HETERONUCLEAR J-COUPLING PRECESSION DURING SPIN-LOCK AND ADIABATIC PULSES - USE OF ADIABATIC INVERSION PULSES IN HIGH-RESOLUTION NMR

The J-coupled precession of I spins in an IS J-coupled system is scale d during S irradiation by the factor sin alpha where alpha is the tilt of the effective RF field applied to the S spins. This property is us ed in a spin-locked version of INEPT, dubbed SLINEPT, to transfer pola rization from I to S in a mixed IS and IS2 system, both simultaneously and efficiently, as exemplified by N to H transfer in a uniformly N-1 5-enriched protein. Of more general use is the utilization of this pro perty during adiabatic inversion pulses. In this context, it is shown both theoretically and experimentally that sech/tanh adiabatic inversi on pulses may be applied during the entire J modulation delay period o f any IS pulse sequence. As a result, the length of such adiabatic pul ses is not of critical importance, and they may be used widely in high -resolution NMR: as selective-inversion pulses over 1 kHz or more, as very broadband inversion pulses over more than 100 kHz, or as selectiv e-inversion pulses at any intermediate spectral width. It is also show n that other adiabatic modulation schemes such as sin/cos or constant/ tan are not competitive with the sech/tanh method for these purposes. (C) 1995 Academic Press, Inc.