The alveoli in the human lung have a complex mixture of lipids and proteins that are collectively called pulmonary surfactant (PS). PS is necessary for proper breathing as a deficiency or dysfunction of PS can lead to respiratory distress syndrome (RDS). At present surfactant replacement therapy (SRT) has been used as the preferred treatment for some forms of RDS, however it has not always been proven successful in all cases. In this thesis 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) lipids of the lung, were studied with a Langmuir trough used in conjunction with the Brewster angle microscopy (BAM) on a water subphase as the temperature and the compression rate were varied. Studying fundamental molecular interactions with respect to each lipid may provide greater understanding of morphology, size, and domain numbers which may provide further insight into better treatment options.
Results illustrated that the compression rate did not have a significant impact on the shape of the isotherms, however the domain morphology was affected. In the coexistence region of the monolayer, the domains were influenced by the temperature of the subphase and the compression rate by way of the shapes, sizes and domain numbers observed. Domains that were formed at the onset of domain formation in the coexistence region had a greater tendency to fuse into larger domains as the compression rate increased and when the temperature of the subphase was lower than the main phase transition temperature. The fusion of the domains was believed to be observed with all three lipids, however as the temperature of the subphase was increased in the DPPC monolayer, fusion of the domains appear to decrease. The fusion of the domains as the compression rate increased in a cold monolayer suggest that a faster compression rate can induce enough fluctuations in the monolayer to increase the probability of domain-domain interactions DPPG has a main phase transition temperature that is similar to DPPC and fusion was still observed at 37 oC. These results suggest that DPPG may have a higher phase transition temperature in a monolayer with a neat water subphase. In this thesis, DPPC had the smallest domain size and the largest domain number at 37 oC on average, it can be inferred that the headgroups have a greater ability to interact with water. Conversely, DPPG was shown to have relatively larger domains than DPPC and as such greater lipid-lipid interactions. Based on results in this thesis, as the alveoli contract and expand while breathing, the lipid type and the rate at which this process occurs may have an impact on the morphology and the number of domains formed.