Bernard Monties

Ether linkage between phenolic acids and lignin fractions from wheat straw

Abstract The bonding of the bound-phenolic acids present in three lignin preparations isolated from wheat straw where determined. p -Coumaric acid was mainly ester-linked whereas 35–75% of the recovered ferulic acid was ether-linked to milled straw lignin or enzyme lignin. Ferulic acid ethers accounted for 1.1% dry wt of alkali extracted lignin and might explain the high solubility of Gramineae lignins in soda. Isolated lignins were associated to hemicelluloses, principally arabinoglucuronoxylans. The possible existence of ferulic acid cross-links between lignin and arabinoglucuronoxylans is discussed.

Comparison of Wheat Straw Lignin Preparations - I. Chemical and Spectroscopic Characterizations

Alkali lignin was isolated from wheat straw and compared to two lignin preparations isolated from the same sample by a procedure which allowed to show an heterogeneity of rnonomeric composition between lignin fractions isolated from poplar wood. Using C NMR-, UV-, IRspectroscopy and nitrobenzene oxidation, no significative difference in monomeric composition was found in the case of wheat; difference of condensation degree between these fractions was however suggested by nitrobenzene oxidation. Arabinoxylans, proteins and silica were found in each preparation and a very close association between lignin and polysaccharides is suggested.

STRUCTURE AND COMPOSITION OF SWEET SORGHUM STALK COMPONENTS

Abstract Stem bark and pith of sweet sorghum were analyzed with reference to their sucrose, simple reducing sugars, cellulose, hemicelluloses, lignin and associated phenolic acids contents. Moreover, lignin monomeric units (guaiacyl and syringyl) engaged in non-condensed structures were characterized by thioacidolysis, whereas cell wall associated phenolic acids ( p- coumaric and ferulic acids) were estimated by alkaline hydrolysis at 170°C. The results obtained showed that bark and pith are heterogeneous as far as their chemical composition and the structure of their chemical components are concerned. In particular, the pith content in water soluble sugars is twice as high compared with the one in the bark, whereas bark is enriched in lignocellulosic fibres. Bark lignin is twice as important in content and less condensed in structure compared to pith lignin. p- Coumaric acid is the predominant p- hydroxycinnamic acid associated to the cell walls, whereas ferulic acid is present in significant quantities.

Insoluble ellagitannins in Castanea sativa and Quercus petraea woods

Sapwood and heartwood samples of sweet chestnut (Castanea sativa) and sessile oak (Quercus petraea) were extracted with aqueous acetone. Ellagitannins were estimated in both extracts and extraction residues, by the Folin-Ciocalteu method and by determination of ellagic acid formed after acid degradation. Ellagitannins were found to accumulate in comparable concentrations (ca 10% DM) in the heartwoods of both species. The concentrations of soluble ellagitannins slowly decreased from the periphery to the centre of the heartwood as it ages. This decrease was balanced by an equivalent increase of insoluble ellagitannins, resulting probably from the slow oxidative polymerization or copolymerization with cell-wall components of soluble ellagitannins.

Polyphenols of Quercus robur: Adult tree and in vitro grown calli and shoots

Abstract Bark, wood, leaves and in vitro grown calli and shoots from pedunculate oak ( Quercus robur ) were extracted by aqueous methanol. The polyphenols, analysed by paper chromatography and HPLC, were principally hexadroxydiphenoylesters-vescalagin, castalagin and pedunculagin-proanthocyanidins and pentagalloylglucose. In the adult tree, inner bark, heartwood and leaves were found to contain high amounts of hexahydroxydiphenoylesters (3.5 to 8.7% DM), mainly castalagin and vescalagin. Leaves were also rich in pedunculagin. Proanthocyanidins were characteristic of bark and leaves. Calli synthesized both hexahydroxydiphenoylesters and proanthocyanidins; the former were largely oxidized and poorly resolved by chromatography. In in vitro grown shoots phenolic compounds in leaves were similar to those of adult tree leaves, whilst stems did not contain pedunculagin but were rich in pentagalloylglucose.

On the molecular origin of the alkali solubility of Gramineae lignins

Abstract The molecular origin of the alkali solubility of Gramineae lignins was investigated, in the case of wheat and triticale straws. The role of the phenolic hydroxyl groups was particularly examined. Straw samples were therefore thoroughly methylated with diazomethane to etherify these groups. It was found that this mild methylation step drastically decreased the dissolution of straw lignins by alkali. The molecular mechanism of such an effect is discussed.

Two-stage acid-catalyzed fractionation of lignocellulosic biomass in aqueous ethanol systems at low temperatures

Abstract Wheat straw was fractionated into cellulosic fibres, hemicellulose sugars and solid lignin oligomers through a two-stage, acid-catalyzed process. During the first stage, raw material was treated with dilute H2SO4 (0·5–2·5 n ) at reflux temperature (99·5 ± 1·0°C) for 10–60 min. Subsequently, delignification was conducted with H2SO4 (2 n ) in aqueous ethanol (62·5–87·5% EtOH v/v) at reflux temperature (81·0 ± 2·0°C) for 90 min. Selective hydrolysis of about 50% of the straw hemicelluloses (w/w on original straw hemicelluloses), converted to water-soluble oligo- and monosaccharides (first stage), followed by delignification in 87·5% v/v EtOH (second stage), led to optimal component fractionation efficiency with negligible cellulose loss (less than 2% w/w on original straw cellulose) and high lignin removal (more than 70% w/w on original straw lignin). By this two-stage process, high overall fibre yields (more than 60% on original raw material) and good pulp mechanical properties were achieved.

Characterization of Poplar Lignins Acidolysis Products: Capillary Gas-Liquid and Liquid-Liquid Chromatography of Monomeric Compounds

Identification of monomeric compounds from acidolysis of poplar lignins was performed by means of capillary gas chromatography-mass spectrometry of their trimethylsilyl derivatives. Some direct analyses without derivatizaton of these compounds could be done, by means of high pressure liquid chromatography. Heterogeneity of two lignin fractions isolated from poplar wood was confirmed with these methods.

Formation of Ether Linkage between Phenolic Acids and Gramineae Lignin: A Possible Mechanism Involving Quinone Methides

Occurrence of phenolic acids bound by an ether linkage to lignin fractions isolated from wheat straw, has recently been reported (Scalbert et al. 1985). Different mechanisms may be proposed to explain the formation of these ether bonds. Phenolic acids might be dehydrogenated, like lignin precursors (Freudenberg 1968), the resulting phenoxy radicals would combine with other lignin radicals to yield an aryl ether. Dehydropolymerisation experiments (Shimada et al.

Photosynthetically 13C-Labelled Poplar Lignins: - 13C NMR Experiments

Poplars were grown from cuttings under air containing CO2 with C at about 20% C, in a growth chamber during three months. C-labelled lignin fractions were isolated and characterized by C NMR spectroscopy. Advantage was taken of the C enrichment to perform C NMR resolution enhancement and editing experiments. Some effects of LiCl, added to the DMSO-d6 Solutions, on the C NMR spectra are discussed. It was also attempted to assign more accurately the polysaccharidic peaks found in the C NMR spectra of lignin fractions in Order to study the lignin-carbohydrate relationships.