2-DIMENSIONAL ASSEMBLY FORMATION OF HYDROPHOBIC HELICAL PEPTIDES AT THE AIR-WATER-INTERFACE - FLUORESCENCE MICROSCOPIC STUDY

Monolayer formation of hydrophobic a-helical peptides, X-(Ala-Aib)(8)- Y (X = Boc-, HOOCCH2CH2CO-, biotinyl, biotinyl-(Sar)(3)-; Y = OMe, OBz l, OH), at the air/water interface was studied by the fluorescence mic roscopic method. Some peptides showed a mound in the pi-A isotherm. Wh en the monolayer containing a small amount of FITC-labeled peptide was held at the surface pressure corresponding to the top of the mound, b right and dark domains were observed by fluorescence microscopy. Domai n formation was also observed by the addition of a cationic dye (DiIC( 1)) into the subphase underneath the peptide monolayer. The mound in t he pi-A isotherm is, therefore, ascribed to the phase transition from an expanded state to a condensed state. Two different shapes (leaflet and needle) of solid domains were observed and discussed in terms of d ifferent orientations of the peptides in the monolayer.