R.H. Fokkens

Peptide bond formation in gas-phase ion-molecule reactions of amino acids: a novel proposal for the synthesis of prebiotic oligopeptides.

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.

Covalent capture of dynamic hydrogen-bonded assemblies

Covalent linkage of the three calix[4]arene units in hydrogen-bonded assemblies 13(DEB)6via a threefold ring closing metathesis (RCM) reaction quantitatively converts the dynamic assemblies into covalent systems (123-membered macrocycles) that can be easily characterized using MALDI-TOF MS and HPLC.

Loss of chlorine from C60 and C70-chlorides

Abstract Fullerene contents of chlorinated C60 and C70 were determined with HPLC. n-Values of C60Cln and C70Cln were determined from mass increase during synthesis, MALDI-TOF mass spectrometry, PIXE, Nuclear Microprobe (12C[d,p]13C), and Electron Microprobe analysis. n-Values obtained immediately after synthesis were in the range 31-45. Best values obtained later were in the range 10-20. It is suggested that (i) the samples lost CS2 or CS2/CCl4, or Cl of “crystallization” after synthesis, (ii) after synthesis the samples lost Cl bound to C60 (iii) Cl was lost during the analysis, or (iv) some of all three.

Site of Protonation of benzonitrile hydrogen interchange in the protonated species

The site of protonation of gaseous benzonitrile in reactions with H3+, CH3OH2+, 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+ (DC ) 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 C6X5+ + XNC.

On the rearrangement of the cyanomethyl cation derived from gaseous acetonitrile

Abstract 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 .

On the structure and isomerization/dissociation reactions of C3H6N+ generated by methylation of acetonitrile in the gas phase

Abstract The structure and dissociation reactions of the C 3 H 6 N + 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, H 3 CC N + CH 3 , of these ions has been obtained from their metastable and collisionally induced decompositions. Deuterium and 13 C-labeling has shown that the metastable decomposition of the H 3 CC N + CH 3 ions proceeds through two reaction pathways, i.e. by (1) a direct cleavage into CH + 3 and CH 3 CN or CH 3 NC 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 H 2 and H 3 CC N + CH 3 has been uncovered by the applied deuterium labeling. Collisional activation of H 3 CC N + CH 3 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 CH 3 CN ⇌ CH 3 NC via H 3 CC N + CH 3 in the terrestrial atmosphere.

Rearrangement and fragmentation of protonated acetonitrile

Abstract 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.

A study of the applicability of various ionization methods and tandem mass spectrometry in the analyses of triphenyltin compounds

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.

Ion-neutral complexes in gas-phase dissociations of protonated nitriles: n-C3H7CNH+ and i−C3H7CNH+

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

Stability of C70O in toluene.

Abstract C70O dissolved in toluene transforms to as yet undetermined compounds when exposed to light at room temperature. After 140 days, only 21% of the original C70O remained. C70 was not formed. C139, or C140O were not found. One possible explanation is that the compounds formed were very insoluble in toluene and that their solids either remained in colloidal solution or attached themselves to the glass walls of the container bottles.