The structure of mixed monolayer films of DPPC and hexadecanol

Although dipalmitoyl phosphatidycholine (DPPC) is the primary surface activ e component of natural lung surfactant (NLS), under physiological condition s it does not adsorb rapidly to the interface or respread efficiently or ra pidly after compression beyond film collapse. Other materials must be prese nt to enhance these functions and one synthetic exogenous surfactant used i n replacement therapy mixes DPPC with hexadecanol and tyloxapol. In the pre sent study the interactions of DPPC and hexadecanol in spread monolayers ha ve been investigated by film balance measurements, and Brewster angle micro scopy. Two phases can be observed when the surface pressure is low and the mole fraction of DPPC is high: a condensed phase of hexadecanol with some D PPC and an expanded phase. Increasing surface pressure generates a second c ondensed phase that is DPPC rich. On further compression the expanded phase disappears and the two condensed phases merge, but miscibility rules indic ate that the expanded phases do not mix even though there is no evidence fo r two phases in the experimental data. (C) 2000 Elsevier Science B.V. All r ights reserved.