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Langmuir 1992,8, 1136-1144
Photophysical Properties of a Pyrene-Labeled Phospholipid in Matrix Monolayers at the Gas/Water Interface Ramesh C. Ahuja' and Dietmar Mobius Max-Planck-Institut fur Biophysikalische Chemie, Postfach 2841, 0 - 3 4 0 0 Gottingen, FRG Received July 30, 1991. In Final Form: January 2, 1992 We report here on the photophysical properties of the pyrene-labeled phospholipid molecule l,z-bis(1-pyrenyldecanoy1)-L-a-phosphatidylcholine (DPyPC) embedded in unlabeled phosphatidylcholine matrix monolayers at the gadwater interface. Phosphatidylcholines with varying acylchain length such as dilauroyl(DLPC), dimyristoyl- (DMPC), dipalmitoyl- (DPPC), distearyl- (DSPC), and diarachidylphosphatidylcholine (DAPC) were used as the matrix molecules. Surface pressure-, reflection-, and fluorescence-area isotherm measurements were employed for the investigation of photophysical properties of the pyrene chromophore. The reflection spectrum of the DPyPC monolayer (at the aidwater interface) at high surface pressures shows four bands at 278,317,333, and 348 nm, respectively, which are slightly (2-4 nm) red shifted as compared to that for the monomer, indicating pyrene dimer formation. The reflection-area isotherms at 275 and 345 nm show that the longer molecular axis of the chromophore is not normal to the airlwater interface. Increasing the acyl chain length of the matrix molecules leads to changes in the shape of the reflection-area isotherms, indicating that the pyrene chromophore tends to be more and more parallel to the acyl chains. The fluorescence spectrum of the mixed monolayers (DPyPC:DPPC = 150) at a surface pressure of
