Recoupling, decoupling, and multidimensional correlation experiments in magic-angle-spinning (MAS) solid-state NMR can be designed by exploiting the symmetry of internal spin interactions. One such scheme, namely, ${\mathrm{C}\mathrm{5}}_2^1$, and its supercycled version ${\mathrm{S}\mathrm{P}\mathrm{C}\mathrm{5}}_2^1$, notated as a five-fold symmetry sequence, is widely used for double-quantum dipole-dipole recoupling. Such schemes are generally rotor synchronised by design. We demonstrate an asynchronous implementation of the ${\mathrm{S}\mathrm{P}\mathrm{C}\mathrm{5}}_2^1$ sequence leading to higher double-quantum homonuclear polarisation transfer efficiency compared to the normal synchronous implementation. Rotor-synchronisation is broken in two different ways: lengthening the duration of one of the pulses, denoted as pulse-width variation (PWV), and mismatching the MAS frequency denoted as MAS variation (MASV). The application of this asynchronous sequence is shown on three different samples, namely, U–¹³C-alanine and 1,4-¹³C-labelled ammonium phthalate which include ¹³C_α-¹³C_β, ¹³C_α-¹³C_o, and ¹³C_o–¹³C_o spin systems, and adenosine 5′- triphosphate disodium salt trihydrate (ATP⋅3H₂O). We show that the asynchronous version performs better for spin pairs with small dipole-dipole couplings and large chemical-shift anisotropies, for example, ¹³C_o–¹³C_o. Simulations and experiments are shown to corroborate the results.

可以通过利用内部自旋相互作用的对称性来设计魔角旋转 (MAS) 固态 NMR 中的再耦合、去耦合和多维相关实验。一个这样的方案，即${\mathrm{C}\mathrm{5个}}_{\mathrm{2个}}^{\mathrm{1个}}$, 及其超循环版本${\mathrm{小号}\mathrm{P}\mathrm{C}\mathrm{5个}}_{\mathrm{2个}}^{\mathrm{1个}}$，表示为五重对称序列，广泛用于双量子偶极 - 偶极再耦合。此类方案通常通过设计实现转子同步。我们演示了一个异步实现${\mathrm{小号}\mathrm{P}\mathrm{C}\mathrm{5个}}_{\mathrm{2个}}^{\mathrm{1个}}$与正常的同步实施相比，序列导致更高的双量子同核极化转移效率。转子同步以两种不同的方式被破坏：延长其中一个脉冲的持续时间，表示为脉冲宽度变化 (PWV)，以及使 MAS 频率不匹配，表示为 MAS 变化 (MASV)。此异步序列的应用显示在三个不同的样品上，即 U– ¹³ C-丙氨酸和 1,4- ¹³ C 标记的邻苯二甲酸铵，其中包括¹³ C _α - ¹³ C _β、¹³ C _α - ¹³ _Co o 、和¹³ Co _{_}– ¹³ Co_自旋系统和腺苷 5'- 三磷酸二钠盐三水合物 (ATP⋅3H ₂ O)。_{我们表明异步版本对于具有小}偶极-偶极耦合和大化学位移各向异性的自旋对表现更好，例如¹³ Co – ¹³ Co。显示模拟和实验以证实结果。