Synthesis and crystal structure of dinitroxyl crown ether biradical with indole groups in the side chains

Dinitroxyl crown ether biradical, 4,13-bis2-hydroxy-3-(2,2,4,4-tetramethyl-3-oxylo1,2,3,4-tetrahydro-γ-carbol-9-yl)propyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane, was synthesized and studied by X-ray structural analysis and ESR spectroscopy. The ESR spectra in aqueous and aqueous-alcoholic solutions show a triplet with ^a N = 1.65±0.05 mT. This triplet is retained in the presence of Na⁺, K⁺, and Mg²⁺ ions. On addition of Ca²⁺ ions, the triplet is transformed into the quintet because of the change in the conformation of the crown ether biradical and decrease in the distance between the nitroxyl groups. The new crown ether biradicdl containing hydrophobic indole groups may be used for studying the mechanism of Ca²⁺ ion transport in biomembranes by ESR spectroscopy.