Hybrid supported lipid bilayers (HSLBs) deposited in reversed-phase chromatographic silica particles are a useful cell membrane model which can be utilized to predict the bioavailability of compounds and separate them based on their affinity for phospholipid membranes. In HSLBs, an upper leaflet of phospholipid molecules self-assembles on a lower leaflet of C18-modified silica. Confocal Raman microscopy studies of these bilayers, within individual particles, have allowed for structural characterization of the membrane and quantification of a small molecule analyte partitioned into the bilayer. Unfortunately, although HSLBs are useful, phospholipids are expensive, and modifying an entire chromatographic column with phospholipids can be expensive. In this work, we propose an alternative hybrid membrane model where an upper-leaflet of surfactants is used in place of phospholipid. These hybrid supported surfactant bilayers (HSSBs) offer the benefit of lower cost and can provide a variety of head-group structures. To form a HSSB within a silica particle, we mimic a phospholipid by using two oppositely charged surfactants with similar headgroups and acyl chain lengths as a phospholipid molecule. Using Raman microscopy, the structure and melting transition of HSSBs was studied and compared with a HSLB, where similar structural characteristics were observed. Small-molecule toxicity, drug efficacy, and accumulation of molecules in biological systems can be predicted based on measurement of the phospholipid-water partition coefficient (Kpw). Here, we demonstrate the use of HSSBs to measure phospholipid water partitioning of the small molecule naphthoic acid within an individual particle. The value of Kpw measured in HSSBs was compared to the value determined from the same measurement in HSLBs. The partitioning of naphthoic acid in both hybrid bilayers is similar. Finally, the pH dependence of naphthoic acid partitioning was measured. Here, partitioning depends on the pKa of the solute and the surface charge of the bilayer; by controlling pH, it was possible to determine the affinity of the neutral and anionic forms of the naphthoic acid. The resulting titration curve was used to calculate the pKa of naphthoic acid which was similar for both HSSB and HSLB. Interestingly, the measured pKa was lower than the pKa of aqueous naphthoic acid in aqueous due to the pH local to the interface as determined based on measurement of the interfacial zeta potential.

Confocal Raman microscopy investigation of small-molecule partitioning in hybrid supported bilayers

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.