(J. Magn. Reson., 2014, 242, 214–219)
在魔角旋转固体NMR中，DCP被广泛用于13C-15N异核极化传递。但是，DCP对实验设置非常敏感，很小的射频场偏差或变化可能极大降低DCP效率。本文报道了一种用于选择性13C-15N极化传递的方法——非对称相位同步反转交叉极化(Asymmetric simultaneous phase-inversion cross polarization, aSPICP)。通过模拟以及固态生物样品的实验证实：aSPICP有助于化学位移各向异性较大的13C/15N自旋间的极化传递，对Hartmann-Hahn条件的偏差不敏感，因此对于高磁场条件下膜蛋白样品的长时间实验非常有用。
Asymmetric simultaneous phase-inversion cross-polarization in solid-state MAS NMR: Relaxing selective polarization transfer condition between two dilute spins
Abstract Double cross polarization (DCP) has been widely used for heteronuclear polarization transfer between 13C and 15N 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 13C and 15N 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 13C and 15N even with large chemical shift anisotropies in the presence of B1 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.
