NMR-STUDIES OF THE INTERACTION OF CATECHOL AND ASCORBIC-ACID WITH THECROWN-ETHER

Various crown ethers have been electropolymerized onto a platinum elec trode for the determination of catechol and catecholamines by static p otentiometry and potentiometric-flow injection analysis(FIA). The resp onse mechanism of this modified electrode was investigated by scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDAX), and electron spectroscopy for chemical analysis(ESCA). However, these studies were not conclusive with respect to possible mechanisms, and, therefore, nuclear magnetic resonance (NMR) studies were carried out on similar soluble crown ethers to determine the mode of interaction. As the crown ether resonances were shifted to higher fields by the add ed catechol in D2O but not d(6)-DMSO, it is postulated that the crown ether and catechol associate via interactions between hydrophobic surf aces. Hydrophilic ascorbic acid showed no NMR shifts which is consiste nt with its lack of potentiometric response. The EDAX and ESCA results indicated that then was also an interaction of catechol with the crow n itself but the NMR shows that this interaction is a secondary effect in the overall electrode response.