The additional phase transition of DPPC monolayers at high surface pressure confirmed by GIXD study

Shen, Chen; Kloesgen, Beate; de la Serna, Jorge; Struth, Bernd

Poster

PUBDB-2017-14112

The additional phase transition of DPPC monolayers at high surface pressure confirmed by GIXD study

Shen, C. ; de la Serna, J. ; Struth, B.DESY* ; Kloesgen, B. (Corresponding author)

2016

5th Iberian Biophysics Congress, Porto, Portugal, 15 Jun 2016 - 17 Jun 2016 [10.3204/PUBDB-2017-14112]

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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-14112

Abstract: Pulmonary surfactant forms the alveolar monolayer at the air/aqueous interface within the lung. During the breathing process, the surface pressure periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. The monolayer consists of ~90% of lipid with 10% integrated proteins. Among its lipid compounds, di- palmitoyl-phosphatidylcholine (DPPC) dominates (~45wt%). No other lipid but DPPC was so far reported to be compressible to very high surface pressure (~70mN/m [1]) before its monolayer collapsed. Its liquid-expanded/liquid-condensed (LE/LC) phase transition at ~10mN/m is well known [2].Here we present results from Langmuir isotherm measurements that evidence a so far not documented second phase transition at elevated surface pressure Π (~50mN/m). The varying lateral structures of the monolayer at 8mN/m, 20mN/m, 30mN/m, 40mN/m, 50mN/m, 60mN/m, 70mN/m were investigated by grazing incidence X-ray diffraction (GIXD). The results report on the 2D packing lattice with the inter-chain distance dxy. Moreover, the tilt angle of the palmitoyl chains was calculated combining the lattice parameters and the geometrical boundary conditions. The course of the inter-chain distance versus surface pressure exhibits three regimes, separated by the LE/LC transition and the second phase transition at the higher pressure. This feature may assign a functional task to DPPC in the lung surfactant since it contributes to the mechanical stability of the alveolae monolayer and at the same time allows reduction of the interfacial tension to ~0mN/m.References:[1] G. Ma and H. C. Allen, Langmuir 22 (12), 5341 (2006).[2] K. Y. C. Lee, A. Gopal, A. von Nahmen, J. A. Zasadzinski, J. Majewski, G. S. Smith, P. B. Howes, and K. Kjaer, Journal of Chemical Physics 116 (2), 774 (2002).

Note: The poster won the "Best Poster Award - Second Place" at the conference.

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