Discerning Poly- and Monosaccharide Enrichment Mechanisms: Alginate and Glucuronate Adsorption to a Stearic Acid Sea Surface Microlayer

Poly- and monosaccharides are ubiquitous in the marine environment and are enriched in sea spray aerosol but the mechanisms for their enrichment are not fully understood. We expand upon previously defined co-adsorption mechanisms by investigating the co-absorption of alginate and its representative monomeric form, glucuronate, to a stearic acid monolayer as a function of saccharide concentration on an ocean proxy solution. Using Langmuir isotherms, surface-sensitive infrared reflection-absorption spectroscopy, and Brewster angle microscopy, we demonstrate that the mechanism of co-adsorption significantly differs between alginate and glucuronate. We find that film thickness increases from -.3.5 to 4.8 nm and from -.3.5 to -.3.7 nm upon co-adsorption of alginate and glucuronate to stearic-d35 acid monolayers, respectively, indicating that alginate forms multilayers underneath the monolayer. Glucuronate shows a different co-adsorption where it likely intercalates and induces significant reorganization within the monolayer. We quantify the Langmuir adsorption coefficients and halfsaturation concentrations of both alginate and glucuronate co-adsorption to stearic-d35 acid. We find that alginate co-adsorption produces the Langmuir adsorption constants Kalginate = 0.089 +/- 0.015 and C1/2,alginate = 11 +/- 1.9 mg/L alginate and glucuronate coadsorption produces Kglucuronate = 0.081 +/- 0.015 and C1/2,glucuronate = 12 +/- 2.3 mg/L glucuronate. Thus, we demonstrate that the use of monosaccharides alone as a proxy for saccharide enrichment is insufficient, and we provide important parameters for better representation of saccharides in marine aerosol investigations.

Automated summary

This study expands upon the understanding of the mechanisms of saccharide enrichment in marine aerosols by investigating the co-adsorption of alginate and glucuronate. The study reveals significant differences in the co-adsorption mechanism between these two saccharides, with alginate forming multilayers beneath the monolayer and glucuronate inducing reorganization within the monolayer. The study provides important parameters for better representation of saccharides in marine aerosol investigations.