@article{bova_tran_balakshin_chen_capanema_naskar_2016, title={An approach towards tailoring interfacial structures and properties of multiphase renewable thermoplastics from lignin-nitrile rubber}, volume={18}, ISSN={["1463-9270"]}, DOI={10.1039/c6gc01067a}, abstractNote={High-performance multiphase thermoplastics were synthesized by reactive mixing of unmodified industrial lignin and low-cost additives in a matrix of general-purpose acrylonitrile-butadiene rubber (NBR).}, number={20}, journal={GREEN CHEMISTRY}, author={Bova, Tony and Tran, Chau D. and Balakshin, Mikhail Y. and Chen, Jihua and Capanema, Ewellyn A. and Naskar, Amit K.}, year={2016}, pages={5423–5437} }
 @article{balakshin_capanema_santos_chang_jameel_2016, title={Structural analysis of hardwood native lignins by quantitative C-13 NMR spectroscopy}, volume={70}, ISSN={["1437-434X"]}, DOI={10.1515/hf-2014-0328}, abstractNote={Abstract
               Milled wood lignins from alkaline pretreated wood with very low sugar content and a wide range of syringyl-to-guaiacyl (S/G) ratio between 1.2 and 3.0 were isolated from 12 industrially valuable hardwood (HW) species. The lignin preparations were investigated by means of a comprehensive 13C nuclear magnetic resonance (NMR) methodology to address the possibilities and limitations of this approach for HW native lignins and to estimate the structural variations within HW lignins. Good correlations were found for different independent methods for the quantification of major lignin moieties. The results were reliable at the C6 level and not only for relative comparison. The correlation was good between methoxyl group determinations by wet chemistry and those by 13C NMR spectroscopy. The limitations of the 13C NMR method were also pointed out. The differences in the S/G ratios can be large, but other structural deviations are less significant. Strong correlations between the S/G ratios and the amounts of other structural peculiarities could not be found by the 13C NMR approach. However, with increasing S/G ratios, the β-O-4 content showed increasing tendencies and the degree of condensation showed decreasing tendencies.}, number={2}, journal={HOLZFORSCHUNG}, author={Balakshin, Mikhail Yu and Capanema, Ewellyn A. and Santos, Ricardo B. and Chang, Hou-min and Jameel, Hasan}, year={2016}, month={Feb}, pages={95–108} }
 @article{capanema_balakshin_katahira_chang_jameel_2015, title={HOW WELL DO MWL AND CEL PREPARATIONS REPRESENT THE WHOLE HARDWOOD LIGNIN?}, volume={35}, ISSN={["1532-2319"]}, DOI={10.1080/02773813.2014.892993}, abstractNote={Hardwood lignin preparations were isolated using classical milled wood lignin (MWL) and cellulolytic enzyme lignin (CEL) protocols. Furthermore, we managed to produce a lignin preparation of a very high yield, above 90%, with high purity and minimal structural degradation. This was achieved by dissolution and regeneration of milled wood prior to enzymatic hydrolysis, along with the use of 80% dioxane for lignin extraction. This preparation (RCEL-80) yield was about 4.5 and 2.5 times higher than the yields of the traditional MWL and CEL preparations, correspondingly, at the same milling time. The preparations obtained were comprehensively analyzed with state-of-the-art quantitative NMR techniques and wet chemistry methods. CELs were representative preparations for hardwood lignins as the S/G ratios in the CELs were equivalent to those in lignin in situ. Degradation of the main lignin subunits was very low. Importantly, the structures of CELs were independent of the preparation yield and were very similar to the structure of the high-yield lignin, RCEL-80. In contrast, the structures of MWLs were noticeably dependent on the preparation yield, especially when the yield was below 15–20% of total wood lignin. In particular, the S/G ratio increased with increasing MWL yield, but was still lower than the S/G ratios of the whole lignins in situ, even at high MWL yields. The amounts of β-O-4 lignin units in MWL were lower than those in the corresponding CEL preparations. It has been concluded that CEL preparations were representative of the whole wood lignin whereas MWLs represent a fraction with a lower S/G ratio.}, number={1}, journal={JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY}, author={Capanema, Ewellyn and Balakshin, Mikhail and Katahira, Rui and Chang, Hou-min and Jameel, Hasan}, year={2015}, pages={17–26} }
