Introduction: General Theory of Nuclear Relaxation

Abstract

Publisher Summary The relaxation parameters are of great interest as they arise from the various interactions to which nuclear spins are subjected with the most common being the classical dipolar interaction (between the magnetic dipoles associated with nuclear spins). To be active, these interactions must be time dependent, for instance via molecular motions. Therefore relaxation parameters not only encompass structural information (through the interactions themselves), but also dynamical information (through this time modulation). The information can be about (1) overall motions, translational or rotational, governed essentially by the molecular volume and the viscosity of the medium embedding the molecules under investigation, (2) local motions such as internal rotations around C–C bonds, or segmental motions in molecules or aggregates of appreciable size, and (3) exchange between two different molecules or between two distinct sites within the same molecule. The chapter discusses the various relaxation mechanisms and considers the experimental methods that yield relaxation parameters with accuracy and reliability.