The mass spectra of spiro-alkanones with five- and six-membered rings

The mass spectral fragmentations of three spiro-undecanones and four dispiro-hexadecanones with six-membered rings, and of two spiro-nonanones with five-membered rings are recorded and discussed. The fragmentation patterns for the spiro[4,4]nonanones and the spiro[5,5]undecanones have been determined by using specific deuterium labelling and in some cases the measurement of metastable transitions by the defocusing technique. The most important fragment ions in the spectra of four dispiro-hexadecanones could be explained by assuming the same types of fragmentation as found for the monospiro-ketones. The composition of the fragment ions has been checked by high resolution mass measurements.     

Azabicyclo Compounds—XI. A study of the fragmentation processes of quinuc-lidine and some of its derivatives

The mass spectra of quinuclidine, all the ring position deuterated analogues and some methyl homologues have been measured. Plausible mechanistic interpretations of principal fragment ions are discussed, in the case of quinuclidine, with the help of deuteration in all the ring positions.     

Characteristic fragmentation of thromboxane B2 in thermospray high-performance liquid chromatography-mass spectrometry

Cyclo- and lipo-oxygenase metabolites of arachidonic acid have been reported to have very simple thermospray mass spectra. However, thromboxane B2 (TXB) in ammonium acetate-methanol and at interface temperatures below the point of total vaporization shows a mass spectral pattern characterized by abundant ions at low masses. The more abundant TXB fragment ions have been characterized as adducts from four principal fragments with molecular masses of 156, 170, 196 and 326. Positive- and negative-ion mass spectra, and mass spectra obtained with an alternative thermospray buffer (butylammonium acetate) support the molecular masses of these fragments. A tentative assignment of the fragments can be made by comparison of the thermospray mass spectra of TXB, 2,3-dinor-TXB and some of their methyl ester and methyl oxime derivatives. Interface temperature and solvent composition effects on the fragmentation, as well as in the electron-capture processes observed when working in the filament-on mode, are discussed. Fragmentation mechanisms can be related to those observed for monosaccharides, and imply retro-Diels-Alder as well as retroaldolic condensation-type rearrangements.     

Doubly charged ion mass spectra 8—alkenes

Doubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.     

A mass spectrometric study of substituted furfuryl compounds

The mass spectra of six furfuryl compounds — namely, furfuryl alcohol, 5-furfuryl-furfuryl alcohol, difurfuryl ether, difurylmethane, 2,5-difurfurylfuran, and 4-furfuryl-2-pentenoic acid-γ-lactone — have been studied. Their fragmentation mechanisms are discussed in detail with particular emphasis on the modes that lead to the formation of aromatic fragments. The majority of the fragment ions are formed by elimination of CO and C₂H₂ from even-electron precursor ions and HCO from odd-electron precursor ions. Molecules containing two furan rings linked by a methylene group give mass spectra that exhibit large abundances of aromatic fragment ions.     

Comparison of laser-induced dissociation and high-energy collision-induced dissociation using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) for peptide and protein identification

The fragmentation of peptides under laser-induced dissociation (LID) as well as high-energy collision-induced dissociation (CID) conditions has been investigated. The effect of the different fragmentation mechanisms on the formation of specific fragment ion types and the usability of the resulting spectra, e.g. for high-throughput protein identification, has been evaluated. Also, basic investigations on the influence of the matrix, as well as laser fluence, on the fragment ion formation and the consequences in the spectral appearance are discussed. The preconditions for obtaining 'pure' CID spectra on matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) instruments are evaluated and discussed as well as the differences between LID and CID in the resulting fragment ion types. While containing a wealth of information due to additional fragment ions in comparison with LID, CID spectra are significantly more complex than LID spectra and, due to different fragmentation patterns, the CID spectra are of limited use for protein identification, even under optimized parameter settings, due to significantly lower scores for the individual spectra. Conditions for optimal results regarding protein identification using MALDI-TOF/TOF instruments have been evaluated. For database searches using tandem mass spectrometric data, the use of LID as fragmentation technique in combination with parameter settings supporting the use of internal fragment ions turned out to yield the optimal results.     

Fragmentation of trimethoprim and other compounds containing alkoxy-phenyl groups in electrospray ionisation tandem mass spectrometry

This work describes electrospray ionisation tandem mass spectrometry studies of trimethoprim and a series of structurally similar compounds containing alkoxy-phenyl groups; using accurate mass measurement to confirm the proposed fragmentations. Radical cations were observed in the spectra obtained for some of the compounds, as well as uncommon fragmentations showing losses of CH4 and C2H6, whereas other compounds showed the formation of even electron ions. Possible structures for the fragment ions have been proposed and explanations for the different types of fragmentations based on the structures of the compounds. In addition an alternate structure for a fragment ion previously reported for tandem mass spectrometry of trimethoprim has been proposed, based on accurate mass measurement.     

