Bernal Franky, Dodin Amro, Kyprianou Constantine, Limmer David T, Saykally Richard J
Department of Chemistry, University of California, Berkeley, CA 94720.
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2418443122. doi: 10.1073/pnas.2418443122. Epub 2025 Jan 10.
Combining Deep-UV second harmonic generation spectroscopy with molecular simulations, we confirm and quantify the specific adsorption of guanidinium cations to the air-water interface. Using a Langmuir analysis of measurements at multiple concentrations, we extract the Gibbs free energy of adsorption, finding it larger than typical thermal energies. Molecular simulations clarify the role of polarizability in tuning the thermodynamics of adsorption, and establish the preferential parallel alignment of guanidinium at the air-water interface. As a polyatomic cation, guanidinium represents one of the few examples of a positively charged species to exhibit a propensity for the air-water interface. As such, these results expand on the growing body of work on specific ion adsorption.
结合深紫外二次谐波产生光谱和分子模拟，我们证实并量化了胍阳离子在气-水界面的特异性吸附。通过对多个浓度下测量数据的朗缪尔分析，我们提取了吸附的吉布斯自由能，发现其大于典型的热能。分子模拟阐明了极化率在调节吸附热力学中的作用，并确定了胍在气-水界面的优先平行排列。作为一种多原子阳离子，胍是少数表现出倾向于气-水界面的带正电物种的例子之一。因此，这些结果扩展了关于特定离子吸附的不断增长的研究工作。
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