No abstract

A series of semifluorinated n-alkanes (SFAs) of the general formula F(CF 2 ) m (CH 2 ) n H, (in short FmHn) where m ) 10 and n ) 6-20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions such as spreading volume, subphase temperature, and compression speed. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our results show that these "nonclassical" film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are capable of monolayer formation at the air/water interface. It has been observed that with the increase in the molecule's length, its stability at the free water surface increases. The negative sign of the measured surface potential, ∆V, proves that SFA molecules are oriented at the air/water interface with their perfluorinated parts directed toward the air. The effective dipole moments reach the value of -0.65 ( 0.1 D at the minimum for all stable SFAs. The analysis of the direction of the molecular dipole moment in respect to the main axis enabled us to estimate that the minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35°to the surface normal. The relative intensity measurements allow one to conclude that film molecules are tilted in respect to the surface normal at the vicinity of collapse.

Mixtures of cholesterol with stearic (STA), oleic (OA), and linoleic (LA) acids spread as monolayers at the air/water interface were used as model systems to examine the hypocholesterolemic effect of fatty acids. Miscibility and interactions between the components of the cholesterol/fatty acid systems were studied basing on the analysis of surface pressure/area isotherms completed with Brewster angle microscopy images. In monolayers, STA and cholesterol were found to be immiscible. In contrast, OA and LA were found to form miscible, but nonideal mixed monolayers with cholesterol. They exhibit negative deviations from ideality in the surface pressure/area plots. This reflects close-packing arrangements between bulky cholesterol molecule and the hydrocarbon chains of unsaturated fatty acids. The analysis of the excess free energies of mixing shows that the maximum negative value of ΔG exc appears at about X chol = 0.5−0.7. Thus, the formation of the most stable 1:1 and 2:1 complexes between cholesterol and an unsaturated fatty acid molecule may account for the hypocholesterolemic effect of the acids in human organism by complexing free cholesterol, thereby hindering its deposition on artery walls.

To cite this version:J. Miñones, S. Pais, O. Conde, P. Dynarowicz-Łątka. Interactions between membrane sterols and phospholipids in model mammalian and fungi cellular membranes -A Langmuir monolayer study. Biophysical Chemistry, Elsevier, 2009, 140 (1-3) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D