PROPERTIES OF MONOLAYERS OF CROWN-ETHERS BEARING AN AZO AND AZOXY GROUP IN THE MACROCYCLE

Two methods are described for preparing monomolecular layers of crown ethers with an azo or azoxy group in the macrocycle. When the molecule s used to build the monolayer are soluble in aqueous solutions, adsorp tive preconcentration on mercury electrodes was used to prepare the mo nolayer coating. The monolayer was electroactive due to the presence o f the azo or azoxy unit in the molecules. Monolayers of crown ethers b earing an azo group in the macrocycle were shown to recognize alkali m etal cations present in the solution. Changes of the parameters of the voltammetric reduction peaks - peak potential and peak width, served as an indication of specific interactions of the monolayer of 13-membe red and 16-membered azocrown ethers with Na+ and K+ cations, respectiv ely. The monolayers capable of recognizing cations have also been prep ared on the aqueous solution-air interface, using the Langmuir techniq ue. In this approach, amphiphilic derivatives of the azocrowns were sy nthesized and the monolayer has been assembled on the subphase contain ing metal cations. Binding of the cation by the macrocycle has a stabi lizing effect on the monolayer and higher collapse pressures are achie ved than on the pure water subphase. The monolayer was transferred fro m the air-water interface on the solid substrate using the Langmuir-Bl odgett technique. Thin mercury film electrodes on the Ag substrate, or Au films evaporated on glass slides were employed as the electrode su bstrates. The former gave monolayer modified electrodes of higher stab ility.