Chemical ionization of aliphatic nitro compounds

The chemical ionization mass spectra of various aliphatic nitro compounds have been studied. Almost all the nitro compounds form stable [M+H]⁺ ions in sharp contrast to the instability of their ions produced by other ionization techniques. The fragmentations of the [M+H]⁺ ions are discussed, the mechanisms and structures of fragment ions proposed being supported by quantum mechanical calculations. Correlations between chemical ionization mass spectra and structures of compounds studied are outlined. Reliable identification of mono- and polynitroalkanes and some related derivatives may be made by analysis of their chemical ionization mass spectra.     

Mass spectra of some new 3,4-dihydro-2[H]-pyridones

Electrospray ionization (ESI) and tandem mass spectrometry (MS/MS) experiments, as well as electronic impact (EI) and chemical ionization (CI) techniques, have been applied to the title compounds 1a-h. The observation of different fragmentation pathways in the three sets of spectra is in accord with different degrees of internal excitation of the investigated precursors. In ESI (methanol as solvent) and CI (methane as reagent gas) spectra, the MH(+) ion represents the most important peak, while the fragments [M - OH](+) and [M - SO](+) are either the base peak or a very abundant peak in the EI mass spectra of these compounds. ESI-MS/MS experiments on the parent ions [MH](+) show that the loss of a fragment of 140 Da corresponding to p-toluenesulfenic acid is common from all the precursors. As well as competitive pathways, the second generation ions have also been elucidated to allow some observations to be made concerning the relationships between structure type and mass spectrometric characteristics.     

The mass spectral fragmentation of some substituted 3-Amino-2-salicylideneamino-benzofurans

Electron impact mass spectra of eight of the title compounds are discussed. The important fragment ions are shown by high resolution and deuterium labelling to contain the benzofuran nucleus and to involve extensive rearrangement processes. Fragmentation pathways have been confirmed by measurement of daughter ion spectra (B/E linked scans).     

The field desorption mass spectra of some oligosaccharides and their permethylates and peracetylates

Field desorption mass spectra have been obtained for a number of di-, tri- and tetrasaccharides, and for some permethyl and peracetyl derivatives. The free sugars usually show intense [M + 1]⁺ ions thus enabling the determination of molecular weights. The effect of variation of emitter current on the relative intensities of fragment ions has been investigated. Permethylated oligosaccharides show intense molecular ions; in contrast peracetylated oligosaccharides show only weak molecular ions but strong [M ? 60]⁺ ions. Information from electron-impact and field desorption mass spectra is essentially complementary.     

Direct exposure chemical ionization mass spectra of explosives

Mass spectra of explosives, including TNT, tetryl, nitroglycerin, PETN and RDX have been recorded by direct exposure chemical ionization with isobutane as reagent at source temperatures of 50–100°C. The mass spectra contain major [MH]⁺ ions, adduct ions and some fragment ions. The configuration of the relative abundances of these ions has been found to be a function of temperature and source pressure. Maximum [MH]⁺ ion abundance has been obtained at source pressures much lower than normal chemical ionization pressures.     

Mass spectrometry in structural and stereochemical problems—CCXXII: Delineation of competing fragmentation pathways of complex molecules from a study of metastable ion transitions of deuterated derivatives

Data on defocused metastable ions have been obtained for a series of structurally significant fragment ions in the mass spectra of the estrogenic steroid, estrone methyl ether and the alkaloid tropine. These data, in conjunction with measurements on defocused metastable ions in the mass spectra of isotopically labeled analogs and complete high resolution mass spectra provide important insights into the details of fragmentation processes, specifically: (a) an enumeration and determination of the frequent multiple origins of fragment ions in the mass spectra of such complex molecules, (b) specification of skeletal atoms lost and retained in concerted (one step) processes, and at each step of stepwise processes, leading to a particular fragment ion and (c) information on the relative contributions of concerted and stepwise processes resulting in the genesis of a given ion.     

Femtosecond lasers for mass spectrometry: proposed application to catalytic hydrogenation of butadiene

Mass spectra from the interaction of intense, femtosecond laser pulses with 1,3-butadiene, 1-butene, and n-butane have been obtained. The proportion of the fragment ions produced as a function of intensity, pulse length, and wavelength was investigated. Potential mass spectrometry applications, for example in the analysis of catalytic reaction products, are discussed.     

