Nanosieving of anions and cavity-size-dependent association of cyclodextrins on a 1-adamantanethiol self-assembled monolayer.

ABSTRACT

In this paper, we studied charge transfer through a self-assembled monolayer (SAM) of 1-adamantanethiol on gold. Charge transfer through the 1-adamantanethiol SAM depended on the type of anion present when [Fe(CN)6]3- was used as a redox probe. The sluggish charge transfer process was monitored by cyclic voltammetry using the relatively large and hydrophobic perchlorate and hexafluorophosphate ions as the supporting electrolyte. In contrast, the charge transfer kinetics were nearly identical to those measured on bare gold with chloride, sulfate, and nitrate ions as the supporting electrolyte. We investigated the adsorption of alpha- and beta-cyclodextrin on the 1-adamantanethiol SAM via a host-guest interaction. The 1-adamantanethiol SAM could not bind beta-cyclodextrin via a host-guest interaction, probably due to the proximity of neighboring adamantine molecules on the surface. Immobilization of alpha-cyclodextrin by formation of an exterior complex with the SAM suppressed charge transfer. The adsorbed alpha-cyclodextrin was quantified using faradaic impedance experiments. The obtained adsorption isotherm was in good agreement with the Langmuir isotherm with a binding constant of 39.53 M(-1).