Translational dynamics of lipids on monolayers and of proteins in gels

The lateral diffusion of phospholipids in single component dilauroylphosphatidylcholine (DLPC) monolayers and single component dimyristoylphosphatidylcholine (DMPC) monolayers at the air/water interface was studied. The diffusion results for the DLPC monolayer were compared with results for diffusion in DLPC multi-bilayers. In order to address the difference between the two systems, diffusion behavior in DLPC monolayers at the oil/water interface was determined. For linear hydrocarbons, the diffusion coefficient was found to be independent of the oil viscosity and identical to that at the air/water interface, once a given critical surface density was reached. For a non-linear hydrocarbon, the diffusion behavior remained dependent on the oil viscosity for all surface densities of the phospholipid. The difference in behavior stems from the difference in packing of residual hydrocarbons in the monolayer beyond a critical surface density.; The diffusion of a phospholipid probe in mixed monolayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine-N-poly(ethyleneglycol) (DMPE-EG) lipo-polymer monolayer was investigated. Lipo-polymers with a long ethylene oxide tail desorbed from the interface at the collapse pressure of the polymer. Beyond the collapse the diffusion in the mixed monolayer became identical to the diffusion in the pure monolayer. A lipo-polymer with a shorter ethylene oxide tails did not desorb from the monolayer.; The diffusion of a phospholipid probe was measured in mixed monolayers DMPC:DPPC:Dihydrogencholesterol (Dchol). Local minima in a plot of the diffusion coefficient versus Dchol molefraction were seen. The minima were attributed to be either an onset of slow relaxation behavior of the mixed monolayers, or values of more efficient packing in the monolayer. Slow relaxation behavior with similar minima in diffusion coefficient was verified for mixed monolayers of DLPC and poly(t-butylmethacrylate). This was attributed to the collapse of the polymer followed by slow relaxation into a fully spread state.; The bulk diffusion coefficient of fluorescence labeled protein molecules was studied in a novel hydrogel system as a function of protein type and gel crosslinking density. The diffusion was shown to be protein specific in the gels, underscoring that model systems of poly(styrene) beads, commonly used to study diffusion in hydrogels, have little predictive value.