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Calcium Bridging Drives Polysaccharide Co-Adsorption to a Proxy Sea Surface Microlayer

preprint
submitted on 31.03.2021, 21:31 and posted on 01.04.2021, 13:08 by Kimberly Carter-Fenk, Abigail Dommer, Michelle E Fiamingo, Jeongin Kim, Rommie Amaro, Heather Allen
Saccharides comprise a significant mass fraction of organic carbon in sea spray aerosol (SSA), but the mechanisms through which saccharides are transferred from seawater to the ocean surface and eventually into SSA are unclear. It is hypothesized that saccharides cooperatively adsorb to other insoluble organic matter at the air/sea interface, known as the sea surface microlayer (SSML). Using a combination of surface-sensitive infrared reflection-absorption spectroscopy and all-atom molecular dynamics simulations, we demonstrate that the marine-relevant, anionic polysaccharide alginate co-adsorbs to an insoluble palmitic acid monolayer via divalent cationic bridging interactions. Ca2+ induces the greatest extent of alginate co-adsorption to the monolayer, evidenced by the ~30% increase in surface coverage, whereas Mg2+ only facilitates one-third the extent of co-adsorption at seawater-relevant cation concentrations due to its strong hydration propensity. Na+ cations alone do not facilitate alginate co-adsorption, and palmitic acid protonation hinders the formation of divalent cationic bridges between the palmitate and alginate carboxylate moieties. Alginate co-adsorption is largely confined to the interfacial region beneath the monolayer headgroups, so surface pressure, and thus monolayer surface coverage, only changes the amount of alginate co-adsorption by less than 5%. Our results provide physical and molecular characterization of a potentially significant polysaccharide enrichment mechanism within the SSML.

Funding

National Science Foundation Award No. CHE-1801971

Ohio Supercomputer Center Project No. PAS1711

History

Email Address of Submitting Author

carter-fenk.1@buckeyemail.osu.edu

Institution

The Ohio State University

Country

United States of America

ORCID For Submitting Author

0000-0003-0071-7127

Declaration of Conflict of Interest

We declare no conflicts of interest.

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