Superlow tensions and surface compositions of aqueous phospholipids and lung surfactants
Abstract
Spinning bubble tensiometry (SBT) was used for the first time to measure tensions of compressed air/water interfaces of aqueous dispersions of L-$\alpha$-dipalmitoylphosphatidylcholine (DPPC) and other lung surfactants. This method allowed for more accurate measurements of the surface tensions of lung surfactants than the methods previously used. Spectroturbidimetry, $\sp{1}$H NMR, and microscopy were used to probe the phase and dispersion microstructure. Surface tensions as low as 0.6 dyn/cm were observed by SBT. These measurements indicated that the unique surface property of lung surfactants to decrease the surface tension $\gamma$ to superlow values ($\gamma$ $<$ 10 dyn/cm) seemed to be affected more by the concentration of the dispersed particles rather than the type of the dispersed phase or the temperature. Simple models of the transport accounting for the effects of particles were developed. Aging phenomena for DPPC dispersions over weeks and months were shown to be related to DPPC hydrolysis. To directly probe the surface layer composition, a method was developed in which the surface layers at various degrees of surface compression were sampled by Langmuir-Blodgett (L-B) deposition and analyzed by thin-layer chromatography or infrared spectroscopy. Attenuated internal total reflection Fourier transform infrared spectroscopy (ATIR-FTIR) from L-B layers was sensitive enough to analyze monolayers of DPPC-PG (phosphatidylglycerol) on solid substrates. For better distinguishing the spectra of some mixtures, DPPC with deuterated hydrocarbon chains was used. Results from the surface analyses showed that the composition in the surface layers of lung surfactant dispersions changed with surface compression. As mixed surface layers of DPPC-PG were compressed, PG was preferentially expelled from the surface, leaving DPPC-rich surface layers showing superlow tensions. DPPC-PA (palmitic acid) mixed showed no changes in the surface layer composition with surface compression, probably because they formed a nearly ideal mixture in the surface layer. This direct evidence indicates the central role of DPPC in controlling the superlow tensions of lung surfactants and supports the previously proposed "squeeze-out" hypothesis for surface layers of mixed lipids.
Degree
Ph.D.
Advisors
Franses, Purdue University.
Subject Area
Chemical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.