@article{monogioudi_permi_filpponen_lienemann_li_argyropoulos_buchert_mattinen_2011, title={Protein analysis by P-31 NMR spectroscopy in ionic liquid: Quantitative determination of enzymatically created cross-links}, volume={59}, number={4}, journal={Journal of Agricultural and Food Chemistry}, author={Monogioudi, E. and Permi, P. and Filpponen, I. and Lienemann, M. and Li, B. and Argyropoulos, D. and Buchert, J. and Mattinen, M. L.}, year={2011}, pages={1352–1362} }
 @article{li_filpponen_argyropoulos_2010, title={Acidolysis of Wood in Ionic Liquids}, volume={49}, ISSN={["0888-5885"]}, DOI={10.1021/ie1000983}, abstractNote={Three wood species including Eucalyptus grandis (E. grandis), Southern pine (S. pine), and Norway spruce thermomechanical pulp (N. spruce TMP) were dissolved in the ionic liquid (IL) 1-allyl-3-methylimidazolium chloride ([Amim]Cl), and then they were pretreated with small amounts of hydrochloric acid, as a function of time. The materials regenerated from the IL solutions were determined to contain significantly higher amounts of lignin than the original wood. Detailed analyses of the recovered IL revealed the presence of typical wood degradation compounds, such as 5-hydroxymethylfurfural, furan-2-carboxylic acid, catechol, methylcatechol, methylguaiacol, acetoguaiacone, and acetol. The acidic pretreatment of these wood species in IL resulted in not only the near-complete hydrolysis of cellulose and hemicelluloses but also in a significant amount of lignin degradation. Aqueous reactions (under identical acid concentrations) showed a remarkably lower efficiency, demonstrating that ILs offer a unique environ...}, number={7}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Li, Bin and Filpponen, Ilari and Argyropoulos, Dimitris S.}, year={2010}, month={Apr}, pages={3126–3136} }
 @article{li_asikkala_filpponen_argyropoulos_2010, title={Factors Affecting Wood Dissolution and Regeneration of Ionic Liquids}, volume={49}, ISSN={["0888-5885"]}, DOI={10.1021/ie901560p}, abstractNote={Three wood species, eucalyptus grandis (E. grandis), southern pine (S. pine), and Norway spruce thermomechanical pulp (N. spruce TMP) were pretreated by dissolution in the ionic liquid (IL) 1-allyl-3-methylimidazolium chloride ([AMIM]Cl). The wood was regenerated from the ionic liquid in high yield and the recycling of the ionic liquid was nearly quantitative. The lignin contents and the efficiencies of cellulase enzymatic hydrolyses of the regenerated wood were examined offering an understanding into the IL pretreatment efficiency. The components that remained within the recycled ILs were qualitatively characterized by 31P NMR spectroscopy. Wood density, pulverization intensity, and the nature of the regeneration nonsolvents were investigated as factors affecting the overall process. An increase in the wood density decreased the efficiency of the pretreatment, whereas extended pulverization periods decreased the yield of the regenerated wood after the IL pretreatment,with more glucose being released duri...}, number={5}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Li, Bin and Asikkala, Janne and Filpponen, Ilari and Argyropoulos, Dimitris S.}, year={2010}, month={Mar}, pages={2477–2484} }
 @article{filpponen_argyropoulos_2010, title={Regular Linking of Cellulose Nanocrystals via Click Chemistry: Synthesis and Formation of Cellulose Nanoplatelet Gels}, volume={11}, ISSN={["1526-4602"]}, DOI={10.1021/bm1000247}, abstractNote={Over a number of years work in our laboratory has been developing new chemistry for the use of cellulose nanocrystals (CNCs) as scaffolds for the creation of nanomaterials with novel, stimuli responsive characteristics. Our work takes advantage of the rigid nature of CNCs, the unique nanopattern etched on their surface in the form of regularly spaced primary OH groups, and the fact that these materials have all reducing end groups located on one end. In this communication, a method for the grafting of amine-terminated monomers onto surface-modified CNCs followed by click chemistry is demonstrated. Initially the primary hydroxyl groups on the surface of the CNCs were selectively activated by converting them to carboxylic acids by the use of TEMPO-mediated hypohalite oxidation. Further reactions using the activated TEMPO-oxidized CNCs were carried out via carbodiimide-mediated formation of an amide linkage between precursors carrying an amine functionality and the carboxylic acid groups on the surface of the TEMPO-oxidized CNCs. Subsequently, two sets of CNCs were prepared, containing on their surface an azide derivative and an alkyne derivative, respectively. Finally, the click chemistry reaction, that is, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between the azide and the alkyne, surface-activated CNC was employed, bringing together the nanocrystalline materials in a unique regularly packed arrangement demonstrating a degree of molecular control for creating these structures at the nano level.}, number={4}, journal={BIOMACROMOLECULES}, author={Filpponen, Ilari and Argyropoulos, Dimitris S.}, year={2010}, month={Apr}, pages={1060–1066} }
