Coexisting phases in PEGylated phosphocholine membranes: a model study.

Understanding the phase behavior of PEGylated phosphocholine membranes is becoming increasingly important in many biomedical applications. Here, we used binary mixtures of phosphocholines and PEG-phospholipids in monolayers on phosphate buffered saline as ideal models of PEGylated phosphocholine membranes. Several phase states and transitions between homogeneously mixed and completely immiscible phases have been visualized in these mixtures by epifluorescence microscopy, which is neither predicted nor easily explained by the existing interpretive schemes.

Lateral distribution of a poly(ethylene glycol)-grafted phospholipid in phosphocholine monolayers studied by epifluorescence microscopy.

Mixed monolayers of distearoylphosphatidylcholine (DSPC) and a poly(ethylene glycol)-(PEG)-grafted distearoylphosphatidylethanolamine with a PEG molecular weight of 2000, DSPE-PEG2000, spread on phosphate-buffered saline (PBS) were used as models of bio-non-fouling membrane-mimetic surfaces in order to visualize the lateral distribution of PEG2000-phospholipid in the host phospholipid matrix. Epifluorescence microscopy (EFM) was used to locate DSPE-PEG2000 molecules in the DSPC matrix by detecting the fluorescence from a fluorescein fluorophore attached to the distal end of the PEG2000 chain. Comparative analysis of surface pressure-area isotherms and EFM images revealed that DSPE-PEG2000 mixes nonideally with DSPC in monolayers on a PBS subphase.