Selective Relaxation Techniques

This chapter discusses the selective relaxation techniques. The selective excitation of single protons simplifies the nuclear relaxation pathway and can be performed by a variety of techniques. If the experimental conditions are such that the selective relaxation process of a nucleus involved in dipole-dipole interactions is described by the reported equations, simple and reliable methods of calculation of relaxation parameters from selective relaxation measurements can be used, and structural and/or dynamic information can be obtained. In molecular systems in which closely spaced resonances and short relaxation times are present, the DANTE excitation technique or the one-dimensional version of the NOESY experiment should be used. Following a single or multiple selective excitations, peak intensities from partially relaxed spectra can be measured; initial rates can be obtained provided that the experiment is correctly carried out and theoretical problems do not quench the dipolar relaxation strategy. The formation of intermolecular adducts can be followed by selective relaxation measurements. It has been shown that the ligand-receptor interaction induces large changes in the direct relaxation contributions of the proton signals of the ligand.