Two- and Three-Dimensional ¹³C-¹⁷O Heteronuclear Correlation NMR Spectroscopy for Studying Organic and Biological...

We report two- and three-dimensional (2D and 3D) ¹³C-¹⁷O heteronuclear correlation solid-state NMR experiments under magic-angle spinning (MAS) conditions. These experiments utilize the D-RINEPT (Dipolar-mediated Refocused Insensitive Nuclei Enhanced by Polarization Transfer) scheme with symmetry-based SR4₁² recoupling blocks for coherence transfer between ¹³C and ¹⁷O nuclei. First, a 2D ¹⁷O → ¹³C correlation experiment was performed for the [1-¹³C,¹⁷O]-Gly/Gly·HCl cocrystal and [U-¹³C, 1-¹⁷O]-α/β-d-glucose samples. Second, a 2D ¹⁷O → ¹³C MQ-D-RINEPT correlation experiment where the indirect dimension incorporates the multiple-quantum MAS (MQMAS) scheme was tested for obtaining isotropic ¹⁷O resolution with [U-¹³C, 1-¹⁷O]-α/β-d-glucose. Third, a new 3D ¹⁷O → ¹³C → ¹³C correlation experiment was demonstrated where ¹⁷O → ¹³C and ¹³C → ¹³C correlations are achieved by D-RINEPT and DARR (Dipolar Assisted Rotational Resonance) sequences, respectively (thus termed as a 3D D-RINEPT/DARR OCC experiment). This new 3D ¹⁷O NMR experiment is implemented with the aim for site-resolved solid-state ¹⁷O NMR studies.