Lateral diffusion in substrate-supported lipid monolayers as a function of ambient relative humidity.
We analyzed the influence of water activity on the lateral self-diffusion of supported phospholipid monolayers. Lipid monolayer membranes were supported by polysaccharide cushions (chitosan and agarose), or glass. A simple diffusion model was derived, based on activated diffusion with an activation energy, E(a), which depends on the hydration state of the lipid headgroup. A crucial assumption of the derived model is that E(a) can be calculated assuming an exponential decay of the humidity-dependent disjoining pressure in the monolayer/substrate interface with respect to the equilibrium separation distance. A plot of ln(D) against ln(p(0)/p), where D is the measured diffusion coefficient and p(0) and p are the partial water pressures at saturation and at a particular relative humidity, respectively, was observed to be linear in all cases (i.e., for differing lipids, lateral monolayer pressures, temperatures, and substrates), in accordance with the above-mentioned diffusion model. No indications for humidity-induced first-order phase transitions in the supported phospholipid monolayers were found. Many biological processes such as vesicle fusion and recognition processes involve dehydration/hydration cycles, and it can be expected that the water activity significantly affects the kinetics of these processes in a manner similar to that examined in the present work.
Max-Planck Institute for Polymer Research, D-55128 Mainz, Germany.
Tobias
T
Baumgart
Andreas
A
Offenhäusser
D055592:Biophysical Phenomena; D001703:Biophysics; D002686:Chitin / Q000031:analogs & derivatives* / Q000737:chemistry; D048271:Chitosan; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D000431:Ethanol / Q000494:pharmacology; D005898:Glass; D007700:Kinetics; D008055:Lipids / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D008567:Membranes, Artificial; D008856:Microscopy, Fluorescence; D015233:Models, Statistical; D010713:Phosphatidylcholines / Q000737:chemistry; D038761:Photobleaching; D011134:Polysaccharides / Q000737:chemistry; D012685:Sepharose / Q000737:chemistry; D012997:Solvents / Q000494:pharmacology; D013997:Time Factors
D008055:Lipids; D008563:Membrane Lipids; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D011134:Polysaccharides; D012997:Solvents; D002686:Chitin; D000431:Ethanol; D012685:Sepharose; D048271:Chitosan; D004134:Dimyristoylphosphatidylcholine