Mass-analyzed Ion Kinetic Energy Research Articles

Loss of CO from the molecular ions of o‐, m‐ and p‐anisoyl fluorides, CH3OC6H4COF, with fluorine atom migration

AbstractLoss of CO from the molecular ions ([CH3OC6H4COF]+˙) of o‐, m‐ and p‐anisoyl fluorides has been investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring.In the cases of o‐ and p‐anisoyl fluorides, the fluorine atom migrates via a three‐membered transition state to form the molecular ions ([CH3OC6H4F]+˙) of o‐ and p‐fluoroanisoles, respectively. On the other hand, in the case of m‐anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three‐ or four‐membered transition state.

On the structure of [C9H6O]+· ions originating by electron impact induced decomposition of chalcone

The electron impact induced fragmentations of chalcone have been studied with the aid of high resolution measurements, using metastable decompositions by linked scans and mass-analysed ion kinetic energy spectroscopy through collisional experiments by ion-trap mass spectrometry and labellng by 13C deuterium. Based on the data obtained, two different mechanisms for the formation of m/z 130 ions have beenproposed.

Determination of the glycosidic linkage in peracetylated disaccharides comprised of d‐glucopyranose units by use ofr desorption electron‐ionization mass spectrometry

An oxonium ion at m/z317 is present in the desorption electron ionization and ammonia desorption chemical ionization mass spectra of peracetylated disaccharides, comprised of glucopyranose units linked (1-->2), (1-->3), (1-->4) and (1-->6), but is absent in the spectra of the (1-->1)-linked isomer. The ion at m/z317, which is derived from the reducing moiety, has an O-formyl group at the position of linkage to the non-reducing moiety, and O-acetyl groups at each of the remaining positions. The isomeric monoformyl, triacetyl oxonium ions (at m/z317), derived from the (1-->2)-, (1-->3)-, (1-->4)- and (1-->6)-linked disaccharides, give distinctly different mass-analysed ion kinetic energy spectra, thereby enabling the linkage position to be assigned unambiguously.

Mass spectra ofN-arylaminosulphonylcarbethoxydiazoacetamides

The electron impact mass spectra of N-arylaminosulphonylcarbethoxydiazoacetamides were studied. On the basis of high-resolution mass spectrometric data, mass-analysed ion kinetic energy Spectrometry and linked scan experiments a detailed scheme of the fragmentation is proposed. A number of possibilities of charge Iocalization are revealed in the complex decomposition processes of the molecular ions.

Mass-analysed ion kinetic energy spectra and collisional activation spectra of cluster ions of methly 2,3,4,6-tetra-o-methly-d-hexopyranosides with ammonia and methylamine

Mass-analysed ion kinetic energy spectra and collisional activation spectra of cluster ions of methly 2,3,4,6-tetra-o-methly-d-hexopyranosides with ammonia and methylamine

Fast atom bombardment tandem mass spectrometry in the identification of isomeric ribomononucleotides

Analysis of isomeric ribomononucleotides by positive-ion fast atom bombardment tandem mass spectrometry is described. Daughter ion spectra generated by collision-induced dissociation—mass-analysed ion kinetic energy scanning on a sector instrument are compared with daughter ion spectra from a triple quadrupole mass spectrometer, and criteria are established for the differentiation of the 2′-, 3′- and 5′-monophosphate isomers of adenosine, guanosine and cytosine, based on their characteristic fragmentation patterns. The value of tandem mass spectrometry in the identification of nucleotides extracted from biological systems and isolated by high-performance liquid chromatography and in the study of nucleotide metabolism is discussed.

Dissociation dynamics of m-iodotoluene molecular ion: photodissociation and metastable ion decomposition

The dissociation dynamics of the m-iodotoluene molecular ion has been studied on nanosecond and microsecond time scales using photodissociation and metastable ion decomposition techniques. The rate constant for the iodine loss reaction has been determined by the photodissociation — mass-analyzed ion kinetic energy spectrometry method developed previously. Kinetic energy release distributions determined at widely different dissociation time scales have been found to be composite. This was attributed to the participation of two competing reaction channels, namely the formation of the m-tolyl and tropylium ions. The investigated reaction seems to be well explained by the statistical theories.

