@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={Lignin-derived thermoplastics and elastomers with both versatile performance and commercialization potential have been an elusive pursuit for the past several decades. Lignin content has been limited to about 30 wt%, often requiring chemical modification, solvent fractionation of lignin, or prohibitively expensive additives. Each of these factors is a deterrent to industrial adoption of lignin-based polymers, limiting the potential of this renewable resource. Herein we describe high-performance multiphase thermoplastics made with a blend of 41 wt% unmodified industrial lignin and low-cost additives in a matrix of general-purpose acrylonitrile-butadiene rubber (NBR). Hardwood soda lignin (HSL) and softwood Kraft lignin (SKL) were blended under high shear conditions with NBR, carbon black (CB), polyethylene oxide (PEO), boric acid (BA), and dicumyl peroxide (DCP). This combination with SKL lignin in the proper proportions resulted in a thermoplastic with a tensile strength and failure strain of 25.2 MPa and 9%, respectively; it exhibited an unexpected tensile yield, similar to that of ABS, a commodity thermoplastic. The analogous HSL lignin compositions are tough materials with tensile strengths of 7.3–16.7 MPa and failure strain of 80–140%. The contrasting ductility and yield stress behavior were analyzed based on the compositions’ morphology and interfacial structure arising from the chemical nature of each lignin studied. The roles of CB as a reinforcement in the rubbery phase, DCP and BA as cross-linkers to create multiphase networks, and PEO to promote the adhesion and compatibility of lignin in commercial-grade NBR are also discussed in detail.}, 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{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}, 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{berlin_balakshin_gilkes_kadla_maximenko_kubo_saddler_2006, title={Inhibition of cellulase, xylanase and beta-glucosidase activities by softwood lignin preparations}, volume={125}, ISSN={["0168-1656"]}, DOI={10.1016/j.jbiotec.2006.02.021}, abstractNote={The conversion of lignocellulosic biomass to fuel ethanol typically involves a disruptive pretreatment process followed by enzyme-catalyzed hydrolysis of the cellulose and hemicellulose components to fermentable sugars. Attempts to improve process economics include protein engineering of cellulases, xylanases and related hydrolases to improve their specific activity or stability. However, it is recognized that enzyme performance is reduced during lignocellulose hydrolysis by interaction with lignin or lignin-carbohydrate complex (LCC), so the selection or engineering of enzymes with reduced lignin interaction offers an alternative means of enzyme improvement. This study examines the inhibition of seven cellulase preparations, three xylanase preparations and a beta-glucosidase preparation by two purified, particulate lignin preparations derived from softwood using an organosolv pretreatment process followed by enzymatic hydrolysis. The two lignin preparations had similar particle sizes and surface areas but differed significantly in other physical properties and in their chemical compositions determined by a 2D correlation HSQC NMR technique and quantitative 13C NMR spectroscopy. The various cellulases differed by up to 3.5-fold in their inhibition by lignin, while the xylanases showed less variability (< or = 1.7-fold). Of all the enzymes tested, beta-glucosidase was least affected by lignin.}, number={2}, journal={JOURNAL OF BIOTECHNOLOGY}, author={Berlin, Alex and Balakshin, Mikhail and Gilkes, Neil and Kadla, John and Maximenko, Vera and Kubo, Satoshi and Saddler, Jack}, year={2006}, month={Sep}, pages={198–209} }
 @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{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} }
 @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{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{balakshin_chen_gratzl_kirkman_jakob_2001, title={Biobleaching of pulp with dioxygen in laccase-mediator system - effect of variables on the reaction kinetics}, volume={16}, ISSN={["1873-3158"]}, DOI={10.1016/S1381-1177(01)00062-5}, abstractNote={Comparative studies were carried out on the kinetics and mechanism of pulp biobleaching with laccase-mediator system (LMS) with two different mediators, 1-hydroxybenzotriazole (HOBT) and N-hydroxyacetanilide (NHAA). The optimal NHAA and laccase charge was found to be 0.1 mmol and 10 U per gram of pulp with pulp consistency of 10%, at the reaction temperature of 40 °C for 8 h under atmospheric pressure, respectively. The kinetic studies on Kappa number reduction and dioxygen uptake suggest that a very fast rate of delignification with NHAA at the beginning of the process is the result of fast formation of the oxidized mediator species. However, a very slow delignification rate after the initial phase (0.5–1 h) could be caused by low stability of the mediator species. After the reaction time of 2 h, the degree of delignification is higher when HOBT is used as mediator. In contrast to the delignification with NHAA, the formation of the oxidized mediator species is the rate-determining step of the pulp biobleaching with dioxygen in the LMS using HOBT as mediator. Increase in temperature increases the rate of chemical reactions, but decreases the laccase stability. The optimal temperature for pulp biobleaching with HOBT and laccase from Coriolus versicolor is 40 °C. Increasing oxygen pressure improves the efficiency of delignification due to better penetration of the reagents, but does not affect the rate of chemical reactions. The reaction mechanism is discussed based on the kinetic data.}, number={3-4}, journal={JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC}, author={Balakshin, M and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2001}, month={Dec}, pages={205–215} }
