Method for the nmr based determination of the affinity of drugs for a target protein

The document relates to a method for the determination of the binding properties of at least one first chemical compound to at least one second chemical compound between a free essentially dissociated state and a bound essentially associated state by using nuclear magnetic resonance (NMR) measurements, wherein at least one of the first chemical compound or the second chemical compound comprises two coupled 1/2 spins in inequivalent molecular sites, wherein the relaxation of a long-lived state of the spin pair is measured as a function of the concentration of at least one of said first chemical compound for the determination of the equilibrium constant (KD) between the free state and the bound state.