Determination of enzyme kinetic parameters of cyclic CMP‐specific phosphodiesterase by quantitative fast atom bombardment tandem mass spectrometry

AbstractThe determination of cytidine 3′,5′‐cyclic monophosphate‐specific phosphodiesterase activity by means of fast‐atom bombardment (FAB) mass Spectrometry with mass‐analysed ion kinetic energy (MIKE) spectrum scanning is described. Initial efforts to determine the activity of the enzyme by this method were unsuccessful owing to the obfuscation of sample‐related peaks by peaks emanating from the incubation buffer and cation adducts; dilution of buffer and a desalting procedure overcame these difficulties. In the resulting positive‐ion FAB mass spectra, characteristic peaks of the enzyme substrate and product could be readily identified and the protonated molecular ions selected for MIKE scanning. By spiking enzyme incubates with known amounts of substrate and product, and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the substrate/product ratio at the end of a series of phosphodiesterase incubations was determined. From the data obtained, the Km and Vmax of the phosphodiesterase were calculated as 6.08 mM and 11 μmol min−1 mg−1, respectively, showing good agreement with the analogous values of 8.06 mM and 5.8 μmol−1 min−1 mg−1 obtained by radioactive assay.

Collision‐Induced decomposition of peptides. An investigation into the effect of collision gas pressure on translational energy losses

AbstractThe dependence on the gas pressure of translational energy losses, ΔE, suffered by incident ions in collision with helium target gas atoms was investigated for the [M + Na]+ ion of valinomycin. ΔE was measured from the fragment ion peak positions in the mass‐analysed ion kinetic energy (MIKE) spectra. The variation of ΔE with target gas pressure was found to be different for different fragment ions. The implications of the results for the number of collisions which may occur under normal collision‐induced decomposition conditions (30–40% transmission) are discussed.

Dissociation of ionized keto-enol tautomers of some 1,3-dicarbonyl compounds

Unimolecular dissociation processes of ionized keto-enol tautomers of 2,4-pentanedione ( 1), 1,1,1-trifluoro-2,4-pentanedione ( 2) and 1,1,1,3,3,3-hexafluoro-2,4-pentanedione ( 3) have been investigated by mass analyzed ion kinetic energy (MIKE) and photoionization mass spectrometry. The MIKE spectra show that the predominant fragmentation of the enol molecular ion of 1 at low internal energy is loss of CH 3, while the diketo molecular ion of 1 preferentially eliminates a CO molecule with a relatively large kinetic energy release (KER: T 0.5 = 78 meV). The metastable fragmentations of fluorinated 2 + and 3 + are characterized by loss of CF 3. The KER values for the CF 3 loss are strongly different (182 meV for 2 and 28 meV for 3). The potential energy profiles for the low energy dissociation processes of 1 + and 2 + are probed by measuring the ionization and appearance energies for the appropriate ions. The profiles provide a rationale for the fragmentation characteristics of the metastable molecular ions. The enthalpy change for the keto-enol tautomerization of 1 + ion is found to be 77 kJ mol -1. Mechanistic proposals for the losses of CH 3 and CO from 1 + and the loss of CF 3 from 2 + and 3 + are presented.

Mass spectral fragmentation patterns of deuterated hexanitrobibenzyl and hexanitrostilbene

Mass-analysed ion kinetic energy (MIKE) spectrometry with collision-induced dissociation (CID) has been used to study the fragmentation processes of the MH+ ions produced by chemical ionization (CI) of a series of deuterated hexanitrostilbene (HNS) and hexanitrobibenzyl (HNBB) compounds. Typical fragment ions obtained in both groups were due to loss of OR′, 2OR′ and NO2 and due to the cleavage of the CC single bond in HNBB and of the double bond in HNS. In HNS there is a preferential loss of NO. A great similarity was observed between the fragmentation pattern of 2,4,6-trinitrotoluene (TNT) and that of HNS. In negative-ion chemical ionization (NCI) the fragment ion which forms the base peak in the mass spectra of the HNS compounds is the [(M/2)+O]− ion, while in the HNBB compounds it is the [M/2]− ion.

Unusual neutral and radical losses in 2′‐substituted N‐phenylanthranilic acids on electron impact

AbstractUnusual expulsions of [H2O + CO2] from the M+˙ of N‐(o‐carboxyphenyl)anthranilic acid, [H2O + CH2O] from the M+˙ of N‐(o‐methoxyphenyl)anthranilic acid and [H2O + ˙NO2] from the M+˙ of N‐(o‐nitrophenyl) anthranilic acid were observed under electron impact conditions. These processes are stepwise in the corresponding para‐substituted N‐phenylanthranilic acids. The proposed fragmentation pathways and their mechanisms are supported by B/E linked‐scan spectra, collision‐activated decomposition (CAD)–mass‐analysed ion kinetic energy (MIKE) spectra, high‐resolution data, deuterium labelling and chemical substitution.

