Liang Lixin, Ji Yi, Zhao Zhenchao, Quinn Caitlin M, Han Xiuwen, Bao Xinhe, Polenova Tatyana, Hou Guangjin
State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Zhongshan Road 457 Dalian 116023 China
University of Chinese Academy of Sciences Beijing 100049 China.
Chem Sci. 2021 Jul 20;12(34):11554-11564. doi: 10.1039/d1sc03194e. eCollection 2021 Sep 1.
Heteronuclear dipolar coupling is indispensable in revealing vital information related to the molecular structure and dynamics, as well as intermolecular interactions in various solid materials. Although numerous approaches have been developed to selectively reintroduce heteronuclear dipolar coupling under MAS, most of them lack universality and can only be applied to limited spin systems. Herein, we introduce a new and robust technique dubbed phase modulated rotary resonance (PMRR) for reintroducing heteronuclear dipolar couplings while suppressing all other interactions under a broad range of MAS conditions. The standard PMRR requires the radiofrequency (RF) field strength of only twice the MAS frequency, can efficiently recouple the dipolar couplings with a large scaling factor of 0.50, and is robust to experimental imperfections. Moreover, the adjustable window modification of PMRR, dubbed wPMRR, can improve its performance remarkably, making it well suited for the accurate determination of dipolar couplings in various spin systems. The robust performance of such pulse sequences has been verified theoretically and experimentally model compounds, at different MAS frequencies. The application of the PMRR technique was demonstrated on the H-ZSM-5 zeolite, where the interaction between the Brønsted acidic hydroxyl groups of H-ZSM-5 and the absorbed trimethylphosphine oxide (TMPO) were probed, revealing the detailed configuration of super acid sites.
异核偶极耦合对于揭示与各种固体材料的分子结构和动力学以及分子间相互作用相关的重要信息不可或缺。尽管已经开发出许多方法来在魔角旋转（MAS）下选择性地重新引入异核偶极耦合，但其中大多数缺乏通用性，只能应用于有限的自旋系统。在此，我们引入一种新的强大技术，称为相位调制旋转共振（PMRR），用于在广泛的MAS条件下重新引入异核偶极耦合，同时抑制所有其他相互作用。标准的PMRR仅需要射频（RF）场强为MAS频率的两倍，能够以0.50的大比例因子有效地重新耦合偶极耦合，并且对实验缺陷具有鲁棒性。此外，PMRR的可调窗口修正，称为wPMRR，可显著提高其性能，使其非常适合于精确测定各种自旋系统中的偶极耦合。这种脉冲序列的鲁棒性能已在理论和实验上针对不同MAS频率的模型化合物得到验证。在H-ZSM-5沸石上展示了PMRR技术的应用，其中探测了H-ZSM-5的布朗斯台德酸性羟基与吸附的三甲基氧化膦（TMPO）之间的相互作用，揭示了超强酸位点的详细构型。
