Mass Spectral Behavior Research Articles

Mass spectral fragmentation of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes: ring contraction of pyrrolidine and 1,3-oxazolidine in mass spectrometry.

The mass spectral behaviour of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under fast atom bombardment (FAB) and electron impact (EI) ionization conditions. Under FAB ionization, all compounds show a tendency to form protonated aldehyde or benzophenone ions and to form protonated 1-azabicyclo[3.1.0]hexane ions, which can further lose an ethylene or cyclopropane from the pyrrolidine ring to produce protonated 1-azabicyclo[1.1.0]butane ions and 3H-azirine ions, respectively. Under EI ionization, a similar fragmentation to that under FAB ionization was observed. The title compounds also show a tendency to yield oxirane ions and oxirenium ions by loss of pyrrolidine and pyrrolidine plus H. Ring contractions of 1,3-oxazolidine by loss of an aldehyde or ketone and of pyrrolidine by loss of an ethylene or cyclopropane were observed under both FAB and EI ionization conditions.

Fenarimol solar degradation pathways and photoproducts in aqueous solution

The degradation photoproducts of the fungicide fenarimol obtained from irradiation of aqueous solutions with sunlight were characterised. The photoproducts resulting from samples with different exposure times were extracted and separated using chromatographic techniques. Seven main photoproducts were detected using high performance liquid chromatography with a photodiode array detector, gas chromatography with mass spectrometry detector and Fourier transform infrared spectroscopy. Structures are suggested for possible photoproducts based on the characterisation results, minimum energy geometry of the parent compound, and the mass spectral behaviour of fenarimol. These correspond to the compounds with m/ z 328 (three structural isomers (a), (b) and (c)), m/ z 294 (two structural isomers (a) and (b)), m/ z 292, 278 and 190. Of the various major products detected, the isomer 328(a) is seen to be particularly unstable under the action of sunlight. The most stable photoproducts are found to be those with m/ z 294(a), 278 and 190. However, upon prolonged solar irradiation all of these break down to produce polar, low molecular weight compounds. Comparison with our own and other results on fenarimol photolysis indicate significant solvent effects on the process. The combination of these structural characterisation results and previous data from spectroscopic and photodegradation kinetics studies allows us to suggest some possible mechanisms for the photodegradation of fenarimol under sunlight.

Structural Investigations of 5-Methylchromone Glycosides from Aloe Species by Liquid Chromatography/Electrospray Tandem Mass Spectrometry

The mass spectral behavior of a series of 5-methylchromone glycosides isolated from two Aloe species was investigated by liquid chromatography/positive-ion electrospray (ES) mass spectrometry using collision-induced dissociation (CID) mass spectrometry. The CID mass spectra of the [M + H]+ ions show a typical fragmentation pattern reflecting the several substructures (substitution at C-7, C-9 and C-10, position and nature of the ester moiety at C-2) of the 5-methylchromone glycosides. Besides a series of known 5-methylchromone glycosides, nine new compounds of this type were identified by LC/ES-CIDMS from Aloe rubroviolacea and Aloe perryi (Aloeaceae).

Microwave Catalyzed Reaction of H-Dimethylphosphonate with N-(2,3-Epoxypropyl)Phthmide

Microwave catalyzed reaction of N-(2,3-epoxypropyl)phthalimide with H-dimethylphosphonate for 4 min yielded via free radical processes: trimethylphosphonate, trimethylphosphate, N-(2-propenyl)phthalimide, 2-(N-phthalimidopropyl) dimethylphosphinates, hydrogen 3-(N-phthalimidopropyl) methylphosphine oxide, hydrogen 3-(N-phthalimidopropyl)methylphosphinate, 2-(N-phthalimidopropyl) dimethylphosphonate, and 2-(N-phthalimidopropyl) dimethyl-phosph-inate. The mechanism of formation of the various compounds along with their mass spectral fragmentation behavior is described in this communication.