Ion-Neutral Complexes in Gas-Phase Dissociations of Protonated Nitriles: n-C 3H 7CNH + and i-C 3H 7CNH +

I n the last decade ion-neutral complexes have been proposed frequently as intermediates in the unimolecular dissociation of many organic ions in the gas phase [l]. For example, for the unimolecularly fragmenting ions n-C,H,R+ and i-C,H,R+, where a.o. R = CHzO, CH&HO and (CH,),CO [2], CH, = NH [3a] and CHsCH = NH [3b] and CO [4], ionneutral complexes have been invoked to rationalize the intramolecular isomerization of [nC&f: . . . R] into [i-CsH: . . R] before elimination of R or, in appropriate systems, the derived alkene(R-H) [2-41. However, for R = CO the presumed involvement of such complexes is very difficult to verify experimentally, as in that case a possible interation between the C,Ht and CO species prior to their separation cannot be probed by H/D exchange. We report here on the occurrence of ion-neutral complexes in the unimolecular fragmentation of the metastable ions n-CsH&NH+, 1, and iCsHJNH+, 2, which are iso-electronic with nCsH,CO+ and i-C,H,CO+, respectively. The proton (deuteron) on nitrogen in these ions serves as a valuable tool to probe the interaction between the C,Hg ion and the (H,C,N) neutral before they separate from each other. Experiments were performed by the mass-analyzed ion kinetic energy spectrometry technique [S] using a VG ZAB-2HF mass spectrometer. The ions 1 and 2 were prepared by chemical ionization using various protonating agents in combination with deuterium and r3C-labeling. Our results (Table 1) show that both 1 and 2 predominantly dissociate b of (H,C,N) to give C3Hg (m/z 43).The data of ysloss C-labeling studies on n-CsH, 3CNH+ establish that the 13C atom is fully retained in the expelled (H,C,N) neutra1. This

Revision of the amino acid sequence of the smallest bc1 complex subunit: use of fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrum analysis.

We have isolated the smallest bc1 complex subunit from an acidic chloroform/methanol extract of bovine cardiac muscle. The identification of the polypeptide was made possible by classical Edman degradation and amino acid analysis. The measurement of its exact molecular weight by fast atom bombardment mass spectrometry (m/z 6519.8), the characterization of a tryptophan cleavage peptide and pepsic peptides by mass measurements and by mass-analysed ion kinetic energy spectrum analysis allow rectification of the amino acid sequence of the smallest bc1 complex subunit. We found a serine residue instead of Gln 22 and tryptophan residues in place of Ser 34 and Ser 38.

Tandem MAss Spectrometry Studies of Acetone and Acetone/Water Cluster Ions

Ion clusters were formed in a temperature-variable high-pressure ion source from neat acetone and acetone/water mixtures and subjected to tandem mass spectrometry studies—unimolecular and collisionally activated mass-analyzed ion kinetic energy spectroscopy. The predominance of water loss from H +(H 2O)(A) l=3 , where A  acetone, suggests that the solvation sphere around H 3O + does not close at l = 3, contrary to the case of acetonitrile or dimethyl ether. The results may be interpreted in terms of suggested ion structures which involve isomerization enroute to dissociation. The virtual absence of H/D scrambling in the collissionally activated dissociation of H 3O +(DA) 3, DA  acetone- d 6, and of D 3O +(A) 3 means that if enolization takes place, it is a rate-determining step in an irreversible isomerization. The stability of H +(H 2O)(A) 3 is a dominant factor in the observation of acetone loss from H +(H 2O)(A) 4.

Diatomic monocations and dications containing germanium and a rare gas atom.

Diatomic dications and monocations GeY2+ and GeY+, where Y = Ne, Ar, Kr or Xe, have been detected on the microsecond time scale. They are characterized via appearance energies, charge stripping of GeY+ ions, and mass-analysed ion kinetic energy spectroscopy. The formation of GeAr+ is found to involve an excited state of Ar in a Hornbeck-Molnar process.

Metastable ion study of organosilicon compounds. Part IV. 1,1,1,3,3,3-Hexamethyldisilazane and 1,1,3,3-tetramethyldisilazane.

