IR Spectroscopic Studies of Gas-Phase Peptides

Proteins are vital biological molecules found in every living organism, and their function is determined by what shape they fold into. Peptides are essentially subsets of proteins, and therefore ideal as model systems for protein folding. The structure of a molecule is closely related to its vibrational absorption spectrum, which lies in the infrared (IR) range. However, in vivo IR spectroscopy is hindered by interference from the surrounding water. Therefore, peptides are preferably studied isolated from solution, in the gas phase. This chapter summarizes the recent IR spectroscopy studies of gas-phase peptides. The collected works show that IR spectroscopy combined with quantum chemical calculations is a powerful tool for deducing the molecular structure. Moreover the wealth of experimental spectra makes possible the evaluation of different quantum chemical models, which can be applied to the larger proteins.