Theoretical and experimental investigations of chemical shielding in amino acids, proteins and model compounds

Theoretical methods have been used to investigate chemical shielding in amino acids, polypeptides and proteins in an effort to increase the resolution of protein structures determined by nuclear magnetic resonance (NMR) spectroscopy. The work presented in this thesis includes an evaluation of the effects of different basis sets and theoretical methods on the calculation of individual chemical shielding tensor orientations and magnitudes. Variations in tensor orientation and magnitude can be correlated to changes in local structure in proteins, and thus can be employed as restraints in the structure refinement process. Amino acid model calculations have been utilized in an investigation of chemical shielding in proteins and solid state polypeptides, while metalloporphyrin model compounds have been studied to provide insight into small ligand binding in respiratory metalloproteins. The results of these investigations lend considerable support to the continued use of theoretical methods in NMR structural studies.