The unimolecular fragmentations of 1,1,1,3,3,3-hexamethyldisilazane (1), and 1,1,3,3-tetramethyldisilazane (2) were investigated by mass-analyzed ion kinetic energy (MIKE) spectra. D-Labelling studies and high resolution data were also included. One of the characteristic fragmentations of these compounds was the loss of CH4 after the expulsion of CH3 or H from the molecular ions.In the case of 1, D-labelling study indicated that the hydrogen atom bonded to nitrogen atom concerned this CH4 loss. Almost complete scrambling of CH3 groups occurs prior to loss of CH4. An unusual NH3 elimination was found in the MIKE spectra of the [M-CH3-CH4]+ ion for 1 and of the [M-CH3]+ ion for 2.The fragmentations of 2 were compared with those of its carbon analogue, diisopropylamine, 3.

Particle beam liquid chromatography—mass spectrometry on a double-focusing sector instrument

A commercially available particle beam interface developed by the Vestec Corporation has been coupled to a double-focusing high-resolution mass spectrometer (VG ZAB 2F) via a momentum separator. An ultraviolet detector was in-line with the interface and allowed monitoring of the eluting materials. With this instrumentation, complete electron-impact (EI) mass spectra on synthetic mixtures of steroids, nucleosides, and several derivatives of amino acids were recorded. Amongst these the EI mass spectra of 2,4-dinitrophenyl, 9-fluorenylmethoxycarbonyl and phenylthiohydantoin derivatives were obtained. The standard LC conditions used here (250 mm × 4.6 mm I.D., reversed-phase C 18 column, 1.0 or 1.5 ml/min flow-rate, isocratic or gradient programming) allowed separation of the mixtures. The resulting mass spectra were compared with those obtained using a direct insertion probe. The agreement was excellent in most cases. Sensitivity measurements were performed on cholesterol and caffeine. A complete low-resolution mass spectrum can be obtained on 100 ng of cholesterol. Single-ion monitoring of the M + of 200 pg of caffeine gave a 4:1 signal-to-noise ratio at m/z 194. Complete high-resolution mass spectra were obtained on 5 μg of cholesterol (loop injection) and on every peak of a five-steroid mixture of 5 μg each. The accuracy of the mass measurements were better than 5 m.m.u. for most cases. Three to four scans could be obtained for each liquid chromatographic peak. Mass-analyzed ion kinetic energy spectra were recorded on the M + of 2.5 μg of cholesterol at m/z 386. Similarly the B/E linked scan of the same ion was recorded on 2.5 μg and 500 ng.

Isolated excited electronic states in the unimolecular gas-phase ion dissociation processes of the radical cations of isocyanogen and cyanogen

The unimolecular gas-phase chemistry of CNCN +· and NCCN · has been investigated by electron-impact mass spectrometry, mass-analysed ion kinetic energy mass spectrometry and a theoretical density-functional method. The CN + formation appears to compete with the C +· 2 formation in the microsecond time scale, in spite of an energy gap of 3.5 eV (CNCN) and 3.0 eV (NCCN) between the two processes. This observation is explained by assuming that the fragmentation to CN + proceeds via an isolated excited electronic state of the molecular ion. The C +· 2 fragment ion must be formed from both isomeric C 2N 2 +· parent ions by a rearrangement reaction. While NCCN +· is more stable than CNCN +· by 0.6 eV, the kinetic energies released in both rearrangements and theoretical calculations indicate that the corresponding intermediates are not only much closer in energy, but even reversed in energetic order with respect to their precursor ions.

Gas chromatography—mass spectrometry and gas chromatography—tandem mass spectrometry of cyclic fatty acid monomers isolated from heated fats

The analysis of hydrogenated cyclic fatty acid monomers isolated from heated linseed and sunflower oils is achieved by gas chromatography—tandem mass spectrometry of their pentafluorobenzyl esters. Collisionally activated dissociation of the carboxylate anions produced by electron-capture ionization shows remote charge-site fragmentation that allows location of cyclopentane and cyclohexane rings by examining the resulting mass-analysed ion kinetic energy spectra. Oxidative ozonolysis of the methyl esters of the unsaturated cyclic fatty acid monomers allows location of some double bonds. However, preliminary results obtained with remote charge fragmentation of synthetic unsaturated models make this approach an alternative for double bond location in the cyclic fatty acid monomers isolated from heated fats.