SYNTHESIS AND CRYSTAL-STRUCTURE OF DINITROXYL CROWN-ETHER BIRADICAL WITH INDOLE GROUPS IN THE SIDE-CHAINS

Dinitroxyl crown ether biradical, pyl]-1,7,10,16-tetraoxa-4,13-diazacy clooctadecane, was synthesized and studied by X-ray structural analysi s and ESR spectroscopy. The ESR spectra in aqueous and aqueous-alcohol ic solutions show a triplet with a(N) = 1.65+/-0.05 mT. This triplet i s retained in the presence of Na+, K+, and Mg2+ ions. On addition of C a2+ ions, the triplet is transformed into the quintet because of the c hange in the conformation of the crown ether biradical and decrease in the distance between the nitroxyl groups. The new crown ether biradic al containing hydrophobic indole groups may be used for studying the m echanism of Ca2+ ion transport in biomembranes by ESR spectroscopy.