Asymmetric simultaneous phase-inversion cross-polarization in solid-state MAS NMR: Relaxing selective polarization transfer condition between two dilute spins

摘要

Double cross polarization (DCP) has been widely used for heteronuclear polarization transfer between ~(13)C and ~(15)N in solid-state magic-angle spinning (MAS) NMR. However, DCP is such sensitive to experimental settings that small variations or deviations in RF fields would deteriorate its efficiency. Here, we report on asymmetric simultaneous phase-inversion cross polarization (referred as aSPICP) for selective polarization transfer between low-γ ~(13)C and ~(15)N spins. We have demonstrated through simulations and experiments using biological solids that the asymmetric duration in the simultaneous phase-inversion cross polarization scheme leads to efficient polarization transfer between ~(13)C and ~(15)N even with large chemical shift anisotropies in the presence of B_1 field variations or mismatch of the Hartmann-Hahn conditions. This could be very useful in the aspect of long-duration experiments for membrane protein studies at high fields.