 @article{balakshin_capanema_chen_gratzl_kirkman_gracz_2001, title={Biobleaching of pulp with dioxygen in the laccase-mediator system - reaction mechanisms for degradation of residual lignin}, volume={13}, ISSN={["1873-3158"]}, DOI={10.1016/S1381-1177(00)00225-3}, abstractNote={Pine Kraft-AQ pulp was biobleached with pressurized dioxygen at 40°C in laccase-mediator system (LMS), i.e. in acetate buffer (pH 4.5) containing Coriolus-laccase and 1-hydroxy-benzotriazole (HOBT), the latter being as a mediator. The LMS-treatment was followed by alkaline extraction (E) under standard conditions. The structures of the residual lignins before and after the biobleaching did not differ appreciably. This indicates that only a part of the residual lignin in the pulp undergoes oxidative degradation in the LMS treatment. In contrast, the treatment resulted in strong changes in the structure of the lignin isolated from E-effluents. The 2D HMQC (1H13C correlation) spectra showed the disappearance of β-O-4′, β-β′ and β-5′ bonds in the structure of the alkaline soluble lignin (ASL) from E-effluents, which are present in the 2D spectrum of the original residual lignin (RKL). In addition, the spectra exhibited new signals that are assigned to ArCOOH in biphenyl (5-5′) moieties. This implies that oxidative cleavage of side chains plays an important role in the delignification of pulp. The NMR studies also indicated that intensive degradation of aromatic ring has occurred in the biobleaching. However, premethylation of neither benzyl alcohol nor phenolic hydroxyl groups of the residual lignin in pulp before the biobleaching affected the rate of delignification. The latter indicates that phenolic moieties participate not only in oxidative degradation but also dehydrogenative polymerization reactions in the biobleaching. This is consistent with an appreciable increase in the proportion of fractions with higher molecular mass in lignin isolated from E-effluents.}, number={1-3}, journal={JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC}, author={Balakshin, M and Capanema, E and Chen, CL and Gratzl, J and Kirkman, A and Gracz, H}, year={2001}, month={Apr}, pages={1–16} }
 @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} }
 @article{capanema_balakshin_chen_gratzl_gracz_2001, title={Structural analysis of residual and technical lignins by H-1-C-13 correlation 2D NMR-spectroscopy}, volume={55}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2001.050}, abstractNote={Summary Structural analysis was conducted on residual lignin from pine Kraft AQ pulp, Eucalyptus Kraft lignin from Eucalyptus globulus and Repap Organosolv lignin by 2D 13C-1H correlation NMR spectroscopic techniques such as HMQC sequence. These lignins contain a rather wide variety of saturated aliphatic groups. The HMQC NMR spectra of the lignins do not verify the presence of diarylmethane moieties in any lignin investigated. The type and amount of other condensed structures depend on the nature of lignin preparation. All the lignins investigated still contained β-O-4′, pino- and syringayresinol (β-β′) and phenylcoumarane (β-5′) structures. Stilbene structures were also identified. Vinyl ether structures were present only in Eucalyptus Kraft lignin. All the lignins contain α-carbonyl groups conjugated to aromatic moieties as terminal side chains rather than involving β-O-4′ structures. No coniferyl alcohol and coniferyl aldehyde type structures are detected in the lignins after pulping. The spectra of kraft lignins show some new signals, the origin of which is discussed.}, number={3}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Gracz, H}, year={2001}, pages={302–308} }
 @article{balakskin_chen_gratzl_kirkman_jakob_2000, title={Biobleaching of pulp with dioxygen in the laccase-mediator system. Part 1. Kinetics of delignification}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.066}, abstractNote={Summary Kinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects of variable factors on the delignification were studied. The delignification was conducted in acetate buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage of 10 U Coriolus laccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The amounts of dioxygen consumed per removal of one C9-unit equivalent of residual lignin is rather high, 1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed by alkaline extraction (E), (LMS-E)4, decreased kappa number of a pine kraft-AQ pulp from 21.8 to less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.}, number={4}, journal={HOLZFORSCHUNG}, author={Balakskin, M and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={390–396} }
 @article{balakshin_chen_gratzl_kirkman_jakob_2000, title={Kinetic studies on oxidation of veratryl alcohol by laccase-mediator system - Part 1. Effects of mediator concentration}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.028}, abstractNote={Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.}, number={2}, journal={HOLZFORSCHUNG}, author={Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={165–170} }
 @article{balakshin_chen_gratzl_kirkman_jakob_2000, title={Kinetic studies on oxidation of veratryl alcohol by laccase-mediator system. Part 2. The kinetics of dioxygen uptake}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.029}, abstractNote={Summary The kinetics of dioxygen uptake in the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of ABTS, the mediator, was studied. The kinetics of dioxygen uptake consists of two phases: (1) the initial phase up to a reaction time of one hour, and (2) the second phase, after a reaction time of one hour. In the initial phase, ABTS is mainly oxidized to the corresponding cation radical. The kinetics of dioxygen uptake follows a pseudo-zero order rate law. The dioxygen uptake under the reaction condition correlates with the initial ABTS concentration according to the stoichiometric relationship of 0.25 moles dioxygen per mole ABTS. In the second phase, veratryl alcohol is mainly oxidized to veratraldehyde. The kinetics of the dioxygen uptake follows a pseudo-first order rate law. The dioxygen uptake correlates linearly with the yield of veratraldehyde. The stoichiometric ratio between the formation of veratraldehyde and the consumption of dioxygen differs slightly at different M/S ratios. On average, however, it is 0.42 moles of dioxygen per one mole of veratraldehyde formed. The reaction mechanism is discussed on the basis of the kinetic data.}, number={2}, journal={HOLZFORSCHUNG}, author={Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={171–175} }