Dissociative electron attachment to gas-phase N-methylformamide

Gas-phase dissociative electron attachment (DEA) measurements to N-methylformamide (NMF, HC(O)NHCH3), a simple molecule containing the peptide linkage, were performed. The anion yields as a function of electron energy below 15 eV were obtained using a crossed molecular beam/Quadrupole Mass Spectrometer (QMS) setup. DEA to NMF produces CN-, OCN-, NH2-, 0-, HCO-, and NH-, similar to formamide. Isotopic studies with N-methyl-d3-formamide (d3-NMF, HC(0)NHCD3) have confirmed and clarified assignments. Newly observed dissociation channels from NMF result in the formation of CH3NHC(0)-/CH3NC(0)H-, CH3NH-, CO-, and CH3-. The dominant fragmentation pathways involve the formation of CN- and OCN- near 1.5 eV, which are produced from the electron capture by the Tr* orbital of the C=0 combined with the scission of the N CH3 bond and simultaneous formation of a C=N Tr bond. The methyl neutral by-product assists in lowering the thermodynamic threshold for CN- and OCN- production as compared with the DEA to formamide. The [Parent-HI- signal at m/z 61 from d3-NMF confirms site-selectivity for formation of this ion and excludes H loss from the methyl group of NMF. Peptide bond (0=C N H) dissociation is observed resulting in both CH3NH- and HCO-, but these channels require higher energies (>5 eV) to occur. (C) 2013 Elsevier B.V. All rights reserved.