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The structural characterization of the ions generated by the electron ionization-induced loss of ammonia from the molecular ions of α,ω-diamines, using ion/molecule reactions in combination with collision-induced dissociation (CID) studies, is described. The results of the experiments of ion/molecule reactions using dimethyl disulfide exclude the distonic radical cation structure for those long-lived ions proposed earlier by other authors for ions generated within a few microseconds following ionization. The unimolecular and CID characteristics of the ions [M---NH3]√+ of 1,4-diaminobutane and 1,5-diaminopentane and of their fragment ion m/z=56, are discussed in terms of the structures CH3CH2CH=CHNH2√+ and CH3CH2CH2CH=CHNH2√+ for the ions [M---NH3]√+, respectively. The structure of the closed shell ions resulting from loss of ammonia from the protonated α,ω-diamines was also probed through the CID spectra of model ions prepared by chemical ionization with methane in the chemical ionization source of the mass spectrometer.

There is a general fascination with regard to the origin of life on Earth. There is an intriguing possibility that prebiotic precursors of life occurred in the interstellar space and were then transported to the early Earth by comets, asteroids and meteorites. It is probable that some part of the prebiotic molecules may have been generated by gas-phase ion/molecule reactions. Here we show experimentally that gaseous ion/molecule reactions of the amino acids, Glu and Met, may promote the synthesis of protonated dipeptides such as (Glu-Glu)H(+) and (Glu-Met)H(+) and their chemical growth to larger protonated peptides.

Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnA(n)+1 - mH2O and DnA(n) - mH2O, where m = 1-2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnA(n)+1 - mH2O and DnA(n) - mH2O (m = 1-2) clusters in the ESI spectrum. The absence of -OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnA(n)+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnA(n)+1 - mH2O and DnA(n) - mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition.

The reactivity of the nitrosonium ion, NO+, with the amino acid Glu and the dipeptide γ‒Glu–Met in the gas phase has been investigated using the combination of chemical ionisation mass spectrometry and MS/MS. It is shown that NO+reacts efficiently with both Glu and Glu–Met leading to the formation of the nitroso‒group containing ions atm/z159 and 288.The formation ofm/z159, (GluNO‒18)+, is rationalized by a mechanism involving an electrophilic attack of NO+upon the carbonyl oxygen atom of one of the carboxylic groups of Glu and the N‒terminal carboxylic group of Glu–Met leading to the neutral losses of H2O and Met, respectively. The unimolecular decompositions of the metastable and collisionally activatedm/z159 ions lead primarily to the elimination of the neutral species HNO (major) and the (Glu‒18) residue (minor). The formation of them/z288 ions can be described by a mechanistic scheme which involves the ion‒molecule interaction ofm/z159 with Glu and Glu–Met and subsequent losses of H2O and Met, respectively. Unimolecular and collisionally activated dissociations ofm/z288 suggest the formation of the proton‒bridged ion‒neutral complex [(GluNO‒18)···H+···(Glu‒18)].

The molecular ion of 3-phenyl-1-bromopropane is known to eliminate ethylene containing the methylene groups of positions 1 and 2 following an exchange between the hydrogen atoms from position 1 and the ortho positions of the phenyl ring. During this reaction migration of the bromine atom to some position in the molecular ion must take place. The eventual position to which the bromine atom has migrated has been probed by studying the metastable behaviour and collision-induced dissociation reactions of the (M–C 2 H 4 ) •+ ion. From comparison with appropriate reference ions it is found that the (M–C 2 H 4 ) •+ ion has the structure of ionized benzyl bromide. The mechanistic implication of this finding is briefly discussed.

Triphenyltin compounds are widely introduced into the Dutch aquatic environment. To be able to detect them in environmental samples, the ionization methods of electron ionization, chemical ionization, fast atom bombardment, field desorption, thermospray and electrospray have been applied to triphenyltin acetate, chloride, fluoride and hydroxide to find out which of these methods is best suited to obtain molecular weight information on the intact molecules. For this purpose, field desorption is shown to be the most appropriate method giving, without fragmentation, molecular ion peaks, with the exception of triphenyltin hydroxide. The latter compound gives rise to the base peak at mz 716, due to the formation of bis(triphenyltin)oxide. Field desorption tandem mass spectrometry, applied to the molecular ions, has shown that the main decomposition pathway corresponds to the loss of a phenyl radical. Subsequently, sediment and surface water samples from the Dutch inland water, without and with the use of clean-up procedures, have been analyzed by the application of field desorption in combination with tandem mass spectrometry. Within the limits of detection, no signals for the presence of triphenyltin compounds in these environmental samples has been found. Upon spiking these samples with triphenyltin acetate, chloride, fluoride and hydroxide, it has appeared that the covalently bonded non-aromatic substituent of the molecules is exchanged for hydroxyl.

