Desorption of 4-aminobenzenethiol bound to a gold surface

Desorption of 4-aminobenzenethiol (ABT) bound to a gold surface in bulk ethanol solution was studied by the measurement of the UV-absorption of the solution, from the points of both thermodynamics and kinetics. By eliminating the kinetic effects, we evaluated the equilibrium ratio of the adsorbed species with respect to the initial concentration of ABT in the solution. We found that the gold surface is fully covered by ABT above the bulk concentration of 0.5 mmol/dm(3). By analyzing the kinetics of the surface reaction from adsorbed ABT to 4,4'-diaminodiphenyl disulfide (DDD) and of the desorption of DDD, we deduced the rate of desorption of DDD from a fully covered gold surface. We found that the rate of desorption is extremely small, 1.6 x 10(-5) min(-1), due to rather strong binding of ABT to the native gold surface. These results suggest that there are two different processes for the desorption of DDD from a gold surface; one is from a native surface and the other is from a modified surface.