Charges in phospholipid layers

Interaction between the lipid bilayer and different substrates is often dependant on the bio-physico-chemical properties of the interface. Surface of a membrane is the first site of interaction. The access to the bilayer and its local structural modifications upon interaction with an adsorbing guest molecule are influenced significantly by the presence of charges, and local changes in surface charge density. To investigate these properties we chose model mono- and bilayers made of zwitterionic POPC (and 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine) and cationic E-POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine). In the first step of our studies we performed isothermal compression of POPC monolayers into which charges were introduced by addition of the ethylated lipid derivative (EPOPC). Charge effects on POPC monolayers at the air-water interface were investigated by addition of different percentages of the cationic EPOPC. The isotherms obtained for the mixtures are compared with pure POPC monolayer isotherms as a reference system. As a second step, for better understanding of this system, diffusion within a POPC bilayer with the same charge addition as for the monolayer study was investigated. For that single molecular tracking analysis on giant unilamellar vesicles was done. Initial results suggest linear decrease in the diffusion coefficient of the dye molecule (DiI-C18). Presented results and future work will be focused on transfer of the phospholipid monolayers to hydrogel support cushion formed on solid support.