Publication - Journal Article Molecular-level origin of the carboxylate head group response to divalent metal ion complexation at the air–water interface

Proceedings of the National Academy of Sciences, vol. 116, iss. 30, pp. 14874-14880, 2019

Joanna K. Denton, Patrick J. Kelleher, Mark A. Johnson, Marcel D. Baer, Shawn M. Kathmann, Christopher J. Mundy, Bethany A. Wellen Rudd, Heather C. Allen, Tae Hoon Choi, Kenneth D. Jordan

Significance The transport of divalent metal ions (e.g., Mg 2+ and Ca 2+ ) into the troposphere is thought to arise from preferential complexation with anionic head groups of fatty acids at sea-spray aerosol surfaces. Attempts to quantify the formation of these complexes by monitoring the vibrational frequencies of the CO stretching vibrations have proven to be inconclusive, however, because the metal ion-driven spectral response is surprisingly similar to that displayed by the fully hydrated anion. We trace the origin of these spectral responses by measuring the stepwise hydration behaviors of both the carboxylate head group and the contact ion pair. These trends reveal the critical contribution of chain deformation to the structural interpretation of surface-sensitive spectral signatures of ion complexation at the interface.