Sachleben J R, Beverwyk P, Frydman L
Department of Chemistry (M/C 111), University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois, 60607-7061, USA.
J Magn Reson. 2000 Jun;144(2):330-42. doi: 10.1006/jmre.2000.2070.
Aseries of uni- and multidimensional variants of the dipolar exchange-assisted recoupling (DEAR) NMR experiment is described and applied to determinations of (13)C-(14)N dipolar local field spectra in amino acids and dipeptides. The DEAR protocol recouples nearby nuclei by relying on differences in their relative rates of longitudinal relaxation, and has the potential to give quantitative geometric results without requiring radiofrequency pulsing on both members of a coupled spin pair. One- and two-dimensional variants of this recoupling strategy on generic I-S pairs are discussed, and measurements of (13)C-(14)N distances and 2D local field experiments sensitive to the relative orientation of CN vectors with respect to the (13)C shielding tensor are presented. Since these measurements did not involve pulsing on the broad nitrogen resonance, their results were independent of the quadrupolar parameters of this nucleus. High-resolution 3D NMR versions of the 2D experiments were also implemented in order to separate their resulting local field patterns according to the isotropic shifts of inequivalent (13)C sites. These high-resolution 3D acquisitions involved collecting a series of 2D DEAR NMR data sets on rotating samples as a function of spinning angle, and then subjecting the resulting data to a processing akin to that involved in variable-angle correlation NMR. Once successfully tested on l-alanine this experiment was applied to the analysis of a series of dipeptides, allowing us to extract separate local field (13)C-(14)N spectra from this type of multisite systems.
本文描述了一系列偶极交换辅助重耦（DEAR）核磁共振实验的单维和多维变体，并将其应用于测定氨基酸和二肽中的（13）C-（14）N偶极局部场谱。DEAR方法通过依赖附近原子核纵向弛豫相对速率的差异来重耦它们，并且有潜力在不需要对耦合自旋对的两个成员都进行射频脉冲的情况下给出定量的几何结果。讨论了这种重耦策略在一般I-S对上的一维和二维变体，并展示了（13）C-（14）N距离的测量以及对CN向量相对于（13）C屏蔽张量的相对取向敏感的二维局部场实验。由于这些测量不涉及对宽氮共振进行脉冲，其结果与该原子核的四极参数无关。还实现了二维实验的高分辨率三维核磁共振版本，以便根据不等价（13）C位点的各向同性位移来分离其产生的局部场模式。这些高分辨率三维采集包括在旋转样品上收集一系列二维DEAR核磁共振数据集作为旋转角度的函数，然后对所得数据进行类似于可变角度相关核磁共振中所涉及的处理。一旦在L-丙氨酸上成功测试，该实验就被应用于一系列二肽的分析，使我们能够从这种多位点系统中提取单独的局部场（13）C-（14）N谱。
