Enhancing NMR Sensitivity of Natural-Abundance Low-γ Nuclei by Ultrafast Magic-Angle-Spinning Solid-State NMR Spectroscopy.

Although magic-angle-spinning (MAS) solid-state NMR spectroscopy has been able to provide piercing atomic-level insights into the structure and dynamics of various solids, the poor sensitivity has limited its widespread application, especially when the sample amount is limited. Herein, we demonstrate the feasibility of acquiring high S/N ratio natural-abundance 13 C NMR spectrum of a small amount of sample (≈2.0 mg) by using multiple-contact cross polarization (MCP) under ultrafast MAS. As shown by our data from pharmaceutical compounds, the signal enhancement achieved depends on the number of CP contacts employed within a single scan, which depends on the T1ρ of protons. The use of MCP for fast 2D 1 H/13 C heteronuclear correlation experiments is also demonstrated. The significant signal enhancement can be greatly beneficial for the atomic-resolution characterization of many types of crystalline solids including polymorphic drugs and nanomaterials.