FORMATION AND GC-MS CHARACTERIZATION OF UNUSUAL CYCLIC SULFIDES

connection with another project involving the cleavage of the thiirane ring of cyclohexene episulfide in the presence of trifluoromethylthiocopper, the presence of several unusual cyclic sulfides (5–10, Fig. 1) was observed both in the reaction product and the starting material itself. The formation of these compounds has been rationalized on the presence and participation of the thiyl radical species. Details pertaining to their formation and characterization based on their mass spectral fragmentation behavior are presented in this communication.

Characterization of selenium species in biological extracts by enhanced ion-pair liquid chromatography with inductively coupled plasma-mass spectrometry and by referenced electrospray ionization-mass spectrometry

Selenium is an essential nutrient for humans; selenium compounds catalyze intermediate metabolism reactions and inhibit the toxic effects of heavy metals such as arsenic, cadmium and mercury. Some extracts of selenium-enriched biological materials show cancer preventive effects, tentatively attributable to the biological functions of selenoamino acids. An improved ion pair chromatographic method with methodological enhancements for the separation, qualitative and quantitative determination of non-volatile selenium compounds extracted from different samples has been developed using ICP-MS as an element-selective detector. Separation power early in the chromatogram was increased to baseline separation in the standard mixture as a result of decreasing spray chamber size from 97 to 14 ml, and increasing trifluoracetic acid (TFA) concentration in the mobile phase from 0.1 to 0.6%. The former pH was restored by the addition of ammonia to the mobile phase, which also served to increase the column recovery of inorganic anions. Calibration curves for different selenoamino acids showed statistically different behavior. Biological sample extracts were characterized using HPLC-ICP-MS. Mass spectral behavior of selenoamino acids, using electrospray and ion trap technology with direct infusion and liquid chromatographic sample introduction, is also reported.

Reaction of ethynylcyclopentanol with trifluoromethylsulfenyl chloride

Based on the mass spectral fragmentation behavior of the reaction products, the free radical reaction of 1-ethynyl-1-cyclopentanol ( 1) with trifluoromethylsulfenyl chloride ( 2) has been found to furnish 13 compounds formed from addition and elimination reactions. Two compounds are noteworthy in that one does not have the side chain, while the other carries an extended `tri-ynyl' side chain. This paper presents the mechanism of formation of the various compounds and their GC-MS characterization.

Electrospray mass spectrometry of the peroxide adduct of a monomeric Fe(III) complex containing a phenol group

Electrospray mass spectral measurements on solutions containing an iron(III) compound containing a phenol group and H 2 16O 2 (or H 2 18O 2) revealed that facile peroxide adduct formation of an end-on type has occurred in the solution, and the difference in mass spectral behavior between the peroxide adducts with H 2 16O 2 and H 2 18O 2 was demonstrated.

Charge-remote molecular hydrogen removal in protonated and alkali-cationized long-chain fatty acid esters upon cesium ion bombardment

The mass spectral behavior of cationized saturated fatty acid derivatives has been studied in order to gain insight into the loss of molecular hydrogen during cesium ion bombardment. It is shown that molecular hydrogen and hydrogen radical loss occurs for protonated and alkali (Li +/Na +)-cationized fatty acid methyl esters as well as for protonated acylcarnitines and that molecular hydrogen loss is dependent upon the acyl chain length. Investigation of ion structures by collision-induced dissociation tandem mass spectrometry indicates that in the case of alkali-cationization a hydrogen radical is lost from all positions of the saturated acyl chain, whereas in the case of protonated molecules a hydrogen radical is predominantly eliminated from the protonated ester group. For the primary reaction of the dehydrogenation chemistry, an ion-beam-induced excitation of a cationized molecule is proposed, yielding a diradical species that gives rise to an intermolecular reaction with a neutral analyte molecule. Subsequent cationization of the neutral [M–H 2] species formed in this primary reaction leads to the formation of the satellite ion at m/ z values 2 u lower compared to the cationized molecule.

