Carboxylate Ion Availability at the Air-Water Interface
Carboxylate Ion Availability at the Air-Water Interface
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DOI：
10.1021/acs.jpca.6b08868
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发表时间：
2016-11-24
影响因子：
2.9
通讯作者：
Kajii, Yoshizumi
中科院分区：
文献类型：
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作者：
Enami, Shinichi;Fujii, Tomihide;Kajii, Yoshizumi
气-水界面上的两亲性有机物在大气气溶胶的成核、生长和老化过程中起着关键作用。表面活性物质预计将优先与大气中的氧化剂，如OH自由基，在空气-水界面通过特定的机制。然而，在大气相关条件下，建立不同两亲性物质在空气-水界面处对气相氧化剂的相对可用性是具有挑战性的。在这里，我们报告了大气相关的羧酸根离子R-n-COO-（n = 1-7）和n-，环状，芳香族-R-6-COO-在空气-水界面的界面可用性，通过一种新的应用质谱的水微射流。微射流的破碎机制，让我们确定在环境条件下，在1 μ M至1 mM范围内的相应的羧酸的等摩尔溶液中的羧酸根离子的相对界面亲和力。我们发现，除了在R-1-COO-的情况下，R-n-COO-的界面亲和力增加指数链长和溶剂可及表面积（SASA）。测定了正庚酸酯（n-R-6-COO-）>环己烷羧酸酯（c-R-6-COO-）>苯甲酸酯（Ar-R-6-COO-）的相对界面亲和力。我们将三种羧酸根离子中Ar-R-6-COO-在空气-水界面处的最小可用性归因于芳环与水分子之间的强π-H键合。羧酸根离子在空气-水界面的可用性的分子机制和大气的影响进行了讨论。
Amphiphilic organic compounds at the air-water interface play key roles in the nucleation, growth, and aging process of atmospheric aerosol. Surface-active species are expected to react preferentially with atmospheric oxidants, such as the OH radical, at the air-water interface via specific mechanisms. Establishing the relative availability of the different amphiphilic species to gas-phase oxidants at the air-water interface under atmospherically relevant conditions is, however, challenging. Here we report the interfacial availability of atmospherically relevant carboxylate ions R-n-COO- (n = 1-7) and n-, cyclo-, aromatic-R-6-COO- at the air-water interface via a novel application of mass spectrometry of aqueous microjets. The breakup mechanism of microjets lets us determine the relative interfacial affinities of carboxylate ions in equimolar solutions of the corresponding carboxylic acids in the 1 mu M to 1 mM range under ambient conditions. We find that the interfacial affinity of R-n-COO- increases exponentially with both chain-length and solvent-accessible surface area (SASA) except in the case of R-1-COO-. The relative interfacial affinities for n-heptanoate (n-R-6-COO-) > cyclohexanecarboxylate (c-R-6-COO-) > benzoate (Ar-R-6-COO-) are also determined. We attribute the smallest availability of Ar-R-6-COO- at the air-water interface among the three carboxylate ions to a strong pi-H bonding between the aromatic ring and water molecule. Molecular mechanisms on the availability of carboxylate ions at the air-water interface and the atmospheric implications are discussed.