α-Glycyl cation, radical, and anion (H2NCH+/·/−COOH): Generation and characterization in the gas phase

The title species are synthesized in the gas phase and their unimolecular chemistry is determined by a combination of tandem mass spectrometry methods. Dissociative electron ionization of the α-amino acids valine, leucine, isoleucine, or serine produces the α-glycyl cation, H 2 NCH + COOH, in high yield and purity. At threshold, this ion dissociates by CO loss to form the proton-bound complex HC≡N…H + …OH 2 via a tight 1,4-H migration that is associated with a high reverse barrier. After collisional activation, additional channels open, most notably the formation of the complementary and structure-characteristic fragments H 2 NCH +· (ionized aminocarbene) and + COOH and the elimination of OH · . Charge reversal and neutralization—reionization of H 2 NCH + COOH conclusively show that α-glycyl anion, H 2 NCH − COOH, and α-glycyl radical, H 2 NCH · COOH, are stable species residing in deep potential energy wells. In the microsecond time window of the experiments, a small fraction of the α-glycyl radical decomposes by sequential elimination of H 2 O and CO. The α-glycyl anions arising by charge reversal of the cation or reionization of the radical partly undergo rearrangement losses of H 2 and H 2 O, direct cleavages to − COOH, OH −, and H 2 N −, and consecutive fragmentation of these primary product anions.