Study on the surface dissociation properties of 6-(10-mercaptodecaoxyl)quinoline self-assembled monolayer on gold by chemical force titration

Chemical force microscopy (CFM) was used to measure the adhesion force betw een quinolyl group (-Q)-terminated Au-coated tip and gold substrate (abbrev iated as -Q/-Q) modified with self-assembled monolayers (SAMs) of 6-(10-mer captodecaoxyl)quinoline (MDQ) in pH buffer solution. From the plot of adhes ion force vs. pH value, which is called force titration curve, the pK(1/2) of surface -Q group of MDQ SAM can be estimated to be 5.3, which correspond s to the pH value at the peak. By using the -OH group as a general probe, t he similar pK(1/2) value, estimated from the force titration curve of -OH/- Q and -Q/-OH, which also corresponds to the pH at the peak, is 5.7 and 5.4, respectively. From the conventional contact angle titration, pK(1/2) = 5.9 was obtained. The difference of the obtained pK(1/2) values arises from tw o different measurement methods and their measurement accuracies. (C) 1999 Elsevier Science S.A. All rights reserved.