Computer-based system for correlating molecular structures with mass spectral data Methods for generating molecular substructures and for incorporating fragmentation rules

The masses of ions observed in the mass spectrum of a pure compound are correlated with the masses of the molecular substructures of the compound. Three methods are described for generating molecular substructures. Each method is evaluated to establish how effectively it generates the molecular substructures and correlates the masses of the molecular substructures with the masses of the observed fragment ions. Rules for mass-spectral fragmentation processes are incorporated into the mass spectral analysis software and illustrated for retro-aldol and lactone-ester reactions occurring in the thermospray mass spectra of oligomycin antibiotics.     

Studies on the complexation of polyols and carbohydrates with excess borate using thermospray mass spectrometry

Complex formation between different polyols, carbohydrates and borate was studied by thermospray mass spectrometry. The analytes were dissolved in 0.1 M ammonium borate buffer and introduced through a standard thermospray interface into a quadrupole mass spectrometer. The formation of various complexes which gave rise to relatively abundant ions in the thermospray spectra was observed. A correlation has been found between the relative intensities of these ions and the orientation of the hydroxyl groups involved in the complexation.     

Hydrocarbon polymer analysis by external MALDI fourier transform and reflectron time of flight mass spectrometry

The traditional solvent-based matrix-assisted laser desorption ionization (MALDI) preparation method has been used to analyze nonpolar polymers of various molecular weights. High resolution silver cationized oligomers with masses of up to 12 KDa were measured using 9.4 tesla Fourier transform mass spectrometry (FTMS) with an external ionization source. It was observed that when time-of-flight mass spectrometry was used, the spectra of polyethylene polymers showed abundant low mass fragment ions. However, these fragments were absent from the FTMS spectra.     

The mass spectra of some O-methyloximes of aliphatic aldehydes and ketones

The mass spectra of O-methyloximes of fifteen aliphatic aldehydes and ketones of various molecular weights and degrees of branching have been examined. All give molecular ions, and many of the fragmentations parallel those of aldoximes and ketoximes. The formation of some ions is better explained by the initial production of a novel substituted cyclopropene ion. O-Methyloximes of of the long-chain aldehydes and methyl ketones are readily distinguished by the masses of abundant products of McLafferty rearrangement at m/e 73 and 87, repectively.     

Comparision of FAB and MALDI Mass Spectrometry of Ginsenosides

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A study of rearrangement processes in the mass spectra of substituted diphenyl-ethers

An investigation of the mass spectra of a number of substituted diphenyl ethers has shown that the major fragment ions are commonly due to cleavage of the molecule into the two benzene ‘half’ fragments although in many cases the molecular ion is the most abundant species observed. Little evidence is seen of M? CO or M? CHO peaks in these molecules but a large number of different rearrangement processes have been observed which involve ortho-substituents. These rearrangement ions, although in some cases not very abundant, can be diagnostic in the problem of locating substituents in the diphenyl ether nucleus.     

Positive-ion mass spectra and collision-induced dissociation of some 2,3-didehydro amino acids

The positive-ion mass spectra of a number of didehydro amino acids, ionized by electron impact and/or thermospray, and collision-induced dissociation spectra taken at collision energies of a few electron volts and keV have been performed on multiple quadrupole and reversed geometry sector instruments. Observed differences in the mass spectra and in the fragmentation patterns are explained in terms of different isomeric structures, different internal excitation energies and different ion transit times between the ion source and the collision cell. Molecular ions of unhydrated amino acids are efficiently formed both by electron impact and thermospray, whilst molecular ions of the hydrated compounds are formed more efficiently by the latter technique. The present investigation demonstrates that the use of different ionization techniques combined with mass spectrometry/mass spectrometry measurements at different collision energies yields a wealth of information relevant to structural characterization of this important class of molecules.     

MASSPEC: a graphics-based data system for correlating a mass spectrum with a proposed structure

A graphics-based user-friendly data system called MASSPEC was developed to aid in the analysis of a mass spectrum when a proposed structure is provided. The proposed chemical structure is drawn and combinatorial algorithms correlate the masses of the substructures with the masses of the fragment ions observed in the mass spectrum. These substructures are subsequently drawn on the terminal screen. The commands and algorithms for operating MASSPEC are described. The MASSPEC data system can be used to interpret either nominal or exact mass data generated from relatively large molecules in any ionization mode. Illustrations utilizing MASSPEC include the interpretation of mass spectra generated on tandem mass spectrometers in the thermospray and fast atom bombardment (FAB) modes and the analysis of a FAB mass spectrum of a digested polypeptide to reveal post-translational modifications.     

Comparison of Triple Quadrupole and Double Focusing Mass Spectrometers to Investigate Collision-Induced Dissociation and Metastable Ions of Glycoconjugates

Glycoconjugates, such as chromophore-labeled disaccharides and permethylated glycosphingolipids (GSL) were used for comparison of triple quadrupole and double focusing mass spectrometers in analysis of product ions. A profound effect of collision energy was observed in the product ion spectra of ceramide ions (fragment ions of permethylated GSL): more product ions were observed from a double focusing mass spectrometer. Besides collision energy, the structure of the analyte had a significant effect on the formation of product ions. Despite the fact that masses of protonated molecular ions (MH⁺) of permethylated GSL are significantly larger than their ceramide fragments, the low-energy and high-energy product ion spectra of MH⁺ are, in general, similar. In a double focusing mass spectrometer of reversed geometry, more metastable ions were observed in the first field free region (FFR) than in the second FFR. The metastable ions observed in the second FFR were similar to those observed in low-energy collision-induced dissociation (CID). Although a double focusing mass spectrometer is superior to triple quadrupole instrument for detection of product ions, the poor resolution in either the selection of precursor ion or in the product ion spectra can be a serious problem in analysis of a mixture with similar masses.     

