Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

Abstract

By use of 9.7 GHz and 94 GHz ESR spectra and electron spin echo (ESE)-detected spectra the six radical centres produced by c-irradiation of cellobiose were identified. The radicals are localized on different carbon atoms. Use of high-frequency ESR spectra with computer resolution enhancement methods enabled unique radical identification and determination of g-factors and proton hyperfine splitting, A, with high accuracy. For radiation doses below 20 kGy three radicals dominate: on C 1 with isotropic doublet A = 1.8 mT; on C 2 , C 3 and C 4 with triplet A = 2.9 mT; and localized on CH 2 with anisotropic triplet. For doses above 100 kGy the radical on C 1 dominates, because of cleavage of the glycosidic bonds. Electron spin-lattice relaxation shows that radiation damage of the cellulose structure around the radical centres is significant and radical molecules do not participate in phonon dynamics of the host lattice. The relaxation is because of tunnelling motions of the ring or OH-groups, with tunnelling splitting 2.4 cm -1 . Electron spin echo dephasing results identify cellobiose ring torsions with activation energy 117 cm -1 .

Wood Sawdust/Natural Rubber Ecocomposites Cross-Linked by Electron Beam Irradiation

“…More than 20 different cellulose macro-radicals, including primary and secondary species, can be formed and distinguished. Some of them are thermodynamically favored and thus far more likely to be created [ 36 , 47 , 48 ]. During irradiation of cellulose, radicals with localized unpaired electrons are formed, mainly in positions 1, 2, 3, 4 and 5 of the pyranose ring, as is showed in Figure 14 a.…”

Primary Radiation Defect Production in Polyethylene and Cellulose

“…A considerable number of experimental studies relating to radiation chemistry and physics of polyethylene − has been published, but only few computational studies are available . Some recent experimental studies on the irradiation of cellulose are available ,− but none where MD-simulations would have been utilized.…”

Water Absorption Kinetics in Natural Rubber Composites Reinforced with Natural Fibers Processed by Electron Beam Irradiation

“…Over 20 different cellulose macro-radicals, including primary and secondary species, can be formed and distinguished. Some of them are thermodynamically favored and, thus, are far more likely to be created [ 44 , 58 , 59 , 60 ]. By EB irradiation of fibers, radicals having localized unpaired electrons from cellulose are formed, especially in the positions 1, 2, 3, 4, and 5 of the pyranose ring.…”