 @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{mattinen_filpponen_jarvinen_li_kallio_lehtinen_argyropoulos_2009, title={Structure of the Polyphenolic Component of Suberin Isolated from Potato (Solanum tuberosum var. Nikola)}, volume={57}, ISSN={["1520-5118"]}, DOI={10.1021/jf9020834}, abstractNote={Suberin is present in the underground parts of vegetables and in the bark of trees. Characterization of suberin and the structure of its polyphenolic component have been hampered by insolubility of the polymers. Thus, enzymatically isolated and extractive free suberin enriched fraction from potato, Solanum tuberosum var. Nikola, and the chemically further fractionated phenolics were characterized in solid state by FTIR, DSC, and elemental analysis to identify the groups and to verify success of isolation. For MW and quantitative determination of the groups, polymers were solubilized in ionic liquid derivatized and analyzed by GPC and (31)P NMR. Suberin enriched fraction, MW = ca. 44 x 10(3) g/mol, is a mixture of carbohydrates and polyesters of aliphatic long chain hydroxy fatty acids and diacids linked via ester bonds to the phenolics, MW = ca. 27 x 10(3) g/mol, formed by guaiacyl- and p-hydroxyphenyl structures. Phenolics in peels may be important sources of antioxidants for various applications.}, number={20}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Mattinen, Maija-Liisa and Filpponen, Ilari and Jarvinen, Riika and Li, Bin and Kallio, Heikki and Lehtinen, Pekka and Argyropoulos, Dimitris}, year={2009}, month={Oct}, pages={9747–9753} }
 @article{filpponen_argyropoulos_2008, title={Determination of Cellulose Reactivity by Using Phosphitylation and Quantitative P-31 NMR Spectroscopy}, volume={47}, ISSN={["0888-5885"]}, DOI={10.1021/ie800936x}, abstractNote={The phosphitylation of cellulose with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane [P(II)], is proposed as a means to determine its reactivity via an evaluation of its accessible hydroxyl groups. A variety of cellulose samples were subjected to this phosphitylation reaction, and the consumption of phosphitylation reagent was followed by quantitative 31P NMR spectroscopy. This consumption was found to be directly proportional to the amount of reactive hydroxyl groups on the cellulosic material. To further evaluate the quantitative reliability of this methodology, cellulose samples were subjected to a series of mechanical beating treatments, and the changes in the amount of accessible OH groups were evaluated. In addition, cellulose samples were equilibrated to various moisture contents, and their accessible OH groups were determined using the developed methodology. Both variables examined were found to affect the amount of reactive OH groups present on the samples with variations in the moisture con...}, number={22}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Filpponen, Ilari and Argyropoulos, Dimitris S.}, year={2008}, month={Nov}, pages={8906–8910} }
 @article{guerra_filpponen_lucia_argyropoulos_2006, title={Comparative evaluation of three lignin isolation protocols for various wood species}, volume={54}, ISSN={["1520-5118"]}, DOI={10.1021/jf062433c}, abstractNote={Milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and enzymatic mild acidolysis lignin (EMAL) were isolated from different wood species and characterized by various techniques. The EMAL protocol offered gravimetric lignin yields 2-5 times greater than those of the corresponding MWL and CEL. The purities of the EMALs were 3.75-10.6% higher than those of their corresponding CELs, depending upon the wood species from which they were isolated. Molecular weight analyses showed that the EMAL protocol isolates lignin fractions that are not accessed by the other procedures evaluated, while 31P NMR spectroscopy revealed that MWL is more condensed and bears more phenolic hydroxyl groups than EMAL and CEL. The yields and purities of EMAL, MWL, and CEL from hardwood were greater than those obtained for the examined softwoods. Structural details obtained by DFRC (derivatization followed by reductive cleavage)/31P NMR revealed different contents of condensed and uncondensed beta-O-aryl ether structures, dibenzodioxocins, and condensed and uncondensed phenolic hydroxyl and carboxylic acid groups within lignins isolated from different wood species.}, number={26}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Guerra, Anderson and Filpponen, Ilari and Lucia, Lucian A. and Argyropoulos, Dimitris S.}, year={2006}, month={Dec}, pages={9696–9705} }
