19 F NMR transverse and longitudinal relaxation filter experiments for screening: a theoretical and experimental analysis.

Ligand-based 19 F NMR screening represents an efficient approach for performing binding assays. The high sensitivity of the methodology to receptor binding allows the detection of weak affinity ligands. The observable NMR parameters that are typically used are the 19 F transverse relaxation rate and isotropic chemical shift. However, there are few cases where the 19 F longitudinal relaxation rate should also be used. A theoretical and experimental analysis of the 19 F NMR transverse and longitudinal relaxation rates at different magnetic fields is presented along with proposed methods for improving the sensitivity and dynamic range of these experiments applied to fragment-based screening.