Indirect detection of nitrogen-14 in solid-state NMR spectroscopy
Indirect detection of nitrogen-14 in solid-state NMR spectroscopy
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DOI：
10.1002/cphc.200700049
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发表时间：
2007-06-25
期刊：
影响因子：
2.9
通讯作者：
Bodenhausen, Geoffrey
中科院分区：
文献类型：
--
作者：
Cavadini, Simone;Antonijevic, Sasa;Bodenhausen, Geoffrey
通过在魔角旋转粉末中间接检测获得的 N-14（旋转 1 = 1）矿石的 NMR 谱。该方法依赖于从 S = 1/2 的邻近“间谍”核（例如 C-13 或 H-1）到 IN 核的单量子或双量子跃迁的相干性转移。相干性的转移可以通过标量和残余偶极分裂（RDS）的组合来实现；后者矿石也称为二阶四极-偶极交叉项。二维核磁共振谱揭示了由二阶和三阶四极耦合确定的粉末图案。这些光谱取决于四极耦合常数 Co（通常为几兆赫）、N-14 核的不对称参数 il 以及 I (N-14) 和 S (spy) 核之间的核间矢量 ris 相对于四极张量的方向。这些可能受到运动过度影响的参数可以揭示有关含氮固体的结构和动力学的有价值的信息。将该技术应用于各种氨基酸（富含 C-13 或具有天然碳同位素丰度），并在不同磁场下记录光谱，说明了该方法的范围。
NMR spectra of N-14 (spin 1 = 1) ore obtained by indirect detection in powders spinning at the magic angle. The method relies on the transfer of coherence from a neighboring "spy" nucleus with S = 1/2, such as C-13 or H-1, to single- or double-quantum transitions of IN nuclei. The transfer of coherence can occur through a combination of scalar and residual dipolar splittings (RDS); the latter ore also known as second-order quadrupole-dipole cross terms. The two-dimensional NMR spectra reveal powder patterns determined by second- and third-order quadrupolar couplings. These spectra depend on the quadrupolor coupling constant Co (typically a few megahertz), on the asymmetry parameter il, of the N-14 nucleus, and on the orientation of the internuclear vector ris between the / (N-14) and S (spy) nuclei with respect to the quadrupolar tensor. These parameters, which can be subject to motional overoging, can reveal valuable information about the structure and dynamics of nitrogen-containing solids. Application of this technique to various amino acids, either enriched in C-13 or with natural carbon isotope abundance, with spectra recorded at various magnetic fields, illustrates the scope of the method.