ETD of doubly protonated model peptides. a) propanylcysteine, b) benzylcysteine, c) 4-cyanobenzylcysteine, d) perfluorobenzylcysteine, e) 3,5-dicyanobenzylcysteine, f) 3-nitrobenzylcysteine and g) 3,5-dinitrobenzylcysteine containing peptides, respectively. Supplemental activation was performed prior to reaction with fluoranthene anion. Symbolic superscript appendixes °, Δ and ▼ indicates loss of hydroxyl radical from [b+1]+• and [y+1]+• ions, and ammonia, water from b and y ions, respectively.