TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Serilingampally, Hyderabad 500107, Telangana, India.
TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Serilingampally, Hyderabad 500107, Telangana, India.
J Magn Reson. 2019 Nov;308:106563. doi: 10.1016/j.jmr.2019.07.050. Epub 2019 Jul 18.
Rotational-echo double resonance (REDOR) and Dipolar-coupling chemical-shift correlation (DIPSHIFT) are commonly used experiments to probe heteronuclear dipole-dipole couplings between isolated pairs of spin-12 nuclei in magic-angle-spinning (MAS) solid-state NMR. Their widespread use is due to their robustness to experimental imperfections and a straightforward interpretation of data. Both of these experiments use rotor-synchronised π pulses to recouple the heteronuclear dipole-dipole couplings, and the observed intensity of resonances is modulated by a recoupled phase factor depending on the position or duration of the recoupling pulses. Several modifications to both of these experiments have been proposed, for example, the development of DIPSHIFT which employs strategies that mimic the multi-rotor-period nature of REDOR. We show here that REDOR and DIPSHIFT are in fact alternate implementations of the same experiment. The overt similarity in the design of REDOR and DIPSHIFT is also reflected in their theoretical description. Dipolar dephasing curves in REDOR are obtained by increasing the recoupling duration whilst keeping the position of the pulses constant, which results in a dephasing factor that is a function of only the dephasing time. DIPSHIFT, on the other hand, is a constant-time version of REDOR; the dipolar dephasing is a function of the position of the pulses with respect to the rotor period. We discuss the advantages and disadvantages of each implementation and suggest domains of applicability for these sequences.
旋转回波双共振（REDOR）和偶极耦合化学位移相关（DIPSHIFT）是常用的实验方法，用于探测魔角旋转（MAS）固态 NMR 中孤立自旋-1/2 核对之间的异核偶极-偶极耦合。它们的广泛应用是由于它们对实验不完善的稳健性以及对数据的直接解释。这两个实验都使用转子同步的π脉冲来重新耦合异核偶极-偶极耦合，并且共振的观察强度由取决于重新耦合脉冲的位置或持续时间的重新耦合相位因子调制。这两个实验都提出了几种改进方法，例如开发了 DIPSHIFT，它采用了模拟 REDOR 的多转子周期性质的策略。我们在这里表明，REDOR 和 DIPSHIFT 实际上是同一实验的不同实现。REDOR 和 DIPSHIFT 的设计明显相似，这也反映在它们的理论描述中。在 REDOR 中，通过增加重新耦合持续时间而保持脉冲位置不变来获得偶极退相曲线，这导致退相因子仅取决于退相时间的函数。另一方面，DIPSHIFT 是 REDOR 的恒时版本；偶极退相是脉冲相对于转子周期的位置的函数。我们讨论了每种实现的优缺点，并为这些序列建议了适用的领域。
