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首页> 外文期刊>Polymers >Thermodynamic Analysis of the Conformational Transition in Aqueous Solutions of Isotactic and Atactic Poly(Methacrylic Acid) and the Hydrophobic Effect
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Thermodynamic Analysis of the Conformational Transition in Aqueous Solutions of Isotactic and Atactic Poly(Methacrylic Acid) and the Hydrophobic Effect

机译：等规和无规聚甲基丙烯酸水溶液的构象转变热力学分析及疏水作用

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摘要

The affinity of amphiphilic compounds for water is important in various processes, e.g., in conformational transitions of biopolymers, protein folding/unfolding, partitioning of drugs in the living systems, and many others. Herein, we study the conformational transition of two isomer forms of poly(methacrylic acid) (PMA), isotactic (iPMA) and atactic (aPMA), in water. These isomers are chemically equivalent and differ only in the arrangement of functional groups along the chain. A complete thermodynamic analysis of the transition of the PMA chains from the compact to the extended form (comprising the conformational transition) in water in the presence of three alkali chlorides is conducted by determining the free energy, enthalpy, and entropy changes of the process as a function of temperature, and therefrom also the heat capacity change. The heat capacity change of the transition is positive (+20 J/K mol) for aPMA and negative (?50 J/K mol) for iPMA. This result suggests a different affinity of PMA isomers for water. The conformational transition of iPMA is parallel to the transfer of polar solutes into water, whereas that of aPMA agrees with the transfer of nonpolar solutes into water.
机译：两亲化合物对水的亲和力在各种过程中都很重要，例如，在生物聚合物的构象转变，蛋白质折叠/解折叠，药物在生命系统中的分配以及许多其他过程中。在本文中，我们研究了两种异构体形式的聚甲基丙烯酸（PMA）在水中的等规构象（iPMA）和无规构象（aPMA）的构象转变。这些异构体在化学上是等价的，并且仅在沿着链的官能团的排列上不同。在存在三种碱金属氯化物的情况下，对水中PMA链从致密物到扩展形式（包括构象转变）的转变进行完整的热力学分析，方法是确定该过程的自由能，焓和熵变随温度变化，热容也随之变化。转变的热容量变化对aPMA为正（+20 J / K mol），对iPMA为负（？50 J / K mol）。该结果表明PMA异构体对水具有不同的亲和力。 iPMA的构象转变与极性溶质向水中的转移平行，而aPMA的构象转变与非极性溶质向水中的转移相一致。

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