Identification of tyrosine sulfation in Conus pennaceus conotoxins alpha-PnIA and alpha-PnIB: further investigation of labile sulfo- and phosphopeptides by electrospray, matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry.

Liquid chromatography/electrospray ionization mass spectrometry was used to investigate the peptide composition of the venom of Conus pennaceus, a molluscivorous cone shell from the Red Sea. Based on observed M(r)s, this venom contained all known conotoxins previously isolated and identified from this species. Interestingly, the doubly protonated species of only two of these conotoxins, alpha-PnIA and alpha-PnIB, showed additional related ions at +40 m/z (+80 Da), indicating the presence of either sulfation or phosphorylation in both components. High-performance liquid chromatographic (HPLC) fractions containing these two conotoxins were examined by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry in both positive and negative ion modes, as well as by MALDI high-energy collision-induced dissociation. These experiments established the presence of a single sulfated tyrosine residue within both alpha-PnIA and alpha-PnIB. Hence their post-translationally modified sequences are GCCSLPPCAANNPDY(S)C-NH2 (alpha-PnIA) and GCCSLPPCALSNPDY(S)C-NH2 (alpha-PnIB). This assignment was supported by comparison of their mass spectral behavior with that of known sulfated and phosphorylated peptides. This data clarified further the distinguishing features of the ionization and fragmentation of such modified peptides. Selective disulfide folding of synthetic alpha-PnIB demonstrated that both sulfated and non-sulfated toxins co-elute on reversed-phase HPLC and that alpha-PnIB possesses the same disulfide connectivity as other 'classical' alpha-conotoxins reported previously.

Nanoelectrospray—more than just a minimized-flow electrospray ionization source

The comparison between electrospray ionization (ESI) mass spectra from NaCl solutions with and without analyte obtained under ionspray and nanospray conditions reveals different mass spectral behavior of the two ESI techniques. This can be attributed to the different initial droplet sizes which are in the μm range for ionspray, while in nanospray they are believed to be about one order of magnitude smaller. In the context of the widely accepted uneven-fission model, nanospray would then enter one fission generation later; in addition, a higher initial droplet surface charge density in nanospray results in early fissions without extensive evaporation and thus increase in sample and salt concentration. This rationalizes that ionspray spectra closely resemble nanospray spectra from solutions with about one order of magnitude higher salt concentrations, showing a higher tolerance of nanospray towards salt contamination. When the analyte is a peptide (in a solution containing a high molar surplus of salt), molecule ion formation effectively competes with salt cluster ion formation; when the analyte is a sugar, it is detectable beside a high salt concentration only with nanospray, indicating the supporting effect of surface activity on ion release in the case of peptides. A model is presented which explains the different mass spectral behaviour of ionspray and nanospray by suggesting different “predominant fission pathways” depending on the size of the initial droplets.

SYNTHESIS AND MASS SPECTRAL CHARACTERIZATION OF DIISOPROPYLAMINO-ETHANETHIOL, -SULFIDES AND -DISULFIDES AND VINYL SULFIDES

The sulfur containing chemical agent, O-ethyl-S-2-(diisopropylaminoethyl) methylphospho-nothiolate (VX), is an extremely potent inhibitor of the enzyme acetylcholinesterase and exhibits extended neurological effects. It undergoes degradation on standing alone or in the environment. Hence, identification of its primary degradation products assumes considerable importance. The synthesis and mass spectral fragmentation behavior of the title compounds, some of which are present in the VX degradation products, has not received much attention. This communication describes the synthesis and mass spectral characterization of the title compounds.

The feasibility of the detection and quantitation of beta-adrenergic blockers by solid-phase extraction and subsequent derivatization with methaneboronic acid.

