Carbon particulates (CPs) are ubiquitous throughout the environment and can adversely affect biological membrane properties. Complicating efforts to understand CP – membrane interactions is that CPs change over time. Freshly generated particulates may start out hydrophobic but can become hydrophilic and soluble in aqueous media as they age. In order to quantify the surface activity of soluble CPs and their effects on lipid monolayers, we used surface specific nonlinear optical spectroscopy and thermodynamic methods to measure how soluble poly-hydroxylated fullerenes (PHFs) alter organization, orientation and compressibility in lipid monolayers adsorbed to aqueous – air interfaces. Surface tension measurements show that PHFs are surface active with terminal monolayer coverages of ~70-90 Å2/particle. PHF surface activity also manifests in 2nd order nonlinear optical measurements. Fixed wavelength second harmonic generation (SHG) experiments show large amplitude fluctuations at PHF aqueous concentrations below 0.25 mg/mL. At higher concentrations, SHG data become much less erratic. Previous work suggests that CPs are likely to form aggregates. To reduce presumed aggregation, equivalent experiments were carried out with 50 mM NaCl, leading to significantly reduced SHG signal fluctuations. Further support for PHF aggregation at the aqueous – air interface comes from surface specific vibrational sum frequency generation (VSFG) experiments. In the absence of NaCl, PHFs increase the lipid acyl chain ordering in 55Å2/molecule DPPC films at both very low PHF concentrations and PHF concentrations above 5 mg/ml. Such behavior is consistent with PHF aggregates occupying area at the aqueous – air interface, effectively compressing DPPC domains. In contrast, PHF solutions containing NaCl induce disorder in DPPC monolayers, suggesting that isolated PHF monomers disrupt lipid monolayer organization. Taken together, our findings demonstrate how data from complementary methods can identify how non-biological, nano – sized carbonaceous materials impact model biological membrane organization and properties.

Carbon particulate adsorption to aqueous – air interfaces and their effects on lipid film structure and organization

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.