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The first-time determination of the ionization energy (IE) of DCTB [(H3C)(sub 3)C-p-Ph-CH=C(CH3)-trans-CH=(CN)(sub 2)] by applying photoelectron (PE) spectroscopy is presented. The results are in agreement with the assumption that DCTB-MALDI is governed by electron transfer reactions between matrix ions and analyte.

Resonant electron captures mass spectra of aliphatic and aromatic amino acids and their methyl esters show intense [M-H](super minus) negative ions in the low-energy range. The results have significant implications in biological systems as they suggest that amino acids could serve as radiation protectors since they are found to efficiently thermalize electrons.

A prototype electron monochromator (EM) reflectron time-of-flight (TOF) mass spectrometer has been constructed and demonstrated to record resonant electron capture (REC) mass spectra of electron-capturing compounds. The electron energy is ramped from -1.7 to +25 eV at a preset frequency, and the energy spread of the electron beam at 15 nA is 100 meV or better. Ions are orthogonally extracted into the analyzer at a frequency of up to 80 kHz while maintaining an upper m/z-limit of at least 300 and a mass resolving power of ~1000. A complete REC mass spectrum, which includes an effective yield versus electron energy curve for each negative ion formed from the compound being analyzed, typically takes several days to produce with a quadrupole or magnetic sector mass spectrometer. With the EM TOF described in this work, three-dimensional negative ion electron capture spectra are recorded in an interval on the order of only 1 s and displayed in real time. This new analytical capability could make it possible to perform GC REC mass spectrometry as well as easier (a) to measure the temperature dependence of REC cross sections, (b) to determine enthalpies of negative ion formation (accurate determination of the enthalpy of ion formation requires knowledge of the translational energy released during a dissociative capture event), and (c) to provide complete thermochemical descriptions of dissociative electron attachment by measuring ion lifetimes.

A [C.sub.60][H.sub.30] polycylic aromatic hydrocarbon (PAH) that incorporates all 60 carbon atoms and 75 of the 90 carbon-carbon bonds required to form the fullerene [C.sub.60] has been synthesized in nine steps by conventional laboratory methods. Laser irradiation of this [C.sub.60][H.sub.30] PAH at 337 nanometers induces hydrogen loss and the formation of [C.sub.60], as detected by mass spectrometry. A specifically labeled [[sup.13][C.sub.3]][C.sub.60][H.sub.30] retains all three [sup.13]C atoms during the cage formation process. A structurally related [C.sub.48][H.sub.24] PAH that lacks the three peripheral benzene rings cannot be transformed into [C.sub.60], whereas the next higher homolog, a [C.sub.80][H.sub.40] PAH, degrades to the [C.sub.60][H.sub.30] PAH, which then loses hydrogen to give [60]fullerene. These control experiments verify that the [C.sub.60] is formed by a molecular transformation directly from the [C.sub.60][H.sub.30] PAH and not by fragmentation and recombination in the gas phase., Despite more than a decade of intensive research on fullerenes (1), chemists worldwide still have no general methods or strategies available for the rational synthesis of these polyhedral carbon allotropes [...]

High mass resolving power was applied to study resonance electron capture by glycine, alanine, and valine, and accurate mass measurements helped to distinguish between some negative ions having the same nominal masses. It was established that the C- and N-terminal negative ions of the same nominal masses were formed at different electron energies from different resonance states. The typical fragmentation pathways in deprotonated amino acids via loss of water initiated by collisional activation were not observed upon resonant electron capture by aliphatic amino acids. Instead, [M-18]- negative ions in the vicinity of 5 eV were found to be associated with simultaneous loss of either ammonia and a hydrogen atom or an amino group and a hydrogen molecule. [ABSTRACT FROM AUTHOR]

A simple robust method to study resonance gas-phase reactions between neutral peptides of low volatility and free electrons has been designed and implemented. Resonance electron capture (REC) experiments were performed by several neutral model peptides and two naturally occurring peptides. The assignment of negative ions (NIs) formed in these gas-phase reactions was based on high mass-resolving power experiments. From these accurate mass measurements, it was concluded that fragment NIs formed by low (1–2 eV) energy REC are of the same types as those observed in electron capture/transfer dissociation, where the positive charge is a factor. The main feature resulting from these REC experiments by peptides is the occurrence of zn-1 ions, which are invariably of the highest abundances in the negative ion mass spectra of larger peptides. [M–H]- NIs presumably the carboxylate anion structure dominate the REC spectra of smaller peptides. There was no evidence for the occurrence of the complementary reaction, i.e., the formations of cn+1 ions. Instead, cn ions arose without hydrogen/proton transfer albeit with lower abundances than that observed for zn-1 ions. Only the amide forms of small peptides showed more abundant ion peaks for the cn ions than for the zn-1 ions. The mechanisms for the N–Cα bond cleavage are discussed. [ABSTRACT FROM AUTHOR]

The high-pressure treatment of C60 in an H2 atmosphere at high temperatures leads to the efficient formation of a covalently bound dimer and some oligomeric species. The results indicate a much stronger bonding between the (C60Hx)(sub 2) units than present in cycloaddition products.

The long-lived negative ions are generated from C60H18 following the application of several ionization methods such as laser desorption/ionization, negative ion chemical ion chemical ionization, and resonant free electron capture. The negative molecular ions that result from capture of thermal electrons at a molecular temperature of 600 K a maximum mean lifetime in the range of 1 ms.

