| Description |
A stable model of a cell membrane, useful for predicting the bioavailability and for investigating small molecule - lipid membrane interactions, can be prepared by the assembly of a phospholipid monolayer on the hydrophobic surfaces of C18-modified porous silica particles. These hybrid-supported lipid bilayers (HSLBs) have been demonstrated to be a reasonable model of phospholipid vesicles. In this research, the partitioning of small molecules in HSLBs was investigated using confocal Raman microscopy. In addition, C18-chromatographic particles modified with phospholipid molecules (HSLBs) were compared with cationic-anionic hybrid-supported surfactant bilayers (HSSBs). These in situ studies are carried out within individual chromatographic particles, which require much less analyte, achieve equilibration in short times, and report quantitative information on analyte partitioning and the model-membrane structure. The pH-dependent partitioning of ionizable solutes in HSLBs was investigated in light of the influence of the surface potential of the lipid-bilayer on the local acid-base equilibrium. A model is developed based on the measured zeta potential of HSLBs versus pH, which is used to predict the local interfacial pH using the Poisson-Boltzmann equation (Chapter 2). The separation of small molecules based on their shape is crucial for resolving organic pollutants such as polycyclic aromatic hydrocarbons. Depending on the length and degree of saturation of phospholipid molecules in HSLBs, one can form either highly-ordered or disordered separation media. The partitioning of both planar and nonplanar iv molecules in HSLBs was studied to indicate the effect of the carbon chain order on their shape selectivity (Chapter 3). Modification of a reversed-phase chromatographic column with phospholipids can be costly, and furthermore, phospholipids lack versatility in headgroup structure and resulting analyte interactions. These limitations were addressed by modifying C18 particles with structurally-related anionic-cationic surfactant mixtures. The structure and melting transitions of these mixed-surfactant hybrid bilayers were found to be comparable to lipid-modified C18 surfaces. The capability of these surfactant hybrid bilayers to serve as a membrane model was demonstrated by comparing a small molecule partitioning in HSLBs and HSSBs, where HSSB showed a greater partitioning of a planar solute, which is likely due to the greater alkyl-chain order of the HSSB (Chapter 4). |
