Center of Smart Interfaces, Technische Universität Darmstadt, Petersenstrasse 32, 64287 Darmstadt, Germany.
J Phys Chem B. 2011 Nov 24;115(46):13781-7. doi: 10.1021/jp208583w. Epub 2011 Oct 28.
Dissolved electrolytes interact with peptides and proteins in aqueous solution. Herein, we study small amide compounds in aqueous electrolyte solutions and link their salting-in and salting-out propensities to molecular-level structural details obtained with molecular simulations. Aqueous solutions of NaF, NaCl, NaBr, NaI, NaNO(3), and NaClO(4) with N-isopropylacrylamide (NiPAM) and N-methylacetamide (NMA) have been investigated. Our results show that NiPAM is salted-in by NaI, mediated through iodide interactions with nonpolar groups, while being salted-out by the other salts. Hydrogen-bonding interactions of anions with the amide group of NiPAM could not be identified, while in the systems with NMA all Hofmeister anions formed stable hydrogen bonds with the amide group. These results indicate that the immediate chemical environment of the backbone amide groups should be considered in studies of protein destabilization by dissolved electrolytes. We furthermore report that all salts but NaI provoke a hydrophobic collapse transition of poly(N-isopropylacrylamide) in water at 300 K, in qualitative agreement with experimentally measured salt effects on the lower critical solution temperature of this system.
溶解的电解质在水溶液中与肽和蛋白质相互作用。在此，我们研究了水溶液中的小酰胺化合物，并将它们的盐溶和盐析倾向与通过分子模拟获得的分子水平结构细节联系起来。研究了含 N-异丙基丙烯酰胺（NiPAM）和 N-甲基乙酰胺（NMA）的 NaF、NaCl、NaBr、NaI、NaNO(3) 和 NaClO(4)的水溶液。我们的结果表明，碘化钠通过与非极性基团的碘相互作用使 NiPAM 盐溶，而其他盐则使 NiPAM 盐析。阴离子与 NiPAM 酰胺基团的氢键相互作用无法确定，而在 NMA 体系中，所有的 Hofmeister 阴离子都与酰胺基团形成稳定的氢键。这些结果表明，在研究溶解电解质对蛋白质的失稳作用时，应考虑到肽链酰胺基团的直接化学环境。此外，我们还报告说，除了 NaI 之外的所有盐都会在 300 K 时引发聚（N-异丙基丙烯酰胺）在水中的疏水塌陷转变，这与实验测量的该体系下临界溶液温度的盐效应定性一致。
