Ion-gating phenomena of self-assembling glutathione films on gold piezoelectrodes

The adsorption of glutathione (GS) on a gold coated quartz crystal resonator surface was investigated to evaluate the saturation surface excess of GS, solvent content in the glutathione films on gold (AuSG), and conformational transitions in these films induced by interactions of AuSG with metal cations. It has been found that the resonant frequency shift recorded during the GS self-assembly agrees well with the resonator response predicted on the basis of molecular modeling of a GS film with GS molecules in the closed-gate conformation. The association interactions of AuSG film with Ba2+ ions lead to a transformation of GS molecule to the open-gate conformation which is characterized by an elongated shape and results in solvent uptake by AuSG film. Other metal ions able to form carboxylate complexes, Pb2+ and Ni2+, were also found to be able to cause conformational transformation of GS molecule and open the ion gates in AuSG film. The film permeation by Pb2+ ions is followed by Pb0 deposition in the open channels and formation of nuclei at the film ∣ solution interface. In the case Ni2+, the ion transport through the gates is followed by discharge and formation of a wedged interlayer between the Au substrate and the adsorbed GS molecules. Some organic compounds including neurotransmitters dopamine and serotonin and cationic drugs such as chlorpromazine, can also open the ion gates in AuSG films but conformational changes in the GS molecule are less reversible due to the partial retention of organic compounds in the film after medium exchange.