CPMG sequences with enhanced sensitivity to chemical exchange

Improved relaxation-compensated Carr-Purcell-Meiboom-Gill pulse sequences are reported for studying chemical exchange of backbone (1)5N nuclei. In contrast to the original methods [J. P. Loria, M. Rance, and A. G. Palmer, J. Am. Chem. Soc. 121, 2331-2332 (1999)], phenomenological relaxation rate constants obtained using the new sequences do not contain contributions from H-1-H-1 dipole-dipole interactions. Consequently, detection and quantification of chemical exchange processes are facilitated because the relaxation rate constant in the limit of fast pulsing can be obtained independently from conventional N-15 spin relaxation measurements. The advantages of the experiments are demonstrated using basic pancreatic trypsin inhibitor.