ABSTRACT
Nuclear magnetic resonance (NMR) is an extremely powerful
method for detecting and quantifying both the structure of mole-
cules and dynamic processes that are occurring involving these
molecules. An example of a dynamic process is chemical exchange,
which is special in that this process can be used to impart large
signal contrast in NMR imaging (MRI), as we will describe in detail
in this textbook. Herein, we define chemical exchange as a nuclear
spin experiencing a change in its molecular environment with these
environmental changes imparting a perturbation in the chemical
shift of the nuclear spin. NMR spectra are sensitive to many forms
of chemical exchange via the parameters of chemical shift, scalar
coupling, dipolar coupling, and relaxation. Further, NMR can be used
to study chemical exchange without the use of dyes or tracers and
thus can measure chemical exchange dynamics without perturbing
the physical system and under equilibrium conditions. As such
NMR is a leading research and clinical tool for measuring exchange
phenomena, including investigations of protein dynamics, substrate
binding, and since NMR is the foundation of MRI, for generating MRI
contrast related to these phenomena.
