Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the surface acid-base property of carboxylic acid-terminated self-ass embled monolayers (SAMs). A carboxylic acid-terminated thiol, such as thioc tic acid (1,2-dithiolane-3-pentanoic add), was self-assembled on gold elect rodes. Electron transfer between the bulk solution and the SAM modified ele ctrode was studied at different pH using Fe(CN)(6)(3-) as a probe. The surf ace pK(a) of thioctic acid was determined by cyclic voltammetry and electro chemical impedance spectroscopy to be 5.6 +/- 0.1 and 5.8 +/- 0.1, respecti vely. The method is compared with other methods of monolayer pK(a) measurem ent.