Solvent effects on composition and structure of thiolipid molecular anchors for tethering phospholipid bilayers

Abstract

This article reports the effects of solvent polarity on the formation and properties of multi-component self-assembled monolayers (SAMs) for surface immobilization of tethered bilayer membranes (tBLMs). Monolayers were formed on polycrystalline gold using a synthetic 1-thiahexa(ethylene oxide) thiolipid serving as molecular anchor mixed with the β-mercaptoethanol backfiller. The properties of SAMs and tBLMs prepared in different solvents were monitored by the electrochemical impedance spectroscopy, spectroscopic ellipsometry and polarization modulation infrared reflection absorption spectroscopy. We found that the solvent polarity allows controlling the surface concentration of molecular anchors on a surface in the range from 9% to 57% while keeping constant adsorbate concentration in solution. A solvent polarity also determines the structural arrangement of the molecular components. A low polarity environment favours sparser accommodation of molecular anchors and a more compact arrangement of backfillers, while the high polarity solvent favours clustering of the hydrophobic polymethylene parts, which adopt more vertical orientation tilted ~25° to a surface normal. Both composition and structure affect both the physical and functional properties of tBLMs. In general, the nature of the solvents used in the assembly of SAMs used in tBLM technologies should be taken into account if specific functional features of tBLMs are being sought.