  Many applications of magnetic resonance are limited by rapid loss of spin
coherence caused by large transverse relaxation rates. In nuclear magnetic
resonance (NMR) of large proteins, increased relaxation losses lead to poor
sensitivity of experiments and increased measurement time. In this paper we
develop broadband relaxation optimized pulse sequences (BB-CROP) which approach
fundamental limits of coherence transfer efficiency in the presence of very
general relaxation mechanisms that include cross-correlated relaxation. These
broadband transfer schemes use new techniques of chemical shift refocusing
(STAR echoes) that are tailored to specific trajectories of coupled spin
evolution. We present simulations and experimental data indicating significant
enhancement in the sensitivity of multi-dimensional NMR experiments of large
molecules by use of these methods.
