Through-space heteronuclear correlation experiments under magic-angle spinning (MAS) conditions can provide unique insights into inter-atomic proximities. In particular, it has been shown that experiments based on two consecutive coherence transfers, 1H → I → 1H, like D-HMQC (dipolar-mediated heteronuclear multiple-quantum correlation), are usually more sensitive for the indirect detection via protons of spin-3/2 quadrupolar nuclei with low gyromagnetic ratio. Nevertheless, the resolution is often decreased by the second-order quadrupolar broadening along the indirect dimension. To circumvent this issue, we incorporate an MQMAS (multiple-quantum MAS) quadrupolar filter into the t1 evolution period of the D-HMQC sequence, which results in a novel pulse sequence called D-HMQC-MQ. The triple-quantum coherences evolving during this filter are excited and reconverted using cosine-modulated long-pulses synchronized with the sample rotation to avoid spinning sidebands in the indirect dimension. The desired coherence transfer pathways during this sequence are selected using two nested cogwheel phase cycles with 56 steps. This high-resolution heteronuclear correlation technique is demonstrated experimentally for the indirect detection via 1H of spin-3/2 isotopes, such as 11B, 23Na and 35Cl, in zinc borate hydrate, NaH2PO4 and l-histidine hydrochloride, respectively. We show that this experiment can be applied at high magnetic fields up to 28.2 T for protons subject to chemical shift anisotropies larger than 20 ppm, provided the MAS frequency is sufficiently stable since the D-HMQC-MQ experiment, like the parent D-HMQC, is sensitive to MAS fluctuations, which can produce t1-noise.

中文翻译：

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使用多量子过滤的通过空间 D-HMQC 实验对固体中的自旋-3/2 四极原子核进行高分辨率间接检测


在魔角自旋 （MAS） 条件下的穿越空间异核相关实验可以为原子间接近性提供独特的见解。特别是，已经表明，基于两个连续相干转移的实验，即 1H → I → 1H，如 D-HMQC（偶极介导的异核多量子相关），通常对通过质子间接检测具有低旋磁比的自旋 3/2 四极原子核更敏感。然而，分辨率通常会因沿间接维度的二阶四极展宽而降低。为了规避这个问题，我们将 MQMAS （多量子 MAS）四极滤波器整合到 D-HMQC 序列的 t1 进化期，从而产生一种称为 D-HMQC-MQ 的新型脉冲序列。在该滤波器过程中演变的三量子相干性使用与样品旋转同步的余弦调制长脉冲被激发和重新转换，以避免在间接维度上旋转边带。在此序列中，使用两个具有 56 个步骤的嵌套齿轮相位循环来选择所需的相干转移途径。这种高分辨率异核相关技术在实验中被证明用于通过 1H 间接检测硼酸锌水合物、NaH2PO4 和 l-组氨酸盐酸盐中的自旋-3/2 同位素，例如 11B、23Na 和 35Cl，分别。我们表明，如果 MAS 频率足够稳定，因为 D-HMQC-MQ 实验与母体 D-HMQC 一样，对 MAS 波动敏感，该实验可以应用于高达 28.2 T 的高磁场中，这会产生 t1 噪声。