Liu Dagang, Tian Huafeng, Jia Xuewei, Zhang Lina
Department of Chemistry, Wuhan University, Wuhan 430072, China.
Macromol Biosci. 2008 May 13;8(5):401-9. doi: 10.1002/mabi.200700217.
Novel protein-based nanocomposites were well prepared by in vivo synthesis and co-precipitation of soy protein isolate (SPI) with calcium carbonate (CaCO3) in an aqueous solution. The resultant CaCO3 in the nanocomposites was identified as calcite- and aragonite-type, respectively. The morphology and structure of the CaCO3/SPI composites were investigated by means of wide-angle X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy, and high-resolution transmission electron microscopy. The results revealed that the polymorph and the size of CaCO3 in the nanocomposites were dependent on its content, pH, and the conformation of soy protein. At the content of more than 5%, CaCO3 was changed into calcite crystal with the preference of growing along (104) plane. However, at lower content of less than 5%, CaCO3 preferred to form aragonite in the composite as a result of the modulation by soy protein. The aragonite nanocrystals were arrayed in the direction of (111) plane and self-assembled along beta-sheet planes of soy protein polypeptides. The mechanical properties, thermal stability, and water resistance of the CaCO3/SPI nanocomposites were significantly improved as a result of the nanosized effects. Interestingly, the aragonite/SPI nanocomposite exhibited higher tensile strength (about 50 MPa) than that of calcite/SPI, owing to a good compatibility and strong interaction between aragonite and soy protein polypeptides. This work provided a simple pathway to develop the soy protein-based bio-hybrid materials with high mechanical strength and valuable information on their structure-properties relationship.
通过在水溶液中大豆分离蛋白（SPI）与碳酸钙（CaCO₃）的体内合成和共沉淀，成功制备了新型蛋白质基纳米复合材料。纳米复合材料中生成的CaCO₃分别被鉴定为方解石型和文石型。通过广角X射线衍射、傅里叶变换红外光谱、扫描电子显微镜和高分辨率透射电子显微镜对CaCO₃/SPI复合材料的形态和结构进行了研究。结果表明，纳米复合材料中CaCO₃的多晶型和尺寸取决于其含量、pH值以及大豆蛋白的构象。当含量超过5%时，CaCO₃转变为方解石晶体，优先沿（104）面生长。然而，当含量低于5%时，由于大豆蛋白的调制作用，CaCO₃在复合材料中更倾向于形成文石。文石纳米晶体沿（111）面方向排列，并沿大豆蛋白多肽的β-折叠面自组装。由于纳米尺寸效应，CaCO₃/SPI纳米复合材料的力学性能、热稳定性和耐水性得到了显著改善。有趣的是，文石/SPI纳米复合材料表现出比方解石/SPI更高的拉伸强度（约50 MPa），这归因于文石与大豆蛋白多肽之间良好的相容性和强相互作用。这项工作为开发具有高机械强度的大豆蛋白基生物杂化材料提供了一条简单途径，并提供了有关其结构-性能关系的有价值信息。
