DETERMINATION OF REAL COMPOSITION OF 3-MERCAPTOPROPIONIC ACID AND 1-OCTADECANETHIOL MIXED SELF-ASSEMBLED MONOLAYERS BY USING ELECTROCHEMICAL AND ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE MEASUREMENTS

In order to clarify the electrochemical response of cytochrome c at th e gold electrode modified with mixed monolayers of carboxylic acid ter minated alkanethiol (promoter molecule) and n-alkanethiol (barrier mol ecule), electrochemical and electrochemical quartz crystal microbalanc e (EQCM) measurements were carried out during the reductive desorption of the mixed monolayer of 3-mercaptopropionic acid and 1-octadecaneth iol (C18SH) in alkaline solution. The ratio of mercaptopropionic acid in the mixed monolayer was found to be smaller than that in the modify ing solution, showing that C18SH adsorbed more preferentially than mer captopropionic acid. The peak potentials for the reductive desorption of mercaptopropionic acid became more negative upon increasing the C18 SH content in the monolayer. This means mercaptopropionic acid and C18 SH did not form patched domains but were mixed well with each other. T he mercaptopropionic acid molecules in a well-mixed monolayer should b e stabilized through the affinity between the mercaptopropionic acid a nd C18SH and becomes difficult to be desorbed from the electrode.