The post-translational modification of proteins by electrophilic oxylipids is emerging as an important mechanism that contributes to the complexity of proteomes. Enzymatic and non-enzymatic oxidation of biological lipids results in the formation of chemically diverse electrophilic carbonyl compounds, such as 2-alkenals and 4-hydroxy alkenals, epoxides, and eicosanoids with reactive cyclopentenone structures. These lipoxidation products are capable of modifying proteins. Originally considered solely as markers of oxidative insult, more recently the modifications of proteins by lipid peroxidation products are being recognized as a new mechanism of cell signaling with relevance to redox homeostasis, adaptive response and inflammatory resolution. The growing interest in protein modifications by reactive oxylipid species necessitates the availability of methods that are capable of detecting, identifying and characterizing these protein adducts in biological samples with high complexity. However, the efficient analysis of these chemically diverse protein adducts presents a considerable analytical challenge. We first provide an introduction into the chemistry and biological relevance of protein adductions by electrophilic lipoxidation products. We then provide an overview of tandem mass spectrometry approaches that have been developed in recent years for the interrogation of protein modifications by electrophilic oxylipid species. © 2013 Wiley Periodicals, Inc. Mass Spec Rev 33: 157-182, 2014. [ABSTRACT FROM AUTHOR]

The high-pressure treatment of C60 in an H2 atmosphere at high temperatures leads to the efficient formation of a covalently bound dimer and some oligomeric species. The resulting hydrogenated C120 is an example of the bulk production of covalently bound derivatized fullerene cores. Matrix-assisted laser desorption/ionization in conjunction with reflectron time-of-flight mass spectrometry has been applied to the product analysis. The dissociation pattern of selected C120H2x+ ions (x > 30) indicates the dimeric structure of (C60Hx)2, as opposed to a giant hydrofullerene species possessing a fused C120 core. However, the results also clearly indicate a much stronger bonding (multiple σ bonding) between the C60Hx units than present in cycloaddition products. Evidence of a covalently linked dimer was obtained in labeling experiments, on the basis of which any laser-induced gas-phase aggregation of the C60Hx monomer during the analysis is discounted. [ABSTRACT FROM AUTHOR]

The hydrogenation of the aza[60]fullerene C59N⋅ has been studied in situ. The C59N⋅ monomer is formed by thermal evaporation and dissociation of the (C59N)2 dimer and is hydrogenated in the heated inlet channel of a mass spectrometer, which is used subsequently for the product analysis. In addition to the expected formation of C59NH, the abundant production of C59NH5 is observed. Increasing the availability of hydrogen for the reduction enhances the formation of C59NH5, which is eventually obtained as the main product. The effective yield curves of the negative ions C59NHx−, where x=0, 1 and 5 are detailed and contrasted with the ion yields of C60Hx−, where x=0, 2 and 6. It is found that increasing hydrogen attainment reduces the energy range in which long-lived molecular ions can result from electron capture. [Copyright &y& Elsevier]

Examines the synthesis of C[sub 60]H[30] polycyclic aromatic hydrocarbons to form fullerene C[sub 60]. Inducement of hydrogen loss in laser irradiation; Role of peripheral benzene rings in the transformation; Formation of C[ sub 60] H[sub 30] PAH through molecular transformation.

Modification of a method for processing positive ion ionization efficiency curves of polyatomic molecules, as developed earlier by Ma¨rk and coworkers, has been described. Based on the method, the first, second, and third ionization energies of C60 have been re-examined and found to be in excellent agreement with the most reliable literature data. The ionization energies for C60H18 and C60H36 have been measured for the first time and were established as 7.3±0.3 eV and 7.01±0.25 eV, respectively. Although the appearance energy of C60H362+ (18.7±0.2 eV) has been determined to be lower than that of C602+ (18.98±0.35 eV), the reverse scenario is true for the second ionization energies of C60H36 and C60. [Copyright &y& Elsevier]

A simple robust method to study resonance gas-phase reactions between neutral peptides of low volatility and free electrons has been designed and implemented. Resonance electron capture (REC) experiments were performed by several neutral model peptides and two naturally occurring peptides. The assignment of negative ions (NIs) formed in these gas-phase reactions was based on high mass-resolving power experiments. From these accurate mass measurements, it was concluded that fragment NIs formed by low (1-2 eV) energy REC are of the same types as those observed in electron capture/transfer dissociation, where the positive charge is a factor. The main feature resulting from these REC experiments by peptides is the occurrence of z(n)-1 ions, which are invariably of the highest abundances in the negative ion mass spectra of larger peptides. [M-H](-) NIs presumably the carboxylate anion structure dominate the REC spectra of smaller peptides. There was no evidence for the occurrence of the complementary reaction, i.e., the formations of c(n)+1 ions. Instead, c(n) ions arose without hydrogen/proton transfer albeit with lower abundances than that observed for z(n)-1 ions. Only the amide forms of small peptides showed more abundant ion peaks for the c(n) ions than for the z(n)-1 ions. The mechanisms for the N-C(alpha) bond cleavage are discussed.

Resonant electron capture by Gly, Ala and Phe esters have shown that the most efficient negative ion (NI) fragmentations are associated with the C-termini. A new mechanism for the negative ion-forming processes at energies lower than those associated with the pi*(OO) shape resonance involves coupling between dipole-bound and valence negative ion states of the same symmetry for amino acid conformers with high permanent dipoles. The interaction avoids crossing of the NI states and instead leads to formation of two adiabatic potential energy surfaces. Underivatized amino acids most effectively fragment from the bottom adiabatic surface via generation of [M-H](-) carboxylate anions by hydrogen-atom tunneling through the barrier; fragmentation of the their esters with formation of analogues [M-X](-) NIs occurs through the upper adiabatic state without penetration of the barrier in which the energy of the valence sigma*OX resonance exceeds the bond dissociation energy of the neutral molecule. Low and high temperature resonant electron capture experiments point to the importance of conformational preferences of the amino acids for optimum dissociation of the parent NIs in the gas phase.