 @article{santos_capanema_balakshin_chang_jameel_2012, title={Lignin Structural Variation in Hardwood Species}, volume={60}, ISSN={["1520-5118"]}, DOI={10.1021/jf301276a}, abstractNote={A comprehensive lignin structure analysis of ten industrially relevant hardwood species is presented. Milled wood lignin (MWL) was isolated from each species using a modified protocol and all milled wood lignin preparations were analyzed through quantitative (13)C NMR spectroscopy, elemental analysis, methoxyl analysis, sugar analysis, and nitrobenzene oxidation. Nitrobenzene oxidation and ozonation were carried out on extractive-free wood, alkali-extracted wood, milled wood lignin, and alkali-extracted lignin. Milled wood lignin isolated by the modified protocol was found to be representative of the total lignin in alkali-extracted wood. Significant variations in lignin structures, such as syringylpropane/guaiacylpropane ratio (S/G ratio), arylglycerol-β-aryl ether (β-O-4), degree of condensation, and elemental and methoxyl contents, were found among the hardwood species studied. These structural variations among species appear to be correlated to a single factor, the syringyl/guaiacyl ratio. A new method to predict the S/G ratio of total lignin in wood was developed, using a calibration line established by the syringaldehyde/vanillin (S/V) ratio (nitrobenzene oxidation) and the S/G ratio ((13)C NMR) of milled wood lignin (MWL).}, number={19}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Santos, Ricardo B. and Capanema, Ewellyn A. and Balakshin, Mikhail Yu and Chang, Hou-min and Jameel, Hasan}, year={2012}, month={May}, pages={4923–4930} }
 @article{martin-sampedro_capanema_hoeger_villar_rojas_2011, title={Lignin Changes after Steam Explosion and Laccase-Mediator Treatment of Eucalyptus Wood Chips}, volume={59}, ISSN={["1520-5118"]}, DOI={10.1021/jf201605f}, abstractNote={Eucalyptus globulus chips were steam exploded followed by treatment with a laccase-mediator system (LMS) under different experimental conditions. Removal of hemicelluloses and, to a lesser extent, lignin was observed. Thermogravimetic analyses of whole meal obtained from chips before and after steam explosion indicated an increase in lignin degradation temperature due to lignin condensation. In contrast, application of LMS treatment caused a reduction in lignin and polysaccharide degradation temperatures. Lignins were isolated from wood samples before and after each treatment and analyzed by 2D NMR and (13)C NMR. An increase in carboxyl and phenolic hydroxyl groups and a significant decrease in β-O-4 structures were found in steam-exploded samples. The most relevant changes observed after laccase treatment were increased secondary OH and degree of condensation.}, number={16}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Martin-Sampedro, Raquel and Capanema, Ewellyn A. and Hoeger, Ingrid and Villar, Juan C. and Rojas, Orlando J.}, year={2011}, month={Aug}, pages={8761–8769} }
 @article{balakshin_capanema_gracz_chang_jameel_2011, title={Quantification of lignin-carbohydrate linkages with high-resolution NMR spectroscopy}, volume={233}, ISSN={["0032-0935"]}, DOI={10.1007/s00425-011-1359-2}, abstractNote={A quantitative approach to characterize lignin-carbohydrate complex (LCC) linkages using a combination of quantitative ¹³C NMR and HSQC 2D NMR techniques has been developed. Crude milled wood lignin (MWLc), LCC extracted from MWLc with acetic acid (LCC-AcOH) and cellulolytic enzyme lignin (CEL) preparations were isolated from loblolly pine (Pinus taeda) and white birch (Betula pendula) woods and characterized using this methodology on a routine 300 MHz NMR spectrometer and on a 950 MHz spectrometer equipped with a cryogenic probe. Structural variations in the pine and birch LCC preparations of different types (MWL, CEL and LCC-AcOH) were elucidated. The use of the high field NMR spectrometer equipped with the cryogenic probe resulted in a remarkable improvement in the resolution of the LCC signals and, therefore, is of