MIXING OF SATURATED AND UNSATURATED PHOSPHATIDYLCHOLINES AND PHOSPHATIDYLGLYCEROLS IN MONOLAYERS AT THE AIR WATER INTERFACE/

In the context of understanding the properties of model lung surfactan t systems, surface phase behavior of spread monolayers containing mixt ures of dipalmitoylphosphatidylcholine (DPPC), with various unsaturate d phosphatidylcholine (PC) and phosphatidylglycerol(PG) derivatives, h as been determined using surface pressure area isotherms on Tris buffe r (pH 7.4, 15 mM NaCl) and fluorescence microscopy. DPPC, at all surfa ce pressures below collapse, is completely miscible with dipalmitoylph osphatidylglycerol and with 1-palmitoyl-2-oleoylphosphatidylcholine di oleoylphosphatidylcholine up to mole fractions of at least 0.70 DPPC. On the other hand, DPPC is partially immiscible at mole fractions of 0 .50 and greater when mixed with 1-palmitoyl-2-oleoylphosphatidylglycer ol and dioleoylphosphatidylglycerol, with immiscibility increasing as the surface pressure is increased and with the replacement of 15 mM Na Cl of the buffered subphase by 5 mM Ca2+. The substitution of one unsa turated acyl chain into PO appears to produce phase separation equival ent to that produced by two saturated acyl chains of PG with about fou r carbons less than saturated acyl chains of DPPC. When DPPC/unsaturat ed PG mixtures are considered in model lung surfactant studies or as a rtificial lung surfactant systems, such strong tendencies for surface phase separation may be important and should be taken into account. (C ) 1997 Academic Press.