JEOL : Novel Three-Dimensional Correlation Experiments to Reveal Local Proton Networks under Fast Magic-Angle Spinning at Natural 13C Abundance

H double quantum (DQ)/H single quantum (SQ) correlation solid-state NMR spectroscopy is widely used to obtain internuclear H-H proximities, especially at fast magic angle spinning (MAS) rate > 60 kHz. However, H signals are not well-resolved due to intense H-H homonuclear dipolar interactions even at the attainable maximum MAS frequencies of ~100 kHz to date. We have recently introduced novel three-dimensional (3D) experiments to resolve the H DQ/H SQ correlation peaks using the additional C dimension. Although the low natural abundance of C (1.1%) significantly reduces the sensitivities, the H indirect measurements alleviate this issue and make this experiment possible. The two different implementations of C/H DQ/H SQ correlations and H DQ/C/H SQ correlations have been discussed and demonstrated using L-histidine.HCl.HO at natural abundance to reveal the local H-H networks nearby each C. In addition, the complete H resonance assignments have been achieved from a single 3D C/H DQ/H SQ experiment. We have also demonstrated the applicability of our proposed method on a biologically relevant molecule capsaicin.

The 2D H DQ/H SQ spectrum of capsaicin (left) is too complex due to signal overlaps. On the other hand, the C-filtered spectrum (right) yields well-resolved peaks and thus signal assignment is possible. Both spectra were recorded at 70 kHz MAS. Please refer to the original paper for more detail.

• M. Malon, M. K. Pandey and Y. Nishiyama, J. Phys. Chem. B, 2017, 121, 8123-8131.