Determination of Surface pKa Values of Surface-Confined Molecules Derivitized with pH-Sensitive Pendant Groups.

摘要

Two methods for in-situ electrochemical measurements of surface pKa values air, reported. The methods are applied to surface-confined monolayers consisting of organomercaptan molecules derivitized with pH-sensitive pendant groups. The first technique relies upon pH-dependent electrostatic binding of redox probe molecules to the charged monolayer surface: the surface concentration of the probe molecules reflects the degree of surface protonation. The second method relates the differential capacitance of the monolayer-modified electrode surface to the surface pKa. The two methods yield essentially identical results and are consistent with a recently developed theoretical model. The surface pKa values of 4-mercaptopyridine and 4-aminothiophenol are 3.7 and 5.7, respectively.