Phase diagram of mixed monolayers of stearic acid and dimyristoylphosphatidylcholine. Effect of the acid ionization

FRANCO VEGA MERCADO,BRUNO MAGGIO, NATALIA WILKE

ELSEVIER IRELAND LTD

Año: 2011 vol. 164 p. 386 - 386

The aim of this work is to study the phase diagram of mixed monolayers composed of dimyristoylphosphatidylcholine(DMPC) and stearic acid (SA) at different ionic strength and bulk pH of the aqueoussubphase. In this way, the effect of ionization of SA on the interaction and thus on phase separation withthe DMPC matrix can be analyzed. To this purpose, we first determined the ionization state of pure SAmonolayers as a function of the bulk subphase pH. The SA monolayers are nearly fully ionized at pH 10and essentially neutral at pH 4 and the mixture of DMPC and SA was studied at those two pHs. We foundthat the DMPC-enriched phase admits more SA if the SA monolayer is in a liquid-expanded state, whichis highly related to the acid ionization state, and thus to the bulk pH and ionic strength. At pH 4 themolecules hardly mix while at pH 10 the mixed monolayer with DMPC can admit between 30 and 100%of SA (depending on the lateral press