Abstract
Optimized selection of the slow-relaxing components of single-quantum (13)C magnetization in (13)CH(3) methyl groups of proteins using acute (< 90°) angle (1)H radio-frequency pulses, is described. The optimal selection scheme is more relaxation-tolerant and provides sensitivity gains in comparison to the experiment where the undesired (fast-relaxing) components of (13)C magnetization are simply 'filtered-out' and only 90° (1)H pulses are employed for magnetization transfer to and from (13)C nuclei. When applied to methyl (13)C single-quantum Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments for studies of chemical exchange, the selection of the slow-relaxing (13)C transitions results in a significant decrease in intrinsic (exchange-free) transverse spin relaxation rates of all exchanging species. For exchanging systems involving high-molecular-weight species, the lower transverse relaxation rates translate into an increase in the information content of the resulting relaxation dispersion profiles.