alpha-glycyl cation, radical, and anion (H2NCH+/center dot/-COOH): Generation and characterization in the gas phase

The title species are synthesized in the gas phase acid their unimolecular chemistry is determined by a combination of tandem mass spectrometry method s. Dissociative electron ionization of the alpha-amino acids valine, leucin e, isoleucine, or serine produces the alpha-glycyl cation, H2NCH+COOH, in h igh yield and purity. At threshold, this ion dissociates by CO loss to form the proton-bound complex HC=N ... H+... OH2 via a tight 1,4-H migration th at is associated with a high reverse barrier. After collisional activation, additional channels open, most notably the formation of the complementary and structure-characteristic fragments H2NCH+. (ionized aminocarbene) and COOH and the elimination of OH.. Charge reversal and neutralization-reioniz ation of H2NCH+COOH conclusively show that alpha-glycyl anion, H2NCH-COOH, and alpha-glycyl radical, (H2NCHCOOH)-C-., are stable species residing in d eep potential energy wells. Ln the microsecond time window of the experimen ts, a small fraction of the alpha-glycyl radical decomposes by sequential e limination of H2O and CO. The alpha-glycyl anions arising by charge reversa l of the cation or reionization of the radical partly undergo rearrangement losses of H-2 and H2O, direct cleavages to -COOH, OH-, and H2N-, and conse cutive fragmentation of these primary product anions. (C) 1999 American Soc iety for Mass Spectrometry.