NMR is one of the most useful techniques for monitoring molecular interactions. It is particularly useful for characterizing weakly interacting systems. Typically, weakly interacting systems produce spectra that are in fast exchange, i.e. the NMR observables are detected as population weighted averages. By manipulating the populations, through changing concentration for example, a series of spectra can be obtained from which information like the dissociation constant (KD) and the dissociation rate (koff) may be determined. Titrating one molecule with another and monitoring the chemical shift changes is a common method for determining KD.
