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The reactions of isolated [Al13.sup.-] clusters with hydrogen chloride, following their oxidation through the application of Fourier transform ion cyclotron resonance mass spectrometry is presented. The resulting reaction scheme proves to be a molecular model for the dissolution of a metal in an acid, revealing the initial steps of an unknown fundamental heterogeneous reaction.

The photoelectron spectrum of the anionic uracil-H2S anionic complex (UH2S)(super -) is recorded with 2.540 eV photons. The (UH2S)(super -) spectrum reveals a broad feature with its maximum between 1.7 and 2.1 eV.

The parent anions of the nucleotides, adenosine-5′-monophosphate (AMPH) and 2′deoxyadenosine-5′-monophosphate (dAMPH) were generated in a novel source and their photoelectron spectra recorded with 3.49 eV photons. Vertical detachment energy (VDE) and the adiabatic electron affinity (EAa) values were extracted from each of the two spectra. Concurrently, Kobylecka et al. [J. Chem. Phys. 128, 044315 (2008)] conducted calculations which explored electron attachment to dAMPH. Based on the agreement between their calculated and our measured VDE and EAa values, we conclude that the dAMPH- anions studied in these experiments were formed by electron-induced, intramolecular, (barrier-free) proton-transfer as predicted by the calculations. Given the similarities between the photoelectron spectra of dAMPH- and AMPH-, it is likely that AMPH- can be described in the same manner. [ABSTRACT FROM AUTHOR]

The nucleoside parent anions 2′-deoxythymidine-, 2′-deoxycytidine-, 2′-deoxyadenosine-, uridine-, cytidine-, adenosine-, and guanosine- were generated in a novel source, employing a combination of infrared desorption, electron photoemission, and a gas jet expansion. Once mass selected, the anion photoelectron spectrum of each of these was recorded. In the three cases in which comparisons were possible, the vertical detachment energies and likely adiabatic electron affinities extracted from these spectra agreed well with the values calculated both by Richardson et al. [J. Am. Chem. Soc. 126, 4404 (2004)] and by Li et al. [Radiat. Res. 165, 721 (2006)]. Through the combination of our experimental results and their theoretical calculations, several implications emerge. (1) With the possible exception of dG-, the parent anions of nucleosides exist, and they are stable. (2) These nucleoside anions are valence anions, and in most cases the negative charge is closely associated with the nucleobase moiety. (3) The nucleoside parent anions we have generated and studied are the negative ions of canonical, neutral nucleosides, similar to those found in DNA. [ABSTRACT FROM AUTHOR]

We have observed and characterized two new double Rydberg anions N6H19- and N7H22- through their anion photoelectron spectra. The vertical detachment energies of these anions were found to be 0.443 and 0.438 eV, respectively. In addition, for three of the seven double Rydberg anions now known, we measured photodetachment transitions not only to the ground electronic states of their corresponding neutral Rydberg radicals but also to their first electronically excited states. In each spectrum, the energy spacing between the resulting peaks provided the ground-to-first electronically excited-state transition energy for the double Rydberg anion’s corresponding neutral Rydberg radical. For the radicals, N4H13, N5H16, and N6H19, the spacings were found to be 0.83, 0.70, and 0.67 eV, respectively. These values are in excellent agreement with ground-to-first excited-state transition energies measured in absorption for the same neutral Rydberg radicals by Fuke and co-workers [Eur. Phys. J. D 9, 309 (1999); J. Phys. Chem. A 106, 5242 (2002).] The duplication of this neutral Rydberg property by photodetachment of double Rydberg anions further confirms that double Rydberg anions are indeed the negative ions of their corresponding neutral Rydberg molecules and cluster-like systems. [ABSTRACT FROM AUTHOR]

