Giavani Tania, Bildsøe Henrik, Skibsted Jørgen, Jakobsen Hans J
Instrument Centre for Solid State NMR Spectroscopy, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
J Magn Reson. 2004 Feb;166(2):262-72. doi: 10.1016/j.jmr.2003.10.023.
Experimental strategies for the acquisition of high-quality 14N magic-angle spinning (MAS) NMR spectra of the simple amino acids, which exhibit 14N quadrupole coupling constants (C(Q)) on the order of 1.2 MHz, are devised. These are the first useful 14N MAS spectra reported for nitrogen compounds having a C(Q)(14N) value in excess of 1 MHz. The complete manifolds of spinning sidebands (ssbs), i.e., about 300 ssbs for a spinning frequency of 6.0 kHz, have been observed in the 14N MAS NMR spectra of a series of amino acids. In their crystal structure these amino acids all exhibit the zwitterionic form and thus the 14N MAS NMR spectra represent those of a rotating -NH(3)(+) group and not of an amino (-NH(2)) group. Computer simulations combined with fitting of simulated to the experimental ssb intensities result in the determination of precise values for the 14N quadrupole coupling (C(Q)) and its associated asymmetry parameter (eta(Q)) for the nitrogen sites in these molecules. For some of the amino acids the 14N MAS NMR spectra exhibit overlap between the manifolds of ssbs from two different nitrogen sites in accordance with their crystal structures. Computer analysis of these spectra results in two different sets of (C(Q), eta(Q)) values which mainly differ in the magnitudes for eta(Q).
设计了用于获取简单氨基酸高质量14N魔角旋转（MAS）核磁共振谱的实验策略，这些氨基酸的14N四极耦合常数（C(Q)）约为1.2 MHz。这是首次报道的关于C(Q)(14N)值超过1 MHz的含氮化合物的有用的14N MAS谱。在一系列氨基酸的14N MAS核磁共振谱中观察到了完整的旋转边带（ssb）流形，即对于6.0 kHz的旋转频率约有300个ssb。在它们的晶体结构中，这些氨基酸均呈现两性离子形式，因此14N MAS核磁共振谱代表的是旋转的 -NH(3)(+)基团而非氨基（-NH(2)）基团的谱。计算机模拟以及将模拟结果与实验ssb强度进行拟合，从而确定了这些分子中氮位点的14N四极耦合（C(Q)）及其相关不对称参数（eta(Q)）的精确值。对于某些氨基酸，根据其晶体结构，14N MAS核磁共振谱显示来自两个不同氮位点的ssb流形之间存在重叠。对这些谱进行计算机分析得到两组不同的（C(Q)，eta(Q)）值，它们主要在eta(Q)的大小上有所不同。
