@article{zoia_argyropoulos_2010, title={Detection of ketyl radicals using P-31 NMR spin trapping}, volume={23}, ISSN={["0894-3230"]}, DOI={10.1002/poc.1630}, abstractNote={AbstractOur recent work has allowed the development of 31P NMR spin trapping techniques for the detection and, at times, absolute quantification of many oxygen‐ and carbon‐centered free radical species. These methods are based on the ability of the nitrone phosphorus compound, 5‐diisopropoxy‐phosphoryl‐5‐methyl‐1‐pyrroline‐N‐oxide (DIPPMPO), to react with free radical species and form stable radical adducts, which are suitably detected and accurately quantified using 31P NMR. Our continuing efforts have now been focused on the application of this powerful system for the trapping of ketyl radicals, which are very difficult intermediates to be detected and quantified with traditional techniques (i.e., EPR). Ketyl radicals were initially produced using photochemical reactions of acetophenone, whose excited triplet state is able to abstract hydrogen from an H donor. As such, the 31P NMR signals for the radical adducts of the DIPPMPO spin trap with the ketyl radicals were assigned. Furthermore, in an effort to confirm the structure of these adducts, their mass spectra and fragmentation patterns were carefully examined under Gas Chromatography–Mass Spectrometry (GC–MS) conditions. Subsequently, the DIPPMPO spin trapping system was applied to the oxidation of 1‐(3,4‐dimethoxyphenyl)ethanol in the presence of horseradish peroxidase (HRP), hydrogen peroxide, and 1‐hydroxybenzotriazole (HBT) as the electron carrier (mediator). Our work confirmed that the mechanism consists of a hydrogen abstraction reaction from the α position, involving the ketyl radical: during the oxidation, the hydroxyl, hydroperoxyl, and ketyl radical intermediates were all detected. These efforts demonstrate the efficacy of our methodology that provides for the first time a facile means for the detection of the otherwise elusive ketyl radical species, with important implications in biology, chemistry, and biochemistry. Copyright © 2009 John Wiley & Sons, Ltd.}, number={6}, journal={JOURNAL OF PHYSICAL ORGANIC CHEMISTRY}, author={Zoia, Luca and Argyropoulos, Dimitris S.}, year={2010}, month={Jun}, pages={505–512} }
 @article{king_zoia_filpponen_olszewska_xie_kilpelainen_argyropoulos_2009, title={In Situ Determination of Lignin Phenolics and Wood Solubility in Imidazolium Chlorides Using P-31 NMR}, volume={57}, ISSN={["1520-5118"]}, DOI={10.1021/jf901095w}, abstractNote={Corn stover, Norway spruce, and Eucalyptus grandis were pulverized to different degrees. These samples were subjected to quantitative analyses, upon the basis of predissolution into the imidazolium chloride-based ionic liquids [amim]Cl and [bnmim]Cl followed by labeling of hydroxyl groups as phosphite esters and quantitative (31)P NMR analysis. Analysis of different pulverization degrees provided semiempirical data to chart the solubility of Norway spruce in these ionic liquids. Further method refinment afforded an optimized method of analysis of the lignin phenolic functionalities, without prior isolation of the lignin from the fiber. The lignin in these samples was further enriched using cellulase and acidolysis treatments, allowing for comparison with the fibrous samples. Analysis of all samples charts the polymerized-monomer availability for each stage of the treatment. Conditions required for adequate signal-to-noise ratios in the (31)P NMR analysis were established with a notable improvement observed upon the lignin enrichment steps.}, number={18}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={King, Alistair W. T. and Zoia, Luca and Filpponen, Ilari and Olszewska, Anna and Xie, Haibo and Kilpelainen, Ilkka and Argyropoulos, Dimitris S.}, year={2009}, month={Sep}, pages={8236–8243} }
 @article{zoia_orlandi_argyropoulos_2008, title={Microwave-Assisted Lignin Isolation Using the Enzymatic Mild Acidolysis (EMAL) Protocol}, volume={56}, ISSN={["1520-5118"]}, DOI={10.1021/jf801955b}, abstractNote={The use of microwaves is explored in an effort to further improve the recently developed lignin isolation protocol termed EMAL (enzymatic mild acidolysis lignin). Because the presence of the lignin-carbohydrate linkages seems to be rather pronounced within wood, a microwave reactor was used to replace traditional refluxing during the mild acidolysis step. This was done in an attempt to augment the selectivity of this step toward cleaving lignin-carbohydrate bonds as well as reducing the overall intensity of this step toward inducing changes in the lignin structure, thus affording lignin in greater yields and purities. Consequently, in this study the yields, purities, and structures of lignins isolated from spruce (softwood) by the EMAL protocol under various microwave conditions were examined. The variables studied included microwave power, microwave heating time, hydrochloric acid concentration and water content of the reaction medium. Microwave heating afforded EMAL samples of high purity (90%, comparable to the conventional protocol) but in significantly greater gravimetric yields. Quantitative (31)P NMR and SEC data confirmed that the structure of lignin was similar to that obtained by traditional EMALs, with comparable contents of beta-aryl ether bonds, phenolic hydroxyls (condensed and uncondensed), and carboxylic acids.}, number={21}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Zoia, Luca and Orlandi, Marco and Argyropoulos, Dimitris S.}, year={2008}, month={Nov}, pages={10115–10122} }