CONFORMATION CHARACTERIZATION OF BOMBYX-MORI SILK FIBROIN IN THE SOLID-STATE BY HIGH-FREQUENCY C-13 CROSS POLARIZATION MAGIC ANGLE SPINNING NMR, X-RAY-DIFFRACTION, AND INFRARED-SPECTROSCOPY
CONFORMATION CHARACTERIZATION OF BOMBYX-MORI SILK FIBROIN IN THE SOLID-STATE BY HIGH-FREQUENCY C-13 CROSS POLARIZATION MAGIC ANGLE SPINNING NMR, X-RAY-DIFFRACTION, AND INFRARED-SPECTROSCOPY
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DOI：
10.1021/ma00152a009
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发表时间：
1985-01-01
期刊：
影响因子：
5.5
通讯作者：
SAITO, H
中科院分区：
文献类型：
--
作者：
ASAKURA, T;KUZUHARA, A;SAITO, H
我们记录了在不同条件下制备的家蚕固体丝素样品的X射线衍射、~(13)C CP-MAS核磁共振和红外光谱，以比较不同方法得到的构象特征。这三种方法提供了关于存在最稳定的丝素II形式的一致数据。虽然化学位移是相同的，但丝素I和无规卷曲形式只能通过13C核磁共振峰中线宽的程度来区分。~(13)C CP-MAS核磁共振方法最明显的优点是，这种方法本质上是非破坏性的，非常方便地评估同一样品中丝素I和II的相对比例。我们发现，即使在液氮温度下也会形成粉末，导致从丝素I向无规卷曲的转变，但丝素II的数量在此过程中保持不变。根据样品的制备条件以及丝素I和无规卷曲的~(13)C化学位移和红外光谱的相似性，可以认为无规卷曲是丝素I类的混合物，其长程晶体堆积扭曲到了产生晕X射线衍射的程度。
We recorded X-ray diffraction, 13C CP-MAS NMR, and infrared spectra of silk fibroin samples from Bombyx mori in the solid state, prepared under different conditions, in order tocompare conformational features obtained by the respective methods. These three methods provided consistent data as to the presence of the most stable silk II form. Silk I and random-coil forms were distinguishable only by the extent of line broadening in 13C NMR peaks, although the chemical shifts are the same. The most obvious advantage of the 13C CP-MAS NMR approach is that this method is intrinsically nondestructiveand very convenient for evaluation of the relative proportion of silk I and II forms in the same sample. Wefound that powder formation even at liquid-nitrogen temperature caused a change from silk I to random-coil form, although theamount of silk II form remainsunchanged duringthis procedure. In view of the sample preparation conditions as well as the similarity of the 13C chemical shifts and infrared spectra between the silk I and random-coil forms, it is plausible that the random-coil form is a mixture of silk I type forms whose long-rangecrystalline packing is distorted to the extent togive halo X-ray diffraction.