Strohmeier Mark, Grant David M
Department of Chemistry, University of Utah, 315 South. 1400 East, Salt Lake City, Utah 84112-0850, USA.
J Am Chem Soc. 2004 Jan 28;126(3):966-77. doi: 10.1021/ja037330e.
The determination of backbone conformations in powdered peptides using 13C and 15N shift tensor information is explored. The 13C and 15N principal shift values in natural abundance 13C and 15N melanostatin (L-Pro-L-Leu-Gly amide) are measured using the FIREMAT technique. Furthermore, the orientation of the C-N bond in the 13C shift principal axis system for the backbone carbons is obtained from the presence of the 13C-14N dipolar coupling. The Ramachandran angles for the title compound are obtained from solid-state NMR data by comparing the experimentally determined shift tensor information to systematic theoretical shielding calculations on N-formyl-L-amino acid-amide models. The effects of geometry optimization and neglect of intermolecular interactions on the theoretical shielding values in the model compounds are investigated. The sets of NMR derived Ramachandran angles are assembled in a set of test structures that are compared to the available single-crystal X-ray structure. Shift tensor calculations on the test structures and the X-ray structure are used to further assess the importance of intermolecular interactions when the shift tensor is used as a structural probe in powdered peptides.
本文探索了利用¹³C和¹⁵N化学位移张量信息来确定粉末状肽段的主链构象。使用FIREMAT技术测量了天然丰度¹³C和¹⁵N的促黑素（L-脯氨酸-L-亮氨酸-甘氨酰胺）中的¹³C和¹⁵N主化学位移值。此外，通过¹³C-¹⁴N偶极耦合的存在，获得了主链碳的¹³C化学位移主轴系统中C-N键的取向。通过将实验测定的化学位移张量信息与N-甲酰基-L-氨基酸酰胺模型的系统理论屏蔽计算进行比较，从固态NMR数据中获得了标题化合物的拉马钱德兰角。研究了几何优化和忽略分子间相互作用对模型化合物中理论屏蔽值的影响。将NMR衍生的拉马钱德兰角集组装到一组测试结构中，并与现有的单晶X射线结构进行比较。对测试结构和X射线结构进行化学位移张量计算，以进一步评估当化学位移张量用作粉末状肽段的结构探针时分子间相互作用的重要性。