primary importance for an accurate quantification of LCC linkages. The preparations investigated showed the presence of different amounts of benzyl ether, γ-ester and phenyl glycoside LCC bonds. Benzyl ester moieties were not detected. Pine LCC-AcOH and birch MWLc preparations were preferable for the analysis of phenyl glycoside and ester LCC linkages in pine and birch, correspondingly, whereas CEL preparations were the best to study benzyl ether LCC structures. The data obtained indicate that pinewood contains higher amounts of benzyl ether LCC linkages, but lower amounts of phenyl glycoside and γ-ester LCC moieties as compared to birch wood.}, number={6}, journal={PLANTA}, author={Balakshin, Mikhail and Capanema, Ewellyn and Gracz, Hanna and Chang, Hou-min and Jameel, Hasan}, year={2011}, month={Jun}, pages={1097–1110} }
 @article{schmidt_schwartzberg_perera_weber-bargioni_carroll_sarkar_bosneaga_urban_song_balakshin_et al._2009, title={Label-free in situ imaging of lignification in the cell wall of low lignin transgenic Populus trichocarpa}, volume={230}, ISSN={["1432-2048"]}, DOI={10.1007/s00425-009-0963-x}, abstractNote={Chemical imaging by confocal Raman microscopy has been used for the visualization of the cellulose and lignin distribution in wood cell walls. Lignin reduction in wood can be achieved by, for example, transgenic suppression of a monolignol biosynthesis gene encoding 4-coumarate-CoA ligase (4CL). Here, we use confocal Raman microscopy to compare lignification in wild type and lignin-reduced 4CL transgenic Populus trichocarpa stem wood with spatial resolution that is sub-μm. Analyzing the lignin Raman bands in the spectral region between 1,600 and 1,700 cm−1, differences in lignin signal intensity and localization are mapped in situ. Transgenic reduction of lignin is particularly pronounced in the S2 wall layer of fibers, suggesting that such transgenic approach may help overcome cell wall recalcitrance to wood saccharification. Spatial heterogeneity in the lignin composition, in particular with regard to ethylenic residues, is observed in both samples.}, number={3}, journal={PLANTA}, author={Schmidt, M. and Schwartzberg, A. M. and Perera, P. N. and Weber-Bargioni, A. and Carroll, A. and Sarkar, P. and Bosneaga, E. and Urban, J. J. and Song, J. and Balakshin, M. Y. and et al.}, year={2009}, month={Aug}, pages={589–597} }
 @article{balakshin_capanema_chang_2007, title={MWL fraction with a high concentration of lignin-carbohydrate linkages: Isolation and 2D NMR spectroscopic analysis}, volume={61}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2007.001}, abstractNote={Abstract
            A preparation enriched in lignin-carbohydrate fragments (LCC-AcOH) was isolated in the course of purification of loblolly pine crude milled wood lignin (MWL). The preparation contained approximately equal amounts of lignin and carbohydrates, with high amounts of arabinose and galactose compared to their levels in wood. LCC-AcOH was investigated by 2D 1H-13C (HMQC and HMBC) correlation NMR techniques and quantitative 13C NMR. The HMQC spectra allowed direct detection of phenyl glycoside, ester and benzyl ether lignin-carbohydrates linkages in high amounts. The assignment of these structures was supported by the HMBC technique. It is noteworthy that in the ester lignin-carbohydrate linkages, a uronic acid residue was attached not to the benzylic position of lignin, as commonly believed, but to the γ-position of the side chain.}, number={1}, journal={HOLZFORSCHUNG}, author={Balakshin, Mikhail Yu. and Capanema, Ewellyn A. and Chang, Hou-min}, year={2007}, pages={1–7} }
