29] Nuclear relaxation measurements of water protons and other ligands

Abstract

Publisher Summary This chapter discusses the way nuclear relaxation rates are measured and only those aspects of the theory that elucidate the methods and their applications. The measurement of the relaxation rates of magnetic nuclei is a specialized branch of nuclear magnetic resonance spectroscopy, which, especially when carried out with paramagnetic probes, can provide thermodynamic, structural, and kinetic information on enzyme complexes. Specifically, the stoichiometry and dissociation constants of binary and ternary complexes of enzymes with paramagnetic ions, paramagnetic substrate analogs, and diamagnetic substrates may be measured. Coordination schemes and interatomic distances between enzyme-bound paramagnetic metal ions or substrate analogs and the substrate molecules have been determined. The exchange rates of substrates into paramagnetic and diamagnetic environments on enzymes have been estimated. By analogy, when a population of magnetic nuclei is placed in a magnetic field, the magnetic vectors experience a torque and precess about the direction of the field. Energy may be applied to this system to align the magnetic vectors of the nuclei to precess in phase with each other.