2H-13C HETCOR MAS NMR for indirect detection of 2H quadrupole patterns and spin-lattice relaxation rates

Two-dimensional (2D) cross-polarization magic angle spinning (CP-MAS) H-2-C-13 heteronuclear correlation (HETCOR) experiments were utilized to indirectly detect site-specific deuterium MAS powder patterns. The H-2-C-13 cross-polarization efficiency is orientation-dependent and non-uniform for all crystallites. This leads to difficulty in extracting the correct H-2 MAS quadrupole powder patterns. In order to obtain accurate deuterium line shapes, C-13 spin lock rf field, spin lock rf ramp and CP contact time were carefully calibrated with the assistance of theoretical simulations. The extracted quadrupole patterns for U-[H-2/C-13/N-15]-alanine indicate that the methyl deuterium undergoes classic, three-site jumping in the fast motion regime (10(-8)-10(-12) s) and the methine deuterium has a rigid deuterium powder pattern. For U-[H-2/C-13/N-15]-phenylalanine, indirectly detected deuterium line shapes illustrate that the aromatic ring undergoes 180 degrees flips in the fast motion regime while H-2 beta and H-2 alpha are completely rigid. The experimental deuterium line shapes for U-[H-2/C-13/N-15]-proline reflect that H-2 beta, H-2 gamma and H-2 delta are subjected to fast, two-site reorientations at an angle of (15 +/- 5)degrees, (30 +/- 5)degrees and (25 +/- 10)degrees respectively. In addition, an approach that combines a composite inversion pulse with H-2-C-13 CP-MAS is applied to measure H-2 spin-lattice relaxation times in a site-specific, C-13-detected fashion. (C) 2012 Elsevier Inc. All rights reserved.