Some synthetically obtained linear and cyclic phosphopeptides of low molecular weight have been studied by fast-atom bombardment and tandem mass spectrometry to verify the position of the phosphate group in these compounds. Based upon the occurrence/non-occurrence of loss of phosphoric acid from low abundance fragment ions induced by low- and high-energy collisions with target gases, it is shown that the position of the phosphate group in the phosphopeptides studied can be determined unequivocally.

It is shown that metastably decomposing molecular ions of the title compounds eliminate sulfur dioxide via two reaction pathways provided that an α-hydrogen atom adjacent to the heterocyclic ring nitrogen atom is present. One of the channels leads to the initial formation of an o-azaxylylene ionic species and is associated with the narrow component of the accompanying composite metastable peak. The other channel involvel a multistep pathway which eventually leads to the formation of an aldimine ionic species and which is associated with the broad component of the accompanying composite metastable peak. Collision-induced dissociation and deuterium-labelling experiments have provided evidence that the initially generated o-azaxylylene ionic species, both as long-lived and as decomposing ions, have rearranged to the aldimine ionic species via a 1,5-shift of the α-hydrogen atom adjacent to the heterocyclic ring nitrogen atom.

The electron impact-induced fragmentation patterns of 2,1-benzisothiazoline 2,2-dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked-scan), parent ion, and constant neutral loss spectra in metastable and collision-induced dissociation modes and deuterium labelling.

Gas-phase reactions of MnO2− and MnO3− ions with a series of monofluoro- and pentafluoro-aromatic compounds, i.e. C6H4FX with X = o-, m- and p-CHO and o-, m- and p-OH and C6F5Y with Y = OH, OCH3, CHO, CN, NO2, COCH3 and F, were studied at low pressures by Fourier transform ion cyclotron resonance mass spectrometry. The principal reaction channels identified involve electron transfer from the MnO2− and MnO3− ions to the fluorinated aromatic substrates and proton abstraction and nucleophilic displacement of fluorine by these oxometallate ions. The results obtained indicate that in the gas phase MnO2− is less basic than MnO3− and that neutral MnO2 has a lower electron affinity than MnO3, both values lying between 0.52 and 0.94 eV.

The mechanism of [H, C, N) loss from metastable molecular ions of benzyl cyanides containing an F, Cl, CF3, CH3, HO or CH3O substituent was investigated by deuterium and 13C labelling. The elimination of [H, C, N] from the metastable molecular ions of benzyl cyanides substituted with F, CI or CF3 is preceded by randomization of the hydrogen atoms and tc some extent by a skeletal rearrangement of the CH2CN function, which leads to incorporation of the benzylic carbon atom in 20–30% of the expelled [H, C, N] molecules. By contrast, the metastable molecular ions of benzyl cyanides with a CH3, HO or CH3O substituent eliminate [H, C, N] molecules containing the intact cyano function and predominantly a hydrogen atom from fhe substituent. This preference for a hydrogen atom from the substituent irrespective of its position with respect to the CH2CN function is proposed to be the result of a rearrangement of the meta and para isomers to the ortho isomer possibly involving norcaradiene/cycloheptatriene radical cations. In addition to (H, C, N] loss, the metastable ions of o-, m- and p-methoxybenzyl cyanide eliminate a [H2, C2, N]˙ radical consisting of the cyano function and the carbon atom and mainly two of the hydrogen atoms from the methoxy substituent. The occurrence of this reaction from the metastable ions of m- and p-methoxybenzyl cyanide supports the indicated isomerization to the ortho configuration prior to dissociation. This skeletal rearrangement is manifested also in the loss of [H, C, N, O] from the metastable ions of m-andp-hydroxybenzyl cyanide.

Positive and negative ion fast atom bombardment (FAB) combined with tandem mass spectrometry (MS/MS) has been used to sequence four fully protected nucleopeptides. Protonated and deprotonated molecules and some structurally significant fragments, predominantly sodium cationized/decationized adducts, are observed. The tandem mass spectra of the protonated/deprotonated molecules help to identify (bidirectionally) the main building blocks and the sequence ions of the peptide part of the nucleopeptide components. It is found that the cleavage of the peptide-phosphate backbone mainly occurs due to 1,5-H shift from the side chain of the neighbouring amino acid to the oxygen of the phosphate. It is also observed that the number of amino acids present in the peptide part has a potential influence on the location of the cationization (Na+) which in turn influences the fragmentation pattern in the mass spectrometer.

The regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1-phenyl-2-aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision-induced dissociation and neutralization-reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety.

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 2 N 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.

Fourier transform ion cyclotron resonance and tandem mass spectrometry in combination with deuterium and 13 C-labelling have been applied to study the product C 3 H 4 N + ion from the gas phase reaction of the C 2 H 2 N + ion from CH 3 CN with its neutral precursor. This has provided evidence for associative cyclization of the cyanomethyl CH 2 CN + cation generated by electron bombardment of acetonitrile. The unimolecular dissociation of the metastably decomposing C 3 H 4 N + ion leads predominantly to HCNH + + C 2 H 2 . This reaction proceeds through a multistep pathway involving cyclic intermediates and is discussed in terms of structures and energies of the C 3 H 4 N + system. Collision-induced dissociation of the C 3 H 4 N + ions shows competitive fragmentations being higher energy demanding than that generating HCNH + + C 2 H 2 .

A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides γ-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H+, reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu + Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu − H2O)···H+··· (Glu − H2O) and (Glu − H2O)3·H+. The adduct ions, [(Glu − H2O) + H + Glu]+ and [(Glu − H2O) + H + Met]+, and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (γ-Glu-Met) and its protonated form, (γ-Glu-Met)H+, at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed. Copyright © 2001 John Wiley & Sons, Ltd.

Results of gas-phase reactions of MnO and MnO ions with a series of aliphatic C1C4 alcohols show that C2C4 primary alcohols are oxidized by MnO in reaction channels which involve proton abstraction and hydride-ion transfer, along with the appearance of [H.Mn.O.OH]− ions. Secondary alcohols are oxidized in slower processes while menthanol and t-butanol are unreactive. MnO/alcohol reactions are more complex and involve the formation of [H.MnO3]−, [H.Mn.O2.OH]−, [RO.Mn.O.OH]−, [(RO)2 Mn.O]− and the terminal solvated ion [(RO)3.Mn.OH]−.

It is shown by mass-analyzed ion kinetic energy spectrometry that the metastably decomposing molecular ions of octopamine (p-HOC6H4CH(OH)CH2NH2) and synephrine (p-HOC6H4CH(OH)CH2NHCH3) yield only protonated methylamine and dimethylamine, respectively, as product ions. From deuterium labeling and variation of the internal energy of the molecular ions, experimental support has been obtained that these product ions are generated via the occurrence of a distonic ion-neutral complex. In the case of octopamine, this complex would consist of a nitrogen-protonated aminomethyl radical and p-hydroxylbenzaldehyde in which the former species abstracts the aldehydic or phenolic hydrogen atom from the latter to give protonated dimethylamine.

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

The proton affinity (PA) of cis-4-tert-butylcyclohexyl methyl either with an axial methoxy group is higher by ∼0.1 kcal mol−1 (1 kcal = 4.184 kJ) than the trans isomer with the equatorial ether group. The gas-phase basicity shows a similar small difference of 0.1 kcal mol−1 between the two stereoisomeric ethers. A greater difference in PA has been observed between the stereoisomeric 4-phenylcyclohexyl methyl and ethyl ethers (1.0 and 1.2 kcal mol−1, respectively), in favour of the cis isomers with the equatorial ether groups. The latter result is explained by the internal hydrogen bond with the π-system of the phenyl ring.

In negative ion field desorption mass spectrometry (M - H) − ions are generated from non-acidic compounds such as saccharides and nucleosides. These ions are not “preformed” in a sample solution but are generated by ion molecule reactions in the space charge region of the negatively charged sample layer. The chemistry of the ionization by proton abstraction is investigated and discussed.

It is shown that the γ- or 1,5-hydrogen shift in the molecular ion of 1-nitropropane leads to three primary fragmentation reactions. They are the loss of a hydroxyl radical, a molecule of ethylene and a molecule of nitric oxide. The structures and chemistry of the resulting ions have been investigated by a series of experiments including deuterium labelling, spontaneous and collisionally induced dissociations and accurate mass measurements.

