CONDENSING AND EXPANDING EFFECTS OF THE ODORANTS (-CARVONE AND (-)-CARVONE ON PHOSPHOLIPID MONOLAYERS())

Interactions of the odorants (+) and (-)-carvone (5-isopropenyl-2-meth yl-2-cyclohexenone) with alpha-1,2-dipalmitoyl-sn-glycerol-3-phosphoch oline (L-DPPC) monolayers are studied using surface pressure versus ar ea isotherms measured in the temperature range 10-35 degrees C in the presence and absence of 5 mM odorants in the subphase. The data indica te that the molecular area occupied by the L-DPPC monolayer becomes la rger when the monolayer is spread on the subphase containing (-)-carvo ne and that, in contrast, it becomes smaller when the monolayer is exp osed to (+)-carvone. Both expanding and condensing effects are depende nt on temperature. L-DPPC monolayers with (-)-carvone absorb twice as much heat as those with (+)-carvone when compressed at 30 degrees C. U nder the same conditions, monolayers with (-)-carvone undergo a larger entropy change than monolayers with(+)-carvone. Variations in molecul ar areas and thermodynamic properties may contribute to membrane recog nition of optical isomers.