Slow ion interaction with N-methylglycine and N-acetylglycine

N-acetyl glycine and N-methyl glycine molecules in the gas phase are ionized by electron exchange with slow O6+ ions at an energy of 48 keV. After ionization, the methyl and acetyl substituted glycines dissociate into fragments analogous to that resulting from ionization and fragmentation of amino acids and peptides, respectively. N-acetylglycine which contains a peptide bond also effectively tautomerizes to the diol form. Such tautomerization is typical for amino acids, however, we show that the tautomerization mechanism of the N-acetylglycine is differen

Solvation of Silver Ions in Noble Gases He, Ne, Ar, Kr, and Xe

We use a novel technique to solvate silver cations in small clusters of noble gases. The technique involves the formation of large, superfluid helium nanodroplets that are subsequently electron ionized, mass-selected by deflection in an electric field, and doped with silver atoms and noble gases (Ng) in pickup cells. Excess helium is then stripped from the doped nanodroplets by multiple collisions with helium gas at room temperature, producing cluster ions that contain no more than a few dozen noble gas atoms and just a few (or no) silver atoms. Under gentle stripping conditions, helium atoms remain attached to the cluster ions, demonstrating their low vibrational temperature. Under harsher stripping conditions, some of the heavier noble gas atoms will be evaporated as well, thus enriching stable clusters of NgnAgm+ at the expense of less stable ones. This results in local anomalies in the cluster ion abundance, which is measured in a high-resolution time-of-flight mass spectrometer. On the basis of these data, we identify specific “magic” sizes n of particularly stable ions. There is no evidence, however, for enhanced stability of Ng2Ag+, in contrast to the high stability of Ng2Au+ that derives from the covalent nature of the bond for heavy noble gases. “Magic” sizes are also identified for Ag2+ dimer ions complexed with He or Kr. Structural models will be tentatively proposed. A sequence of magic numbers n = 12, 32, and 44, indicative of three concentric solvation shells of icosahedral symmetry, is observed for HenH2O+

Formation and Fragmentation of Protonated Molecules after Ionization of Amino Acid and Lactic Acid Clusters by Collision with Ions in the Gas Phase

International audienceCollisions between O3+ ions and neutral clusters of amino acids (alanine, valine and glycine) as well as lactic acid are performed in the gas phase, in order to investigate the effect of ionizing radiation on these biologically relevant molecular systems. All monomers and dimers are found to be predominantly protonated, and ab initio quantum–chemical calculations on model systems indicate that for amino acids, this is due to proton transfer within the clusters after ionization. For lactic acid, which has a lower proton affinity than amino acids, a significant non-negligible amount of the radical cation monomer is observed. New fragment-ion channels observed from clusters, as opposed to isolated molecules, are assigned to the statistical dissociation of protonated molecules formed upon ionization of the clusters. These new dissociation channels exhibit strong delayed fragmentation on the microsecond time scale, especially after multiple ionization

N-Acetylglycine Cation Tautomerization Enabled by the Peptide Bond

International audienceWe present a combined experimental and theoretical study of the ionization of N-acetylglycine molecules by 48 keV O6+ ions. We focus on the single ionization channel of this interaction. In addition to the prompt fragmentation of the N-acetylglycine cation, we also observe the formation of metastable parent ions with lifetimes in the microsecond range. On the basis of density functional theory calculations, we assign these metastable ions to the diol tautomer of N-acetylglycine. In comparison with the simple amino acids, the tautomerization rate is higher because of the presence of the peptide bond. The study of a simple biologically relevant molecule containing a peptide bond allows us to demonstrate how increasing the complexity of the structure influences the behavior of the ionized molecule

The role of the environment in the ion induced fragmentation of uracil

International audienceThe fragmentation of uracil molecules and pure and nano-hydrated uracil clusters by 12C4+ ion impact is investigated. This work focuses on the fragmentation behavior of complex systems and the effect of the environment. On the one hand, it is found that the environment in the form of surrounding uracil or water molecules has a significant influence on the fragmentation dynamics, providing an overall ‘protective’ effect, while on the other hand we observe the opening of specific fragmentation channels. In particular, we report on the first observation of a series of hydrated fragments. This indicates a strong interaction between uracil and water molecules, holding the water clusters bound to the observed molecular fragments