Synthesis and Electrochemical Characterization of 4-Thio Pseudo-Glycolipids as Candidate Tethers for Lipid Bilayer Models.

Abstract

Two 4-thio pseudo-glycolipids, a disulfide and a thiol, were synthesized as candidates to build tethered bilayer lipid membranes (tBLMs) on gold (111) surface. Monolayers of the disulfide and thiol were built on gold surfaces using the self-assembly and Langmuir-Blodgett (LB) transfer methods. Monolayers were prepared in several solvents and at various temperatures; their quality was assessed by differential capacitance. Best monolayers were achieved when the disulfide was self-assembled in ethanol. The quality of such monolayers was further improved by allowing the assembly to proceed under stirring of the solution at increased temperatures. The charge number per adsorbed molecule and surface concentration of disulfide on gold (111) surface were determined by chronocoulometry. A DPhPC/disulfide tBLM was then built by vesicle fusion of 1,2-diphytanyl-sn-glycero-3-phosphocholine (DPhPC) on top of the disulfide monolayer. The minimum capacitance of the gold electrode with tBLM (1.3 mF cm 2) was close to the value of a real cell membrane and the AFM force spectroscopy measurements showed that the DPhPC/disulfide tBLM had a thickness of 6.2 ± 0.6 nm consistent with the thickness expected for a bilayer. Finally, the potential of the tBLM to study transmembrane proteins was assessed by investigating the reconstitution of gramicidin A into the membrane by polarization modulation infrared absorption spectroscopy (PM-IRRAS). These results demonstrate that the disulfide is a good candidate to construct tBLMs on gold surface and to study transmembrane proteins.