Transverse 1H cross relaxation in 1H-15N correlated 1H CPMG experiments

Transverse H-1 cross relaxation was observed in Carr-Purcell-Meiboom-Gill (CPMG) experiments by recording N-15-H-1 correlated spectra of amides in HIV protease that was perdeuterated at nonexchangeable sites. Perdeuteration suppresses H-1-H-1 J coupling and improves spectral resolution and sensitivity. Measurements of cross-peak intensities, arising from cross relaxation, were made as a function of (i) Delta f, the frequency difference between the spins, and (ii) tau(CPMG), one-half of the duration between CPMG pi pulses. Cross peaks were observed when tau(CPMG) was less than 1/(2 Delta f), in agreement with theoretical calculations.