 @article{capanema_balakshin_chen_gratzl_2006, title={Oxidative ammonolysis of technical lignins. Part 4. Effects of the ammonium hydroxide concentration and pH}, volume={26}, ISSN={["0277-3813"]}, DOI={10.1080/02773810600582350}, abstractNote={Abstract The effects of ammonium hydroxide concentration and pH on the kinetics and reaction mechanism of oxidative ammonolysis of Repap organosolv lignin were studied. The reactions were carried out at 100°C with an oxygen pressure of 8 bar (116 psi) and 0.4–1.6 M [NH4OH] and 9–12.7 pH. The resulting N‐modified lignins were analyzed for elemental composition and methoxyl group content. An increase in ammonium hydroxide concentration increased the rate of nitrogen incorporation, oxygen consumption, CO2 formation, and lignin dissolution. The rate of nitrogen incorporation was 0.5 order with respect to NH4OH concentration. The amount of oxygen consumed, oxygen incorporated into the lignin, CO2 formed, and OMe groups eliminated per mole of nitrogen incorporated decreased with increasing ammonium hydroxide concentration indicating that the increase in [NH4OH] accelerated nitrogen incorporation more than lignin oxidation. The dependence of the rate of nitrogen incorporation on the reaction pH went through a maximum leading to the conclusion that HO− competes with ammonia in reactions with electrophilic lignin centers resulting in interruption of nitrogen incorporation into the lignin.}, number={1}, journal={JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS}, year={2006}, pages={95–109} }
 @article{balakshin_capanema_goldfarb_frampton_kadla_2005, title={NMR studies on Fraser fir Abies fraseri (Pursh) Poir. Lignins (vol 59, 488, 2005)}, volume={59}, ISSN={["1437-434X"]}, DOI={10.1515/hf.2005.112}, abstractNote={Abstracting & Indexing}, number={6}, journal={HOLZFORSCHUNG}, author={Balakshin, MY and Capanema, EA and Goldfarb, B and Frampton, J and Kadla, JF}, year={2005}, pages={706–706} }
 @article{capanema_balakshin_kadla_2005, title={Quantitative characterization of a hardwood milled wood lignin by nuclear magnetic resonance spectroscopy}, volume={53}, ISSN={["1520-5118"]}, DOI={10.1021/jf0515330}, abstractNote={The structure of Eucalyptus grandis milled wood lignin (MWL) was investigated by 2D 1H-13C HSQC, HMQC, and 1H-1H TOCSY correlation NMR techniques and by quantitative 13C NMR as well as by the permanganate oxidation degradation technique. The combination of 2D NMR and quantitative 13C NMR spectroscopy of nonacetylated and acetylated lignin preparations allowed reliable identification and calculation of the amount of different lignin structures. About 85% of side-chain moieties were estimated on the structural level. This information was substantiated by data on the quantity of various functional groups and interunit linkages as a whole. A modified method for calculation of the h:g:s ratio has been suggested and compared with previously suggested approaches. E. grandis MWL has been determined to have an h:g:s ratio of 2:36:62. The amounts of various phenolic/etherified noncondensed/condensed guaiacyl and syringyl moieties were approximately estimated. E. grandis MWL contained approximately 0.60/Ar of beta-O-4 moieties along with small amounts of other structural units such as pino/syringyresinol (0.03/Ar), phenylcoumaran (0.03/Ar), and spirodienone (0.05/Ar). The degree of condensation was estimated at approximately 21%; the main condensed structures are 4-O-5 moieties (approximately 0.09/Ar). The structure of E. grandis MWL was compared with those of other lignin preparations isolated from various hardwoods.}, number={25}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Capanema, EA and Balakshin, MY and Kadla, JF}, year={2005}, month={Dec}, pages={9639–9649} }
 @article{yeh_yamada_capanema_chang_chiang_kadla_2005, title={Rapid screening of wood chemical component variations using transmittance near-infrared spectroscopy}, volume={53}, ISSN={["1520-5118"]}, DOI={10.1021/jf0480647}, abstractNote={A rapid transmittance near-infrared (NIR) spectroscopy method was developed to predict the variation in chemical composition of solid wood. The effect of sample preparation, sample quantity (single versus stacked multiple wood wafers), and NIR acquisition time on the quantification of alpha-cellulose and lignin content was investigated. Strong correlations were obtained between laboratory wet chemistry values and the NIR-predicted values. In addition to the experimental protocol and method development, improvements in calibration error associated with utilizing stacked multiple wood wafers as opposed to single wood wafers are also discussed.}, number={9}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Yeh, TF and Yamada, T and Capanema, E and Chang, HM and Chiang, V and Kadla, JF}, year={2005}, month={May}, pages={3328–3332} }
