APPLICATION OF CRYOGENIC ULTRAVIOLET AND INFRARED SPECTROSCOPY FOR DETERMINATION OF SECONDARY STRUCTURE OF GAS PHASE PEPTIDE IONS
thesisposted on 27.07.2021, 18:16 by John T LawlerJohn T Lawler
Gas phase studies of the secondary structure of peptides and proteins have become increasingly popular as they offer distinct advantages of small sample usage and experiment time. The mass spectrometer is key to performing these experiments as ions can be manipulated based on their mass to charge ratio. Combining mass spectroscopy with laser spectroscopy birthed a new method for determining gas phase structures, ion spectroscopy. This document begins with an overview of secondary structure analysis using several techniques in solid, liquid, and gas phases. It then describes how ion spectroscopy can also be utilized to obtain detailed fingerprint infrared spectra of ions which are then matched with density functional theory calculations to determine the 3D structure of an ion. After describing the instrumental apparatus, four examples of the use of ion spectroscopy to determine structure are presented. The first study looked to understand the effect of increased flexibility around a proline residue in the diastereomeric pair YAD/LPGA and how a simple switch to glycine can greatly affect beta turn formation in peptides. The next three studies describe an attempt to form a single turn alpha helix in the gas phase using a highly stable tethered peptide motif. Failure to form the single turn helix in the first study led to an interesting examination of the use of computational chemistry to lead the synthesis of peptides where a specific structure is required. After observing the single turn helix attention is then diverted to expanding and controlling its handedness via stereochemistry. In all, this document will guide the reader through the methods and experiments possible with ion spectroscopy.