Attenuation of Cross-Peak Intensities in QUIET-BIRD-NOESY Experiments

The buildup curves in QUIET-BIRD-NOESY expts., which are designed to isolate two-spin subsystems within macromols., are attenuated by transverse relaxation and evolution under homonuclear couplings during the bilinear rotation decoupling (BIRD) pulse sandwich. If the signals of both source and target spins are attenuated equally (uniform damping), this is readily accounted for by normalizing the cross peaks with respect to the diagonal peaks. However, unequal attenuation of source and target spins (differential damping) affects the initial buildup slopes and hence leads to apparent cross-relaxation rates that are significantly distorted from their true values. A simple method for recognizing this situation and extg. accurate cross-relaxation rates is presented. (c) 1999 Academic Press. [on SciFinder (R)]