Nuclear Spin-Lattice Relaxation Studies of Biomolecular Dynamics

Nuclear Magnetic Relaxation Dispersion (NMRD) measurements are useful for discovering low frequency dynamics of many systems, including biologically-relevant ones as in this thesis. Two methods of measuring NMRD profiles exist. Fast fieldcycling NMR instruments use current-switched electromagnets to measure rapid nuclear spin relaxation rates at the cost of resolution while spatial translation of a sample through the static field of a superconducting magnet provides a way to obtain high resolution but is not capable of measuring quickly-relaxing samples. The shuttling system is also prone to mechanical failure, notably breakage of the shuttle containing the sample and collateral damage to the probe. Work described here to improve shuttling experiments includes different types of shuttles tested and a test of using an inductively-coupled dual coil probe and shuttle system. The spin-fracton theory has been successfully used to model the spin dynamics of proteins. Like proteins, DNA is a linear polymer, but it also has some very significant differences in structure. NMRD profiles of dry calf thymus DNA are presented and the power law fit and temperature dependence both indicate that the spin-fracton model is valid for the description of calf thymus DNA. An isotopic dilution experiment on a cross-linked protein gel to characterize dynamics of water at the protein interface by isolating the intermolecular and intramolecular contributions to the proton spin-lattice relaxation is demonstrated. The intramolecular contribution was isolated and is shown to not be the dominant factor in the total magnetic field dependence compared to the intermolecular contribution from the protein protons. The results are compared to 2 H results for the same samples. The data iii are fit with the aid of the spin-fracton theory and the results are discussed in light of a theory recently developed by Korb and Bryant to model the data and provide a picture of the low frequency dynamics in protein gel systems.

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