Lateral mobility of phospholipid molecules in thin liquid films

Abstract

Abstract. The Fluorescence Recovery After Photobleaching (FRAP) method was applied to measure the lateral mobility of the fluorescent lipid analog, dioctadecylindocarbocyanine perchlorate (DiI-C 18), in microscopic thin liquid films (Foam Films (FFs)). The foam film structures were comprised of two phosphatidylcholine monolayers adsorbed at air/water interfaces which sandwiched a thin liquid core. Lateral diffusion of the DiI molecules in the plane of the monolayers was determined as a function of the thickness of the thin liquid core of the film between the FF monolayers. The results obtained indicated that the diffusion coefficient was strongly dependent both on the distance between the FF monolayers in the range 4 nm to 85 nm (corresponding to the FF thickness) and on the film type. The applicability of the FRAP method for studying the molecular mobility in phospholipid FFs was demonstrated. Considerable differences in the surface diffusion coefficient of DiI were observed, ranging between 2 x 10 -8 cm2/s and 22 x 10 -8 cm2/s in so called yellow, gray, common black and Newton black FFs. The effect of the presence of polyethylene glycol (PEG-400) in the liquid core of lecithin FFs on surface diffusion was also studied. The surface diffusion results from the FF studies were compared with data from black lipid membranes (BLMs). These structures are related in thickness terms but the molecular orientation in FFs is the reverse of that in BLMs.

Lateral Diffusion in Substrate-Supported Lipid Monolayers as a Function of Ambient Relative Humidity

“…The proximal monolayer would be transferred onto a hydrophobised substrate or chemically attached. In free-standing foam films, a correlation between the thickness of the water film and monolayer mobility has been found in a number of works (Lalchev et al, 1994(Lalchev et al, , 1995. In that case, however, the thickness of the water layer was adjusted by the salt concentration, which regulates DLVO forces.…”