Detection of remote proton-nitrogen correlations by 1H-detected 14N overtone solid-state NMR at fast MAS
Detection of remote proton-nitrogen correlations by 1H-detected 14N overtone solid-state NMR at fast MAS
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DOI：
10.1039/d2cp00155a
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发表时间：
2022-03-07
影响因子：
3.3
通讯作者：
Nishiyama, Yusuke
中科院分区：
文献类型：
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作者：
Duong, Nghia Tuan;Nishiyama, Yusuke
在固体核磁共振中检测质子和氮的关联对于确定生物和化学体系的结构具有重要意义。在快速魔角旋转下基于质子检测的方法的最新进展促进了固体核磁共振对H-1-N-14关联的检测。然而，用这些方法观察遥远的H-1-N-14关联仍然是一个挑战，特别是对于具有大的四极耦合的N-14位。为了解决这个问题，我们引入了H-1-N-14泛音连续波旋转-回波饱和-脉冲双共振(H-1-N-14OT CW-RESPDOR)序列。与间接维度记录在时间域中的常规二维关联实验不同，H-1-N-14OT CW-RESPDOR实验直接在频域中观察到。在不同的N-14OT频率下记录了一组H-1-N-14OT CW-RESPDOR滤波的H-1谱。由于N-14OT脉冲的选择性，只有当N-14OT频率达到N-14OT中心带或其中一个自旋边带的位置时，才会出现滤波的H-1谱。这组滤波的H-1谱代表了2D H-1-N-14OT相关图。我们还研究了CW-RESPDOR的优化参数，发现这些参数对于我们14.1T的工作磁场并不是严格需要的，因此，实验很容易建立，几乎不需要优化。我们论证了H-1-N-14OTCW-RESPDOR对单斜晶系L-组氨酸和L-丙氨基-L-丙氨酸的实验可行性。无论N-14四极相互作用有多大，都能有效地探测到H-1-N-14远场关联，并与晶体结构相吻合。此外，基于L组氨酸的非质子化N-14位的H-1-N-14关联，我们可以毫不含糊地区分正交形和单斜形。
Detecting proton and nitrogen correlations in solid-state nuclear magnetic resonance (NMR) is important for the structural determination of biological and chemical systems. Recent advances in proton detection-based approaches under fast magic-angle spinning have facilitated the detection of H-1-N-14 correlations by solid-state NMR. However, observing remote H-1-N-14 correlations by these approaches is still a challenge, especially for N-14 sites having large quadrupolar couplings. To address this issue, we introduce the H-1-N-14 overtone continuous wave rotational-echo saturation-pulse double-resonance (H-1-N-14 OT CW-RESPDOR) sequence. Unlike regular 2D correlation experiments where the indirect dimension is recorded in the time domain, the H-1-N-14 OT CW-RESPDOR experiment is directly observed in the frequency domain. A set of H-1-N-14 OT CW-RESPDOR filtered H-1 spectra is recorded at varying N-14 OT frequencies. Thanks to the selective nature of the N-14 OT pulse, the filtered H-1 spectra appear only if the N-14 OT frequency hits the positions of the N-14 OT central band or one of the spinning sidebands. This set of filtered H-1 spectra represents a 2D H-1-N-14 OT correlation map. We have also investigated the optimizable parameters for CW-RESPDOR and figured out that these parameters are not strictly needed for our working magnetic field of 14.1 T. Hence, the experiment is easy to set up and requires almost no optimization. We have demonstrated the experimental feasibility of H-1-N-14 OT CW-RESPDOR on monoclinic l-histidine and l-alanyl l-alanine. The remote H-1-N-14 correlations have been efficiently detected, no matter how large the N-14 quadrupolar interaction is, and agree with the crystal structures. In addition, based on the remote H-1-N-14 correlations from the non-protonated N-14 site of l-histidine, we can unambiguously distinguish the orthorhombic and monoclinic forms.