Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

Abstract

Palmitic acid (PA) has been found to be a major constituent in marine aerosols, and is commonly used to investigate organic containing atmospheric aerosols, and is therefore used here as a proxy system. Surface pressure-area isotherms (π-A), Brewster angle microscopy (BAM), and vibrational sum frequency generation (VSFG) were used to observe a PA monolayer during film compression on subphases of ultrapure water, CaCl 2 and MgCl 2 aqueous solutions, and artificial seawater (ASW). π-A isotherms indicate that salt subphases alter the phase behavior of PA, and BAM further reveals that a condensation of the monolayer occurs when compared to pure water. VSFG spectra and BAM images show that Mg . π-A isotherms and BAM were also used to monitor mixed monolayers of PA and cerebroside, a simple glycolipid. Results reveal that PA also has a condensing effect on the cerebroside monolayer. Thermodynamic analysis indicates that attractive interactions between the two components exist; this may be due to hydrogen bonding of the galactose and carbonyl headgroups. BAM images of the collapse structures show that mixed monolayers of PA and cerebroside are miscible at all surface pressures. These results suggest that the surface morphology of organic-coated aerosols is influenced by the chemical composition of the aqueous core and the organic film itself.

Sea Spray Aerosol: The Chemical Link between the Oceans, Atmosphere, and Climate

“…29,30 Interestingly, studies seeking to replicate microbial blooms in a controlled manner (using informed representative organic species for each stage of the bloom) showed that N 2 O 5 uptake on SSA did not differ significantly from simplistic laboratory-generated NaCl particles (see Figure 3b). 31 This implies either (1) the complex nature of the organic species result in loose surface packing 20,32 or (2) the organic species are well mixed or present in low enough concentrations so as not to impact uptake. Both have significant implications for understanding how chemical changes dictate aerosol climate properties (i.e., heterogeneous reactivity, hygroscopicity, and interaction with solar radiation).…”

Lipid composition and molecular interactions change with depth in the avian stratum corneum to regulate cutaneous water loss

“…In general, more polar lipids with short, saturated alkyl chains of uniform length pack more closely, and are thus less prone to gauche defects than lipids that are more non-polar and have long, unsaturated chains of variable length (Casal and McElhaney, 1990;Adams and Allen, 2013). However, we could not find a clear pattern of polarity or chain length with respect to depth in the SC, and our method of thin layer chromatography cannot detect the degree of saturation.…”

“…The mechanism by which more polar ceramides and cerebrosides inhibit water loss may involve the formation of strong hydrogen bonds between polar lipid headgroups and adjacent lipid headgroups to create a tight packing arrangement (Adams and Allen, 2013).…”

“…Additionally, the frequencies of both OH peaks may have been influenced by increases with depth in the absorbance of glucose from cerebrosides (∼3350 cm Forming strong hydrogen bonds with adjacent lipid headgroups within a bilayer is one mechanism by which polar lipids such as ceramides and cerebrosides may reduce CWL. As a result of these strong headgroup interactions, water molecules may be impeded from inserting themselves into spaces between lipid headgroups (Adams and Allen, 2013;Golden et al, 1986;Alonso et al, 1996), thus improving each bilayer's resistance to water permeation. Additionally, headgroup interactions may increase the cohesiveness of the SC in general to make it less susceptible to mechanical stress and therefore better able to maintain intact lipid barriers to water loss (Chapman et al, 1991).…”

“…In birds, ceramide and cerebroside headgroups are thought to play a major role in preventing water permeation through lipid layers, as more polar headgroups may form strong hydrogen bonds with each other and consequently influence water infiltration (Adams and Allen, 2013). In current models of lipid organization within the avian SC, glucose moieties of cerebrosides project into the hydrophilic space outside lipid layers .…”