Hybrid-supported lipid bilayers (HLSBs) employ an outer-leaflet of phospholipid self-assembled on an inner-leaflet of n-alkyl chains covalently bound to the surface of reversed-phase chromatographic silica. The structure of HSLBs has recently been characterized using confocal-Raman microscopy. The results show that acyl-chains of phosphatidylcholine are interdigitated with the n-alkyl chains, and the ordered chains undergo temperature-dependent melting transitions much like phospholipid bilayers. We recently showed that the ordered structure of zwitterionic phospholipid hybrid bilayers can be mimicked by pairs of oppositely-charged surfactants with comparable head-group composition and hydrocarbon-chain lengths. The surfactant bilayers have additional benefits of providing freedom in head-group composition that controls partitioned solute interactions. To extend the range of surfactants employed to prepare ordered hybrid-bilayers on n-alkane modified silica, we have sought an alternative class of surfactants with neutral head groups (long-chain alcohols) to modify reversed-phase chromatographic surfaces. We have assembled saturated, long-chain alcohol monolayers on C18-modified silica and investigated their structure with confocal-Raman microscopy. The results reveal a stable layer of long chain alcohols, which does not desorb upon exposure to surfactant-free aqueous solution. The alcohol surfactant density and chain ordering are consistent with interdigitated hydrocarbon chains. In temperature-dependent experiments, it was shown that the alcohol monolayer melts along with the covalently bound carbon chains on the silica surface. This would strongly suggest interdigitation of the hydrocarbon chains. We also tested the effect of pore size on the structure and ordering of these bilayers, and with smaller pore sizes, the alkyl-chain ordering decreases when the dimensions of the surface curvature become comparable to the length of the hydrocarbon chains. These hybrid alcohol structures demonstrate the ability to combine the stability of n-alkane-silane modified silica surfaces and customizability of interfacial properties with a stable, ordered monolayer of a long chain neutral head-group surfactant.

Confocal Raman microscopy investigation of the structure of long-chain alcohol monolayers on n-alkyl-chain functionalized silica surfaces

ACS Spring 2022

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