Suzuki Yu, Takahashi Rui, Shimizu Tadashi, Tansho Masataka, Yamauchi Kazuo, Williamson Mike P, Asakura Tetsuo
Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16, Nakacho, Koganei, Tokyo 184-8588, Japan.
J Phys Chem B. 2009 Jul 23;113(29):9756-61. doi: 10.1021/jp903020p.
A combination of solid state 1H NMR chemical shift measurements and empirical chemical shift calculations has been used to interpret 1H solid state chemical shifts of a model peptide (Ala-Gly)15 for the crystalline domain of Bombyx mori silk fibroin in silk I and silk II structures, including a treatment of both intra- and intermolecular arrangements. Silk I and silk II are the structures of silk fibroin before and after spinning, respectively. Two peaks with equal intensity were observed for the amide protons of (AG)15 in silk I, whereas only one broad peak was observed for silk II, reflecting a difference of 1.1 ppm in Ala HN shift between silk I and silk II, but a difference of only 0.2 ppm in Gly HN shift. Chemical shift calculations predicted chemical shifts that are in good agreement with the experimental observations and showed that the origin of these chemical shift differences was predominantly the magnetic anisotropy effect from the C=O bond that hydrogen bonds with HN, which has a more favorable geometry for Ala HN in silk II than for the other HN. This result shows that we could distinguish between proton chemical shift effects arising from intermolecular interactions and those from intramolecular interactions by combining observation of the solid state 1H NMR chemical shift and empirical chemical shift calculation.
固态¹H NMR化学位移测量与经验化学位移计算相结合，用于解释家蚕丝素蛋白结晶域模型肽（Ala-Gly）₁₅在丝I和丝II结构中的¹H固态化学位移，包括对分子内和分子间排列的处理。丝I和丝II分别是丝素蛋白纺丝前后的结构。在丝I中，（AG）₁₅的酰胺质子观察到两个强度相等的峰，而丝II中只观察到一个宽峰，这反映出丝I和丝II之间丙氨酸HN位移相差1.1 ppm，但甘氨酸HN位移仅相差0.2 ppm。化学位移计算预测的化学位移与实验观察结果高度吻合，表明这些化学位移差异的主要来源是与HN形成氢键的C=O键的磁各向异性效应，丝II中丙氨酸HN的几何结构比其他HN更有利。该结果表明，通过结合固态¹H NMR化学位移观察和经验化学位移计算，我们可以区分分子间相互作用和分子内相互作用引起的质子化学位移效应。
