Interaction of Biomolecules at the Air-Water Interface: Evaluating the Role of Lipid Composition when Interacting with Lung Surfactant Proteins and Engineered Carbon Nanodiamonds

Abstract

Lung surfactants (LSs) are a complex mixture of lipids and proteins that are found in the alveolar lining of the lungs. Their primary objective lies in lowering the surface tension of the aqueous layer on which they reside. By doing so, LSs reduce the energy involved in breathing, and any loss/ dysfunction of the surfactants can cause fatal respiratory complications. Successful treatment methods require a thorough understanding of the biophysical properties of the LSs, and their interaction with any material that may come in contact. This dissertation aims at evaluating the interaction of the different lipids found in the surfactant pool with such plausible candidates at the air-water interface. Engineered carbon nanodiamonds (ECNs) is selected because of their potential in becoming a candidate for drug delivery through the respiratory tract. Therefore, it is necessary to evaluate any possible toxic outcome from ECNs. Here, we observe that both the lipid headgroup charge and the tail saturation impact the biophysical properties of the monolayer. We also evaluate the impact of the protein, Mini-B, which is a synthetic analog of the native surfactant protein, SP-B, on the biophysical properties of the LSs. Mini-B is a suitable candidate for surfactant replacement therapy (SRT), which is associated with lung diseases. Thus, Mini-B needs a thorough biophysical analysis. Lastly, we observe the effectiveness of Mini-B in countering the deleterious effects of cholesterol. Cholesterol is found in the native mixture and helps in fluidizing the monolayer. However, cholesterol has been reported to have some harmful impact on the LSs. Thus, it is a highly disputed component in SRT, with some formulations removing cholesterol from their product. We observe that 1 to 5 wt.% of Mini-B can counter the harmful effects of small quantities of cholesterol, providing a wholesome mixture.