The photoelectron spectrum of the uracil–alanine anionic complex (UA)[sup -] has been recorded with 2.540 eV photons. This spectrum reveals a broad feature with a maximum between 1.6 and 2.1 eV. The vertical electron detachment energy is too large to be attributed to an (UA)[sup -] anionic complex in which an intact uracil anion is solvated by alanine, or vice versa. The neutral and anionic complexes of uracil and alanine were studied at the B3LYP and second-order Møller–Plesset level of theory with 6-31++G** basis sets. The neutral complexes form cyclic hydrogen bonds and the three most stable neutral complexes are bound by 0.72, 0.61, and 0.57 eV. The electron hole in complexes of uracil with alanine is localized on uracil, but the formation of a complex with alanine strongly modulates the vertical ionization energy of uracil. The theoretical results indicate that the excess electron in (UA)[sup -] occupies a π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of alanine to the O8 atom of uracil. As a result, the four most stable structures of the uracil–alanine anionic complex can be characterized as a neutral radical of hydrogenated uracil solvated by a deprotonated alanine. Our current results for the anionic complex of uracil with alanine are similar to our previous results for the anion of uracil with glycine [Eur. Phys. J. D 20, 431 (2002)], and together they indicate that the BFPT process is not very sensitive to the nature of the amino acid’s hydrophobic residual group. The BFPT to the O8 atom of uracil may be relevant to the damage suffered by nucleic acid bases due to exposure to low energy electrons. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results of experimental and theoretical studies of dipole-bound negative ions of the highly polar molecules ethylene carbonate (EC, C[sub 3]H[sub 4]O[sub 3],μ=5.35 D) and vinylene carbonate (VC, C[sub 3]H[sub 2]O[sub 3],μ=4.55 D) are presented. These negative ions are prepared in Rydberg electron transfer (RET) reactions in which rubidium (Rb) atoms, excited to ns or nd Rydberg states, collide with EC or VC molecules to produce EC[sup -] or VC[sup -] ions. In both cases ions are produced only when the Rb atoms are excited to states described by a relatively narrow range of effective principal quantum numbers, n[sup *]; the greatest yields of EC[sup -] and VC[sup -] are obtained for n[sub max][sup *]=9.0±0.5 and 11.6±0.5, respectively. Charge transfer from low-lying Rydberg states of Rb is characteristic of a large excess electron binding energy (E[sub b]) of the neutral parent; employing the previously derived empirical relationship E[sub b]=23/n[sub max][sup *2.8] eV, the electron binding energies are estimated to be 49±8 meV for EC and 24±3 meV for VC. Electron photodetachment studies of EC[sup -] show that the excess electron is bound by 49±5 meV, in excellent agreement with the RET results, lending credibility to the empirical relationship between E[sub b] and n[sub max][sup *]. Vertical electron affinities for EC and VC are computed employing aug-cc-pVDZ atom-centered basis sets supplemented with a (5s5p) set of diffuse Gaussian primitives to support the dipole-bound electron; at the CCSD(T) level of theory the computed electron affinities are 40.9 and 20.1 meV for EC and VC, respectively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A series of 18 alcohols (ROH) is designed with an enthalpy of deprotonation in the gas phase in the range 13.8-16.3 eV. For ROHs with deprotonation enthalpies smaller than 14.3 eV, the excess electron attachment to the ROH...U- complex always induces a barrier-free proton transfer from the hydroxyl group of ROH to the O8 atom of U, with the product being RO-...HU.

The parent negative ions of 5-chlorouracil, UCl- and 5-fluorouracil, UF- have been studied using anion photoelectron spectroscopy in order to investigate the electrophilic properties of their corresponding neutral halouracils. The vertical detachment energies (VDE) of these anions and the adiabatic electron affinities (EA) of their neutral molecular counterparts are reported. These results are in good agreement with the results of previously published theoretical calculations. The VDE values for both UCl- and UF- and the EA values for their neutral molecular counterparts are much greater than the corresponding values for both anionic and neutral forms of canonical uracil and thymine. These results are consistent with the observation that DNA is more sensitive to radiation damage when thymine is replaced by halouracil. While we also attempted to prepare the parent anion of 5-bromouracil, UBr-, we did not observe it, the mass spectrum exhibiting only Br- fragments, i.e., 5-bromouracil apparently underwent dissociative electron attachment. This observation is consistent with a previous assessment, suggesting that 5-bromouracil is the best radio-sensitizer among these three halo-nucleobases. [ABSTRACT FROM AUTHOR]

