Mixing behavior of a poly(ethylene glycol)-grafted phospholipid in monolayers at the air/water interface

Langmuir. 2008 Nov 18;24(22):13019-29. doi: 10.1021/la801868j. Epub 2008 Oct 23.

Abstract

Mixed phospholipid monolayers hosting a poly(ethylene glycol) (PEG)-grafted distearoylphosphatidylethanolamine with a PEG molecular weight of 5000 (DSPE-PEG5000) spread at the air/water interface were used as model systems to study the effect of PEG-phospholipids on the lateral structure of PEG-grafted membrane-mimetic surfaces. DSPE-PEG5000 has been found to mix readily with distearoylphosphoethanolamine-succinyl (DSPE-succynil), a phospholipid whose structure resembles closely that of the phospholipid part of the DSPE-PEG5000 molecule. However, properties of mixed monolayers such as morphology and stability varied significantly with DSPE-PEG5000 content. In particular, our surface pressure, epifluorescence microscopy (EFM), and Brewster angle microscopy (BAM) studies have shown that mixtures containing 1-9 mol % of DSPE-PEG5000 form stable condensed monolayers with no sign of microscopic phase separation at surface pressures above approximately 25 mN/m. Yet, at 1 mol % of DSPE-PEG5000 in mixed monolayers, the two components have been found to behave nearly immiscibly at surface pressures below approximately 25 mN/m. For monolayers containing 18-75 mol % of DSPE-PEG5000, a high-pressure transition has been observed in the low-compressibility region of their isotherms, which has been identified on the basis of continuous BAM imaging of monolayer morphology, as reminiscent of the collapse nucleation in a pure DSPE-PEG5000 monolayer. Thus, the comparative analysis of our surface pressure, EFM, and BAM data has revealed that there exists a rather narrow range of mixture compositions with DSPE-PEG5000 content between 3 and 9 mol %, where somewhat homogeneous distribution of DSPE-PEG5000 molecules and high pressure stability can be achieved. This finding can be useful to "navigating" through possible mixture compositions while developing guidelines to the rational design of membrane-mimetic surfaces with highly controlled bio-nonfouling properties.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Air
  • Chemistry, Physical / methods
  • Microscopy / methods
  • Microscopy, Fluorescence / methods
  • Models, Chemical
  • Models, Statistical
  • Phosphatidylethanolamines / chemistry
  • Phospholipids / chemistry*
  • Polyethylene Glycols / chemistry*
  • Pressure
  • Surface Properties
  • Temperature
  • Thermodynamics
  • Water / chemistry*

Substances

  • Phosphatidylethanolamines
  • Phospholipids
  • Water
  • 1,2-distearoylphosphatidylethanolamine
  • Polyethylene Glycols