Urine specimens containing 11 common beta blockers were processed using solid-phase extraction technology to extract the drugs from the urine matrix, then converted to their cyclic methaneboronates by treatment with methaneboronic acid in ethyl acetate. The compounds tested included acebutolol, atenolol, alprenolol, bisoprolol, betaxolol, carteolol, penbutolol, propranolol, pindolol, timolol, nadolol, sotalol, labetolol, metoprolol, and oxprenolol. The extraction efficiencies were greater than 90% for all drugs tested. The cyclic methaneboronates formed by this procedure generally possessed good chromatographic properties. The mass spectral behavior of the methaneboronates was excellent, with all compounds containing several high mass fragments and every tested compound possessing a unique mass spectrum.

Mass Spectrometric Study of Some Organotellurium(IV) Compounds

A series of tetracoordinated organotellurium(IV) compounds with potential immunomodulating properties were studied mass spectrometrically using high-resolution positive ion desorption chemical ionization and constant B/E and B 2 /E linked-scanning techniques. The nature of the organic ligand bonded to the Te(IV) has a major influence on the mass spectral behavior of these compounds. When only monodentate ligands -OR are bonded to the Te(IV), no molecular or protonated molecular ion appears in the spectrum, although polynuclear species are present. When the compounds contain bis-bidentate ligands of the type -ORO-, the protonated molecular ion becomes the base peak and the polynuclear species are not present.

Mass Spectral Study of Some Phenyl-mono and Dinitropyridyl Sulfide, Ether, Amine and Sulfone Derivatives

The electron impact ionization of some mono- and dinitropyridylphenylsulfide, ether, amine and sulfone derivatives were studied at 70 ev energy. All the 8 compounds studied underwent ring closure during the formation of a carbazole radical cation as a general feature in their mass spectra. The basic differences in the mass spectral behaviour are mainly attributed to the position of the nitro group in the pyridyl ring and the fragmentation pathway is directed by the sulfur, oxygen or nitrogen moiety. The base peak in the mass spectra is determined by such differences. © 1997 John Wiley & Sons, Ltd.

One-step syntheses of Ph 3P-substituted selenido carbonyl iron and ruthenium clusters Part 2. Crystal structures of Fe 2(μ 2-Se 2)(CO) 6- n(PPh 3) n( n=1 or 2) Fe 3(μ 3-Se) 2(CO) 8(PPh 3) and Ru 4(μ 4-Se) 2(μ-CO) 2(CO) 8(PPh 3), and HPLC behaviour of the iron derivatives

Ph 3PSe reacts with Fe 3(CO) 12 giving six products ( 1–6) belonging to three different families of clusters: Fe 3(μ-Se 2)(CO) 9- n L n (two products, 3,5, n = 1, 2, Fe 3( μ 3-Se) 2(CO) 9- n L n (three products, 1, 2, 4, n= 0–2) and Fe 3-Se)( μ- CO) 9- n L n (one product, 6, n = 2). Under the same conditions, Ru 3(CO) 12 affords Fe 3(μ 3-Se) 2(CO) 9- n (PPh 3) n (three products 7,8,10, n = 1–3) and the tetraruthenium clusters Ru 4(μ 4-Se) 4(CO) 2(CO) 9- n (PPh 3) n (two products, 11, 9, n=1,2). The structures of the clusters 2, 3, 5 and 11 · 1 2 CH 2Cl 2 have been determined by X-ray diffraction methods. The mass-spectral behaviour of iron mono- and disubstituted phosphine derivatives ( 2–6) is characterised by the low abundance (<6%) of polynuclear fragments, even under NICI conditions. Gas-phase rearrangements are considered to take place in order to explain the presence of certain peaks. The six iron derivatives are effectively separated by HPLC, the elution order depending on the degree of phosphine substitution and the kind of cluster framework.

The Unexpected Formation of a Tetradentate Tripyrrolic Complex of Nickel(II)

Abstract(2‐Pyrrolylmethane)(2‐pyrrolylmethyl)imine (2) and an equimolar amount of 2‐formylpyrrole give, in the presence of nickel(II) in hot methanol, the novel tripyrrolic nickel(II) complex [SP‐4]‐[(2‐dipyrrinato‐k2N,N′‐methyl)(2‐pyrrolylmethenato‐ kN′′)imine‐kN′′′]nickel(II) (4). This planar complex has been characterized by X‐ray crystallography, a mechanism for its formation is proposed and its mass spectral behavior is discussed.

