NMR rotating-frame relaxation measurements of conformational exchanges on the microsecond time scale. Part I: Theory



NMR rotating-frame spin-lattice relaxation (Tip) is a potentially powerful tool for the investigation of chemical exchange processes in the microsecond time range, a time range that is not readily examined by the usual solution NMR methods. This article deals with on-resonance rotating-frame-relaxation measurements. The relaxation mechanism is analyzed to provide a theoretical basis for accurate evaluation of the contribution of chemical exchange to T1p rates. The procedure described permits T1p measurements for medium-sued and large molecules in solution. Interpretation of the exchange contribution provides the dynamic parameters of exchange lifetime and chemical shift difference between exchange sites.