It can be concluded that all the thiol and disulfide compounds examined do form adlayers on gold surfaces. However the available data suggest that these layers are disordered. The XPS, contact angle and electrochemistry results indicate that dithiols such as 223 - 225 may form thicker layers containing unbound disulfide and thiol groups, consistent with the tendency of these compounds to undergo aerial oxidation in solution. Estimation of layer thickness by XPS, ellipsometry or UV/visible spectroscopy might clarify this. Monolayers of strapped porphyrin disulfides were not identical to the analogous dithiols, and electrochemistry indicated the former layers to be thinner and more permeable to ions.
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