Complexation of metal ions by azocrown ethers in Langmuir–Blodgett monolayers

Abstract

Monomolecular films of amphiphilic derivatives of crown ethers bearing an azo group in the macrocycle were formed on the surfaces of pure water or aqueous solutions of metal cations and transferred onto a thin mercury film electrode using the Langmuir–Blodgett technique. The properties of the monolayer modified electrodes were studied by voltammetry. The azocrown molecules assembled in monolayers at the air–solution and electrode–solution interfaces were found to interact with selected alkali metal cations. This was revealed by the changes of the parameters of the surface–pressure and surface–potential isotherms recorded during the formation of monolayers at the air–solution interface, and by the electrochemical behaviour of the monolayer covered electrodes. The stability constants of the complexes formed by Na⁺, K⁺ and Ca²⁺ cations with the neutral (K_ox) and reduced (K_red) forms of the macrocyclic ligand in the monolayer, and the reaction coupling efficiency (K_ox/K_red), were calculated.