Lipid and protein interactions at air-water interface: correlating structural organization with rheological properties

Abstract

Biological compounds such as lipids and proteins are building blocks of all living species and therefore, understanding how interactions between these molecules contribute to proper biological functioning is of great importance. Among the various perspectives of understanding lipid and protein interactions, this thesis is focused on the interaction of these molecules at the air-water interface. Lipid and proteins at the liquid interfaces are both abundant and influential. A few of the biological and physiologically relevant interfaces include cell membrane, tear film, and lung surfactant. While biological interactions of lipids and proteins regulate cell process, enable the lung function and keep us alive, some of these interactions could also be unfavorable in industrial applications. For example, interaction of proteins at the interfaces has been a source of concern in pharmaceutical industry due to the protein aggregation and particle formation initiated or increased in presence of the interfaces. This thesis has been focused in both biologically and industrially relevant studies of lipids and proteins at the air-water interface to learn how to better measure and predict these interactions. An active microrheology, imaging techniques, and surface energy measurements have been used to visualize and characterize the chemical-mechanical behavior of the lipids and proteins at the interface. The results showed interesting points on the influence of lipid chemistry, including headgroup charge, size, and saturation of the tail, on its interfacial rheological properties. The effect of subphase properties such as pH had a great influence on lipid packing. Additionally the interaction of lipids at the interfaces is greatly influenced by presence of even small ratios of protein or nanoparticles; the lipid-protein mixtures were significantly more viscose than lipid mixtures. Moreover our studies using a model IgG1 mAb had shown the role of air-water interface and its renewal due to mechanical stress on protein particle formation. The interfacial properties of the protein films were influenced greatly by the liquid buffer properties such as pH. Future studies on correlating the chemical-mechanical properties of lipids and proteins and their macroscale behavior at interface could shed light on important physiologically and industrially relevant questions.