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    Mode of Interaction of Amphiphilic a-Helical Peptide with Phosphatidylcholines at the Air-Water Interface

    Year: 2006

    Journal: Langmuir, 2006, 22 (3), pp 1182–1192, 20111221

    Authors: Hiromichi Nakahara,† Shohei Nakamura, Takato Hiranita, Hideya Kawasaki, Sannamu Lee, Gohsuke Sugihara, and Osamu Shibata

    Organizations: Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan; Department of Chemistry, Graduate School of Science, Kyushu University, 6-1-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan; and Department of Chemistry, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Johnan-ku, Fukuoka 814-0180, Japan

    Surface pressure (π)−, surface potential (ΔV)−, and dipole moment (μ)−area (A) isotherms and morphological behavior were examined for monolayers of a newly designed 18-mer amphiphilic α-helical peptide (Hel 13-5), DPPC, and DPPC/egg-PC (1:1) and their combinations by the Wilhelmy method, ionizing electrode method, fluorescence microscopy (FM), and atomic force microscopy (AFM). The newly designed Hel 13-5 showed rapid adsorption into the air−liquid interface to form interfacial films such as a SP-B function. Regardless of the composition and constituents in their multicomponent system of DPPC/egg-PC, the collapse pressure (πc; 42 mN m-1) was constant, implying that Hel 13-5 with the fluid composition of egg-PC is squeezed out of Hel 13-5/DPPC/egg-PC monolayers accompanying a two- to three-dimensional phase transformation. FM showed that adding a small amount of Hel 13-5 to DPPC induced a dispersed pattern of ordered domains with a “moth-eaten” appearnce, whereas shrinkage of ordered domains in size occurred for the DPPC/egg-PC mixture with Hel 13-5. Furthermore, AFM indicated that (i) the intermediate phase was formed in pure Hel 13-5 systems between monolayer states and excluded nanoparticles, (ii) protrusions necessarily located on DPPC monolayers, and (iii) beyond the collapse pressure of Hel 13-5, Hel 13-5 was squeezed out of the system into the aqueous subphase. Furthermore, hysteresis curves of these systems nicely resemble those of the DPPC/SP-B and DPPC/SP-C mixtures reported before.