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. These stable supported bilayers can be employed as chromatographic stationary phases, where retention of both small molecules and membrane-active peptides were found to be comparable to their affinities for phospholipid vesicle membranes. The structure of HSLBs has 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 typical of phospholipid bilayers. We recently showed that the 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 aqueous solutions. 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 together with the covalently bound carbon chains on the silica surface, a result that strongly suggests interdigitation of the carbon chains. We have also investigated the effect of pore size on the structure and ordering of these bilayers. The hybrid alcohol structures demonstrate the ability to combine the stability of n-alkane-silane-modified silica surfaces with the adsorption of a long-chain alcohol monolayer to customize the interfacial structure and properties of a stable hybrid-bilayer surface.

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

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