Mass Spectrometry-Based Analysis of Photochemical Cross-linking between Nitrile Imine and Trp, Phe, and Tyr Amino Acid Residues in Gas-Phase Ions

Abstract

In this study, conjugates of 2,5-diaryltetrazole and peptapeptides were photodissociated by 213 nm UV light. The nitrile imine group was generated from the tetrazole by losing a nitrogen molecule and cross-linked with carbonyl group of amide or amino acid side chain through intramolecular reactions. By analyzing the tandem mass spectra of ultraviolet photodissociation (UVPD) mass spectrometry (MS) and collision induced dissociation (CID) mass spectrometry, product structures were proposed. Theoretical calculations based on Born-Oppenheimer molecular dynamics (BOMD) were conducted for the conformational analyses of the proposed structures, and density-functional theory (DFT) based computations were used to evaluate isomer energies. Nitrile-imine cross-linking reaction mechanisms were suggested based on calculated structures of the peptide conjugates and product ions.