ADIABATIC J-CROSS-POLARIZATION WITH AND WITHOUT LOCALIZATION

A theoretical description of heteronuclear adiabatic J cross polarizat ion is presented. The principle of the technique is level-crossing in the rotating frames. Suitable adiabaticity conditions are derived. The transferred polarization for isolated IS spin-1/2 pairs have been tre ated for different preparation procedures. The objectives are to achie ve (i) J cross polarization insensitive to the Hartmann/Hahn mismatch, and (ii) volume-selective J cross polarization in the presence of a g radient of the main magnetic field. The dependence of the transferred polarization on the sweep time is specified, as well as the covered ra nge of coupling constants J and the permitted degree of off-resonance excitation. The theory is discussed in comparison with experimental (C H)-C-13-H-1 and (NH)-N-15-H-1 data. The formalism also applies to the case when a magnetic fields gradient is present. Cross polarization th en becomes slice selective and can be used for localized spectroscopy (AJCP-LOSY). The theoretical slice profile is in good agreement with e xperimental data recorded with formic acid. Applications of this princ iple for direct or proton-detected C-13 localized spectroscopy or imag ing are discussed. (C) 1994 Academic Press, Inc.