 @article{capanema_balakshin_kadla_2004, title={A comprehensive approach for quantitative lignin characterization by NMR spectroscopy}, volume={52}, ISSN={["1520-5118"]}, DOI={10.1021/jf035282b}, abstractNote={A detailed approach for the quantification of different lignin structures in milled wood lignin (MWL) has been suggested using a combination of NMR techniques. 1H-13C heteronuclear multiple quantum coherence and quantitative 13C NMR of nonacetylated and acetylated spruce MWL have been found to have a synergetic effect, resulting in significant progress in the characterization of lignin moieties by NMR. About 80% of side chain moieties, such as different beta-O-4, dibenzodioxocin, phenylcoumaran, pinoresinol, and others, have been identified on the structural level. The presence of appreciable amounts of alpha-O-alkyl and gamma-O-alkyl ethers has been suggested. Although the quantification of various condensed moieties was less precise than for side chain structures, reliable information can be obtained. Comparison of the calculated results with known databases on spruce MWL structure shows that the suggested approach is rather informative and comparable with the information obtained from the combination of various wet chemistry methods. Discrepancies between the results obtained in this study and those previously published are discussed.}, number={7}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Capanema, EA and Balakshin, MY and Kadla, JF}, year={2004}, month={Apr}, pages={1850–1860} }
 @article{capanema_balakshin_chen_2004, title={An improved procedure for isolation of residual lignins from hardwood kraft pulps}, volume={58}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2004.070}, abstractNote={Abstract
            Residual lignin preparations were isolated from birch, aspen and Eucalyptus grandis kraft pulp by enzymatic hydrolysis of the pulps with cellulase:hemicellulase mixture. Residual lignin preparations were characterized by investigation of nitrogen content, carbohydrate composition and molecular mass distribution. The use of enzyme with high activity and optimization of enzyme charge resulted in significant decrease in protein contaminants in residual lignin preparations as compared to previously published results. A second order law correlation between enzyme mass charge and nitrogen content in birch residual lignin preparations indicates a strong effect of enzyme charge on the amount of protein contaminants. However, the enzyme charge in the range studied does not appreciably affect either the yields of the residual lignin preparations or percentage and composition of carbohydrates in these preparations. The optimal enzyme charge was highest for Eucalyptus grandis pulp and lowest for birch pulp. It has been suggested that a significant part of the hardwood residual lignin in pulps, especially in E. grandis pulp, consists of low molecular mass lignin fragments bonded to pulp carbohydrates. Higher amount of glucose in E. grandis residual lignin preparation compared to those from birch and aspen implied a higher frequency of lignin-cellulose bonds in eucalypt pulp. Different fractions of birch residual lignin have rather similar molecular mass distribution, which was not affected by the charge of the enzyme. Eucalypt residual lignin preparation had higher molecular mass than birch residual lignin.}, number={5}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL}, year={2004}, pages={464–472} }
 @inproceedings{yu_capanema_batista_josserand_johnson_nelson_mckeand_mackay_kadla_li_et al._2004, title={Tracking down the effects of a rare mutant gene in loblolly pine: a first report}, booktitle={2004 Paper Summit, Spring Technical and International Environmental Conference}, publisher={CD-ROM published by TAPPI,  Norcross, GA}, author={Yu, Q. and Capanema, E. and Batista, V. B. and Josserand, S. and Johnson, G. and Nelson, C. D. and McKeand, S. E. and MacKay, J. J. and Kadla, J. F. and Li, B. and et al.}, year={2004} }
