Strong adsorption of guanidinium cations to the air-water interface

• 成果类型: Article
• 署名作者: Bernal, Franky; Dodin, Amro; Kyprianou, Constantine; Limmer, David T.; Saykally, Richard J.
• 署名单位: University of California System; University of California Berkeley; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10845
• DOI: 10.1073/pnas.2418443122
• 发表日期: 2025-01-14
• 关键词: molecular-dynamics simulation; 2nd harmonic-generation; 2nd-harmonic generation; thiocyanate anions; surface-tension; solvation; ions; charge; spectroscopy; hydration

摘要

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.