Proton-Bound 3-Cyanophenylalanine Trimethylamine Clusters: Isomer-Specific Fragmentation Pathways and Evidence of Gas-Phase Zwitterions

The structures and dissociation pathways of the proton-bound 3-cyanophenylalanine.trimethylamine cluster have been studied using a combination of infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations. Three isomer motifs are identified: charge-solvated, zwitterionic, and trimethylamine (TMA)-bridged. While the TMA-bridged structures fragment to yield protonated TMA (channel 1) and protonated 3-cyanophenylalanine (channel 2), charge-solvated species exclusively fragment via channel 1 and zwitterionic species exclusively fragment via channel 2. Mechanisms are proposed.