论文标题
通过固态HMQC NMR实验的间接检测14N检测的激发方案的评估
Evaluation of excitation schemes for indirect detection of 14N via solid-state HMQC NMR experiments
论文作者
论文摘要
以前已经证明，可以通过HMQC实验可靠地获得$ {}^{14} $ n NMR光谱。此方法利用了单个（sq）或双Quantum（dq）$ {}^{14} $ n coherences和合适的spin-1/2'spy'nucleus的SQ相干，例如$ {}^1 $ h。必须注意的是，SQ-SQ方法需要经过精心优化的设置，以最大程度地减少与一阶四极相互作用相关的扩展（即，非常适应性的魔法角度和高度稳定的旋转速度），而DQ-SQ却没有。在这项工作中，使用基于J-HMQC的基于J-HMQC的数值模拟以及SQ-SQ-SQ或DQ-SQ $ {} $ h - n-c n-inim of On sq $ {} $ h - n-c n-inim of On SQ-SQ或DQ-SQ $ {} $ h - n-c n- L-齐丁氨酸HCl和N-乙酰基-L-缬氨酸在18.8 T和62.5 kHz Mas。结果表明，但丁和SLP都比XIX和HP提供了更有效的14N激发曲线。此外，显示出SLP方案：（i）在大量四极相互作用上是有效的，（ii）高度健壮，可以抵消和RF-pulse的长度和振幅，并且（III）非常易于设置。这些因素使SLP非常适合在含氮材料的固态NMR分析中广泛，非专业的使用。
It has previously been shown that ${}^{14}$N NMR spectra can be reliably obtained through indirect detection via HMQC experiments. This method exploits the transfer of coherence between single- (SQ) or double-quantum (DQ) ${}^{14}$N coherences, and SQ coherences of a suitable spin-1/2 'spy' nucleus, e.g., ${}^1$H. It must be noted that SQ-SQ methods require a carefully optimized setup to minimize the broadening related to the first-order quadrupole interaction (i.e., an extremely well-adjusted magic angle and a highly stable spinning speed), whereas DQ-SQ ones do not. In this work, the efficiencies of four ${}^{14}$N excitation schemes (DANTE, XiX, Hard Pulse (HP), and Selective Long Pulse (SLP)) are compared using J-HMQC based numerical simulations and either SQ-SQ or DQ-SQ ${}^1$H-{${}^{14}$N} D-HMQC experiments on L-histidine HCl and N-acetyl-L-valine at 18.8 T and 62.5 kHz MAS. The results demonstrate that both DANTE and SLP provide a more efficient 14N excitation profile than XiX and HP. Furthermore, it is shown that the SLP scheme: (i) is efficient over a large range of quadrupole interaction, (ii) is highly robust to offset and rf-pulse length and amplitude, and (iii) is very simple to set up. These factors make SLP ideally suited to widespread, non-specialist use in solid-state NMR analyses of nitrogen-containing materials.
