Colorado State University, Fort Collins, Colorado 80523, United States.
J Phys Chem B. 2010 Dec 16;114(49):16594-604. doi: 10.1021/jp105652c. Epub 2010 Nov 22.
Classical molecular dynamics simulations were performed to investigate the effects of salt on the lower critical solution temperature (LCST) of Poly (N-isopropylacrylamide) (PNIPAM). PNIPAM is often studied as a protein proxy due to the presence of a peptide bond in its monomer unit. PNIPAM is a temperature sensitive polymer which exhibits hydrophobic-hydrophilic phase transition at its LCST. The presence of salt in the solution will shift its LCST, typically to a lower temperature. This LCST shift follows the so-called Hofmeister series. Molecular dynamics (MD) simulations of PNIPAM in 1 M of NaCl, NaBr, NaI, and KCl were carried out to elucidate the effects of different salt on LCST and protein stability. Our results suggest that direct interactions between the salt cations and the polymer play a critical role in the shift of LCST and subsequently on protein stability. Further, cations have a much stronger affinity with the polymer, whereas anions bind weakly with the polymer. Moreover, the cation-polymer binding affinity is inversely correlated with the cation-anion contact pair association constant in solution.
采用经典分子动力学模拟研究了盐对聚（N-异丙基丙烯酰胺）（PNIPAM）的低临界溶液温度（LCST）的影响。由于其单体单元中存在肽键，PNIPAM 常被用作蛋白质的模拟物。PNIPAM 是一种温度敏感聚合物，在其 LCST 处表现出疏水性-亲水性相转变。溶液中盐的存在会使其 LCST 发生移动，通常会降低温度。这种 LCST 移动遵循所谓的 Hofmeister 序列。对 1 M 的 NaCl、NaBr、NaI 和 KCl 中的 PNIPAM 进行了分子动力学（MD）模拟，以阐明不同盐对 LCST 和蛋白质稳定性的影响。我们的结果表明，盐阳离子与聚合物之间的直接相互作用在 LCST 的移动以及随后的蛋白质稳定性方面起着关键作用。此外，阳离子与聚合物的亲和力更强，而阴离子与聚合物的结合力较弱。此外，阳离子-聚合物结合亲和力与溶液中阳离子-阴离子接触对缔合常数呈反比关系。
