Position-Tunable Diazirine Tags for Peptide-Peptide Ion Crosslinking in the Gas-Phase.

We report diazirine photochemical tags that can be incorporated at peptide N-termini and in lysine residues using a simple solid-state alkylation procedure. The diazirine-tagged peptides are used for photochemical carbene formation at 355 nm and crosslinking of non-covalent peptide-peptide ion complexes in the gas-phase. The new tags allow one to control the charge sites in the complexes and use tandem mass spectrometry for gas-phase sequencing to localize the cross links.