Interactions in Complex Monolayers
Determining structure/function relations for proteins/peptides and lipids requires a milieu that mimics the interfacial environment in which the molecules function. Monomolecular films at the air/water interface are attractive membrane model systems to study interactions with components dissolved in the adjacent water phase:
- The chemical composition and the density of lipids can be varied in a broad range.
- The energetics of interactions can be measured via the surface tension.
- Structural changes of the interface and of neighboring molecules can be investigated with high precision. In this respect the last two decades have encountered a broad range of new methods like X-ray diffraction and reflection, FT-IR spectroscopy, fluorescence and Brewster angle microscopy (BAM), nonlinear optical spectroscopy, neutron reflection and imaging ellipsometry.
- The subphase composition can be varied as regards ionic strength, pH, coupling ions, molecules and polymers.
Therefore one expects to learn much from studies of monolayers with biomolecules in the subphase, especially details of local interactions and their manipulation. These details are of tremendous importance in many areas of material- and biosciences. In nature there are many biomolecules binding to and interacting with the membrane, and the monolayer in this respect presents the membrane surface. The arrangement of molecules on surfaces is also relevant for modifications of technical surfaces, but also for patterned nanostructures.
The interactions of dissolved biomolecules with the membrane model interface can change the lipid packing density. On the other hand, lipid structural properties can dictate the adsorption behavior of proteins/peptides. During the last years we have concentrated our efforts on ions, DNA, enzymes, peptides and nanoparticles at interfaces.