Characteristics of Protein Aggregation and Flotation in Water and Alcohol-Water Mixture

Investigation of immunoglobulin (IgG) solutions with the concentration of 0.125 mg/mL shows that monomer IgG macromolecules ~10 nm in size form aggregates as large as ~300 nm in water and ~900 nm in the 36.7 vol % ethanol–water mixture (EWM). Shaking results in formation of floating-up bubbles in the solutions of both types. However, efficiency of immunoglobulin bubble flotation in water and EWM is substantially different. This difference can be caused by simultaneous action of two mechanisms for attachment of IgG particles (macromolecules or aggregates) to bubbles in aqueous solutions: direct attraction of IgG particles to the charged surface of a bubble and existence of ion-stabilized nanobubbles with a radius of ~100 nm capable of making up compound particles like nanobubbles–IgG macromolecules/IgG aggregates, which in turn serve as “spatial agents” for flotation of IgG particles on larger bubbles. In the EWM, attachment of IgG particles to floating-up bubbles is ineffective because of weak surface charge of macro- and microbubbles and absence of nanobubbles.