Acetic acid cluster ions for tuning and calibration in thermospray liquid chromotography/mass spectrometry

Combined liquid chromatography and mass spectrometry is frequently performed with the thermospray interface nowadays. With thermospray a special ion source has to be installed. Tuning and calibration of that special source is still a problem which has not been adequately solved, Reference compounds commonly used in conventional electron impact or chemical ionization mass spectrometry cannot be used in the thermospray source. Most of the solutions to this problem reported in the literature cause a rapid contamination of the ion source or may result in memory effects. In this paper the use of acetic acid ammonia cluster ions is proposed for tuning and calibration in thermospray. Abundant cluster ions can be observed over the mass range between m/z = 100 and 1000 when an eluent containing ammonium acetate and 0.5% acetic acid is used. Features of the mass spectra obtained in both filament-off, filament-on and discharge-on modes will be discussed.     

Electrospray mass spectrometry and fragmentation of N-linked carbohydrates derivatized at the reducing terminus

Derivatives were prepared from N-linked glycans by reductive amination from 2-aminobenzamide, 2-aminopyridine, 3-aminoquinoline, 2-aminoacridone, 4-amino-N-(2-diethylaminoethyl)benzamide, and the methyl, ethyl, and butyl esters of 4-aminobenzoic acid. Their electrospray and collision-induced dissociation (CID) fragmentation spectra were examined with a Q-TOF mass spectrometer. The strongest signals were obtained from the [M + Na]+ ions for all derivatives except sugars derivatized with 4-amino-N-(2-diethylaminoethyl)benzamide which gave very strong doubly charged [M + H + Na]2+ ions. The strongest [M + Na]+ ion signals were obtained from the butyl ester of 4-aminobenzoic acid and the weakest from 2-aminopyridine. The most informative spectra were recorded from the [M + Li]+ or [M + Na]+ ions. These spectra were dominated by ions produced by sequence-revealing glycosidic cleavages and "internal" fragments. Linkage-revealing cross-ring cleavage ions were reasonably abundant, particularly from high-mannose glycans. Although the nature of the derivative was found to have little effect upon the fragmentation pattern, 3-aminoquinoline derivatives gave marginally more abundant cross-ring fragments than the other derivatives. [M + H]+ ions formed only glycosidic fragments with few, if any, cross-ring cleavage ions. Doubly charged molecular ions gave less informative spectra; singly charged fragments were weak, and molecular ions containing hydrogen ([M + 2H]2+ and [M + H + Na]2+) fragmented as the [M + H]+ singly charged ions with no significant cross-ring cleavages.     

Mechanisms of repeller-induced effects in thermospray liquid chromatography/mass spectrometry

The application of a high potential at the repeller electrode, positioned opposite to the sampling cone in order to increase the sampling efficiency, can induce fragmentation in thermospray mass Spectrometry. Until now, this fragmentation has been attributed to collision-induced dissociation. As a result of studies on the changes in the reagent gas composition in the thermospray buffer ionization mode as a function of the repeller potential in the positive-ion mode, it appears that three different processes are occurring. At low repeller potentials, the thermospray mass spectra of the eluent are determined by the proton affinities and the concentrations of the various solvent constituents, and the stabilities of the formed cluster ions under the ion source conditions. With an increase in the repeller potential, collision-induced dissociation of the background ions starts to occur. When the kinetic energy of the ions and cluster ions becomes high enough, endothermic proton transfer and solvent-switching reaction pathways are opened. For the relatively volatile analytes studied, e.g. aniline, acetophenone, benzaldehyde and benzoic acid, similar effects are observed.     

羰基原子簇化合物M3(CO)12(M=Fe,Ru,Os)的激光解离研究

在自制的仪器上以冲激光溅射铁、钌、锇的三核羰基原子簇化合物。由原位质谱观察和分析溅射产生的正负离子。比较了解离碎片及分布发现羰基锇原子簇化合物具有特殊的结构稳定性。它们不仅具有很强的金属键,而且锇与羰基分子还形成了很强的配位键。     

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.     

Thermospray mass spectrometry of diazonium and di-, tri- and tetra-quaternary onium salts

Various diazonium, multiply charged ammonium and pyridinium salts and one diphosphonium salt have been analysed by thermospray (TSP) mass spectrometry. The intact cation forms the base peak in all spectra. Typically only a few, yet structurally significant, ions are observed. For diazonium salts the level of fragmentation can be controlled by the temperature of the TSP interface while the fragmentation of the quaternary salts is found to be rather insensitive to interface temperatures.     

Strukturspezifischer Massenspektrometrischer Abbau von mono- und di-n-alkyl-substituierten Acetylenverbindungen

Mass spectra of mono-n-alkyl substituted acetylenes of type 1 containing at least 7 carbon atoms in the alkyl group, R, are characterized by key fragments of mass 82 and 96 which decompose by loss of a methyl radical. Spectra of di-n-alkyl substituted acetylenes of type 2 show these key fragments shifted by an appropriate mass number. These ions suffer further decomposition by loss of a C₅H₁₀ particle of mass 70. In addition key fragments of mass 67, 81, 82 and 95, 96 are again observed.     

Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

The mass spectra of halogenated β-sultones and a comparative study with vinyl methanesulfonates

The mass spectra of some halogenated β-sultones which have been determined show some common features. These include the absence of molecular or ions and the presence of abundant trihalomethyl and [M- trihalomethyl]⁺ ions. The latter can subsequently lose sulfur dioxide, ions are also observed in high abundance.