Rodin Victor V, Belton Peter S
Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz, Austria.
School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK.
Polymers (Basel). 2022 Sep 3;14(17):3665. doi: 10.3390/polym14173665.
silkworm natural silk is a fibrous biopolymer with a block copolymer design containing both hydrophobic and hydrophilic regions. Using H NMR relaxation, this work studied natural silk fibres oriented at 0° and 90° to the static magnetic field to clarify how measured NMR parameters reflect the structure and anisotropic properties of hydrated silk fibres. The FTIR method was applied to monitor the changes in the silk I and -sheet conformations. Unloaded silk fibres at different hydration levels (HL), the silk threads before and after tensile loading in water, and fibres after a stepped increase in temperature have been explored. NMR data discovered two components in and relaxations for both orientations of silk fibres (0° and 90°). For the slower component, the results showed an obvious anisotropic effect with higher relaxation times for the silk fibres oriented at 90° to . The component (water protons, HL = 0.11) was sequentially decreased over a range of fibres: 0° oriented, randomly oriented, silk cocoon, 90° oriented. The degree of anisotropy in relaxation was decreasing with increasing HL. The in silk threads oriented at 0° and 90° also showed anisotropy in increased HL (to 0.42 g HO/g dry matter), at tensile loading, and at an increasing temperature towards 320 K. The changes in NMR parameters and different relaxation mechanisms affecting water molecular interactions and silk properties have been discussed. The findings provide new insights relating to the water anisotropy in hydrated silk fibres at tensile loading and under a changing HL and temperature.
家蚕天然丝是一种纤维状生物聚合物，具有包含疏水和亲水区域的嵌段共聚物结构。本研究利用核磁共振氢谱弛豫技术，研究了与静磁场呈0°和90°取向的天然丝纤维，以阐明所测核磁共振参数如何反映水合丝纤维的结构和各向异性特性。采用傅里叶变换红外光谱法监测丝I和β-折叠构象的变化。研究了不同水合水平（HL）下的未加载丝纤维、在水中拉伸加载前后的丝线以及温度逐步升高后的纤维。核磁共振数据发现，丝纤维两种取向（0°和90°）的T2和T1弛豫均有两个成分。对于较慢的T2成分，结果显示出明显的各向异性效应，与磁场呈90°取向的丝纤维具有更高的弛豫时间。T1成分（水质子，HL = 0.11）在一系列纤维中依次降低：0°取向、随机取向、丝茧、90°取向。T2弛豫的各向异性程度随HL增加而降低。与磁场呈0°和90°取向的丝线在HL增加（至0.42 g H2O/g干物质）、拉伸加载以及温度升高至320 K时，T1也显示出各向异性。讨论了核磁共振参数的变化以及影响水分子相互作用和丝性能的不同弛豫机制。这些发现为拉伸加载以及HL和温度变化时水合丝纤维中的水各向异性提供了新的见解。
