Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces,ACS Earth and Space Chemistry

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Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-09-07 , DOI: 10.1021/acsearthspacechem.1c00272
Nicole C. Auvil ₁ , Maria G. Vazquez de Vasquez ₁ , Heather C. Allen ₁

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Organic coatings on sea spray aerosol are largely comprised of fatty acids in addition to a vast array of other organic molecules including fatty alcohols. The seawater from which sea spray aerosol originates contains metal ions that interact with the organic coating at the air–seawater interface, resulting in transport of these metals into the atmosphere. Metal binding within single-substance monolayers on aqueous solutions has been previously studied. However, such binding events within mixed monolayers, especially those of ocean-relevant ratios, are not well-explored. Here, we examine four monolayer ratios of octadecanoic acid (stearic acid) to octadecanol (stearyl alcohol) on aqueous solutions with varying ZnCl₂ concentrations and a seawater-relevant NaCl concentration of 0.465 M. Surface pressure–area (Π-A) isotherms and infrared reflection–absorption spectroscopy (IRRAS) are used to quantify the Zn²⁺–carboxylate surface binding affinities for each monolayer composition. We find that Zn²⁺–carboxylate binding is enhanced by ∼300 times at the surface when compared to the bulk solution. Addition of 10% octadecanol reduces the apparent surface binding affinity by over 50% from 3.6 × 10³ to 1.4 × 10³ M^–1; this is significantly more than predicted from the slight reduction in viable 1:1 binding sites. Furthermore, 1:2 Zn²⁺–carboxylate binding is shown to only be viable for the 100 and 95% fatty acid film, whereas 1:1 binding is observed for all film ratios investigated.

中文翻译：

代理海水溶液表面上混合十八烷酸和十八烷醇单层中的锌-羧酸盐结合

除了包括脂肪醇在内的大量其他有机分子外，海喷雾气溶胶上的有机涂层主要由脂肪酸组成。产生海喷雾气溶胶的海水含有金属离子，这些金属离子与空气-海水界面处的有机涂层相互作用，导致这些金属迁移到大气中。先前已经研究了水溶液上单物质单层内的金属结合。然而，混合单层内的这种结合事件，尤其是与海洋相关的比率，还没有得到很好的探索。在这里，我们检查了具有不同 ZnCl _{2 的}水溶液中十八烷酸（硬脂酸）与十八烷醇（硬脂醇）的四种单层比率浓度和与海水相关的 NaCl 浓度为 0.465 M。表面压力 - 面积 (Π-A) 等温线和红外反射 - 吸收光谱 (IRRAS) 用于量化每个单层组合物的 Zn ²⁺ - 羧酸盐表面结合亲和力。我们发现与本体溶液相比，Zn ²⁺ -羧酸盐在表面的结合增强了约 300 倍。添加 10% 十八醇使表观表面结合亲和力从 3.6 × 10 ³降低 50% 以上至 1.4 × 10 ³ M ^–1；这大大超过了根据可行的 1:1 结合位点的轻微减少所预测的。此外，1:2 Zn ²⁺– 羧酸盐结合仅对 100% 和 95% 脂肪酸膜有效，而对所有研究的膜比率观察到 1:1 结合。

更新日期：2021-10-22

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