Calcium bridging drives polysaccharide co-adsorption to a proxy sea surface microlayer

Abstract

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...

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

“…Thus, the Π−A isotherms suggest that alginate co-adsorbs to the interface, consistent with previous studies revealing that the mechanism for alginate enrichment or coadsorption is via Ca 2+ bridging to an insoluble monolayer. 47,54 In the case of glucuronate (Figure 1b), we also observed monolayer expansion relative to the stearic acid monolayer spread in the absence of glucuronate. However, this expansion is not monotonic.…”

“…The MD simulations reveal the formation of a second layer beneath the fatty acid monolayer and suggest that Ca 2+ likely serves as a bridge between the two COO − moieties. 54 Glucuronate opposes this finding where it intercalates into the monolayer and does not form a second co-adsorbed layer.…”

“…Deuterated stearic acid was used to spectrally isolate the CD 2 scissoring mode from the carboxylate stretching region. 54,65,67,88 The protonation state of the carboxylic headgroup of stearic-d 35 acid was maintained by adjusting the pH value of the subphase solutions from 5.6 to 8.2. The literature has shown surface pK a shifts to higher values.…”

“…All aqueous solutions were prepared with nanopure water with a resistivity of 18.2 MΩ•cm (Milli-Q Advantage A10, EMD Millipore) in glassware cleaned with a piranha acid bath. 54,58,59 The aqueous solutions consisted of constant marine water concentrations of 476 mN NaCl and 10 mM CaCl 2 and a varying concentration of alginate or glucuronate ranging from 0 to 100 mg/L to a total volume of 1 L. The ionic composition was selected to model the concentration of the most abundant and enriched cations in seawater, without complicating spectral interpretation, while maintaining high ionic strength as in seawater. The nanopure water has a pH of 5.6 ± 0.1 due to atmospheric CO 2 acidification.…”

Emerging investigator series: surfactants, films, and coatings on atmospheric aerosol particles: a review

“…Ab initio MD and quantum mechanics/molecular mechanics (QM/MM) simulations, which are based on electronic structure, are computationally expensive and limited to systems of no more than ∼100 molecules, whereas empirical potential functions can be used to reach larger system sizes into the thousands of molecules. 124 Accordingly, MD simulations have been applied to surfactant systems ranging in complexity from simple surfactant/salt mixtures 125–134 to multi-component mimics for sea spray aerosol 93,135–139 and SOA. 140 Quantum chemical methods such as density functional theory (DFT) 141 have also been applied to heterogeneous processes on atmospheric aerosol particles, 142 often in combination with spectroscopic measurements.…”