title: Electron attachment to the dipeptide dialanine: influence of methylation on site selective dissociation reactions.
abstract: Gas phase dissociative electron attachment (DEA) measurements with methyl-dialanine, C(7)H(14)N(2)O(3), are performed in a crossed electron-molecular beam experiment at high energy resolution (∼120 meV). Anion efficiency yields as a function of the incident electron energy are obtained for the most abundant fragments up to electron energies of ∼15 eV. There is no evidence of molecular anion formation whereas the dehydrogenated closed shell anion (M-H)(-) is one of the most dominant reaction products. Quantum chemical calculations are performed to investigate the electron attachment process and to elucidate site selective bond cleavage in the (M-H)(-) DEA-channel. Previous DEA studies on dialanine have shown that (M-H)(-) formation proceeds through abstraction of a hydrogen atom from the carboxyl and amide groups, contributing to two distinct resonances at 0.81 and 1.17 eV, respectively [D. Gschliesser, V. Vizcaino, M. Probst, P. Scheier and S. Denifl, Chem.-Eur. J., 2012, 18, 4613-4619]. Here we show that by methylation of the carboxyl group, all (calculated) thresholds for H-loss from the different sites in the dialanine molecule are shifted up to a maximum of 1.4 eV. The lowest lying resonance observed experimentally for (M-H)(-) remains operative from the amide group at the electron energy of 2.4 eV due to the methylation. We further study methylation-induced effects on the unimolecular dissociation leading to a variety of negatively charged DEA products.
authors: Institut für Ionenphysik und Angewandte Physik and Center of Molecular Biosciences Innsbruck, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria.
authors: Benjamin
authors: B
authors: Puschnigg
authors: Stefan E
authors: SE
authors: Huber
authors: Michael
authors: M
authors: Probst
authors: Katrin
authors: K
authors: Tanzer
authors: Violaine
authors: V
authors: Vizcaino
authors: Filipe
authors: F
authors: Ferreira da Silva
authors: Paul
authors: P
authors: Scheier
authors: Paulo
authors: P
authors: Limão-Vieira
authors: Stephan
authors: S
authors: Denifl
mesh_terms: D000409:Alanine / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D005740:Gases / Q000737:chemistry; D008745:Methylation; D011789:Quantum Theory
chemical_list: D004151:Dipeptides; D005740:Gases; D000409:Alanine