Mangione M R, Giacomazza D, Bulone D, Martorana V, San Biagio P L
CNR-IBF at Palermo, and DCTF, University of Palermo, Italy.
Biophys Chem. 2003 May 1;104(1):95-105. doi: 10.1016/s0301-4622(02)00341-1.
We have studied, by optical rotation dispersion, light scattering and rheology, the kappa-Carrageenan system to elucidate the processes involved in gel formation (on decreasing the temperature) and gel melting (on increasing the temperature). Our results show that, on decreasing the temperature, a conformational transition from coils to double helices first occurs, followed by aggregation of the double helices into domains and gel formation at appropriate polymer concentration. Structural details of this sequence are better revealed by re-heating the system. Melting appears as a two-step process characterized by first a conformational change of helices involved in junction zones between aggregates, followed by the conformational transition of the helices inside the aggregates. These helices can regain the coil conformation only when the aggregates melt at higher temperature, in full agreement with the old 'domain' model. The full description of the sol-gel mechanism of this system can be useful in the search for new methods to control the gel texture, a relevant property for many industrial applications.
我们通过旋光色散、光散射和流变学方法研究了κ-卡拉胶体系，以阐明凝胶形成过程（降温时）和凝胶熔化过程（升温时）中所涉及的机制。我们的研究结果表明，降温时，首先会发生从卷曲构象到双螺旋构象的转变，随后双螺旋聚集成区域，并在适当的聚合物浓度下形成凝胶。通过重新加热该体系，能更好地揭示这一过程的结构细节。熔化表现为一个两步过程，其特征首先是聚集体间连接区域的螺旋构象发生变化，随后聚集体内部的螺旋构象发生转变。只有当聚集体在更高温度下熔化时，这些螺旋才能恢复为卷曲构象，这与旧的“区域”模型完全一致。对该体系溶胶-凝胶机制的完整描述，可能有助于寻找控制凝胶质地的新方法，而凝胶质地是许多工业应用中的一个重要特性。
