Department of Chemistry, University of Oregon, Eugene, Oregon 97403, United States.
Langmuir. 2012 Oct 9;28(40):14245-53. doi: 10.1021/la302917p. Epub 2012 Sep 28.
The accumulation of polyelectrolytes at the interface between water and nonpolar fluids is an important process in both environmental and biological systems. For instance, polyelectrolytes such as humic acids are highly charged molecules that play a role in the remediation of water contaminated by oil, and the adsorption of other polyelectrolytes such as proteins and DNA to cellular surfaces is essential in biological processes. The properties of these naturally occurring polyelectrolytes are highly tunable and depend strongly on the binding of metal ions commonly found in environmental and biological systems. While the metal complexation behaviors of many polyelectrolytes and biomolecules are well characterized in bulk solution, this work shows in molecular detail that the behavior of a common polyelectrolyte in the presence of metal ions can be quite different when it adsorbs to a hydrophobic-aqueous liquid interface. In these studies, vibrational sum frequency spectroscopy and interfacial tension measurements conducted on poly(acrylic acid) (PAA) at a model oil-water interface show how small amounts of monovalent and divalent cations significantly alter the interfacial conformation of PAA at the interface and act to enhance its interfacial adsorption. The results provide important new insights that have direct relevance for understanding the effect of metal ions on the adsorption of charged macromolecules to a hydrophobic-aqueous boundary layer, specifically in biological and environmental systems.
聚电解质在水和非极性流体界面的积累是环境和生物系统中都很重要的过程。例如，腐殖酸等聚电解质是带高电荷的分子，它们在修复受油污染的水方面发挥着作用，而其他聚电解质（如蛋白质和 DNA）吸附到细胞表面对于生物过程来说也是必不可少的。这些天然聚电解质的性质具有很强的可调节性，强烈依赖于在环境和生物系统中常见的金属离子的结合。虽然许多聚电解质和生物分子的金属络合行为在本体溶液中得到了很好的描述，但这项工作从分子细节上表明，当常见的聚电解质吸附到疏水性-水界面时，其在金属离子存在下的行为可能会有很大的不同。在这些研究中，在模型油水界面上对聚丙烯酸（PAA）进行的振动和频光谱和界面张力测量表明，少量单价和二价阳离子如何显著改变 PAA 在界面处的界面构象，并起到增强其界面吸附的作用。这些结果提供了重要的新见解，对于理解金属离子对带电荷的大分子在疏水性-水边界层的吸附的影响具有直接的相关性，特别是在生物和环境系统中。
