Hung Ivan, Gan Zhehong
National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
J Magn Reson. 2021 Mar;324:106913. doi: 10.1016/j.jmr.2021.106913. Epub 2021 Jan 21.
Multiple-quantum magic-angle spinning (MQMAS) pulse sequences are presented that are capable of obtaining isotropic NMR spectra for large quadrupolar interactions using lower rf fields. These experiments rely on rotor period long pulses applied at a large offset from the central-transition, making them selective to the satellite-transitions. Each such pulse gives rise to an anisotropic phase, which can be cancelled to obtain coherent signal evolution if a pair of pulses are applied in a symmetric manner. Thus, efficient excitation and conversion of triple-quantum coherences from and to the central-transition is achieved for MQMAS even for large quadrupolar couplings, by selective inversion of the satellite-transitions using such low-power pulses. Low-power multiple-quantum magic-angle spinning (lpMQMAS) pulse sequences are demonstrated on a model compound, RbNO, and also applied on β-GaO, a sample with the largest quadrupolar interactions for which isotropic NMR spectra have been obtained to date.
本文介绍了多量子魔角旋转（MQMAS）脉冲序列，该序列能够使用较低的射频场获得适用于大四极相互作用的各向同性核磁共振谱。这些实验依赖于在远离中心跃迁的大偏移处施加的转子周期长脉冲，从而使它们对卫星跃迁具有选择性。每个这样的脉冲都会产生一个各向异性相位，如果以对称方式施加一对脉冲，则该相位可以抵消以获得相干信号演化。因此，即使对于大的四极耦合，通过使用这种低功率脉冲对卫星跃迁进行选择性反转，MQMAS也能实现三量子相干与中心跃迁之间的高效激发和转换。低功率多量子魔角旋转（lpMQMAS）脉冲序列在模型化合物RbNO上得到了验证，并且还应用于β-GaO，这是迄今为止已获得各向同性核磁共振谱的具有最大四极相互作用的样品。