We report the photoelectron spectra of anionic complexes between 1-methylcytosine (mC) and formic acid (FA) in 1 : 1 and 1:2 stoichiometries that have been measured with 2.54 eV photons. Each spectrum consists of a broad peak with maxima at 1.85 and 2.1 eV, respectively, confirming the generation of stable valence anions in the gas phase. The neutral and anionic complexes of mC(FA) and mC(FA)2 were also studied computationally at the B3LYP, second-order Møller-Plesset, and coupled-cluster levels of theory with the 6-31++G** and aug-cc-pVDZ basis sets. Based on the calculations, we conclude that the photoelectron spectra of mC(FA)- and [image omitted] are due to anions that originate from a barrier-free proton transfer (BFPT) triggered by excess electron attachment. They can be viewed as neutral radicals of hydrogenated 1-methylcytosine solvated by a deprotonated formic acid. [ABSTRACT FROM AUTHOR]

Recently, the icosahedral Al13- cluster has been shown to possess some unusual characteristics due to its special stability (Bergeron, D. E.; et al. Science 2004, 304, 84–87; 2005, 307, 231–235). Here we present reactions of isolated Al13-clusters with hydrogen chloride, following their oxidation through the application of Fourier transform ion cyclotron resonance mass spectrometry. Due to the ultra-low-pressure conditions, the reaction time can be expanded to make one intermediate after another come into view. The following intermediates are generated sequentially, releasing AlCl and H2: Al13HCl-, Al12H-, Al12H2Cl-, Al11H2-, Al12Cl-, and Al11-. The resulting reaction scheme proves to be a molecular model for the dissolution of a metal in an acid, revealing the initial steps of a heretofore unknown fundamental heterogeneous reaction. [ABSTRACT FROM AUTHOR]

In order to characterize the oxidation of metallic surfaces, the reactions of O2 with a number of Alx- and, for the first time, Gax- clusters as molecular models have been investigated, and the results are presented here for x = 9-14. The rate coefficients were determined with FT-ICR mass spectrometry under single-collision conditions at O2 pressures of ~10-8 mbar. In this way, the qualitatively known differences in the reactivities of the even- and odd-numbered clusters toward O2 could be quantified experimentally. To obtain information about the elementary steps, we additionally performed density functional theory calculations. The results show that for both even- and odd-numbered clusters the formation of the most stable dioxide species, [MxO2]-, proceeds via the less stable peroxo species, [Mx+...O22-]-, which contains M-O-O-M moieties. We conclude that the formation of these peroxo intermediates may be a reason for the decreased reactivity of the metal clusters toward O2. This could be one of the main reasons why O2 reactions with metal surfaces proceed more slowly than Cl2 reactions with such surfaces, even though O2 reactions with both Al metal and Al clusters are more exothermic than are reactions of Cl2 with them. Furthermore, our results indicate that the spin-forbidden reactions of 3O2 with closed-shell clusters and the spin-allowed reactions with open-shell clusters to give singlet [Mx+...O22-]- are the root cause for the observed even/odd differences in reactivity. [ABSTRACT FROM AUTHOR]

Altered branching and aberrant expression of N-linked glycans is known to be associated with disease states such as cancer. However, the complexity of determining such variations hinders the development of specific glycomic approaches for assessing disease states. Here, we examine a combination of ion mobility spectrometry (IMS) and mass spectrometry (MS) measurements, with principal component analysis (PCA) for characterizing serum N-linked glycans from 81 individuals: 28 with cirrhosis of the liver, 25 with liver cancer, and 28 apparently healthy. Supervised PCA of combined ion-mobility profiles for several, to as many as 10 different mass-to-charge ratios for glycan ions, improves the delineation of diseased states. This extends an earlier study [J. Proteome Res.2008, 7, 1109-1117] of isomers associated with a single glycan (S(1)H(5)N(4)) in which PCA analysis of the IMS profiles appeared to differentiate the liver cancer group from the other samples. Although performed on a limited number of test subjects, the combination of IMS-MS for different combinations of ions and multivariate PCA analysis shows promise for characterizing disease states.