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

By use of 9.7 GHz and 94 GHz ESR spectra and electron spin echo (ESE)-detected spectra the six radical centres produced by γ-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 C1 with isotropic doublet A = 1.8 mT; on C2, C3 and C4 with triplet A = 2.9 mT; and localized on CH2 with anisotropic triplet. For doses above 100 kGy the radical on C1 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.