₃ COO⁻ , ClAc =ClCH2COO⁻ , Cl ₂ Ac =Cl₂ CHCOO⁻ ). The solid phased intermediate and resultant products of thermolysis had been identified. The possible scheme of destruction of the complexes is suggested. The halogenacetato magnesium complexes (II–III) are thermally more stable than the acetatomagnesium complex I. The final products of the decomposition of compounds were MgO. Infrared (IR) data suggest to a unidentate coordination of carboxylate ions to magnesium ions in complexes I–III. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simultaneous Determination of Triptolide and Tripdiolide in Extract of Tripterygium wilfordii Hook. f. by LC–APCI-MS

A novel method using liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry in the negative selected ion monitoring mode has been developed and validated for rapid simultaneous determination of triptolide and tripdiolide in the extract of Tripterygium wilfordii Hook. f. The molecular ions m/z [M–H]⁻ 359 and 375 were selected for the quantification in selected ion monitoring mode for triptolide and tripdiolide. Standard calibration curve was linear over the concentration range of 0.12–24 and 0.15–30 μg mL⁻¹ for triptolide and tripdiolide. The relative standard deviations of intra- and inter-day were in the range of 4.7–9.9 and 8.9–12.6%. The average recoveries were between 96.4 and 104.6%. The limits of quantitation were 2.0 × 10⁻³ and 2.5 × 10⁻³ μg mL⁻¹ for triptolide and tripdiolide.     

Heterophase synthesis and standard enthalpies of formation of metal acetylacetonates

Vaporization of Mn(acac)₃ has been studied by mass spectrometry on a quadrupole mass spectrometer with direct insertion probe, which was not previously used for these purposes. The enthalpy of sublimation of Mn(acac)₃ was calculated to be 130.5 ± 4.0 kJ/mol. Heterophase interactions in the [M-Mn(acac)₃] system were studied directly during the mass spectral experiment (in situ method). The reaction products were judged from the mass spectra of the gas phase. The enthalpies of formation in the gas phase Δ _f H _gas ^T of Pb, In, and Ga acetylacetonates were estimated to be −654, −1057, and −1035 kJ/mol, respectively.     

Theoretical and experimental study of the structure and stability of multiply Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives

The equilibrium geometric parameters and the energetic and spectroscopic characteristics of low lying conformers for series of polyhydroxyl molecules and ions in which sodium atoms are successively substituted for the hydroxyl hydrogen atoms have been calculated by the density functional theory B3LYP method with the 6−31G* and 6−311+G** basis sets. The glucose derivatives [Glu − nH + nNa] and [Glu − nH + (n + 1)Na]⁺ (n = 1−5) and the 2,4,6-trihydroxyacetophenone derivatives [THAP − nH + nNa] and [THAP − nH + (n + 1)Na]⁺ (n = 1−4) have been considered. The affinities of the neutral [Glu − nH + nNa] and [THAP − nH + nNa] molecules for adding Na⁺ cations, as well as the energies of successive substitution of Na atoms for H atoms in the Glu and THAP molecules and the Glu⁺ and THAP⁺ ions in their reaction with sodium acetate molecules, have been estimated. Computations show that the first substitution of Na for H in ions is slightly exothermic and, presumably, can spontaneously occur under common conditions. Further substitutions are endothermic, but the required energy inputs are small. Therefore, successive substitutions for two, three, or more hydroxyl H atoms in the molecules and ions under consideration are possible at relatively low energy inputs. The computation results and conclusions are compared with the MALDI TOF mass spectral data for Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives in the [glucose + CH₃COONa + THAP] system where, in addition to common Glu · Na⁺ and THAP · Na⁺ ion-molecular complexes, multiply substituted positive ions of the [Glu − nH + (n + 1)Na]⁺ (n = 1−4) and [THAP − nH + (n + 1)Na]⁺ (n = 1−3) type have been identified.     

Atmospheric pressure ionization mass spectrometry techniques for the analysis of alkyl ethoxysulfate mixtures

This paper compares two liquid introduction atmospheric pressure ionization techniques for the analysis of alkyl ethoxysulfate (AES) anionic surfactant mixtures by mass spectrometry, i. e., electrospray ionization (ESI) in both positive and negative ion modes and atmospheric pressure chemical ionization (APCI) in positive ion mode, using a triple quadrupole mass spectrometer. Two ions are observed in ESI(+) for each individual AES component, [M + Na]⁺ and a “desulfated” ion [M − SO₃ + H]⁺, whereas only one ion, [M − Na]⁻ is observed for each AES component in ESI(−). APCI(+) produces a protonated, “desulfated” ion of the form [M − NaSO₃ + 2H]⁺ for each AES species in the mixture under low cone voltage (10 V) conditions. The mass spectral ion intensities of the individual AES components in either the series from ESI(+) or APCI(+) can be used to obtain an estimate of their relative concentrations in the mixture and of the average ethoxylate (EO) number of the sample. The precursor ions produced by either ESI(+) or ESI(−), when subjected to low-energy (50 eV) collision-induced dissociation, do not fragment to give ions that provide much structural information. The protonated, desulfated ions produced by APCI(+) form fragment ions which reveal structural information about the precursor ions, including alkyl chain length and EO number, under similar conditions. APCI(+) is less susceptible to matrix effects for quantitative work than ESI(+). Thus APCI(+) provides an additional tool for the analysis of anionic surfactants such as AES, especially in complex mixtures where tandem mass spectrometry is required for the identification of the individual components.