A Comprehensive Approach for Quantitative Lignin Characterization by NMR Spectroscopy (original) (raw)
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Journal of Agricultural and Food Chemistry, 2005
The structure of Eucalyptus grandis milled wood lignin (MWL) was investigated by 2D 1 H-13 C HSQC, HMQC, and 1 H-1 H TOCSY correlation NMR techniques and by quantitative 13 C NMR as well as by the permanganate oxidation degradation technique. The combination of 2D NMR and quantitative 13 C 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 ∼0.60/Ar of -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 ∼21%; the main condensed structures are 4-O-5 moieties (∼0.09/Ar). The structure of E. grandis MWL was compared with those of other lignin preparations isolated from various hardwoods.
Isolation and structural characterization of the milled-wood lignin from Paulownia fortunei wood
2009
The chemical structure of the milled-wood lignin isolated from Paulownia fortunei wood was investigated. The lignins were characterized by analytical pyrolysis and two-dimensional NMR that indicated a predominance of guaiacyl (G) over syringyl (S) units, and only showed small amounts of p-hydroxyphenyl (H) units, with a H:G:S molar ratio of 1:59:40. The heteronuclear single quantum correlation (HSQC) NMR spectrum gave additional information about the relative abundances of the different inter-unit linkages present in the lignin structure. Paulownia lignin showed a predominance of -O-4� aryl ether linkages (62% of total side-chains), followed by � resinol-type (12%) and -5 � phenylcoumaran-type structures (11%) and with lower amounts of other condensed structures such as spirodienone (3%) and dibenzodioxocin (2%) structures. The high lignin content (ca. 23% Klason lignin), together with the low S/G ratio and the abundance of condensed (carbon–carbon linked) structures (together with ...
Structural characterization of milled wood lignins from different eucalypt species
Holzforschung, 2008
The chemical structure of milled-wood lignins from Eucalyptus globulus, E. nitens, E. maidenii, E. grandis, and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, thioacidolysis, and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units. E. globulus lignin had the highest syringyl content. The heteronuclear single quantum correlation (HSQC) NMR spectra yielded information about relative abundances of inter-unit linkages in the whole polymer. All the lignins showed a predominance of b-O-49 ether linkages (66-72% of total side-chains), followed by b-b9 resinoltype linkages (16-19%) and lower amounts of b-59 phenylcoumaran-type (3-7%) and b-19 spirodienone-type linkages (1-4%). The analysis of desulfurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds, and the type of units (syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, 93-94% of the total b-b9 dimers included two syringyl units indicating that most of the b-b9 substructures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound were found which were tentatively identified as arising from a b-b9 syringaresinol substructure attached to a guaiacyl unit through a 4-O-59 linkage.
Isolation and Characterization of Lignin from Tropical and Temperate Hardwood
2010
The okra (Abelmoschus esculentus) plant consists of bast fiber and core (stick). The bast fibre of okra plant was characterized with high α-cellulose (56.7%) and low lignin (12.6%) and stick withlow α-cellulose (34.3%) and high lignin (25.2%) content. Lignin was isolated from the fiber and stick by acidolytic dioxane method and characterized for elemental analysis, methoxyl analysis and FTIR and 1 H-NMR spectroscopy. The C 9 formulas for okra stick and fibre lignin were C 9 H 9. 61 O 4.63 (OCH 3) 1.24 and C 9 H 8.61 O 4.66 (OCH 3) 1.49, respectively. Both of the lignins were of the guaiacyl-syringyl type. The bands of FT-IR spectrum at 1327 cm-1 , 1122 cm-1 and 837 cm-1 associated with syringyl unit was higher in okra fibre lignin than in the okra stick lignin. The structural analysis revealed that the average numbers of proton of β-O-4 (Hα & Hβ) per C 9 unit in okra stick and fibre lignin were 1.53 and 1.20, respectively. The β-O-4 units in these lignins had predominately erythro stereochemistry type.
Lignin Structural Variation in Hardwood Species
Journal of Agricultural and Food Chemistry, 2012
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). Figure 1. The lignin precursors and the most abundant linkage in lignin: arylglycerol-β-aryl ether (β-O-4).
Structural Analysis of Residual and Technical Lignins by 1H-13C Correlation 2D NMR-Spectroscopy
Holzforschung, 2000
Structural analysis was conducted on residual lignin from pine Kraft AQ pulp, Eucalyptus Kraft lignin from Eucalyptus globulus and Repap Organosolv lignin by 2D 13 C-1 H 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 b-O-4', pino-and syringayresinol (b-b') and phenylcoumarane (b-5') structures. Stilbene structures were also identified. Vinyl ether structures were present only in Eucalyptus Kraft lignin. All the lignins contain a-carbonyl groups conjugated to aromatic moieties as terminal side chains rather than involving b-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.
Extraction and characterization of two residual lignins from eucalyptus wood
Ciência Florestal
Lignin, the second most abundant biopolymer on the planet, has properties that can be widely explored, moving from waste to products with high added value. Therefore, this work aimed to extract and characterize Klason and Kraft lignins from sawdust and black liquor, considered industrial waste. The raw material used was Eucalyptus grandis chips. To obtain Klason lignin according to TAPPI 222 om-02 (2002), part of the chips were transformed into sawdust. To obtain Kraft lignin, another part of the chips passed through a digester to obtain black liquor, which was subsequently subjected to acid precipitation. The characterization of lignins was performed by granulometry analysis, scanning electron microscopy with elemental chemical analysis (EDS), transmission electron microscopy, medium infrared spectroscopy, thermogravimetric analysis and differential calorimetry. Microscopy analyzes showed irregular structures of various shapes, including spherical structures, most evident and frequ...
Characterization of Milled Wood Lignin (MWL) in Loblolly Pine Stem Wood, Residue, and Bark
Journal of Agricultural and Food Chemistry, 2011
Milled wood lignin samples from Loblolly pine stem wood, forest residue, and bark were isolated and characterized by quantitative 13 C and 31 P nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC) for molecular weight determination. Results from 13 C NMR show the stem wood and forest residue samples have similar functional group contents. However, the bark has fewer methoxyl groups, β-O-4 structures, dibenzodioxocin, and side chains than the other two lignins. The bark lignin has the highest amounts of p-hydroxyphenyl (h) and C-5 condensed lignin, stem wood has the lowest, and the residue lies between. 31 P NMR analysis indicates that bark lignin contains more C-5 substituted phenolics and fewer aliphatic hydroxyl groups than the lignin isolated from stem wood or residue. The molecular weight distribution analysis indicates the bark lignin has higher weight-average molecular weight (M w) and polydispersity index than the lignin recovered from stem wood or residue.
Holzforschung, 2006
The residual wood meal left after extraction of milled wood lignin (MWL) was extracted with lithium chloride/N,N-dimethylacetamide, which is a well-known cellulose solvent, to afford a soluble fraction (cellulose-lignin fraction; CL) in 36.7% yield. The UV elution curve of CL acetate has the same profile as its refractive index (RI) elution curve. After partial degradation of CL by cellulase, the UV elution curve of CL acetate shifted to the low-molecular-mass region in a similar fashion as its RI elution curve. These results indicate that the lignin in CL (CL lignin) is chemically bonded to cellulose. On the other hand, half of the CL lignin was removed by xylanase treatment. It was concluded that approximately half of the CL lignin existed as a lignin-cellulose-xylan complex.