title: Surface Propensity of Atmospherically Relevant Amino Acids Studied by XPS.
abstract: Amino acids constitute an important fraction of the water-soluble organic nitrogen (WSON) compounds in aerosols and are involved in many processes in the atmosphere. In this work, we applied X-ray photoelectron spectroscopy (XPS) to study aqueous solutions of four amino acids, glycine, alanine, valine, and methionine, in their zwitterionic forms. We found that amino acids with hydrophilic side chains and smaller size, GLY and ALA, tend to stay in the bulk of the liquid, while the hydrophobic and bigger amino acids, VAL and MET, are found to concentrate more on the surface. We found experimental evidence that the amino acids have preferential orientation relative to the surface, with the hydrophobic side chain being closer to the surface than the hydrophilic carboxylate group. The observed amino acid surface propensity has implications in atmospheric science as the surface interactions play a central role in cloud droplet formation, and they should be considered in climate models.
authors.affiliation: Institute of Physics, Brasilia University (UnB) , Box 4455, Brasília 70910-970, Brazil.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Mocellin
authors.affiliation: Institute of Physics "Gleb Wataghin", Department of Applied Physics, University of Campinas (Unicamp) , Campinas 13083-859, Brazil.
authors.forename: Anderson Herbert de Abreu
authors.initials: AHA
authors.lastname: Gomes
authors.affiliation: Institute of Physics, Brasilia University (UnB) , Box 4455, Brasília 70910-970, Brazil.
authors.forename: Oscar Cardoso
authors.initials: OC
authors.lastname: Araújo
authors.affiliation: Institute of Physics "Gleb Wataghin", Department of Applied Physics, University of Campinas (Unicamp) , Campinas 13083-859, Brazil.
authors.forename: Arnaldo Naves
authors.identifier: 0000-0002-9098-444X
authors.initials: AN
authors.lastname: de Brito
authors.affiliation: Department of Physics and Astronomy, Uppsala University , 752 36 Uppsala, Sweden.
authors.forename: Olle
authors.initials: O
authors.lastname: Björneholm