Study of the π–A isotherms of miltefosine monolayers spread at the air/water interface

Abstract

Miltefosine (hexadecylphosphocholine), an anticancer drug based on a phospholipid-like structure, was spread and investigated at the aqueous solution/air interface as Langmuir monolayers by means of surface pressure–area (π–A) isotherms in addition to Brewster angle microscopy. The influence of such factors as subphase temperature, ionic strength, speed of compression, number of molecules spread at the surface on the characteristics of the π–A isotherms was studied. Miltefosine was found to form stable Langmuir monolayers which are nearly not influenced by experimental conditions. The liquid-expanded character of miltefosine films was confirmed with both compressibility modulus values and homogeneous BAM images. Ellipsometric measurements were performed to measure the thickness of miltefosine monolayer, and were used to calculate the orientation angle of miltefosine hydrophobic tail, which was found to change from 78.4 to 65.5 upon full monolayer compression. These results prove that the expanded character of miltefosine monolayer is due to the inclination of the molecule's hydrocarbon tail.