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Analysis of HMQC experiments applied to a spin ½ nucleus subject to very large CSA.
Solid State Nuclear Magnetic Resonance ( IF 1.8 ) Pub Date : 2019-03-06 , DOI: 10.1016/j.ssnmr.2019.03.001
Piotr Paluch 1 , Andrew G M Rankin 2 , Julien Trébosc 2 , Olivier Lafon 3 , Jean-Paul Amoureux 4
Affiliation  

The acquisition of solid-state NMR spectra of “heavy” spin I = 1/2 nuclei, such as 119Sn, 195Pt, 199Hg or 207Pb can often prove challenging due to the presence of large chemical shift anisotropy (CSA), which can cause significant broadening of spectral lines. However, previous publications have shown that well-resolved spectra can be obtained via inverse 1H detection using HMQC experiments in combination with fast magic angle spinning. In this work, the efficiencies of different 195Pt excitation schemes are analyzed using SIMPSON numerical simulations and experiments performed on cis- and transplatin samples. These schemes include: hard pulses (HP), selective long pulses (SLP) and rotor-synchronized DANTE trains of pulses. The results show that for spectra of species with very large CSA, HP is little efficient, but that both DANTE and SLP provide efficient excitation profiles over a wide range of CSA values. In particular, it is revealed that the SLP scheme is highly robust to offset, pulse amplitude and length, and is simple to set up. These factors make SLP ideally suited to widespread use by “non-experts” for carrying out analyses of materials containing “heavy” spin I = 1/2 nuclei that are subject to very large CSAs. Finally, the existence of an “intermediate” excitation regime, with an rf-field strength in between those of HP and SLP, which is effective for large CSA, is demonstrated. It must be noted that in some samples, multiple sites may exist with very different CSAs. This is the case for 195Pt species with either square-planar or octahedral structures, with large or small CSA, respectively. These two types of CSAs can only be excited simultaneously with DANTE trains, which scale up the effective rf-field. Another way to obtain all the information is to perform two different experiments: one with SLP and the second with HP to excite the sites with moderate/large and small/moderate CSAs, respectively. These two complementary experiments, recorded with two different spinning speeds, can also be used to discriminate the center-band resonances from the spinning sidebands.



中文翻译:

对应用于非常大的CSA的自旋½核的HMQC实验进行分析。

由于存在大的化学位移各向异性(CSA),通常难以证明“重”自旋I = 1/2核(例如119 Sn,195 Pt,199 Hg或207 Pb)的固态NMR光谱的采集,这会导致光谱线显着加宽。但是,以前的出版物表明,使用HMQC实验结合快速魔角旋转可以通过1 H检测获得良好分辨的光谱。在这项工作中,不同的效率195使用SIMPSON数值模拟分析铂激发方案,并对顺铂和跨铂样品进行实验。这些方案包括:硬脉冲(HP),选择性长脉冲(SLP)和转子同步的DANTE脉冲序列。结果表明,对于具有非常大的CSA的物种的光谱,HP效率不高,但是DANTE和SLP都可以在很宽的CSA值范围内提供有效的激发曲线。特别地,揭示了SLP方案对偏移,脉冲幅度和长度具有高度鲁棒性,并且易于设置。这些因素使SLP非常适合“非专家”广泛用于进行包含“重”自旋I = 1/2核的材料的分析,这些材料受非常大的CSA影响。最后,存在“中间”激励机制,证明了在HP和SLP之间具有良好的射频场强,这对大型CSA有效。必须注意的是,在某些示例中,可能存在具有非常不同的CSA的多个站点。情况就是这样195种Pt物种具有方形或八面体结构,分别具有较大或较小的CSA。只能通过DANTE列车同时激发这两种类型的CSA,这可以扩大有效的RF场。获取所有信息的另一种方法是执行两个不同的实验:一个是使用SLP,另一个是使用HP,分别激发具有中等/较大和较小/中等CSA的位置。这两个互补的实验,以两种不同的旋转速度记录下来,也可以用来区分中心带共振和旋转边带。

更新日期:2019-03-06
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