Structural changes in layers of lipid mixtures at low surface tensions.

Layers of pulmonary lipids on an aqueous substrate at non-equilibrium conditions can decrease the surface tension of water to quite low values. This is connected with different relaxation processes occurring at the interface and the associated changes in the surface layer structure. Results of measurements by the combination of methods like surface rheology, ellipsometry, Brewster angle microscopy, and IRRAS for spread layers of lipid mixtures open a possibility to specify the dynamics of structural changes at conditions close to the physiological state. At sufficiently low surface tension values (below 5 mN/m) significant changes in the ellipsometric signal were observed for pure DPPC layers, which can be related to a transition from 2D to 3D structures caused by the layer folding. The addition of other lipids can accelerate the relaxation processes connected with squeezing-out of molecules or multilayer stacks formation hampering thereby a decrease of surface tension down to low values corresponding to the folding of the monolayer.

Adsorption layer formation in dispersions of protein aggregates.

The review discusses recent results on the adsorption of amyloid fibrils and protein microgels at liquid/fluid interfaces. The application of the shear and dilational surface rheology, atomic force microscopy and passive particle probe tracking allowed for elucidating characteristic features of the protein aggregate adsorption while some proposed hypothesis still must be examined by special methods for structural characterization. Although the distinctions of the shear surface properties of dispersions of protein aggregates from the properties of native protein solutions are higher than the corresponding distinctions of the dilational surface properties, the latter ones give a possibility to obtain new information on the formation of fibril aggregates at the water/air interface. Only the adsorption of BLG microgels and fibrils was studied in some details. The kinetic dependencies of the dynamic surface tension and dilational surface elasticity for aqueous dispersions of protein globules, protein microgels and purified fibrils are similar if the system does not contain flexible macromolecules or flexible protein fragments. In the opposite case the kinetic dependencies of the dynamic surface elasticity can be non-monotonic. The solution pH influences strongly the dynamic surface properties of the dispersions of protein aggregates indicating that the adsorption kinetics is controlled by an electrostatic adsorption barrier if the pH deviates from the isoelectric point. A special section of the review considers the possibility to apply kinetic models of nanoparticle adsorption to the adsorption of protein aggregates.

Influence of temperature on dynamic surface properties of spread DPPC monolayers in a broad range of surface pressures.

This work is focused on the study of the dynamic surface properties of spread monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), which is the main component of the pulmonary surfactant (PS), in the region of high surface pressures and at different temperatures. The increase of temperature from 25 to 35 °C led to a decrease of surface elasticity in the high surface pressure range corresponding to physiological conditions inside alveoli during breathing. Furthermore, the obtained results evidenced that the relaxation processes in spread DPPC monolayer were accelerated with the increase of temperature, which resulted in two different effects. On one hand, it led to the increase of hysteresis of surface pressure isotherms, which was an important condition for maximizing air penetration into alveoli; whereas on the other hand, it prevented reaching extremely high surface pressure, which could result in a premature alveolar collapse.