Coexisting liquid phases of model membrane systems are chemically identified using imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The systems studied were Langmuir-Blodgett (LB) model membranes of cholesterol (CH) with two different phospholipids, one a major component in the outer plasma membrane bilayer leaflet (dipalmitoylphosphatidylcholine (PC)) and the other a major component in the inner leaflet (dipalmitoylphosphatidylethanolamine (PE)). Binary mixtures of CH with each of the phospholipids were investigated, as well as a ternary system. A single homogeneous phase is evident for PC/CH, whereas both systems containing PE show lateral heterogeneity with phospholipid-rich and CH-rich regions. The interaction between CH and the two phospholipids differs due to the disparity between the phospholipid headgroups. Imaging TOF-SIMS offers a novel opportunity to chemically identify and differentiate the specific membrane locations of CH and phospholipid in membrane regions without the use of fluorescent dyes. This unique imaging method has been used to demonstrate the formation of micrometer-size CH domains in phosphatidylethanolamine-rich systems and is further evidence suggesting that CH may facilitate transport and signaling across the two leaflets of the plasma membrane.

Charge-based interactions that strongly inhibit the antibacterial activity of host cationic antibacterial peptides present in CF sputa have significantly less effect on molecules from the ceragenin family such as CSA-13 due in part to their smaller net charge and distribution of this charge over a hydrophobic scaffold. CSA molecules therefore have potential for the treatment of chronic infections and inflammation that occur in CF airways and other settings in which extracellular polyanions accumulate.

Understanding the influence of molecular environment on phospholipids is important in time-of-flight secondary ion mass spectrometry (TOF-SIMS) studies of complex systems such as cellular membranes. Varying the molecular environment of model membrane Langmuir-Blodgett (LB) films is shown to affect the TOF-SIMS signal of the phospholipids in the films. The molecular environment of a LB film of dipalmitoylphosphatidylcholine (DPPC) is changed by varying the film density, varying the sample substrate, and the addition of cholesterol. An increase in film density results in a decrease in the headgroup fragment ion signal at a mass-to-charge ratio of 184 (phosphocholine). Varying the sample substrate increases the secondary ion yield of phosphocholine as does the addition of proton-donating molecules such as cholesterol to the DPPC LB film. Switching from a model system of DPPC and cholesterol to one of dipalmitoylphosphatidylethanolamine (DPPE) and cholesterol demonstrates the ability of cholesterol to also mask the phospholipid headgroup ion signal. TOF-SIMS studies of simplistic phospholipid LB model membrane systems demonstrate the potential use of these systems in TOF-SIMS analysis of cells.

Bombardment with C60+ primary ions of monolayer and multilayer barium arachidate Langmuir-Blodgett (LB) films is investigated. The behavior of cluster versus atomic (Ga+) bombardment is monitored by the barium-cationized arachidate ion (mass-to-charge ratio (m/z) 449) and a characteristic fragment ion (m/z 209) using 1-, 7-, and 15-layer model systems. The removal rate of material from the films is shown to be on the order of several hundred molecules per C60 impact, a value 100-fold larger than Ga+ impact. The enhancement in secondary ion yield is also shown to be larger for the 15-layer film (400x) than for the monolayer film (100x). Moreover, most of the increase in yield is shown to be associated with ejection of sputtered species rather than an increase in ionization probability. High yields associated with cluster bombardment are also shown to be amenable to depth profiling experiments in which the two ions can be monitored as the film is being removed. In this modality, chemical damage associated with bombardment is removed before it can accumulate on the surface. Due to the similarity of fatty acid LB films to cellular membranes, these results suggest that C60+ primary ion beams may improve the prospects for TOF-SIMS studies of biological systems.