Determination of absolute values of dipolar cross‐relaxation rates for ligands bound to macromolecules using double‐selective T₁

Measuring double‐selective and single‐selective proton relaxation rates has been shown to provide directly the dipolar cross‐relaxation rate of any pair of protons in a ligand molecule. The same measurements for a ligand exchanging between a free and a macromolecule‐bound state yield the cross‐relaxation rate of the bound ligand provided that the rate of exchange is relatively fast, thus allowing one to obtain dynamic and conformational features of the bound ligand. As an example, rigid binding of sulphisomidine to bovine serum albumin has been demonstrated.