Abstract
Deuterium rotating frame solid-state NMR relaxation measurements ((2)H R(1ρ)) are important tools in quantitative studies of molecular dynamics. We demonstrate how (2)H to (13)C cross-polarization (CP) approaches under 10-40 kHz magic angle spinning rates can be combined with the (2)H R(1ρ) blocks to allow for extension of deuterium rotating frame relaxation studies to methyl groups in biomolecules. This extension permits detection on the (13)C nuclei and, hence, for the achievement of site-specific resolution. The measurements are demonstrated using a nine-residue low complexity peptide with the sequence GGKGMGFGL, in which a single selective -(13)CD(3) label is placed at the methionine residue. Carbon-detected measurements are compared with the deuterium direct-detection results, which allows for fine-tuning of experimental approaches. In particular, we show how the adiabatic respiration CP scheme and the double adiabatic sweep on the (2)H and (13)C channels can be combined with the (2)H R(1ρ) relaxation rates measurement. Off-resonance (2)H R(1ρ) measurements are investigated in addition to the on-resonance condition, as they extent the range of effective spin-locking field.