ausblenden:
Schlagwörter:
-
Zusammenfassung:
The radical concentrations and g factors of stable organic radicals in different lignin preparations were determined by X-band EPR at 9 GHz. We observed that the g factor these radicals are largely determined by the extraction process and not by the botanical origin of the lignin. The parameter mostly influencing the g factor is the pH value during lignin extraction. This effect was studied in depth using high-field EPR spectroscopy at 263 GHz. We were able to determine the gxx, gyy and gzz component of the g tensor of the stable organic radicals in lignin. With the enhanced resolution of high-field EPR distinct radical species could be found in this complex polymer. The radical species are assigned to substituted o-semiquinone radicals and can exist in different protonation states SH3, SH2, SH1- and S2-. The proposed model structures are supported by DFT calculations. The g principal values of the proposed structure were all in reasonable agreement with the experiments.
