Electrochemical studies of thiolate monolayers at a Au(111) electrode surface for applications in the development of tethered phospholipid bilayers.
A model of the electrochemical interface between an electrode and electrolyte was derived in order to fully understand and compare interfacial systems in which the electronic properties of the electrode have been modified with either self assembled or Langmuir-Blodgett deposited monolayers. This interfacial model was implemented in the calculation of the surface concentrations and electrosorption valencies of thioglycerol, 2,3-di-O-phytanyl-sn-glycero-1-octaethyleneglycol-DL-α-lipoic acid ester (DPOL), octadecanethiol, thiomalic acid and thioglucose. The model appeared valid over the entire potential range and allowed for operational definitions of the potentials of zero total and free charge to be clarified. Furthermore, the dependence of the electrosorption valency on the actual valency of the adsorbate was explicit in the interfacial model. Based on the calculated surface concentrations, self assembled monolayers (SAMs) of thiomalic acid appeared to be highly dependent on the pH of the self assembly solution, and thioglucose demonstrated possible electro-oxidation at potentials greater than 0.2 VSCE. Mixed monolayers composed of thioglycerol and DPOL were investigated with regards to the proposed model. These mixed monolayers were then used to tether phospholipid bilayers composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC). The tethered bilayers were then electrochemically characterized. In furthering research in the development of biologically relevant phospholipid membrane models, a spectro-electrochemical cell was designed to allow for simultaneous acquisition of electrochemical and spectroscopic data. Preliminary electrochemical results of a DPhPC bilayer supported on a porous substrate indicated that the spectro-electrochemical cell operated as desired.