Temperature effect on thin lipid film elasticity and phase separation: insights from Langmuir monolayer and fluorescence microscopy techniques

Abstract

Langmuir monolayer pressure isotherms and compressibility modulus measurements of phospholipid mixtures in several Langmuir monolayer systems at the air/water interface were investigated in this study. The ultimate aim was to carry out a comparison of the elasticity modulus for monolayers with different mixtures of l,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), l,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and chicken egg yolk sphingomyelin (eSM), in the presence/absence of cholesterol (Chol). In particular, we were able to propose that the leading force beyond the phase separation into liquid expanded (LE-) and liquid condensed (LC-) phases emerges from the increasing barrier to incorporate DOPC molecules into a highly ordered LC-phase. In addition, our findings suggest that DOPC lipid molecules have a priority to incorporate in a disordered LE-phase, while DPPC and eSM prefer the ordered one. Also, Chol seems to split almost equally into both phases, indicating that Chol has no priority for either phase and there are no particular interactions between Chol and saturated lipid molecules.

Keywords:

• Langmuir monolayer technique
• monolayer ordered phase
• monolayer compressibility
• phase transition
• lipid rafts

Acknowledgements

Z. Khattari would like to thank Prof. Thomas Fischer (University of Bayreuth, Germany) for his generous hospitality during carrying out of the experiments in his laboratory.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support from DFG and Hashemite University [grant number Fi 548 11-1] is gratefully acknowledged.