The measurement of the magnetic field strength dependence of the nuclear spin-lattice relaxation rate yields a Magnetic Relaxation Dispersion profile (MRD). The MRD contains all the molecular dynamical information that is available from a nuclear magnetic resonance experiment, and therefore, offers a uniquely powerful a high resolution tool for the characterization of both intra and intermolecular dynamics. To date, the approach has been limited by the poor sensitivity and resolution of field-switched magnetic relaxation dispersion spectrometers. We have assembled a NMR spectrometer that utilizes two magnets, one a high-field and high resolution superconducting magnet, and one a variable field electromagnet, that overcomes the previous problems of both resolution and sensitivity. The usual time scale for these measurements covers the range from milliseconds to nanosecond; however, the timescale may be extended to 100 ms when necessary. This proposal demonstrates a techinique that extends that experimental time scale to the sub picosecond range without loss of sensitivity for the necessary resolution. Thus, the proposed experiments will provide and experimental characterization of the solute dynamics over a time range that has been accessible in high resolution only to molecular dynamics compulations. We request support to apply this new technology to the study of solute spins including particularly peptides, proteins, phospholipids, and low molecular weight solute species that interact with them. Proteins to be studied initially include bovine pancreatic trypsin inhibitor and calmodulin, and T4 lysozyme, which will be isotopically labeled to enhance spectral resolution using multiple spin spectral editing techniques. Ionic solute resonances will be studied to characterize ion- mactomolecules binding lifetime distributions and localized surface translational diffusion constants adjacents to protein and phospholipid membrane. We will examine the magnetic relaxation of liquid spins in geometrically restricted domains like those found in subcellular organelles and will explore the use of level-crossing experiments for indirect detection of rare quadrupolar spins in metalloenzymes.