The deuterium and 13 C-labeling study of metastable and collisionally induced decompositions of gaseous protonated (deuterated) acetonitrile, generated in a chemical ionization source by proton (deuteron) transfer to CX 3 CH (X = H or D) using different reagent gases, reveals two distinct mechanisms for fragmentation of (CX 3 CH)X + . The metastable reactions of (CX 3 CN)X + formed from X + 3 /CX 3 CN occur mainly via the multistep pathway involving isomerization into the nitrilium ion reacting configuration, (X 3 C ⋯ NCX) + , presumably through cyclic configuration(s), while the collisionally induced dissociations proceed directly, i.e., from ion structures which have retained the CCN skeleton. The latter decompositions are similar to both the metastable and collisionally induced decompositions of (CX 3 CN)X + generated from other systems studied. The results obtained indicate that these two pathways are associated with the source of creation of their precursor ions, (CX 3 CN)X + , and are operative independently of each other. This study underlines the important role of the source of energy deposition in the parent ion. The rearrangement of (CX 3 CN)X + is discussed on the basis of structures and energies of the C 2 H 4 N + system.

Field desorption of negative ions can be achieved below the threshold of field electron emission. To this end a mixture of the sample with polyethylene oxide and water was applied to smooth wire cathodes. The mass spectra of some inorganic and organic compounds are reported. Anionization by [CI]− ion attachment is demonstrated with the examples of 20-hydroxycholesterol and sucrose.

Fast atom bombardment (FAB) combined with tandem mass spectrometry has been used to verify the amino acid sequence in Org 2766 [H-Met(O2)-Glu-His-Phe-D-Lys-(Phe-OH)] and its deuterated analogues. It is shown that FAB mass spectrometry in addition to the [M + H]+ ion yields dominantly N-terminal sequence ions and some C-terminal sequence ions. These results together permit determination of the amount of deuterium incorporated and the position of the denterated amino acids in the peptide.

It is demonstrated that each of the molecular ions of cyclopropylbenzene and di- n -propyl sulphide, having the same nominal mass m/z 118 and generated from a nearly 1:1 mixture by 70 eV electron impact in a Fourier transform ion cyclotron resonance mass spectrometer, can be selectively isolated in the cell by ejection of all other ions from the cell. This corresponds to a so-called front-end resolution of primary ion selection for MS/MS experiments in excess of 35 000 at m/z 118. Subsequent collisionally induced dissociation (CID) experiments on each of the mass-selected molecular ions have been performed using helium, introduced via a pulsed valve, as collision gas. A so-called back-end resolution of 205 000–475 000 has been obtained for the CID product ions over the mass range m/z 61–117, while the accuracy of the mass measurements on the corresponding ions is shown to be better than 1 ppm.

Deuterium substitution at remote sites gives rise to inverse secondary kinetic isotope effects on the α-cleavage of a number of tertiary amines in the ion source, but to normal isotope effects on reactions occurring in the field-free regions. The change from normal to inverse secondary isotope effects when the internal energy of the reacting ions increases is consistent with transition-state models that involve slight lowering of vibrational frequencies also for bonds well removed from the site of cleavage. The isotope effect on the reactions of ions of high internal energy is caused by the influence that even small changes of isotope-dependent frequencies have on the state sums (a statistical weight effect favouring loss of the labelled radical), whereas the behaviour of low-energy ions is determined by the zero-point energy changes which favour loss of the unlabelled fragment.

The structure and dissociation reactions of the C3H6N+ ions generated by ion/molecule reactions from various gaseous systems containing acetonitrile have been investigated by use of tandem mass spectrometry. Support for the nitrilium structure, H3CC N + CH3, of these ions has been obtained from their metastable and collisionally induced decompositions. Deuterium and 13C-labeling has shown that the metastable decomposition of the H3CC N + CH3 ions proceeds through two reaction pathways, i.e. by (1) a direct cleavage into CH+3 and CH3CN or CH3NC and (2) a multistep sequence involving intermediates within which hydrogen shifts and ring closure occur before dissociation. In addition, an intermolecular H atom exchange between H2 and H3CC N + CH3 has been uncovered by the applied deuterium labeling. Collisional activation of H3CC N + CH3 promotes the high energy demanding direct cleavage reactions with respect to the competing multistep isomerization/dissociation pathway. The observed reactions may be important for the interconversion CH3CN ⇌ CH3NC via H3CC N + CH3 in the terrestrial atmosphere.

It is shown by 13C and D labelling that the ethyl radical elimination from the molecular ion of 6-methoxy-1-hexene is a very complex process involving at least two different channels. The major channel (80%) is induced by an initial 1,5-hydrogen shift in the molecular ion from C(5) to C(l) leading via a series of steps to methoxy-cyclohexnne, which then undergoes a ring contraction to 2-methyl-1-methoxycyclopentane, being the key intermediate for the ethyl loss. The same key intermediate is formed in the other, minor channel (20%) by ring closure directly following an initial 1,6-hydrogen shift in the molecular ion of 6-methoxy-1-hexene from C(6) to C(l). Collision-induced dissociation experiments on the [M − ethyl]+ ion from 6-methoxy-1-hexene have further established that it has the unique structure of oxygen methyl cationized 2-methyIpropen-2-al. This ion is also generated by ethyl loss from the molecular ion of 2-methyl-1-methoxycyclopentane itself, as shown by collision-induced dissociation experiments, thus confirming the key role of the intermediate mentioned.

