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International audience; SEC elution curves of spruce milled wood lignin (MWL) and guaiacyl lignin polymer models (G-DHPs) in NN-dimethylformamide (DMF) exhibited a bimodal elution profile. Light scattering measurements indicated that these elution profiles were due to association effects between the molecules. This became apparent from the determination of high molar masses in the range 10(5)-10(8) g/mol. To study this effect, MWL and DHP were fractionated by precipitation in tetrahydrofuran (THF). The THF-insoluble fractions were found to be the fractions corresponding to the apparent high molar mass part of the DMF elution profiles. The THF-soluble fractions proved to be the less-associated fractions, with lower apparent molecular mass. The individual fractions proved to be rather stable in DMF. Accordingly, the bimodal elution profiles of the starting materials were not the result of an equilibrium between associated and molecular dispersed molecules but of different structures exhibiting a specific and stable association pattern. The different fractions were further characterised by SEC in THF after acetylation to determine molar masses in molecular disperse solutions.

In this paper, multivariate chemometric analysis of fluorescence spectra of juvenile and mature eucalyptus wood samples is used in order to investigate the existence of any correlation between fluorescence data and, the physical/chemical properties, as well as the pulping data of eucalyptus wood. The results obtained demonstrated that the wood of juvenile and adult trees could be discriminated by fluorescence spectroscopy. Data analysis also has shown the existence of good statistical correlation between fluorescence data on the one hand, and ash content, sodium hydroxide solubility, and lignin monomeric composition of the wood samples on the other hand. Moreover, fluorescence spectral data were found to be well correlated with the pulping yield and the Kappa number of the kraft pulps issued from the adult and juvenile eucalyptus wood.

Lignins definition, potential applications, (macro)molecular structures and properties, analytical characterisations and natural versus induced variability are reviewed with reference to both the biological diversity of lignification patterns in ecotypes, mutants and transgenic plants and the levels of organisation of the lignins polymeric networks. A discrimination between a common primary, guaiacyl type metabolism and a more specific secondary, syringyl type is suggested as a base of this variability and properties.

Times Cited: 10 Cathala, B Aguie-Beghin, V Douillard, R Monties, B Symposium H on Biodegradable Polymers and Macromolecules, at the E-MRS 97/ICAM 97 Conference JUN 16-19, 1997 STRASBOURG, FRANCE 10 SI; International audience; The properties of two DHPs (dehydrogenation polymers) models of lignin are investigated at the air/water interface. Limiting area, relaxation behaviour and dilational modulus are discussed in relation to literature data for plant lignins.

4 tables 3 graph.; International audience; In order to test the reproducibility of the synthesis of dehydrogenation polymer models of lignin (DHPs), four samples obtained by the continous and discontinous synthesis (Zutropf method (ZT) and Zulauf method (ZL)) have been investigated by FTIR, thioacidolysis and GPC.

The monomeric composition of in situ lignins in sorghum, maize and wheat straw stems is investigated by two chemical degradation methods: thioacidolysis and alkaline nitrobenzene oxidation. It is shown that the structural information obtained in the case of lignin characterisation by alkaline nitrobenzene oxidation is strongly dependent on the reaction conditions, namely the temperature and the reaction time, as indicated by the significant variations in the yields of aromatic aldehydes that correspond to the three main constitutive lignin units, p -hydroxyphenyl (H), guaiacyl (G) and syringyl (S). Moreover, the complementary character of the two methods that stems from their different specificities is discussed in view of the molecular heterogeneity of lignins. Finally, the results obtained indicate a significant structural variability of the lignins of the three crops examined.

In plant cell walls, lignins, the second most abundant biopolymers, form 3D crosslinked molecular structures which interact with polysaccharides to form lignin-carbohydrate complexes. The incorporation of these phenolic polymers into synthetic polysaccharide-based composites is currently under investigation. The properties of the final material (mechanical strength, degradability,…) strongly depend on the degree of compatibility between such hydrophilic and hydrophobic molecules. This phenomenon is expected to be in part related to the surface properties of lignins. Organosolve dioxane lignins were isolated from wheat straw and characterized with respect to their HPSEC elution profile ( M n =3.6×10 3 ), total sugar and esterified phenolic acid content (3 and 3.5%, respectively) and to the degradation yield of thioacidolysis (750 μ moles g −1 ). These lignins were then dissolved in a dioxane–water mixture and used for Langmuir trough experiments at the air–water interface. Compression isotherms (pressure/concentration) were obtained at 20°C by compressing the surface deposited layers at specified rates. A particular feature of the interfacial layers of lignin is that surface pressure relaxes strongly when compression is stopped. Thus, the compression isotherms exhibit a surface pressure which is roughly three times higher than the value reached after 48 h relaxation. These data suggest that previously reported isotherms have been determined in conditions far from equilibrium. Dilational moduli, measured at several surface concentrations, range from 13.5 to 72 mN m −1 . These special surface properties should determine a part of the behavior of lignins in blends.

The chemical structure of lignins in Buxus sempervirens wood samples showing a progressive grading from normal wood to reaction wood was investigated by thioacidolysis. The mechanical states of the various samples were assessed quantitatively by measuring the growth strains at the stem surface. Sample woods with the more pronounced compression character showed the highest lignin contents. Buxus lignins are composed of guaiacyl and syringyl units, similar to more evolved angiosperm lignins. The proportion of syringyl units, together with that of labile inter-unit ether bonds, was, however, lower in boxwood lignins than in poplar or birch lignins. More importantly, lignins in boxwood samples with a pronounced compressed character were found to have structural similarities with gymnosperm compression wood lignins, i.e. a higher content of carbon-carbon inter-unit bonds and of p-hydroxyphenyl units, compared with normal wood lignins.

Formation of standard guaiacyl-syringyl lignin has been shown, by thioacidolysis, during healing and suberization of wound potato tuber discs. Recovery of p -hydroxybenzaldehyde after nitrobenzene oxidation has been related to the presence of tyramine. Variations in the relative proportion of hydroxyphenyl, guaiacyl and syringyl degradation products obtained after nitrobenzene oxidation, thioacidolysis and alkaline hydrolysis suggest the formation, during suberization, of a complex phenolic network linked to the cell wall.

The rate of oxidation of spruce milled wood lignin by Phanerochaete chrysosporium was investigated with precipitated lignin as well as lignin finely dispersed in water (colloidal lignin). H2O2 consumption rates in the course of lignin oxidation in the presence of purified lignin peroxidase were much higher with colloidal lignin compared with precipitated lignin. Characterization of reaction products and molecular-size distribution confirms that reaction rate of lignin peroxidase with 14C-lignin is strongly dependent on the physical state of lignin. The lignin peroxidase catalyse mainly repolymerization of colloidal lignin. However, in the presence of veratryl alcohol, both polymerization and depolymerization were observed.

Heartwood of Quercus robur L. contains about 10% (w/w), of hexahydroxydiphenoyl esters (ellagitannins). Five of the most abundant hexahydroxydiphenoyl esters were purified by a combination of chromatography on Sephadex LH-20 and high-performance reversed-phase liquid chromatography. Two of them were identified as castalagin and vescalagin.

The 13 C INADEQUATE experiment has been applied to lignin, a natural biopolymer.