The measurement of heteronuclear transverse relaxation times in ax3 spin systems via polarization-transfer techniques

Abstract

Pulse schemes for the measurement of ¹³C transverse relaxation times in AX₃3 spin systems are described which make use of the sensitive ¹H spin for detection. The experiments are based on reverse-DEPT and reverse-INEPT polarization-transfer sequences. It is shown that relaxation rates obtained from ¹³C-direct-observe and from polarization-transfer experiments are identical only if magnetization from each of the ¹³C transitions is transferred equally to the detected ¹H 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 ¹³C-observe methods.