Search

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.

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 transport of ions through multiple drift regions is modeled to develop an equation that is useful for an understanding of the resolving power of an overtone mobility spectrometry (OMS) technique. It is found that resolving power is influenced by a number of experimental variables, including those that define ion mobility spectrometry (IMS) resolving power: drift field (E), drift region length (L), and buffer gas temperature (T). However, unlike IMS, the resolving power of OMS is also influenced by the number of drift regions (n), harmonic frequency value (m), and the phase number (Φ) of the applied drift field. The OMS resolving power dependence upon the new OMS variables (n, m, and Φ) scales differently than the square root dependence of the E, L, and T variables in IMS. The results provide insight about optimal instrumental design and operation. [Copyright &y& Elsevier]

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.