 @article{filpponen_guerra_hai_lucia_argyropoulos_2006, title={Spectral monitoring of the formation and degradation of polysulfide ions in alkaline conditions}, volume={45}, ISSN={["0888-5885"]}, DOI={10.1021/ie060651p}, abstractNote={The recently developed protocol for the absolute determination of the various polysulfide species based by 1H NMR was applied to monitor the amount of such ions in alkaline media produced at different conditions. The thermal stability of each individual polysulfide species was also evaluated in temperature ranges representative of a typical alkaline pulping process. Overall, the species, S12-, S22-, S32-, S42-, S52-, and S62- were detected and quantified in all alkaline conditions evaluated. The concentration of sodium sulfide and the temperature were found to have a significant effect on the total amount of polysulfides detected. In summary, the di- and trisulfide anions were found to predominate over the other polysulfide species in all examined experimental conditions. Additionally, the experimental values of Ea for the thermal degradation of polysulfide species correlate with the observed stability of the individual species; i.e., S22- has the highest Ea, followed by S32-.}, number={22}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Filpponen, Ilari and Guerra, Anderson and Hai, Abdul and Lucia, n A. Lucia and Argyropoulos, Dimitris S.}, year={2006}, month={Oct}, pages={7388–7392} }
 @article{guerra_filpponen_lucia_saquing_baumberger_argyropoulos_2006, title={Toward a better understanding of the lignin isolation process from wood}, volume={54}, ISSN={["1520-5118"]}, DOI={10.1021/jf060722v}, abstractNote={The recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) coupled with the novel combination of derivatization followed by reductive cleavage (DFRC) and quantitative (31)P NMR spectroscopy were used to better understand the lignin isolation process from wood. The EMAL protocol is shown to offer access at lignin samples that are more representative of the overall lignin present in milled wood. The combination of DFRC/(31)P NMR provided a detailed picture on the effects of the isolation conditions on the lignin structure. More specifically, we have used vibratory and ball milling as the two methods of wood pulverization and have compared their effects on the lignin structures and molecular weights. Vibratory-milling conditions cause substantial lignin depolymerization. Lignin depolymerization occurs via the cleavage of uncondensed beta-aryl ether linkages, while condensed beta-aryl ethers and dibenzodioxocins were found to be resistant to such mechanical action. Condensation and side chain oxidations were induced mechanochemically under vibratory-milling conditions as evidenced by the increased amounts of condensed phenolic hydroxyl and carboxylic acid groups. Alternatively, the mild mechanical treatment offered by ball milling was found not to affect the isolated lignin macromolecular structure. However, the overall lignin yields were found to be compromised when the mechanical action was less intense, necessitating longer milling times under ball-milling conditions. As compared to other lignin preparations isolated from the same batch of milled wood, the yield of EMAL was about four times greater than the corresponding milled wood lignin (MWL) and about two times greater as compared to cellulolytic enzyme lignin (CEL). Molecular weight distribution analyses also pointed out that the EMAL protocol allows the isolation of lignin fractions that are not accessed by any other lignin isolation procedures.}, number={16}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Guerra, Anderson and Filpponen, Ilari and Lucia, Lucian A. and Saquing, Carl and Baumberger, Stephanie and Argyropoulos, Dimitris S.}, year={2006}, month={Aug}, pages={5939–5947} }
 @inproceedings{argyropoulos_filpponen, title={The use of cellulose nanocrystals as scaffolds for nanodevices; supramolecular chemistry using nature's most ambundant template}, booktitle={Research Progress in Paper Industry and Biorefinery (4th ISETPP), vols 1-3}, author={Argyropoulos, D. S. and Filpponen, I.}, pages={26–29} }