Recently a number of macrocyclic compounds have been discovered which are capable of forming complexes with alkali metal ions (for reviews see refs. 1-3). They belong to naturally occurring species as depsipeptides ~ or macrotetrolides z ,4 as well as to synthetic compounds like cyclic polyethers 3 ,s. All these substances uncouple oxidative phosphorylation in mitochondria 6-12 (on this is based their antibiotic action), facilitate the transport of alkali metal ions (particularly of potassium) through artificial phospholipid bilayers 13-1s and enable ion-selective functioning of liquid membranes 2 ,1s-26. These properties are linked to the properties of the internal cavity of the macrocyclic compound, which contains carbonyl or ether oxygens enabling complex formation with alkali metal ions, and to the external lipophilic surface of the resulting complex. The ratio metal: macrocyclic compound in typical complexes is 1 : 1.
The present paper is concerned with the electrochemical reduction of alkali metal complexes with macrocyclic polyethers at a dropping mercury electrode. This study also includes the reduction of the complex with thallium which is sometimes used as a model species for investigation of biological properties of alkali metals z7 . No polarographic reduction of an alkali metal ion complex has been reported so far.