 @article{alves_capanema_chen_gratzl_2003, title={Comparative studies on oxidation of lignin model compounds with hydrogen peroxide using Mn(IV)-Me(3)TACN and Mn(IV)-Me4DTNE as catalyst}, volume={206}, ISSN={["1381-1169"]}, DOI={10.1016/S1381-1169(03)00448-5}, abstractNote={Comparative studies are conducted on the kinetics and reaction mechanism for the oxidation of lignin model compounds, 1-(3,4-dimethoxyphenyl)ethanol (1), 1-(3,4-dimethoxyphenyl)-1-propene (2) and E-1,2-diphenylethene (3) with hydrogen peroxide at reaction temperatures below 80 °C using [LMn(IV)(μ-O)3Mn(IV)L](PF6)2 (C-1) and [L′Mn(IV)(μ-O)3Mn(IV)](ClO4)2 (C-2) as catalyst. The disappearance rate of 1 and 2 in the first phase of C-1-catalyzed oxidation increases up to the temperature range of 50–60 °C then decreases with increasing reaction temperature. The cause for the slow down of the disappearance rate is not known. Based on the kinetic data and reaction products identified, C-1 is found to be more effective as catalyst in the oxidation of 1 and 2 than C-2, but less effective in the oxidation of 3. In the C-1- and C-2-catalyzed oxidation, 1 is oxidized to the corresponding α-carbonyl derivative 4, while 2 readily undergoes epoxidation of the conjugated double bond to produce the corresponding epoxides 5 and 6. The anti-Markovnikov nucleophilic addition of hydroxide and hydroperoxide anions on 5 and 6 then produced α,β-diol 7 and benzaldehyde derivative 8, which are non-catalytic reactions and rate determining steps. The compound 3 also undergoes epoxidation of conjugated aliphatic double bond producing the corresponding epoxide 9. However, none of the corresponding α,β-diol and benzaldehyde derivative is detected in the reaction mixture. In addition, 2 is more susceptible to expoxidation than 3. On the basis of the kinetics and reaction mechanism of the reactions, the catalytic cycles of the C-1- and C-2-catalyzed oxidation of 1–3 are postulated.}, number={1-2}, journal={JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL}, author={Alves, V and Capanema, E and Chen, CL and Gratzl, J}, year={2003}, month={Oct}, pages={37–51} }
 @article{chen_capanema_gracz_2003, title={Comparative studies on the delignification of pine kraft-anthraquinone pulp with hydrogen peroxide by binucleus Mn(IV) complex catalysis}, volume={51}, ISSN={["0021-8561"]}, DOI={10.1021/jf034507f}, abstractNote={Pine kraft-anthraquinone (kraft-AQ) pulp was bleached in alkaline solution with hydrogen peroxide catalyzed by either [L(1)Mn(IV)(micro-O)(3)Mn(IV)L(1)](PF(6))(2)] (C1) or [LMn(IV)(2)(micro-O)(3)] (ClO(4))(2) (C2) at 60 and 80 degrees C for 120 min with a catalyst charge of 10 ppm on pulp. The resulting bleached pulp was hydrolyzed with cellulase to obtain insoluble and soluble residual lignins. The alkaline bleaching effluents were acidified to precipitate alkaline-soluble lignins. These lignin preparations were then characterized by 2D heteronuclear multiple-quantum coherence (HMQC) NMR spectroscopic techniques. The results showed that biphenyl (5-5) and stilbene structures of the residual lignin in the pulp are preferentially degraded in both the C1- and C2-catalyzed bleachings, whereas beta-O-4, beta-5, and beta-beta structures undergo degradation to a lesser extent. In both cases, the degradation of the residual lignin increased with the increase in reaction temperature from 60 to 80 degrees C. Thus, the result of C1-catalyzed delignification is not in agreement with the observed decrease in the disappearance rate for substrates in the C1-catalyzed oxidation of lignin model compounds with hydrogen peroxide when the reaction temperature is increased from 60 to 80 degrees C. In addition, the resulting residual lignins in the C2-catalyzed bleaching at 80 degrees C are less degraded than the corresponding lignins in the C1-catalyzed bleaching at both 60 and 80 degrees C. Thus, C1 is more effective than C2 as catalyst in the binucleus Mn(IV) complex-catalyzed bleaching of pine kraft-AQ pulp with hydrogen peroxide.}, number={21}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Chen, CL and Capanema, EA and Gracz, HS}, year={2003}, month={Oct}, pages={6223–6232} }
