Abundance and Reactivity of Dibenzodioxocins in Softwood Lignin

Department of Chemistry, Pulp and Paper Research Centre, McGill University, 3420 University Street, Montreal, Quebec, Canada.
Journal of Agricultural and Food Chemistry (Impact Factor: 2.91). 03/2002; 50(4):658-66. DOI: 10.1021/jf010909g
Source: PubMed


To define the abundance and comprehend the reactivity of dibenzodioxocins in lignin, model compound studies, specific degradation experiments on milled wood lignin, and molecular modeling calculations have been performed. Quantitative (31)P NMR measurements of the increase of biphenolic hydroxyl groups formed after a series of alkaline degradations in the presence of hydrosulfide anions (kraft conditions) showed the presence of 3.7 dibenzodioxocin rings/100 C9 units in milled wood lignin. The DFRC degradation protocol (Derivatization Followed by Reductive Cleavage) was chosen as an independent means to estimate their abundance. Initial experiments with a dibenzodioxocin model compound, trans-6,7-dihydro-7-(4-hydroxy-3-methoxyphenyl)-4,9-dimethoxy-2,11-dipropyldibenzo[e,g][1,4]dioxocin-6-ylmethanol, showed that it is not cleaved under DFRC conditions, but rather it isomerizes into a cyclic oxepine structure. Steric effects precluded this isomerization from occurring when DFRC was applied to milled wood lignin. Instead, monoacetylated biphenolic moieties were released and quantified by (31)P NMR, at 4.3 dibenzodioxocin rings/100 C9 units. The dibenzodioxocin content in residual lignins isolated from kraft pulps delignified to various degrees showed that during pulp delignification, the initial rate of dibenzodioxocin removal was considerably greater than the cleavage rate of arylglycerol-beta-aryl ether bonds. The activation energy for the degradation of dibenzodioxocins under kraft conditions in milled wood lignin was 96 +/- 9 kJ/mol, similar to that of arylglycerol-beta-aryl ether bond cleavage.

8 Reads
  • Source
    • "The monolignols form structural elements when incorporated into the lignin polymer and are called p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) moieties, respectively. During the process of lignification, a complex three-dimensional polymer is produced through radical coupling of the moieties via b-O-4, a-O-4, b-5, b-1, 5–5, 4-O-5 and b-b linkages that do not form regular and ordered repeating units as found in cellulose (Argyropoulos et al. 2002; Froass et al. 1996; Kukkola et al. 2004). The amount and composition of lignin varies among different cell types, different taxa, and between individual cell wall layers. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Carbon storage in terrestrial ecosystems is contingent upon the natural resistance of plant cell wall polymers to rapid biological degradation. Nevertheless, certain microorganisms have evolved remarkable means to overcome this natural resistance. Lignocellulose decomposition by microorganisms comprises an essential step in closing the loop of the global carbon cycle as it facilitates the recycling of carbon reposited in the form of structural polymers in plant cell walls. The significance of microbial decomposition of lignocellulose has recently risen to greater heights with the revisitation of the potential of lignocellulosic biomass as a valuable and abundant feedstock for the renewable energy and bioproducts industry. The scope of this chapter is to succinctly touch upon the composition of lignocellulosic biomass, the major enzymes involved in decomposing lignocellulosic biomass, and the fungi and bacteria that secrete these enzymes.
    Secretions and Exudates in Biological Systems, Edited by F. Baluška and J. Vivanco, 01/2012: pages 125-153; Springer Berlin Heidelberg., ISBN: 978-3-642-23046-2
  • Source
    • "Aromatic C–H in plane deformation(G[S), methoxyl group deformation, secondary alcohols, and C=O stretching nonconjugated 833 C–H out plane deformation S syringyl unit, G guaiacyl unit Wood Sci Technol (2011) 45:419–431 423 (Karhunen et al. 1995, 1996), and DBDO substructures from wood EMAL have also been explored in quantitative 31 P NMR before and after DFRC (Wu and Argyropoulos 2003; Tohmura and Argyropoulos 2001; Argyropoulos et al. 2002). DBDO substructures (shown in Fig. 3 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Enzyme/mild acidolysis lignin (EMAL) was isolated from wheat straw. The structural characterization of wheat straw EMAL was investigated by FT-IR, 1H NMR, quantitative 31P NMR and DFRC, and DEPT CH (θ=135C°) techniques. The wheat straw EMAL was a GSH-lignin with β-O-4′ structures and several condensed units (β-5′, β-β′, β-1′, 5-5′) and vinyl ether moieties; the contents of DBDO substructures and total β-aryl ether in the wheat straw EMAL were 0.257mmol·g−1 and 0.818mmol·g−1, respectively. Meanwhile, the structure features of the hemicelluloses residues attached to lignin were also investigated using DEPT CH (θ=135C°) spectra.
    Wood Science and Technology 08/2011; 45(3):419-431. DOI:10.1007/s00226-010-0339-1 · 1.92 Impact Factor
  • Source
    • "In earlier work we made extensive attempts to clarify the structural characteristics of residual lignin in kraft pulp (RKL, residual kraft lignin) to better understand the structural alterations that occur during pulping and bleaching processes (Jiang and Argyropoulos 1994; Granata and Argyropoulos 1995; Sun and Argyropoulos 1996; Asgari and Argyropoulos 1998; Argyropoulos and Liu 2000; Tohmura and Argyropoulos 2001; Argyropoulos et al. 2002a,b; Jä a ¨ skelä inen et al. 2003; Wu and Argyropoulos 2003). The coexistence of lignins and carbohydrates is an opportunity to study the nature of lignin carbohydrate bonds on the one hand, and a challenge when lignin analysis is the focus, on the other hand. "
    [Show abstract] [Hide abstract]
    ABSTRACT: An integrated picture of the distribution of functional groups should be provided as a function of molecular size within residual kraft lignins. With this goal we devel-oped a reliable and reproducible method for determina-tion of the molecular weight and molecular weight distribution of residual kraft lignins (RKLs) over the whole delignification range. In general, our data indicate that for reliable measurement of the molecular weight and its dis-tribution of residual lignin in pulps, the lignin-carbo-hydrate bonds have to be cleaved prior to size exclusion chromatography. The recently developed method for iso-lating residual lignins, which involves cellulolytic treat-ment followed by a mild acid hydrolysis step, was found to be the most suitable approach to achieve this. The molecular weight and polydispersity of all RKLs de-creased as a function of delignification. As anticipated, the observed decrease in molecular weight was clearly reflected in the concomitantly decreasing amount of b-O-4 structural linkages present. Similarly, the total phe-nolic hydroxyl content increased as the molecular weight of the RKLs decreased during kraft pulping. Despite the smaller size of the lignin remaining on the kraft fiber at the end of delignification, the preponderance of con-densed phenolic structures within these lignins offers an explanation for delignification problems during bleaching.
    Holzforschung 11/2005; 59(6):612-619. DOI:10.1515/HF.2005.099 · 1.57 Impact Factor
Show more


8 Reads
Available from