Characterization and differentiation of heterocyclic isomers. Part 2. Mass spectrometry and molecular orbital calculations on pyrrolo[1,2-a][1,4]benzodiazepin-4-one, -6-one,and -4,6-dione

Pyrrolo[1,2-a][1,4]benzodiazepin-4-one (1), -6-one (2), and -4,6-dione (3), which are starting materials for the synthesis of pharmacologically interesting compounds that are active as neurotropic agents, have been characterized in the gas phase. The application of different mass spectrometric techniques, such as electron ionization, high-resolution, and tandem mass spectrometry, has allowed the structural characterization and differentiation of their molecular ions and most abundant fragment ions formed in the source. In particular, the two positional isomers 1 and 2 produce quite different mass spectra, and their molecular and the most intense fragment ions yield different metastable mass-analyzed ion kinetic energy spectra. Furthermore, high-resolution mass spectrometry and accurate mass measurements have revealed different elemental compositions and abundances for isobaric fragment ions produced by isomers 1 and 2. From these data and from the comparison with those relevant to compound 3, it has been possible to evaluate the influence of the position of the carbonyl group on the fragmentation pathways. Semiempirical molecular orbital calculations carried out by both the modified neglect of differential overlap and Austin 1 methods have provided useful information on the characterization of the neutrals as well as the molecular ions of compounds 1–3.     

Mass spectral fragmentation patterns of various 6-substituted 2,4-bis-(m-aminoanilino)-s-triazines

The mass spectra of 6-substituted-2,4-bis-(m-aminoanilino)-s-triazines were determined and found to be dominated by intense molecular ions (base peak), strong M-H peaks and fragment ions diagnostic for the arylamino and C-6 substituents. Mechanisms have been proposed for the formation of the major peaks in the spectra. Fragmentation pathways involving hydrogen transfer reactions have been rationalized by concomitant opening of the triazine ring rather than an amino-imino tautornerization as previously suggested. Fragmentation reactions accompanied by rearrangement modes have also been encountered in some of the compounds studied.     

Structural analysis of selected characteristic flavones by electrospray tandem mass spectrometry.

Seven structure analogical flavonoid aglycones have been analyzed using electrospray ionization tandem mass spectrometry (ESI-MSn) in the negative-ion mode. The spectra obtained ESI-MSn allowed us to propose plausible schemes for their fragmentation mechanism. By analyzing the product ions spectra of deprotonated molecule ions [M-H](-), some neutral diagnostic losses and specific retro Diels-Alder fragments were obtained. By using all of these characteristic fragment ions we can specially differentiate the flavone isomer.     

Photodissociation tandem mass spectrometry at 266 nm of an aliphatic peptide derivatized with phenyl isothiocyanate and 4-sulfophenyl isothiocyanate

Photodissociation (PD) tandem mass spectra have been obtained at 266 nm for the protonated molecules of a tryptic peptide, ASHLGLAR, and of its phenyl isothiocyanate and 4-sulfophenyl isothiocyanate derivatives, generated by matrix-assisted laser desorption/ionization. Derivatization with the aromatic chromophores greatly reduced the intensity of the laser required for efficient PD. Major fragment ions observed in the three spectra are quite similar. General features of the PD tandem mass spectra and their potential utility for analytical purposes are discussed.     

Study of electrospray ionization tandem mass spectrometry of the benzofuranone compounds

A detailed analysis of benzofuranone compounds under multiple tandem mass spectrometry （ESI-MS^n） conditions is reported. Element composition data of the fragment ions were obtained with the aid of comparison of the multiple tandem mass spectra of four compounds, and the structures of which are identical except for some substituted groups or epimers or cis-trans-isomers. Attempts have been made to provide rational pathways for the formation of the fragment ions from these protonated compounds. And the structure-fragmentation relationships will facilitate the characterization of the structures of other analogs.     

The chemistry of hexahydro-1,2,4,5-tetrazines—II: Mass spectra of 1,4-dialkylhexahydro-1,2,4,5-tetrazines and 1,4-dialkyl-2,5-diacylhexahydro-1,2,4,5-tetrazines

The mass spectra of twenty-eight 1,4-dialkylhexahydro-1,2,4,5-tetrazines and 1,4-dialkyl-2,5-diacylhexahydro-1,2,4,5-tetrazines (1) have been recorded and interpreted with the aid of deu-terium labelling, high resolution measurements, and the metastable defocusing technique. The principal fragmentations involve initial scission of ring bonds, particularly C-N bonds, leading to characteristic ions of mass M/2 and M/2± 1, and to 2,3-diaza-1,3-butadienyl ions (II). In the spectra of acylated compounds, acyl migration occurs within the molecular ion. The elimination of formaldehyde from the principal fragment ion is discussed.