Polysaccharide gels assembled from the anionic biopolymers pectin and carrageenan have been studied using transmission electron microscopy (TEM). Gels were formed in several different ways: for pectin, hydrogen bonding was used to form junction zones between strands, whereas for carrageenan systems, several different ion types were used to form ionotropic networks. Using this approach, several distinct network architectures were realized. In addition to preparing gelled samples for electron microscopy, a set of samples was taken without performing the additional treatment necessitated by the TEM measurements, and these were studied directly by small-angle X-ray scattering (SAXS). Taking careful consideration of the relative merits of different image sizes and available processing techniques, the real-space images acquired by TEM were used via radial integration of the Fourier transform to produce simulated scattering patterns. These intensity-versus-wavevector plots were compared with the results of SAXS experiments carried out on the unadulterated gels using synchrotron radiation. Although information regarding chain thicknesses and flexibilities was found to be modified by labeling and changes in the dielectric constant and mechanical properties of the surroundings in the TEM, the studies carried out here show that careful protocols can produce data sets where information acquired above ∼20 nm is broadly consistent with that obtained by SAXS studies carried out on unadulterated samples. The fact that at larger length scale the structure of these water-rich networks seems largely preserved in the TEM samples suggests that three-dimensional (3D) TEM tomography experiments carried out with careful sample preparation will be valuable tools for measuring network architecture and connectivity; information that is lost in SAXS owing to the intrinsic averaging nature of the technique.

中文翻译：

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透射电子显微镜对多糖网络的结构分析：与小角X射线散射的比较

已使用透射电子显微镜（TEM）研究了由阴离子生物聚合物果胶和角叉菜胶组装而成的多糖凝胶。凝胶以几种不同的方式形成：对于果胶，氢键被用来形成链之间的连接区，而对于角叉菜胶系统，几种不同的离子类型被用来形成离子网络。使用这种方法，实现了几种不同的网络体系结构。除了准备用于电子显微镜的胶凝样品外，还采集了一组样品，未进行TEM测量所需的额外处理，并且直接通过小角度X射线散射（SAXS）研究了这些样品。仔细考虑不同图像尺寸的相对优点和可用的处理技术，通过傅立叶变换的径向积分，使用通过TEM获得的真实空间图像来生成模拟的散射图。将这些强度-波向量图与使用同步加速器辐射在未掺杂凝胶上进行的SAXS实验结果进行了比较。尽管发现有关链厚度和柔韧性的信息可以通过标记以及TEM中周围环境的介电常数和机械性能的变化而被修改，但此处进行的研究表明，仔细的协议可以生成数据集，其中在约20 nm以上获取的信息与对未掺杂样品进行的SAXS研究获得的结果大致一致。这些富水网络的结构在较大的长度尺度上似乎很大程度上保留在TEM样品中，这一事实表明，精心准备样品进行的三维（3D）TEM层析成像实验将是衡量网络体系结构和连通性的有价值的工具；由于该技术的内在平均特性，在SAXS中丢失的信息。