This research project involves the continued development (now entering its 5th decade) of basic methods and theory for advancing the use of NMR techniques in relevant biomedical areas for detecting less receptive nuclei with special emphasis placed on 13C and 15N. Earlier work stressed the chemical shift structure correlations of liquid samples and more recently these concepts are being developed in the shielding tensor. The 3D aspects of 13C and 15N shielding tensors and their applications to biological systems are well documented in the publications of our laboratory. Further developments of spectroscopic techniques and their correlation with theory continue to be significant aspects of this proposal. Major developments have been made in experimental techniques for determining shielding tensors on either powders or single crystals and their orientation on the molecular frame. Shift tensors, with their three principal values and three angular orientations, provide information on the symmetry and three dimensional structure of molecules not obtainable from isotropic shifts in liquids. Finished tensor work on aromatic systems and sugars is now being extended to relatively large natural products, nitrogen heterocycles, nucleosides, nucleotides, peptides and their related polymeric oligomers. Capabilities now exist to index and thoroughly analyze powdered samples containing dozens of non-equivalent carbons. Furthermore, theoretical methods have improved to the point where it is possible to discuss structural effects on 13C chemical shift changes under 2.5 ppm for neutral molecules with limited charge polarization present. Recent advances in the Utah NMR laboratory on Ewald potentials reveals a very promising way to treat long range charge polarization mechanisms that can also affect chemical shift components by as much as 50 ppm. This charge polarization mechanism is strongly perturbed by electrostatic fields characterized by long range electrostatic forces that give rise to shift perturbations in highly polar molecules. Calculating fields from interactions of monopolar arrays has long been known to require lattice sums that converge very slowly over long distances. New approaches to this problem are proposed in this renewal. Hence, the work at the Utah laboratory will continue to develop experimental and theoretical methods to be employed in the study of shift tensors in peptides, protein conformational analysis, correlations between biochemical structure and shift tensor data in biological complexes, natural products, and hydrogen bonded interactions.
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