Amino Acids Are Driven to the Interface by Salts and Acidic Environments
Kyle J. Angle, Christopher M. Nowak, Aakash Davasam, Abigail C. Dommer, Nicholas Wauer, Rommie E. Amaro, Vicki H. Grassian
Abstract
Amino acids (AAs), the building blocks of proteins, are enriched by several orders of magnitude in sea spray aerosols compared to ocean waters. This suggests that AAs may reside at the air–water interface and be highly surface active. Using surface tension measurements, infrared reflection–absorption spectroscopy, and molecular dynamics simulations, we show that AAs are surface active and that salts and low-pH environments are drivers of surface activity. At typical sea spray salt concentrations and pH values, we determine that the surface coverage of hydrophobic AAs increases by approximately 1 order of magnitude. Additionally, divalent cations such as Ca2+ and Mg2+ can further increase AA surface propensity, particularly at neutral pH. Overall, these results indicate that AAs are likely to be found at increased concentrations at the surface of sea spray aerosols, where they can impact the cloud activation properties of the aerosol and enhance peptide formation under certain conditions.