Chemical Physics Letters, Vol.316, No.1-2, 19-23, 2000
MH2+center dot ion production from protonated polypeptides by electron impact: observation and determination of ionization energies and a cross-section
Irradiation of gas-phase MH+ ions of polypeptides up to MW 3493 by 11 to 70 eV electrons produced further ionization: MH++ e(-) --> MH2+. + 2 e(-), with ionization thresholds of 11.4 +/- 0.5 eV for [Arg-8]-vasopressin (MW 1084), 10.7 +/- 0.5 eV for substance P (MW 1347), 11.4 +/- 0.6 eV for renin substrate (MW 1759) and 10.6 +/- 0.4 eV for melittin (MW 2846). The ionization cross-section of vasopressin MH+ ions was found to be (1.3 +/- 0.4).10(-15) cm(2) for 20 eV electrons. The gas-phase MH2+. ions are rather stable at room temperature, with lifetimes of hundreds of seconds at 10(-10) Torr.