Pica Andrea, Graziano Giuseppe
Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia - 80126, Naples, Italy.
Phys Chem Chem Phys. 2015 Nov 7;17(41):27750-7. doi: 10.1039/c5cp04094a.
It has been shown that sodium salts significantly affect the temperature of the coil-to-globule collapse transition of poly(N-isopropylacrylamide) [J. Am. Chem. Soc., 2005, 127, 14505]. Since this phenomenon resembles the cold renaturation of globular proteins, it can be studied by means of the theoretical approach devised to rationalise the occurrence and the mechanism of cold denaturation [G. Graziano, Phys. Chem. Chem. Phys., 2010, 12, 14245; Phys. Chem. Chem. Phys., 2014, 16, 21755]. It emerges that the collapse transition is driven by the decrease in the solvent-excluded volume in order to maximise the translational entropy of water molecules and ions. At a given temperature, the aqueous solutions of sodium salts have densities higher than that of water. For this reason, the magnitude of the solvent-excluded volume effect proves to be larger, stabilizing the globular conformations of poly(N-isopropylacrylamide). On the other hand, two large ions, iodide and thiocyanate, are poorly hydrated and stabilise the coil conformations of the polymer by a preferential binding mechanism.
已表明钠盐会显著影响聚（N - 异丙基丙烯酰胺）从线圈状到球状的塌陷转变温度[《美国化学会志》，2005年，127卷，14505页]。由于这种现象类似于球状蛋白质的冷复性，所以可以通过设计用于合理解释冷变性的发生和机制的理论方法来研究它[G. 格拉齐亚诺，《物理化学化学物理》，2010年，12卷，14245页；《物理化学化学物理》，2014年，16卷，21755页]。结果表明，塌陷转变是由溶剂排除体积的减小驱动的，目的是使水分子和离子的平动熵最大化。在给定温度下，钠盐的水溶液密度高于水的密度。因此，溶剂排除体积效应的大小被证明更大，从而稳定了聚（N - 异丙基丙烯酰胺）的球状构象。另一方面，两种大离子，即碘离子和硫氰酸根离子，水合程度低，并通过优先结合机制稳定聚合物的线圈状构象。
