Thermal behavior and kinetic analysis of the chain unfolding and refolding and of the concomitant nonpolar solvation and desolvation of two elastin-like polymers
Thermal behavior and kinetic analysis of the chain unfolding and refolding and of the concomitant nonpolar solvation and desolvation of two elastin-like polymers
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DOI：
10.1021/ma034572q
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发表时间：
2003-11-04
期刊：
影响因子：
5.5
通讯作者：
Rodríguez-Cabello, JC
中科院分区：
文献类型：
--
作者：
Reguera, J;Lagarón, JM;Rodríguez-Cabello, JC
水诱导的链动力学改变在许多蛋白质基聚合物中是至关重要的，因为它们在很大程度上决定和影响最终性质的温度依赖性。本文采用差示扫描量热法（DSC）和比浊法研究了聚（Val-Pro-Gly-Val-Gly）和聚（Val-Pro-Ala-Val-Gly）的可逆去折叠和再折叠以及同时发生的脱水和水合过程的热行为。与聚（Val-Pro-Gly-Val-Gly）显示的良好可逆性相反，聚（Val-Pro-Ala-Val-Gly）中甘氨酸被丙氨酸取代在很大程度上扰乱了链解折叠过程。对于后者的聚合物，人们发现，这两个链展开和再水化过程发生在大的过冷度，这表明这两个事件发生远离平衡条件，因此，强烈主导的动力学。在这种情况下，具有动力学性质而不是热力学性质的水合过量的存在是一个显著的观察结果。还通过使用动力学分析的等转化率方法研究了折叠和去折叠的动力学，即，Friedmand等转化率方法正如预期的那样，两种聚合物的非极性部分的溶剂化的动力学表明一个复杂的和多步骤的过程。同样，聚（Val-Pro-Ala-Val-Gly）显示出完全不同的模式，其特征在于急性滞后行为，这似乎决定了该聚合物的水合过程。这两种聚合物之间观察到的差异已被解释在温度诱导的链动力学过程中由丙氨酸中的甲基基团提供的阻碍。
Water-induced chain dynamics alterations are of paramount importance in many protein-based polymers because they determine and affect to a great extent the temperature dependence of the end properties. In this study, the thermal behavior of the reversible unfolding and refolding of poly(Val-Pro-Gly-Val-Gly) and poly(Val-Pro-Ala-Val-Gly) and of their concurrent dehydration and hydration processes has been studied by differential scanning calorimetry (DSC) and turbidimetry. Contrary to the good reversibility shown by poly(Val-Pro-Gly-Val-Gly), the substitution of glycine by alanine in poly(Val-Pro-Ala-Val-Gly) perturbed to a large extent the process of chain unfolding. For the latter polymer, it was found that both chain unfolding and rehydration processes take place at large undercoolings, suggesting that both events occur far from equilibrium conditions and, therefore, are strongly dominated by kinetics. In this context, the existence of an hydration excess with a kinetic rather than a thermodynamic nature is a remarkable observation. The kinetics of folding and unfolding were also studied by using an isoconversional method of kinetic analysis, i.e., the model-free Friedmand's isoconversional method. As expected, the kinetics of the solvation of nonpolar moieties for both polymers indicated a complex and multistep process. Again, poly(Val-Pro-Ala-Val-Gly) showed a quite different pattern characterized by an acute hysteresis behavior which seems to govern the hydration process for this polymer. The differences observed between both polymers have been interpreted in terms of the hindrance provided by the methyl group in alanine during temperature-induced chain dynamics.