The gas-phase structures of protonated uracil, thymine, and cytosine are probed by using mid-infrared multiple-photon dissociation (IRMPD) spectroscopy performed at the Free Electron Laser facility of the Centre Laser Infrarouge d'Orsay (CLIO), France. Experimental infrared (IR) spectra are recorded for ions that were generated by electrospray ionization, isolated, and then irradiated in a quadrupole ion trap; the results are compared to the calculated infrared absorption spectra of the different low-lying isomers (computed at the B3LYP/6-31++G(d,p) level). For each protonated base, the global energy minimum corresponds to an enolic tautomer, whose infrared absorption spectrum matched very well with the experimental IRMPD spectrum, with the exception of a very weak IRMPD signal observed at about 1800 cm(-1) in the case of the three protonated bases. This signal is likely to be the signature of the second-energy-lying oxo tautomer. We thus conclude that within our experimental conditions, two tautomeric ions are formed which coexist in the quadrupole ion trap.

An approach to speciation of selenium incorporated in yeast proteins was developed. The tryptic digest of a water-soluble protein fraction isolated by size-exclusion chromatography was analyzed by reversed-phase HPLC/ICPMS. The selenopeptides selected owing to the detector's elemental specificity were then analyzed by MALDI-TOFMS in order to select target ions for collision-induced dissociation MS. The latter, carried out with an electrospray Q-TOF spectrometer, enabled the sequencing of the selenopeptides detected by HPLC/ICPMS. The approach allowed for the first time the identification of a family of Se-containing proteins resulting from the replacement by selenomethionine of 2-9 methionine residues in a salt-stress-induced protein SIP18 (Mr 8874). The presence of these proteins was confirmed by MALDI-TOFMS of the original (nondigested) protein fraction. Another selenium protein identified was a heat-shock protein HSP12 (Mr 11693) in which the only methionine residue was replaced by selenomethionine. These two Se-containing proteins accounted for more than 95% of selenium in the water-soluble protein fraction.

The gas-phase reactivity of lead(II) ions towards uracil and thymine has been studied by means of mass spectrometry and theoretical calculations. Positive-ion electrospray spectra show that this reactivity gives rise to both singly and doubly-charged species. The singly charged [Pb(nucleobase) n-H] + (n=1-4) complexes are the most intense ions on spectra at low concentration and are produced notably by dissociative proton transfer within the doubly charged [Pb(nucleobase) m ] 2+ (m=6-12) complexes. The most abundant ion, [Pb(nucleobase)-H] + , has been extensively studied by MS/MS experiments. Results obtained with uracil and thymine are rigorously similar and show that this ion mainly dissociates by elimination of isocyanic acid, and by formation of a [PbNCO] + ion. According to labeling experiments, the N3, C2 and O2 centers are exclusively expelled and complexed, respectively. Our experimental data suggest that the complex may correspond to a mixture of several structures. This is supported by stability of the most stable minima which are close in energy. Comparison with the geometry of neutral and deprotonated nucleobases indicates that lead cationization induces significant geometrical modifications, and more particularly an important activation of the N3-C4 bond, which accounts for the observed fragmentations.

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Cobalt cations are open shell systems with several possible electronic states arising from the different occupations of the 3d and 4s orbitals. The influence of these occupations on the relative stability of the coordination modes of the metal cation to glycine has been studied by means of theoretical methods. The structure and vibrational frequencies have been determined using the B3LYP method. Single-point calculations have also been carried out at the CCSD(T) level. The most stable structure of Co(+)-glycine is bidentate, with the Co(+) cation interacting with the amino group and the carbonyl oxygen of neutral glycine, and the ground electronic state being (3)A. For Co(2+)-glycine, the lowest energy structure corresponds to the interaction of the metal cation with the carboxylate group of the zwitterionic glycine, the ground electronic state being (4)A''.

The gas-phase reactions between Cu+ and formamide, as the most simple model of a peptide function, have been investigated through the use of mass spectrometry techniques. The primary products formed in the ion source correspond mainly to three types of complexes:  (i) those formed by direct interaction of Cu+ with formamide:  [formamide-Cu]+, [(formamide)2Cu]+ complexes, (ii) secondary products generated by association of these ions with ammonia:  [formamide-Cu-NH3]+ complexes, (iii) secondary products formed by interactions of [Cu2H]+ clusters with residual HNCO coming from the formamide-Cu+ complexes elimination, namely [HNCO,Cu2H]+ species. The structures and bonding characteristics of these systems were studied by means of the B3LYP DFT approach. The [formamide-Cu]+ potential energy surfaces were studied at the B3LYP/6-311+G(2df,2p) level in order to explore the validity of formamide to model peptidic reactivity with respect to Cu+. This survey shows that the attachment of Cu+ takes place preferentially at the carbonyl group, while attachment at the amino leads to a local minimum which lies 21 kcal/mol higher in energy. The estimated formamide−Cu+ binding energy (56.2 kcal/mol) is equal to that previously reported for ammonia, although its intrinsic basicity with respect to H+ is 7 kcal/mol smaller. The MIKE spectra of the different primary ions formed in the reaction have also been analyzed. For the particular case of formamide, CAD spectra have been also performed in order to have a more complete description of its reactivity. Starting from the [formamide-Cu]+ complexes, several reaction channels leading to the loss of Cu+, H2O, NH3, HCO, and HCN/CNH have been considered.

The gas-phase reactions between urea and Ca 2+ have been investigated by means of electrospray mass spectrometry techniques. The MS/MS spectra of [Ca(urea)] 2+ and [Ca(urea-H)] + complexes show that both ions decompose by losing NH 3 and HNCO. However, for the [Ca(urea)] 2+ system, additional intense peaks are observed at m/z 44, 56 and 82. Density functional theory calculations at the B3-LYP/cc-pWCVTZ level have been used to help rationalize these observations, through an examination of the structures and bonding characteristics of the various stationary points on the [Ca(urea)] 2+ and [Ca(urea-H)] + potential energy surfaces (PESs).