 @article{balakshin_capanema_chen_gracz_2003, title={Elucidation of the structures of residual and dissolved pine kraft lignins using an HMQC NMR technique}, volume={51}, ISSN={["1520-5118"]}, DOI={10.1021/jf034372d}, abstractNote={Comparative studies on the structures of residual and dissolved lignins isolated from pine kraft pulp and pulping liquor have been undertaken using the (1)H-(13)C HMQC NMR technique, GPC, and sugar analysis to elucidate the reaction mechanisms in kraft pulping and the lignin reactivity. A modified procedure for the isolation of enzymatic residual lignins has resulted in an appreciable decrease in protein contaminants in the residual lignin preparations (N content < 0.2%). The very high dispersion of HMQC spectra allows identification of different lignin moieties, which signals appear overlapped in 1D (13)C NMR spectra. Elucidation of the role of condensation reactions indicates that an increase in the degree of lignin condensation during pulping results from accumulation of original condensed lignin moieties rather than from the formation of new alkyl-aryl structures. Among aryl-vinyl type moieties, only stilbene structures are accumulated in lignin in appreciable amounts. Benzyl ether lignin-carbohydrate bonds involving primary hydroxyl groups of carbohydrates have been detected in residual and dissolved lignin preparations. Structures of the alpha-hydroxyacid type have been postulated to be among the important lignin degradation products in kraft pulping. The effect of the isolation method on the lignin structure and differences between the residual and dissolved lignins are discussed.}, number={21}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Balakshin, MY and Capanema, EA and Chen, CL and Gracz, HS}, year={2003}, month={Oct}, pages={6116–6127} }
 @article{chen_capanema_gracz_2003, title={Reaction mechanisms in delignification of pine Kraft-AQ pulp with hydrogen peroxide using Mn(IV)-Me4DTNE as catalyst}, volume={51}, ISSN={["0021-8561"]}, DOI={10.1021/jf020992n}, abstractNote={Pine Kraft-AQ pulp was bleached with hydrogen peroxide catalyzed by [LMn(IV)(2) (mu-O)(3)](ClO(4))(2) at 80 degrees C for 120 min under optimum reaction conditions. The resulting bleached pulp was hydrolyzed with cellulase to obtain insoluble and soluble residual lignins. The alkaline effluent from the bleaching was acidified to precipitate alkaline soluble lignin. These lignin preparations were purified, and then analyzed by 2D HMQC NMR spectroscopic techniques. The results showed that biphenyl (5-5) and stilbene structures are preferentially degraded in the bleaching process, while beta-O-4, beta-5, and beta-beta structures undergo degradation only to a lesser extent. This implies that hydrogen peroxide bleaching using the catalyst is more effective in delignification of softwood pulps than hardwood pulps. The possible reaction mechanisms for the delignification of residual lignin in the pine Kraft-AQ pulp in the bleaching process are discussed on the basis of the 2D HMQC NMR spectroscopic data and the model compound experiments.}, number={7}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Chen, CL and Capanema, EA and Gracz, HS}, year={2003}, month={Mar}, pages={1932–1941} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2002, title={Oxidative ammonolysis of technical lignins - Part 3. Effect of temperature on the reaction rate}, volume={56}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2002.063}, abstractNote={Summary
            The effect of the reaction temperature on the kinetics and the reaction mechanism of oxidative ammonolysis of Repap organosolv lignin have been studied. The reaction was conducted in 0.8 M Nh4oh solution under oxygen pressure of 12 bar and at three different temperatures, 70 °C, 100 °C and 130 °C. The resulting N-modified lignins were analyzed by elemental and methoxyl group. About 20–25% of maximum nitrogen content is incorporated into the lignin very fast, in 1–2 min of the reaction. The reaction kinetics then follows a pseudo-first order reaction law and consists of two phases. The activation energies for nitrogen incorporation and lignin solubilization are rather low, in the range of 33–34 kJ/mol. Linear correlation between nitrogen incorporated into the lignin and molecular oxygen uptake, oxygen incorporation, CO2 formation, O-demethylation and total carbon loss was analyzed at the different reaction temperatures. On the basis of kinetic data obtained so far, we have postulated