Development of 14N high-resolution solid-state NMR and its application

本工作的目的是为我们最近开发的^<14>N高分辨率核磁共振方法建立一个新的核磁共振系统，并进一步应用于多肽等生物分子的结构研究。为了实现观测^<14>N的最佳实验条件，我们购买了一个三共振MAS探针，并对我们现有的核磁共振系统进行了调整。此外，还开发了MAS速度稳定器。(2)间接观测到的^<14>N线形的理论计算对于已知^<14>N四极偶联常数的小分子，我们采用ab-initio分子轨道计算（GAUSSIAN98）来计算四极偶联常数。(3) α螺旋和β片结构的确定对具有α螺旋或β片结构的模型分子进行了理论计算，模拟了^<14>N线形状。发现这两个二级结构可以通过目前的^<14>N观测来区分。因此，我们制备了7个二级结构为α螺旋或β片的肽。虽然观测到的^<14>N线形状表明可以区分二级结构，但趋势与从头计算预测的相反。现在，我们重新审视从头计算。

The aim of this work is to build a new NMR system for a ^<14>N high-resolution NMR method developed recently by us, and further apply to structural studies of biomolecules such as peptides. In the two years, we did(1) Construction of a new NMRE systemTo realize the best experimental condition for ^<14>N observation, a triple-resonance MAS probe was purchased and tuned for our current NMR system. Further, a stabilizer for the MAS speed was developed.(2) Theoretical calculation of indirectly observed ^<14>N lineshapeFor small molecules with known ^<14>N quadrupole coupling constants, we applied ab-initio molecular orbital calculation (GAUSSIAN98) to evaluate quadrupole coupling constants.(3) Determination of α helix and β sheetTheoretical calculation was done for model molecules having α helix or β sheet structures to simulate ^<14>N lineshapes. It was found that these two secondary structures can be distinguished by the present ^<14>N observation. Hence, we prepared 7 peptides, whose secondary structures were known to be either α helix or β sheet. While observed ^<14>N lineshapes indicate it is possible to discriminate the secondary structures, the tendency is opposite to that predicted by ab initio calculation. Presently, we re-examine ab initio calculation.