Computational Investigations of the Structure and Spectroscopy of Small Biomolecules in the Gas Phase

Small biomolecule systems were interrogated using infrared multiple photon dissociation (IRMPD) action spectroscopy and corresponding quantum chemical calculations with a particular focus on peptide fragmentation and protonation site preference. b2+ and b3+ fragment ions with a terminal lysine homolog residue were investigated using IRMPD in the fingerprint region (1000 cm-1 – 2000 cm-1) and a variety of computational methods. We present the first spectroscopic confirmation of b-ion formation with a lactam structure. Infrared spectra for b2+ fragment system indicate the presence of a mixture of structures, though final determination will require further investigation. The b3+ fragment ion infrared spectra show strong support for the presence of a predominantly lactam structure. Extensive computational research in this system suggests the B3LYP method to be the most computationally efficient density functional theory method for spectral predictions. However, the inclusion of p-polarization into the basis set yielded inconclusive results and should be investigated further