It is shown that under field desorption conditions some less volatile or non-volatile compounds such as oligosaccharides, sulphonic acids and fatty acids can be ionized below the threshold of field electron emission by clustering with anions. In all cases the sample, together with polyethylene oxide 4000, is dissolved in water. The source of the clustering anion is provided either by a small amount of a salt added to this solution (sugars) or by the compounds themselves (sulphonic and fatty acids). The solution is applied to unactivated and/or slightly activated 10 μm tungsten wire cathodes. Suitable clustering ions for the sugars appear to be [Cl]−, [NO3]− and to a lesser extent [Br]− and [I]−. Most of the sulphonic acids studied give rise to the formation of [Mn—H]− ions (n⩽5), but their potassium salts yield only unclustered sulphonate anions. However, the addition of a small amount of LiCl to the mixture of benzene sulphonic acid and polyethylene oxide 4000 promotes the formation of clustered anions, [(M—H)2Li]− being by far the most abundant if activated cathodes are used. This addition of some LiCl is essential in the case of fatty acids: without LiCl no anions may be desorbed at all from activated wires, but with the presence of LiCl both [M—H]− and the most abundant [(M—H)2Li]− anions are easily generated.

It is shown by 15N and specific 13C labelling that ∼50% of the molecules of hydrogen cyanide, eliminated within ∼10−6 s upon electron impact of benzonitrile, contains the original cyano carbon atom, whereas the remaining percentage contains one of the phenyl ring carbon atoms at random. This is even more dramatic for the molecular ions of benzonitrile which decompose in the first and second field-free regions of the VG Micromass ZAB-2F high-field mass spectrometer used. Then only 5–7% of the eliminated molecules of hydrogen cyanide contains the original cyano carbon atom. A cycloaddition-cycloreversion process in the molecular ions, leading to ionized 1-cyano-1,3-hexadien-5-yne as an intermediate in the hydrogen cyanide loss, is proposed to explain this.

The site of protonation of gaseous benzonitrile in reactions with H+3, CH3OH+2, and CH3CNH+ as protonating agents has been examined by using tandem mass spectrometry in combination with deuterium and 13C labeling. Metastable and collision-induced dissociation studies of C6X5CNX+ (X = H or D) show that proton attachment occurs on the CN group. The metastably decomposing C6X5CNX+ leads only to C6X5+ + XCN. This reaction proceeds via a mechanism involving H+ (D+) transfer from the CN group to the phenyl ring in which H/D exchange occurs. The efficiency of the CN-to-ring H+ (D+) transfer increases in the order para < meta < ortho position. Evidence for incomplete H/D atom randomization in C6X5CNX+ prior to XCN loss has been obtained. Both processes, CN-to-ring H/D exchange and H/D exchange at the phenyl ring, are affected by the internal energy of the C6X5CNX+ ions. The results have been interpreted in terms of the internal energy distribution of the ions fragmenting within the metastable time window. Collision-induced dissociation of C6X5CNX+ causes the energy-enriched ions to decompose by direct bond cleavage into C6X+5 + XCN.

The anionization of molecules supplied from the gas phase onto a negatively charged [Cl]− or [NO3]− ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO3) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]− and [NO3]− attachment and of some acids by proton abstraction is reported.

Four beta-endorphins (beta-endorphin 6-17, 2-17, 1-16, and 1-17) and two adrenocorticotropic hormone (ACTH) peptides (ACTH 1-10 and (1-16)-NH2) were studied by using fast atom bombardment coupled with tandem mass spectrometry. The capability to reproduce metastable ion and collisionally activated decomposition spectra on two different commercial sector mass spectrometers in two different laboratories was found to be acceptable (deviations in relative abundance are less than +/- 50%). The endorphin peptides fragment metastably or upon collisional activation to give abundant B-series ions as well as Y-series ions, whereas Y-series ions are the principal ionic species produced upon the desorption by fast atom bombardment. The ACTH peptides also fragment to give Y-series ions, but of relatively low abundance compared to those from the endorphins. For both sets of peptides, high-energy collisionally activated decomposition and metastable ion decomposition daughter ion spectra are precise, structurally informative--even for peptides up to m/z 2000--and complementary to spectra of daughter ions produced by desorption ionization alone.