Stokke B T, Brant D A
Department of Chemistry, University of California, Irvine 92717.
Biopolymers. 1990;30(13-14):1161-81. doi: 10.1002/bip.360301303.
Electron micrographs of alginate, xylinan, xanthan, and scleroglucan were prepared by vacuum-drying aqueous glycerol-containing solutions, and then heavy-metal, low-angle rotary replicated. Quantitative methods for excluding streamlining effects and deformation artifacts were developed and applied to the digitized polymer contours prior to analysis of stiffness. The apparent macromolecular dimensionalities were not obtainable on the basis of the change in the scaling coefficient alpha relating the rms end-to-end distance and the contour length, mean value of r2(1/2) approximately L alpha, for chains subject to the excluded volume effect in two and three dimensions. Using a two-dimensional model, the persistence length of these molecules was estimated to be (9 +/- 1) nm (alginate), (25 +/- 4) nm (xylinan), (30 +/- 4) nm (single-stranded xanthan), (68 +/- 7) nm (double-stranded xanthan), and (80 +/- 10) nm (scleroglucan). Monte Carlo calculations for wormlike chains close to an interacting surface or confined to the region between two surfaces showed that (1) strongly adsorbed molecules are essentially two-dimensional and (2) molecules restricted to the space between two surfaces separated by a distance less than 20% of the persistence length are two-dimensional in their directional correlation. The somewhat low estimates of the persistence lengths obtained from the electron micrographs compared with those reported from solution measurements can be accounted for by the adoption of a strictly two-dimensional model in the analysis, whereas the absorbed polymers are most likely intermediate between the two-and three-dimensional cases. The model calculations and the analysis of the electron micrographs suggest that stiffness parameters are obtainable from the electron micrographs when the proper theoretical description are used in the analysis.
通过对含甘油水溶液进行真空干燥，然后进行重金属、低角度旋转复型，制备了藻酸盐、木聚糖、黄原胶和硬葡聚糖的电子显微镜照片。在分析刚度之前，开发了用于排除流线化效应和变形伪像的定量方法，并将其应用于数字化的聚合物轮廓。对于在二维和三维中受到排除体积效应影响的链，基于与均方根端到端距离和轮廓长度相关的标度系数α的变化，无法获得表观大分子尺寸，即r2(1/2)的平均值约为Lα。使用二维模型，估计这些分子的持久长度为(9±1)nm（藻酸盐）、(25±4)nm（木聚糖）、(30±4)nm（单链黄原胶）、(68±7)nm（双链黄原胶）和(80±10)nm（硬葡聚糖）。对靠近相互作用表面或局限于两个表面之间区域的蠕虫状链进行的蒙特卡罗计算表明：(1) 强吸附分子基本上是二维的；(2) 限制在两个表面之间、距离小于持久长度20%的空间中的分子，其方向相关性是二维的。与溶液测量报告的持久长度相比，从电子显微镜照片获得的持久长度估计值略低，这可以通过分析中采用严格的二维模型来解释，而吸附的聚合物很可能介于二维和三维情况之间。模型计算和电子显微镜照片分析表明，当在分析中使用适当的理论描述时，刚度参数可从电子显微镜照片中获得。
