Piculell L, Borgström J, Chronakis I S, Quist P O, Viebke C
Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, Sweden.
Int J Biol Macromol. 1997 Aug;21(1-2):141-53. doi: 10.1016/s0141-8130(97)00054-8.
Mixtures of the added salts NaI and CsI can be used to gradually 'tune' the propensity of kappa-carrageenan (KC) helices to aggregate in solution. We show that this method can be used to resolve the molecular events by which helix formation, under certain conditions, leads to gelation. We also present an overview of the various states of aggregation and organisation that appear for helical KC (non-degraded or ultrasonically degraded) when the NaI/CsI ratio and the concentration of KC are varied. A transition to rigid, superhelical rods is found above a well-defined fraction of cesium. This transition is reflected in a range of experimental measurements, such as cryo-transmission electron microscopy, optical rotation, viscometry and small deformation oscillatory measurements. The superhelical-rod state also seems essential for the association of KC with locust bean gum, and locust bean gum is found to stabilise this state. Novel states of KC alone have been found at cesium contents below the transition threshold. Non-degraded KC forms weak gels at sufficiently high concentrations (> ca. 1%). In contrast, ultrasonically degraded KC forms a chiral nematic liquid crystalline phase at sufficiently high concentrations (> ca. 5%) under these salt conditions.
添加的碘化钠（NaI）和碘化铯（CsI）混合物可用于逐步“调节”κ-卡拉胶（KC）螺旋在溶液中聚集的倾向。我们表明，该方法可用于解析在某些条件下螺旋形成导致凝胶化的分子事件。我们还概述了在改变NaI/CsI比例和KC浓度时，螺旋状KC（未降解或超声降解）出现的各种聚集和组织状态。在铯含量达到明确比例以上时，会发现向刚性超螺旋棒的转变。这种转变反映在一系列实验测量中，如低温透射电子显微镜、旋光性、粘度测定和小变形振荡测量。超螺旋棒状态似乎对于KC与刺槐豆胶的缔合也至关重要，并且发现刺槐豆胶可稳定这种状态。在铯含量低于转变阈值时，已发现单独的KC存在新状态。未降解的KC在足够高的浓度（>约1%）下形成弱凝胶。相比之下，在这些盐条件下，超声降解的KC在足够高的浓度（>约5%）下形成手性向列相液晶相。
