期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 23, 期 30, 页码 16401-16416出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1cp01407b
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资金
- National Science Foundation Center for Aerosol Impacts on Chemistry of the Environment (NSF-CAICE) [CHE-1801971]
- Ohio Supercomputer Center [PAS1711]
The study demonstrates that the marine polysaccharide alginate co-adsorbs with a insoluble palmitic acid monolayer through divalent cationic bridging interactions, with calcium ions inducing the greatest extent of co-adsorption. The presence of magnesium ions only facilitates a third of the co-adsorption due to strong hydration propensity. Surface pressure has minimal impact on the amount of alginate co-adsorption.
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 similar to 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.
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