Mesoporous TiO2 carboxymethyl-γ-cyclodextrate multi-layer host films: effects on adsorption and electrochemistry of 1,1′-ferrocenedimethanol

Abstract

TiO₂ (anatase) nanoparticles are readily deposited layer-by-layer in the form of thin films with a carboxymethyl-γ-cyclodextrate binder. Electron microscopy, voltammetric, and quartz crystal microbalance data demonstrate that the film grows homogeneously and is electrically connected to the ITO electrode surface. 1,1′-Ferrocenedimethanol is employed as an adsorbing redox system to study the voltammetric characteristics of the mesoporous host film. The binding constants for the homogeneous complexation of 1,1′-ferrocenedimethanol with carboxymethyl-γ-cyclodextrin at pH 7, K_red = 1300 ± 200 M⁻¹, and at pH 2, K_red = 1000 ± 200 M⁻¹, are determined assuming 1 ∶ 1 complex formation. In the presence of the TiO₂ carboxymethyl-γ-cyclodextrate films, solution phase voltammetric responses are affected due to a lower rate of diffusion of 1,1′-ferrocenedimethanol across the film (possibly due to binding to receptor sites) and due to slow electron transfer at pH 7 but not at pH 2. The TiO₂ carboxymethyl-γ-cyclodextrate modified electrode, when dipped into 1,1′-ferrocenedimethanol containing solution, rinsed, and transferred into clean buffer solution, shows characteristic signals for adsorbed 1,1′-ferrocenedimethanol, consistent with weak binding and fast release upon oxidation. There is evidence for two distinct binding sites for 1,1′-ferrocenedimethanol both at pH 7 and at pH 2.