Ionic state and chain conformation for aqueous solutions of supergiant cyanobacterial polysaccharide.
Ionic state and chain conformation for aqueous solutions of supergiant cyanobacterial polysaccharide.
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DOI：
10.1103/physreve.87.042607
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发表时间：
2013-04
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影响因子：
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通讯作者：
T. Mitsumata;T. Miura;Natsuki Takahashi;M. Kawai;M. Okajima;T. Kaneko
中科院分区：
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作者：
T. Mitsumata;T. Miura;Natsuki Takahashi;M. Kawai;M. Okajima;T. Kaneko
研究了蓝藻大分子sacran（分子量为1.6×10（7）g/mol）水溶液的电导率、介电弛豫行为和粘度。Sacran是在糖链上具有羧酸根和硫酸根基团的阴离子型淀粉。电导率和零剪切粘度在0.004、0.02和0.1重量%下表现出三个交叉浓度。发现粘度随着骶骨聚糖浓度的增加按~c（1.5）、~c（0.5）、~c（1.5）和~c（3.0）标度。在0.1重量%时，骶骨链形成弱凝胶，其表现出包括纹影织构的宏观液晶域。因此，这些交叉浓度分别被认为是重叠浓度、缠结浓度和凝胶化浓度（或临界缠结浓度）。介电弛豫分析表明，sacran具有两种类型的反离子，具有不同的反离子-聚离子相互作用，即，强束缚和松束缚抗衡离子。介电参数如弛豫时间或弛豫强度对缠结浓度和凝胶浓度都敏感，但对重叠浓度不敏感。由弛豫强度计算的束缚反离子数密度表明，随着sacran浓度的增加，反离子凝聚在sacran链上。骶骨链的电荷密度的降低降低了链之间的排斥力，这将导致螺旋转化或凝胶化行为。结合聚电解质和液晶行为，讨论了骶骨聚糖在纯水中的链构象和凝胶化机理。
We have investigated the electric conductivity, dielectric relaxation behavior, and viscosity for the aqueous solution of cyanobacterial megamolecules, molecular weight =1.6×10(7) g/mol, named sacran. Sacran is an anionic polyelectrolyte which has carboxylate and sulfate groups on the saccharide chain. The electric conductivity and the zero shear viscosity demonstrated three crossover concentrations at 0.004, 0.02, and 0.1 wt%. The viscosity was found to be scaled as ~c(1.5), ~c(0.5), ~c(1.5), and ~c(3.0) with increasing the sacran concentration. At 0.1 wt%, the sacran chain formed a weak gel which exhibits macroscopic liquid crystal domains including Schlieren texture. Therefore, these crossover concentrations are considered to be the overlap concentration, entanglement concentration, and gelation concentration (or critical polyelectrolyte concentration), respectively. Dielectric relaxation analysis exhibited the fact that sacran has two types of counterions with different counterion-polyion interaction, i.e., strongly bound and loosely bound counterions. The dielectric parameters such as relaxation time or relaxation strength are sensitive to both the entanglement concentration and the gelation concentration, but not the overlap concentration. The number density of bound counterions calculated from the relaxation strength revealed that the counterion is condensed on the sacran chain with raising the sacran concentrations. The decrease in the charge density of the sacran chain reduces the repulsive force between the chains and this would cause the helix transformation or gelation behavior. The chain conformation of sacran in pure water and the gelation mechanism are discussed in relation with the behavior of polyelectrolytes and liquid crystals.