Solid State NMR Studies of Structure and Dynamics in Systems

Deuterium NMR provides insight into dynamics over a wide range of kinetic rates. Experimental data can be rigorously fit and rates as well as motional mechanisms extracted. Temperatures dependent studies yield activation energies for key dynamic processes. Two model systems with well-characterized motions were studied to demonstrate this. The ammonium group in L-alanine has an activation energy of 40.5 kJ/mol for threesite hopping. The hopping rate at room temperature is on the order of 106/sec and is comparable to the radio frequency fields and cycle times of many solid state NMR experiments. This explains the anomalous broadening observed in nitrogen magic angle spinning spectra and proton multiple pulse spectra. Barium chlorate monohydrate provides an excellent model system for examining the accuracy and specificity of simulations. Twofold flips of the water molecule about its bisector fit the observed data and simulations yield an activation energy of 30 kJ/mol. Inclusion of vibrational averaging of the quadrupole coupling and nonzero eta lead to a 10% difference in simulated rates. The dynamics of cerebroside bilayers in the La phase were observed using standard inversion recovery and broadbanded Jeener-Broekaert techniques. The deuterium lineshapes of labelled positions in the polymethylene chain are axially symmetric with splittings dependent on temperature and the position. The first seven segments have similar splittings with slight oscillations or an even-odd effect. These oscillations differ from those seen in phosphatidylcholine bilayers. This discrepancy may be explained by incorporating distortions of the polymethylene chain relative to the molecular director. Various models of motion and their corresponding correlation functions are discussed. The calculations of correlation functions in systems with multiple motions is simplified if the motions are uncorrelated. Models incorporating gauche-trans isomerization with axial diffusion via either three-site hopping or continuous rotation are inadequate in modeling the observed relaxation behavior. Reorientation of the molecular director must be taken into account. The recent discovery of short helices which form appreciable amounts of helix provides an ideal system in which helix formation may be observed via deuterium NMR. The helical structure of one such peptide was determined via solid state NMR dipolar recoupling techniques. This peptide was then synthesized with deuterium labels using solidphase peptide synthesis on two different resins. The dynamic behavior of the peptide on these two resins is markedly different. On one of the resins evidence of significant longterm interactions is observed. This has implications for combinatorial peptide libraries on which assays are done while the peptides are still attached to the resin. The second resinpeptide system displays intermediate range dynamics which are being investigated further. Thesis Supervisor: Dr. Robert G. Griffin Title: Professor of Chemistry For my parents who encouraged me, my siblings who helped me keep things in perspective, and the boys, James, Jonathan, and Tahsis, who play with me