Horinaka Jun-Ichi, Kani Kohei, Honda Haruhiko, Uesaka Yoko, Kawamura Takanobu
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto 615-8510, Japan.
Macromol Biosci. 2004 Aug 9;4(8):714-20. doi: 10.1002/mabi.200400067.
The local chain mobility of a gellan, an electrolyte polysaccharide, in aqueous systems was examined with respect to the effect of the temperature, the concentration of gellan (c(G)), and the concentration of added salt (c(S)). The relaxation time of local motion was estimated for fluorescein isothiocyanate (FITC)-labeled-gellan by the fluorescence depolarization technique, and the chain mobility was discussed. The relaxation time increased with decreasing temperature, in particular when accompanying the coil-helix transition due to the great difference in chain mobility between the coil and the helical conformations. The effect of c(G) was observed for gellan solutions even below the critical concentration of chain entanglement (2 wt.-%) for well-expanded nonelectrolyte polymers with size similar to that of the gellan. This suggests that the actual excluded volume of gellan is larger than that of nonelectrolyte polymers due to the electrostatic repulsion between segments. The relaxation time for 0.2 wt.-% systems of gellan in coil conformation is independent of c(S), whereas a c(S) dependence of the relaxation time is clearly observed for 0.5 wt.-% systems. The degree of expansion of the gellan chain is independent of the shielding effect of cations on the electrostatic repulsion between gellan segments due to the stiffness of gellan chain. On the other hand, the c(G) as well as the c(S) dependence of the chain mobility is clearly observed for gellan in the helical conformation, examined over the concentration range, probably due to the partial aggregation of helices induced by the attractive interaction between gellan segments.
就温度、结冷胶浓度（c(G)）和添加盐浓度（c(S)）的影响，对一种电解质多糖——结冷胶在水性体系中的局部链段流动性进行了研究。通过荧光去极化技术估算了异硫氰酸荧光素（FITC）标记的结冷胶局部运动的弛豫时间，并对链段流动性进行了讨论。弛豫时间随温度降低而增加，特别是当伴随着由于线圈构象和螺旋构象之间链段流动性差异很大而导致的线圈-螺旋转变时。即使在结冷胶溶液浓度低于链缠结临界浓度（2 wt.-%）时，对于尺寸与结冷胶相似的充分伸展的非电解质聚合物，也观察到了c(G)的影响。这表明，由于链段间的静电排斥作用，结冷胶的实际排除体积大于非电解质聚合物。对于处于线圈构象的0.2 wt.-%结冷胶体系，弛豫时间与c(S)无关，而对于0.5 wt.-%体系，弛豫时间对c(S)的依赖性则明显可见。由于结冷胶链的刚性，结冷胶链的伸展程度与阳离子对结冷胶链段间静电排斥的屏蔽效应无关。另一方面，在整个浓度范围内对处于螺旋构象的结冷胶进行研究时，明显观察到链段流动性对c(G)以及c(S)的依赖性，这可能是由于结冷胶链段间的吸引相互作用导致螺旋部分聚集所致。
