Dynamic nuclear polarisation enhanced (14)N overtone MAS NMR spectroscopy.
Dynamic nuclear polarisation enhanced (14)N overtone MAS NMR spectroscopy.
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DOI：
10.1039/c4cp00590b
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发表时间：
2014-06
期刊：
影响因子：
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通讯作者：
Aaron J. Rossini;L. Emsley;L. O’Dell
中科院分区：
文献类型：
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作者：
Aaron J. Rossini;L. Emsley;L. O’Dell
动态核极化（DNP）已被用来获得魔角旋转（14）N（OT）（氮-14泛音）固态NMR光谱从几个模型氨基酸，直接和间接观察（14）N（OT）信号。用不溶解结晶相的有机液体的双自由基溶液浸渍结晶固体。然后通过（1）H自旋扩散从高度极化的表面（1）H核极化体相，导致（1）H DNP信号增强约两个数量级。在魔角旋转下，用接触时间相对较短（约100 μs）的标准脉冲序列，证明了从（1）H核直接到（14）N泛频跃迁的交叉极化。该方法可用于获得与模拟线型紧密匹配的（14）N泛音MAS粉末图案，允许测量各向同性化学位移和四极参数。DNP增强还允许从天然丰度粉末样品快速获取2D（14）N（OT）异质相关光谱。（1）H-（14）N（OT）HETCOR和（13）C-（14）N（OT）HMQC脉冲序列用于观察组氨酸盐酸盐一水合物中所有单键H-N和C-N相关性，在几小时内获得光谱。由于（14）N同位素的高天然丰度（99.6%）和观察泛音跃迁的优势，这些方法提供了一种有吸引力的途径来观察天然同位素丰度的样品的C-N相关性，并且能够高分辨率地测量（14）N化学位移和四极相互作用参数。
Dynamic nuclear polarisation (DNP) has been used to obtain magic angle spinning (14)N(OT) (nitrogen-14 overtone) solid-state NMR spectra from several model amino acids, with both direct and indirect observation of the (14)N(OT) signal. The crystalline solids were impregnated with biradical solutions of organic liquids that do not dissolve the crystalline phase. The bulk phase was then polarized via(1)H spin diffusion from the highly-polarized surface (1)H nuclei, resulting in (1)H DNP signal enhancements of around two orders of magnitude. Cross polarisation from (1)H nuclei directly to the (14)N overtone transition is demonstrated under magic angle spinning, using a standard pulse sequence with a relatively short contact time (on the order of 100 μs). This method can be used to acquire (14)N overtone MAS powder patterns that match closely with simulated line shapes, allowing isotropic chemical shifts and quadrupolar parameters to be measured. DNP enhancement also allows the rapid acquisition of 2D (14)N(OT) heteronuclear correlation spectra from natural abundance powder samples. (1)H-(14)N(OT) HETCOR and (13)C-(14)N(OT) HMQC pulse sequences were used to observe all single-bond H-N and C-N correlations in histidine hydrochloride monohydrate, with the spectra obtained in a matter of hours. Due to the high natural abundance of the (14)N isotope (99.6%) and the advantages of observing the overtone transition, these methods provide an attractive route to the observation of C-N correlations from samples at natural isotopic abundance and enable the high resolution measurement of (14)N chemical shifts and quadrupolar interaction parameters.