RIKEN CLST-JEOL collaboration center, RIKEN, Yokohama, Kanagawa 230-0045, Japan.
RIKEN CLST-JEOL collaboration center, RIKEN, Yokohama, Kanagawa 230-0045, Japan; JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan.
Solid State Nucl Magn Reson. 2017 Jul-Aug;84:83-88. doi: 10.1016/j.ssnmr.2016.12.014. Epub 2017 Jan 4.
Recent study has demonstrated the application of the proton-detected heteronuclear multi-quantum coherence (HMQC) at ultrafast Magic Angle Spinning (MAS) to probe quadrupolar nuclei including N and Cl. In addition, for half-integer quadrupolar nucleus like Cl, the quadrupolar product can be calculated based on the shift difference between the center band of satellite transition (ST) and the central transition (CT) peaks. The applicability of this technique is further investigated on spin I=5/2, namely Al nucleus, and kaolin is chosen as the testing sample. However this study is not straightforward owing to a spin quantum number I=5/2 of Al nucleus and a small quadrupolar coupling of kaolin. Furthermore, very fast MAS, which is mandatory for proton-detected experiment to suppress H-H homonuclear dipolar interactions, introduces additional complexities. It induces the partial overlap of CT and the center band of inner ST (ST1) resonance in addition to the insufficiency of CT-selective excitation by soft-pulse irradiation. In the current work, we employ the constant-time D-HMQC experiment, in which the duration between two recoupling blocks is fixed to a constant value and the arbitrary t increment can be used within this duration. This constant-time D-HMQC enables the precise determination of CT and ST resonance shifts through CT- and ST-selective observations by the indirect spectral width (i) with asynchronized sampling to the top of rotational-echoes for STs and (ii) three times larger than the spinning frequency, respectively. We also numerically and experimentally develop a satellite-selective excitation technique, in which the radio frequency field is applied to the first spinning sideband of ST1 resonance. The satellite-selective 1D single pulse and 2D conventional D-HMQC experiments are demonstrated. The quadrupolar product of Al nucleus extracted from the resulting spectra is in good agreement with the literature.
最近的研究表明，质子检测异核多量子相干（HMQC）在超快魔角旋转（MAS）中的应用可以探测包括 N 和 Cl 在内的四极核。此外，对于像 Cl 这样的半整数四极核，根据卫星跃迁（ST）中心带和中央跃迁（CT）峰之间的位移差可以计算出四极偶极乘积。该技术的适用性在自旋 I=5/2 即 Al 核上进一步进行了研究，并选择高岭土作为测试样品。然而，由于 Al 核的自旋量子数 I=5/2 和高岭土的小偶极耦合，这项研究并不简单。此外，为了抑制质子同核偶极相互作用，超快 MAS 是质子检测实验所必需的，这引入了额外的复杂性。它除了通过软脉冲照射不能完全选择性激发 CT 之外，还导致 CT 和内部 ST（ST1）共振中心带的部分重叠。在当前的工作中，我们采用了恒时 D-HMQC 实验，其中两个重新耦块之间的持续时间固定为一个恒定值，并且可以在该持续时间内使用任意的 t 增量。这种恒时 D-HMQC 通过间接谱宽（i）进行 CT 和 ST 选择性观测，使 CT 和 ST 共振位移的精确确定成为可能，其中 i 值为同步采样到 ST 回波顶部的三倍。我们还数值和实验开发了一种卫星选择性激发技术，其中射频场应用于 ST1 共振的第一个旋转边带。演示了卫星选择性 1D 单脉冲和 2D 常规 D-HMQC 实验。从所得光谱中提取的 Al 核的四极偶极乘积与文献值吻合良好。
