Chemical oxidative polymerization of ethacridine

Abstract

Novel electroactive paramagnetic ethacridine oligomers were synthesized by the oxidation of ethacridine lactate with ammonium peroxydisulfate in acidic aqueous solution. The oxidative coupling of ethacridine was proved by gel permeation chromatography and MALDI-TOF mass spectrometry demonstrating the presence of oligomeric chains. Theoretical study of the mechanism of oxidation of ethacridine has been based on the semi-empirical quantum chemical computations of heat of formation and ionization energy of ethacridine, protonated ethacridine, generated reactive species and reaction intermediates, taking into account influence of pH and solvation effects. It was revealed that the prevalent ethacridine dimers are N(C6)C5 coupled. The influence of oxidant to monomer mole ratio on the molecular structure and the morphology of ethacridine oligomers has been studied by elemental analysis, FTIR, Raman, EPR and UV-Visible spectroscopies, MALDI-TOF mass spectrometry and scanning electron microscopy. Besides unoxidized monomeric units as prevalent, oligoethacridines contain the iminoquinonoid and newly formed fused phenazine units. The electroactivity of ethacridine oligomers was investigated by cyclic voltammetry.