Recoupled Polarization Transfer Heteronuclear H–C Multiple-Quantum Correlation in Solids under Ultra-fast MAS

A new approach for high-resolution solid-state heteronuclear multiple-quantum MAS NMR spectroscopy of dipolar-coupled spin- nuclei is introduced. The method is a heteronuclear chemical shift correlation technique of abundant spins, like ¹H with rare spins, like ¹³C in natural abundance. High resolution is provided by ultra-fast MAS and high magnetic fields, high sensitivity being ensured by a direct polarization transfer from the abundant protons to ¹³C. In a rotor-synchronized variant, the method can be used to probe heteronuclear through-space proximities, while the heteronuclear dipolar coupling constant can quantitatively be determined by measuring multiple-quantum spinning-sideband patterns. By means of recoupling, even weak heteronuclear dipolar interactions are accessible. The capabilities of the technique are demonstrated by measurements on crystalline -tyrosine hydrochloride salt.