Coupling of Local and Global Membrane Features

Phospholipid model membranes have been used for a long time to mimic biological cell membranes and are known to exhibit many interesting phenomena on the microscopic (molecular, local) to macroscopic (global) level. Molecular interactions determine the global physical state of the membrane. In turn, the global state is also crucial to the local interactions with any membrane active compound (e.g. protein). The coupling between the local and global membrane features is, however, largely not understood. We will tackle this issue in the present project by determining the global physical membrane parameters of various model membranes and changes to it upon local interactions due to membrane active compounds. The emphasis is on low-dose effects, where the membrane active compound can be regarded as a local defect or impurity. Especially in this low-dose regime, quantitative information is presently lacking mainly due to the fact that most of the existing studies had to use high amounts of membrane active compounds in order to observe any effects. By making use of the latest developments, especially in global x-ray data analysis and their combination with thermodynamic methods, we are much more sensitive to the global physical state. We do not aim to visualize individual membrane active molecules, pores, or defects. We will observe their statistical averaged effects upon the lipid bilayer. Thus, we use the bilayer as a sensor to locally occurring interactions.