Infrared Photoactivation Reduces Peptide Folding and Hydrogen-Atom Migration following ETD Tandem Mass Spectrometry

Peptides see the light: The photoactivation of peptide precursor cations during electron transfer dissociation (ETD) led to the generation of isotopic cluster peaks that more closely resembled theoretically predicted product‐ion distributions. This method should enable the application of ETD to low‐charge‐density peptide precursors, the gas‐phase secondary structure of which prevents the direct formation of c‐ and z.‐type fragment ions.