Vuppu A K, Garcia A A, Vernia C
Arizona State University, Tempe 85287, USA.
Biopolymers. 1997;42(1):89-100. doi: 10.1002/(SICI)1097-0282(199707)42:1<89::AID-BIP8>3.0.CO;2-Y.
Tapping mode Atomic Force Microscopy (TmAFM) has been used to study the fungal polysaccharide scleroglucan deposited from aqueous solution and dimethyl sulfoxide (DMSO) onto a mica surface. The solutions from which the microscope samples were produced were prepared by first dissolving the solid scleroglucan in 0.1M NaOH, then neutralizing the solution with HCl, followed by dilution to the required concentration in either water or DMSO. It was found that from the aqueous solution described above, scleroglucan forms networks. Based on a comparison of the denatured-renatured and aqueous solution samples, network formation is due to the imperfect registration between the chains forming the triple helices. The relatively large stiffness of the scleroglucan triple helix is also assumed to contribute to the formation of the extended networks. The triple helix diameter was measured to be 0.92 +/- 0.27 nm, which is in the same range as that obtained by other researchers using similar techniques. Denatured scleroglucan, deposited from DMSO onto mica, forms a web-like layer on top of which there are sphere-like structures. These morphologies are believed to be due to triple helix denaturation yielding highly flexible single chains in DMSO, which results in coiling and web-like dense packing of scleroglucan upon deposition onto mica. Most interestingly after additional of water to the samples deposited from DMSO, some of the chains can be renatured into short, stiff rod-like structures which are similar to the structures observed by others researchers. The imaging data for aqueous solution deposition can be analyzed by plotting maximum end-to-end distance versus the perimeter of the networks deposited onto mica. This yields a Flory-like exponent of 0.67, which is almost similar in value to that obtained by other researchers for linear structures of scleroglucan but less than that expected for a polymer chain following a self-avoiding walk (upsilon = 0.75) model on a two-dimensional surface. The fractal dimension that can be used to characterize the networks was determined graphically to be 1.22 +/- 0.06.
轻敲模式原子力显微镜（TmAFM）已被用于研究从水溶液和二甲基亚砜（DMSO）沉积到云母表面的真菌多糖硬葡聚糖。制备显微镜样品所用的溶液是通过以下步骤制备的：首先将固体硬葡聚糖溶解在0.1M NaOH中，然后用HCl中和溶液，接着在水或DMSO中稀释至所需浓度。结果发现，在上述水溶液中，硬葡聚糖形成网络。基于对变性-复性样品和水溶液样品的比较，网络形成是由于形成三螺旋的链之间的不完全对齐。硬葡聚糖三螺旋相对较大的刚度也被认为有助于形成扩展网络。测得三螺旋直径为0.92±0.27nm，这与其他研究人员使用类似技术获得的结果在同一范围内。从DMSO沉积到云母上的变性硬葡聚糖形成了一个网状层，在其顶部有球形结构。据信这些形态是由于三螺旋变性在DMSO中产生了高度柔性的单链，这导致硬葡聚糖在沉积到云母上时发生卷曲和网状紧密堆积。最有趣的是，在向从DMSO沉积的样品中加入水后，一些链可以复性成短而硬的棒状结构，这与其他研究人员观察到的结构相似。通过绘制最大端到端距离与沉积在云母上的网络周长的关系图，可以分析水溶液沉积的成像数据。这产生了一个弗洛里指数0.67，其值与其他研究人员对硬葡聚糖线性结构获得的值几乎相似，但小于二维表面上遵循自回避行走（υ = 0.75）模型的聚合物链预期的值。通过图形确定可用于表征网络的分形维数为1.22±0.06。
