Imaging of monolayers composed of palmitic acid and lung surfactant protein B

Near-field scanning optical microscopy and atomic force microscopy are used to probe the sub-micrometre phase structure in palmitic acid monolayers co ntaining the 25 peptide amino terminus of lung surfactant protein B (SP-B1- 25). Monolayers deposited onto mica substrates at a surface pressure of 15 mN m(-1) exhibit a two-phase coexistence across a broad range of SP-B1-25 c oncentrations, Monolayers containing 5 wt,% SP-B1-25 Or less exhibit an exp anse of liquid condensed phase in which elliptical liquid expanded (LE) dom ains with areas of approximately 25 mum(2) coexist. By contrast, monolayers containing 20 wt.% SP-B1-25 exhibit an expanse of liquid expanded phase in which circular ii quid condensed domains coexist. The phase distribution d ependence on SP-B1-25 concentration suggests that the peptide induces disor der in the monolayer.