Discrimination of structural isomers of amphetamine using carbon dioxide negative‐ion chemical ionization mass spectrometry

The negative‒ion chemical ionization mass spectra of a group of structural isomers of amphetamine have been studied using carbon dioxide as the reagent gas. Characteristic and reproducible differences are observed for each member of the set implying that this technique offers a means of distinguishing among groups of amphetamine isomers. Characteristic adducts to the molecular ion are observed in the form (M–[H]+[O]) and (M–[H]+[CO2]). Descriptions of some fragments are given based on the mass spectral behaviour of a set of analogue compounds and the results of oxygen‐18 labelled carbon dioxide reagent gas experiments. Contents of the carbon dioxide plasma and their impact on various analytes is also discussed.

Theoretical Modelling of Mass Spectrometric Behaviour of Peptides: Singly and Doubly Protonated Tetraglycine

Neutral, singly- and doubly protonated tetraglycines have been studied by semiempirical (MNDO) and ab initio (3-21G) methods to model the mass spectral behaviour of singly- and doubly protonated oligopeptides. The favourable bond cleavages in the ions were investigated by using bond orders and energy partitioning values. The most favourable protonation site in singly charged tetraglycine is the N-terminal amine nitrogen. In the doubly protonated forms, protonation at the N- and C-terminal residues is the most favourable energetically, minimizing Coulombic repulsion. Protonation at the amide nitrogen results in a significant weakening of the corresponding amide bond, leading to b+ ion formation from the singly protonated forms, and y+ and b+ or alternatively b2+ ion (ion nomenclature according to P. Roepstorff and J. Fohlman, Biomed. Environ. Mass Spectrom., 11, 601 (1984)) formation from the doubly protonated forms. The critical energy of fragmentation is much lower in the doubly protonated species compared to the singly protonated ones showing the effect of charge repulsion. The relative positions of the two protonated sites also influences the bond cleavages. Most surprisingly, the extended beta-sheet structure, in which the distance between charges is maximized, is not stable, and collapses into a folded conformation, where internal solvation competes successfully with charge repulsion. This suggests that multiply protonated peptides may, generally, have folded and not extended ("linear') structures in the gas phase.

Theoretical Modelling of Mass Spectrometric Behaviour of Peptides: Singly and Doubly Protonated Tetraglycine

Neutral, singly- and doubly protonated tetraglycines have been studied by semiempirical (MNDO) and ab initio (3-21G) methods to model the mass spectral behaviour of singly- and doubly protonated oligopeptides. The favourable bond cleavages in the ions were investigated by using bond orders and energy partitioning values. The most favourable protonation site in singly charged tetraglycine is the N-terminal amine nitrogen. In the doubly protonated forms, protonation at the N- and C-terminal residues is the most favourable energetically, minimizing Coulombic repulsion. Protonation at the amide nitrogen results in a significant weakening of the corresponding amide bond, leading to b+ ion formation from the singly protonated forms, and y+ and b+ or alternatively b2+ ion (ion nomenclature according to P. Roepstorff and J. Fohlman, Biomed. Environ. Mass Spectrom., 11, 601 (1984)) formation from the doubly protonated forms. The critical energy of fragmentation is much lower in the doubly protonated species compared to the singly protonated ones showing the effect of charge repulsion. The relative positions of the two protonated sites also influences the bond cleavages. Most surprisingly, the extended beta-sheet structure, in which the distance between charges is maximized, is not stable, and collapses into a folded conformation, where internal solvation competes successfully with charge repulsion. This suggests that multiply protonated peptides may, generally, have folded and not extended (linear') structures in the gas phase.