Local chain mobility of gellan in aqueous systems studied by fluorescence depolarization.
Local chain mobility of gellan in aqueous systems studied by fluorescence depolarization.
复制标题
DOI：
10.1002/mabi.200400067
复制
发表时间：
2004-08
影响因子：
4.6
通讯作者：
J. Horinaka;K. Kani;Haruhiko Honda;Yoko Uesaka;T. Kawamura
中科院分区：
文献类型：
--
作者：
J. Horinaka;K. Kani;Haruhiko Honda;Yoko Uesaka;T. Kawamura
研究了水溶液体系中结冷胶（一种电解质多糖）的局部链迁移率，考察了温度、结冷胶浓度（c(G)）和添加盐浓度（c(S)）的影响。用荧光去极化技术估计了异硫氰酸荧光素标记结冷胶的局部运动弛豫时间，并讨论了链迁移率。随着温度的降低，弛豫时间增加，特别是当线圈-螺旋转变时，由于线圈和螺旋构象之间的链迁移率差异很大。c(G)对结冷胶溶液的影响甚至低于临界链缠结浓度（2 wt.-%），对尺寸与结冷胶相似的膨胀良好的非电解质聚合物也有影响。这表明结冷胶的实际排除体积比非电解质聚合物大，这是由于节段之间的静电排斥。0.2 wt.-%盘状结冷胶体系的弛豫时间与c(S)无关，而0.5 wt.-%体系的弛豫时间与c(S)有明显的相关性。由于结冷胶链的刚度，阳离子对结冷胶段间静电斥力的屏蔽作用与结冷胶链的膨胀程度无关。另一方面，c(G)和c(S)对链迁移率的依赖在螺旋构象中被清楚地观察到，在浓度范围内检查，可能是由于结冷胶片段之间的吸引相互作用引起的部分螺旋聚集。
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.