Abstract By using a high-resolution electron energy mono- chromator low-energy electron attachment to gas-phase glycine (H 2 NCH 2 COOH, or G) has been studied by means of mass spectrometric detection of the product anions. In the same way as for several other biologically relevant molecules no stable parent anion was formed by free elec- tron attachment. The largest dissociative electron attach- ment (DEA) cross-section, approximately 5×10 –20 m 2 , was observed for (G–H) – +H at an electron energy of 1.25eV. Glycine and formic acid (HCOOH) have several common features, because a precursor ion can be characterized by electron attachment to the unoccupied π* orbital of the –COOH group. At higher incident electron energies sev- eral smaller fragment anions are formed. Except for H – , which could not be observed in this study, there was good agreement with an earlier investigation by Gohlke et al. Keywords Glycine · Negative fragment ion · Free-electron attachment Introduction Recently Sanche and co-workers [1] demonstrated that free ballistic electrons (3–20 eV) efficiently induce single and double strand breaks in supercoiled DNA. Single and double strand breaks of the DNA were proposed to be ini- tiated by the formation and decay of transient negative ion (TNI) states, located on the various DNA components (base, phosphate, deoxyribose, or hydration water). A local max- imum in the number of DNA strand breaks was obtained at an electron energy of around 10eV. Sanche and co- workers [1] observed similar behavior for the H – ion yield emitted from these molecular components in the gas phase or from homogeneous films as a function of the electron energy. In order to distinguish between intrinsic molecular effects and environmental effects, the interaction of pri- mary radiation and low-energy secondary electrons with iso- lated nucleic acid bases has been studied recently by crossed molecular beam techniques [2, 3, 4, 5, 6]. In addition, sev- eral theoretical investigations have been performed on the properties of these various DNA components (electron affinities, ionization energies, etc. [7, 8, 9, 10, 11, 12]). Glycine (H 2 NCH 2 COOH, or G) is the simplest α-amino acid and often serves as a model system for larger and more complex amino acids or proteins. Thus a number of theoretical [13, 14, 15, 16, 17] and experimental [14, 15, 18, 19, 20] investigations on glycine have been published in recent years. For glycine and other amino acids a tau- tomeric equilibrium between neutral and zwitterionic forms exists that is of fundamental importance in biochemistry. Such an equilibrium is extremely sensitive to the effect of the medium. For instance, in the gas phase, glycine exists in the neutral tautomeric form only [21, 22] whereas in aqueous solution and in the solid phase the zwitterion is the predominant form of this amino acid [23, 24]. This may be easily explained by the fact that interactions with the medium are much more stabilizing in the case of the zwitterionic tautomer. Gohlke et al. [20] measured the formation of fragment anions in gas-phase glycine via dissociative electron at- tachment (DEA) reactions from about 0–15 eV electron energy. By far the most intense product observed (using SF 6 as a calibration gas simultaneously present in the gas under study) was the closed shell glycine anion (G–H) – , or (H 2 NCH 2 COO – ), that appears to form a low energy resonance with a peak located at 1.4 eV. Furthermore Gohl- ke et al. [20] determined an absolute cross-section value for this anion of about 10 –20 m 2 . Aflatooni et al. [25] as- signed a strong feature in the electron transmission spec- tra of glycine, adenine, and formic acid to the formation of a temporary negative ion by electron attachment to the empty π* orbital of the –COOH group. For glycine they measured a vertical attachment energy to this π* orbital of 1.93eV, in agreement with theoretical calculations. Ac- cording to Ref. [20] this precursor state decomposes into S. Ptasinska · S. Denifl · A. Abedi · P. Scheier · T. D. Märk Dissociative electron attachment to gas-phase glycine Anal Bioanal Chem (2003) 377 : 1115–1119 DOI 10.1007/s00216-003-2254-x Received: 11 July 2003 / Revised: 21 August 2003 / Accepted: 29 August 2003 / Published online: 22 October 2003 SPECIAL ISSUE PAPER S. Ptasinska · S. Denifl · A. Abedi · P. Scheier · T. D. Märk (✉) Institut für Ionenphysik, Leopold-Franzens Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria e-mail: tilmann.maerk@uibk.ac.at © Springer-Verlag 2003