Structures and Energetics of Protonated Clusters of Methylamine with Phenylalanine Analogs, Characterized by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

摘要

Gas-phase clusters of protonated methylamine and phenylalanine (Phe) derivatives have been studied using infrared multiple photon dissociation (IRMPD) spectroscopy in combination with electronic structure calculations at the MP2/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. Experiments were performed on several Phe derivatives including 4-chloro-L-phenylalanine (4Chloro-Phe), 4-nitro-L-phenylalanine (4Nitro-Phe), 3-cyano-L-phenylalanine (3Cyano-Phe), and 3-trifluoromethyl-L-phenylalanine (3CF(3)-Phe). Through comparisons between experimental IRMPD spectra and stimulated spectra obtained by electronic structure calculations, charge-solvated structures were found to be prevalent in both 4Chloro-Phe and 4Nitro-Phe, whereas 3Cyano-Phe favored zwitterionic structures and 3-CF3-Phe likely have both zwitterionic and charge-solvated structures present.