“Perfect echo” INEPT: More efficient heteronuclear polarization transfer by refocusing homonuclear J-coupling interaction

Abstract

A “perfect echo” based INEPT experiment that demonstrates more efficient heteronuclear polarization transfer over conventional INEPT has been developed. This scheme refocuses the effect of homonuclear 1H–1H J-evolution and simultaneously allows heteronuclear 13C–1H J-evolution to continue during INEPT. This improves one bond heteronuclear polarization transfer efficiency at longer INEPT transfer delays and also enhances the sensitivity of long range INEPT. The refocusing of homonuclear 1H–1H J-coupling could be achieved by doubling the INEPT transfer period leading to a doubling of T2 losses. Therefore, the sensitivity gain is observed when loss of magnetization due to homonuclear 1H–1H J-modulation is more severe than that of T2 decay. However, in general, INEPT transfer period is rather short compared to the longer T2 observed in small molecules. The long range PE-INEPT transfer to carbonyl carbon in beta-butyrolactone, showed much faster build up of C-13 signal than conventional long range INEPT as the long range heteronuclear J-coupling is comparable in magnitude to homonuclear 1H-1H J-coupling in this case. For one bond heteronuclear polarization transfer at shorter delay, PE-INEPT and conventional INEPT displays equal transfer efficiency. Efficient polarization transfer is observed for small molecules dissolved in isotropic as well as weakly aligned media. Further, simulation results obtained using the full propagator and product operator analysis agree well with the experimental observations.