CONFORMATION OF AMYLOSE IN DIMETHYL-SULFOXIDE
CONFORMATION OF AMYLOSE IN DIMETHYL-SULFOXIDE
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DOI：
10.1021/ma00068a023
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发表时间：
1993-08-02
期刊：
影响因子：
5.5
通讯作者：
KITAMURA, S
中科院分区：
文献类型：
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作者：
NAKANISHI, Y;NORISUYE, T;KITAMURA, S
通过光散射、沉降平衡和粘度测量，研究了直链淀粉在二甲基亚砜（DMSO）中的构象，这些样品是直链淀粉及其低聚物的窄分布样品，其重均分子量M（w）范围从342（二聚体）到1.7 × 10（6）。 当M（w）大于10（5）时，z-平均均方回转半径[S2]z和特性粘度[eta]分别为M（w）1.2和M（w）0.7，表明在此分子量范围内，直链淀粉链表现为通过排除体积效应膨胀的无规卷曲。低于M（w）约10（4）时，[eta]对M（w）表现出异常弱的依赖性，最终变得几乎与分子量无关。根据Yoshizaki等人关于未扰动螺旋蠕虫状链的理论，[eta]的这种行为可以通过DMSO分子的溶剂化和直链淀粉链的某些螺旋性质来解释。估计的刚度参数与无规立构聚（甲基丙烯酸甲酯）（一种柔性链）的刚度参数相当，这与M（w）大于10（5）时的[S2]z和[eta]数据得出的上述结论一致。 发现在无限分子量下的特征比约为5，该值接近于水性直链淀粉的报道值。由此进一步得出结论，在没有排斥体积效应的情况下，高分子量直链淀粉在水和DMSO中的构象是相似的。
The conformation of amylose in dimethyl sulfoxide (DMSO) at 25-degrees-C is studied by light scattering, sedimentation equilibrium, and viscosity measurements on narrow-distribution samples of amylose and its oligomers covering a broad range of weight-average molecular weight M(w) from 342 (the dimer) to 1.7 x 10(6). For M(w) above 10(5), the z-average mean-square radius of gyration [S2]z and the intrinsic viscosity [eta] vary as M(w)1.2 and M(w)0.7, respectively, indicating that in this molecular weight region, the amylose chain behaves as a random coil expanded by excluded-volume effect. Below M(w) approximately 10(4), [eta] exhibits an unusually weak dependence on M(w) and finally becomes almost independent of molecular weight. This behavior of [eta] is explained by solvation of DMSO molecules and some helical nature of the amylose chain on the basis of the theory of Yoshizaki et al. for unperturbed helical wormlike chains. The estimated stiffness parameter is comparable to that for atactic poly(methyl methacrylate), a flexible chain, being consistent with the above conclusion from the [S2]z and [eta] data for M(w) above 10(5). The characteristic ratio at infinite molecular weight is found to be about 5, a value close to the reported values for aqueous amylose. Thus it is further concluded that without excluded-volume effect, the conformations of high molecular weight amylose in water and DMSO are similar.