that the reaction temperature affects the reaction rate, but not the reaction pathways. The reaction temperature also affects the ratios between different reaction pathways, though the effect is not very strong. The results obtained are discussed in the terms of competitive reactions of lignin oxidation followed by nitrogen incorporation and lignin deactivation involving nitrogen}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2002}, pages={402–415} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2001, title={Oxidative ammonolysis of technical lignins - Part 1. Kinetics of the reaction under isothermal condition at 130 degrees C}, volume={55}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2001.066}, abstractNote={Summary
            Investigations were conducted on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C in 0.8M NH4OH solution under oxygen pressure of 12 bar. The lignin was completely solubilized at the reaction time of 165 min. The kinetics of the nitrogen incorporation consists of two phases. The first phase is up to the reaction time of approximately 35 min including 15 min heating up period. The rate of nitrogen incorporation in the first phase is 2.3 times higher than that in the second phase: κ1 = 4.58 × 10−4 s−1 
               versus κ2 = 1.90 × 10−4 s−1. The oxygen uptake and CO2 formation in the reaction is rather high. When the nitrogen incorporation was ceased after reaction for 255 minutes, more than 4 moles of oxygen/C9-unit of lignin were consumed and approximately 1.5 moles of carbon dioxide/C9-unit of lignin were released. In addition, extensive O-demethylation of methoxyl groups occurred. The molar ratio of the nitrogen incorporation to the methoxyl group eliminated is approximately 1.4 and 0.7 for the soluble and insoluble N-modified lignins, respectively. Structural analyses of the soluble N-modified lignins by FTIR and 1H NMR spectroscopic techniques showed only quantitative differences in the spectra obtained at different reaction times. This indicates that the reaction pathways do not change in the course of the oxidative ammonolysis. Possible reaction mechanisms of the oxidative ammonolysis are discussed on the basis of the experimental data.}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2001}, pages={397–404} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2001, title={Oxidative ammonolysis of technical lignins - Part 2. Effect of oxygen pressure}, volume={55}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2001.067}, abstractNote={Summary
            Investigations were conducted on the effects of oxygen pressure on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C under oxygen pressure of 5, 8 and 12 bar. The rates of reactions monitored, such as nitrogen incorporation, lignin solubilization, oxygen uptake and CO2 formation, increase with increasing oxygen pressure. Kinetics of nitrogen incorporation under different oxygen pressure consists of two phases and follows a first order law in each phase. Linear correlation between the rate of nitrogen incorporation and oxygen pressure implies that the reaction is first order with respect to oxygen concentration. This indicates that oxygen participates directly in the rate-determining step of nitrogen incorporation. The rate of lignin solubilization also linearly increases with increasing oxygen pressure, implying that the rate of lignin degradation directly depends on oxygen pressure. The nitrogen incorporation is linearly correlated with the oxygen uptake, CO2 formation, oxygen incorporation into lignin, loss of carbon and methoxyl group content under all values of oxygen pressure and during the entire reaction period. This suggests that the reactions in the oxidative ammonolysis of lignin proceed via the same pathways in the different kinetic phases. In addition, the changes in the oxygen pressure were found to have only minor effect upon the coefficients of these linear correlations. This is in good agreement with the structures of N-modified lignin elucidated from FTIR and indicates that oxygen pressure affects only the reaction rate, but not the reaction mechanism.}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2001}, pages={405–412} }