Identification of radiation‐induced radical structure in azocalix[4]arene: an EPR study

• Published in: Magnetic resonance in chemistry Vol. 51; no. 10; pp. 671 - 675
• Main Authors: Usta, Keziban, Ozen Karakus, Ozlem, Usta, Ayhan, Deligoz, Hasalettin
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.10.2013
• Subjects: azocalixarene; Bonding; Carbon; chemical synthesis; electron paramagnetic resonance (EPR); Esters; Free radicals; irradiation effects; Radicals; Scission; Single crystals; Spectra; chemical synthesis; electron paramagnetic resonance (EPR); irradiation effects; azocalixarene
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.3998

A macrocyclic azocalix[4]arene (1) based ester derivative was synthesized. The single crystals of azocalix[4]arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to 60Co gamma rays with a dose rate of 0.980 kGy h‐1 for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C–H bond. This radical is described as •CaHCbH3 The averages of the principal values of the hyperfine parameters and g‐factor are: g = 2.0034, AHa = 1.28 mT, AH1=H2 = 1.00 mT, and AH3 = 0.49 mT. Copyright © 2013 John Wiley & Sons, Ltd. Radical structure occurred by scission of a methylene C‐H bond of a terminal ethyl group because of ionizing radiation, and the unpaired electron was localized on carbon proton (Ca) in the ester moiety of the sample, and the other moiety of the azocalix[4]arene sample in the study does not contribute to the radical induction at all.