Detailed characterization of POSS-poly(ethylene glycol) interaction with model phospholipid membrane at the air/water interface.

Polyhedral oligomeric silsesquioxanes (POSS) derivatives have been receiving remarkable attention due to their potential biomedical application and therefore understanding molecular mechanism of their interaction with cell membranes should be studied at molecular level. Here we investigate the binary mixture of an open silsesquioxane cage POSS-poly(ethylene glycol) (POSS-PEG) and 1,2-myristoyl-sn-glycero-3-phosphoethanolamine (DMPE) as a representative of phospholipid located in biological membranes. The surface pressure-area and surface potential-area compression isotherms, as well as Brewster angle microscopy and interfacial shear rheology were used to study monolayers at the air/water interface. The results show that POSS-PEG exhibits an insoluble monolayer with side group chains anchored to the air/water interface. The outcomes of the conducted experiments show (i) the evidence of a stable incorporation of POSS molecule to the DMPE monolayer modifying its equilibrium and dynamic properties and (ii) squeezing the POSS-polymer out of the lipid monolayer at a higher molecular packing density. The results from the conducted experiments together with thermodynamic analysis suggest area condensation and mutual miscibility at the surface pressure relevant to a real biological membrane.