Real-time investigation of lung surfactant respreading with surface vibrational spectroscopy.
The respreading of a lung surfactant monolayer at the air-water interface is investigated with broad bandwidth sum frequency generation (BBSFG) spectroscopy. The lung surfactant mixture contains chain perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62), palmitoyloleoylphosphatidylglycerol (POPG), palmitic acid (PA), and KL4 (a 21-residue polypeptide analogue to the surfactant protein SP-B). DPPC-d62 serves as a probe molecule for the spectroscopic investigation. The BBSFG spectra of DPPC-d62 in the lung surfactant mixture are obtained in the C-D stretching region in real-time during film compression and expansion in a Langmuir trough. The BBSFG intensity of the CD3 stretch peak from DPPC-d62 terminal methyl groups is used as a measure of the interfacial density of DPPC-d62 after careful consideration of orientation effects. For the first time, the interfacial loss of DPPC in a complex lung surfactant mixture is quantified. Spectroscopic results reveal that there is an 18% DPPC-d62 interfacial loss during film respreading. However, the surface pressure-area isotherm measurements demonstrate that there is a rather large trough area reduction (37%) during film expansion. The relatively small interfacial loss of DPPC-d62 and the rather large trough area reduction indicate that the respreading of DPPC and non-DPPC components in the lung surfactant is not uniform and a surface refinement process exists during film compression and expansion. This refinement process results in a DPPC-enriched monolayer with a significant depletion of non-DPPC components after film respreading. Implication for replacement surfactant design from this work is discussed.
Ma
Gang
G
Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA.
Allen
Heather C
HC
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000818:Animals; D008051:Lipid Bilayers / Q000737:chemistry*; D019308:Palmitic Acid / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods
D008051:Lipid Bilayers; D010715:Phosphatidylglycerols; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; D019308:Palmitic Acid