The measurement of heteronuclear transverse relaxation times in AX3 spin systems via polarization transfer techniques

Pulse schemes for the measurement of “C transverse relaxation times in AX, spin systems are described which make use of the sensitive ‘H spin for detection. The experiments are based on reverse-DEPT and reverse-INEPT polarization-transfer sequences. It is shown that relaxation rates obtained from ‘%-direct-observe and from polarization-transfer ex-periments are identical only if magnetization from each of the 13C transitions is transferred equally to the detected ‘H spins. This requires judicious choices in pulse angles and delays in reverse-DEPT and reverse-INEPT experiments. For application to macromolecules, experimental and theoretical results suggest that polarization-transfer schemes based on reverse INEPT are superior to reverse-DEPT-based sequences and give results which are in good agreement with values measured via ‘%-observe methods. 0 1992 Academic Press, Inc. NMR is a powerful technique for obtaining information regarding internal dynamics of proteins. The measurement of relaxation properties of nuclei such as “N and r3C is particularly promising in this regard since the relaxation of these nuclei is governed by dipolar interactions with directly attached protons and to a lesser extent by chemical