Intramolecular hydrogen atom transfer in hydrogen-deficient polypeptide radical cations

Irradiation of protonated polypeptides NH2-RH+-COOH by >10 eV electrons lea ds to further ionization and fast intramolecular charge transfer to the fre e N-terminus. The resulting species may undergo further hydrogen atom rearr angement to form distonic ions N+H3-RH+-COO .. Such transfer is exothermic but can involve an appreciable barrier, e.g., 2.3 +/- 0.5 eV for MH2+ ions of the peptide ACTH 1-10. Radical polypeptide dications can, therefore, be viewed as hydrogen atom wires. Subsequent capture of low energy electrons r esults in fragmentation. The pattern of this electronic excitation dissocia tion (EED) is consistent with hydrogen transfer prior to electron capture. (C) 2000 Elsevier Science B.V. All rights reserved.