NMR relaxation in multipolar AX systems under spin locking conditions

A relaxation matrix has been calculated for a multipolar AX spin system und er the on-resonance spin-locking condition. Auto- and cross-correlation ter ms between dipolar, quadrupolar, and CSA interactions are considered. It is shown that the spin-lock leads to many relaxation pathways being blocked, resulting in a considerably simplified relaxation network. The presence of spectral densities at zero frequency, associated with locked nuclei, allows efficient relaxation also in the absence of fast molecular motions. (C) 19 99 Academic Press.