Fernandez Martin

Pyrolysis derivatization of humic substances 1. Pyrolysis of fulvic acids in the presence of tetramethylammonium hydroxide

Abstract Humic Acids (HAs) extracted from soils of very different origin have been analyzed by pyrolysis in the presence of tetramethylammonium hydroxide. The thermal degradation products consisted mainly of aliphatic series such as fatty acids methyl esters and α,ω-methoxy fatty acid methyl esters. Triterpenoid compounds with ursane, oleanane and hopane skeletons were also detected in several samples. Aromatic units derived from lignin moieties were also detected although in minor amounts and corresponded mainly to guaiacyl and syringyl units. This procedure seems to release the more labile, aliphatic moieties attached to the aromatic nuclei of the HA structure.

Preservation of aliphatic macromolecules in soil humins

Abstract Two series of alkali-insoluble preparations of soil organic matter (humins) were isolated from three representative types of terrestrial humus by two methods, respectively based on (i) ultrasonic disaggregation followed by flotation in a bromoform-ethanol mixture and (ii) partition in water-methylisobutylketone. The humins amounted to between 7–42% of the total carbon in the soil heavy fraction and were characterized by pyrolysis followed by gas chromatography-mass spectrometry. The pyrolysis patterns of these particulate soil organic fractions differed quantitatively and qualitatively from those typical for terrestrial humic acid or lignocellulosic materials. The humins isolated by both methods yielded major series of alkyl products (56–81% of the total chromatographic area) including very variable amounts of alkanes, fatty acids and olefins. The aromatic pyrolysis products consisted mainly of alkyl-substituted mono and di-phenols, naphthalenes, phenanthrenes, fluorenes and methoxyphenols. The pyrograms of the humins isolated by partition were much more varied and produced a greater yield of alkanes than those isolated by flotation. The differences between humins from the three types of humus were small and tended to coincide in both series of preparations. Both the 13 C NMR spectra and the atomic ratios suggested the presence of stable carbohydrate-like material, which was not evident in the pyrograms or in the total yield of hydrolyzable sugars. The results suggest that humins represent the high-stability aggregate compartments of active terrestrial soils where structural rearrangement of aliphatic biogenic macromolecules may take place, simultaneously to the condensation of recalcitrant macromolecular material tightly bonded on reactive mineral surfaces.

Thermally assisted hydrolysis and alkylation of lignins in the presence of tetra-alkylammonium hydroxides

Three different milled lignins isolated from bamboo, pine and beech, corresponding to the three different structural groups, have been subjected to pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH). Pyrolysis of the lignins in the presence of TMAH releases the methyl esters and methyl ethers of the different lignin monomers. Several moieties bearing carboxylic acid groups, not previously detected using pyrolytic techniques, could be released from the three lignins, suggesting that the presence of these moieties in the lignin structure have been underestimated.

Solid state NMR studies of fire-induced changes in the structure of humic substances

Abstract Several structural changes were recognized by CPMAS 13 C-NMR and resolution-enhanced IR spectroscopy after humic acids (HA) and fulvic acids (FA) were subjected to laboratory heating at 350°C. The NMR results suggested that the HA underwent decarboxylation, selective transformation of aliphatic material, and increase in the number of aromatic carbons when subjected to heating for 120 s, whereas after subsequent heating no predominant aromatic neoformations were observed, and the elimination of alkyl structures occurred preferentially at this stage. The infrared spectroscopy revealed a well-defined lignin pattern in the original HA, that tended to disappear with heating. The results obtained in the laboratory experiments agreed with several of the differences found between the NMR patterns of the humic substances from the unburnt soil area and from that affected by forest fire. It is suggested that the changes observed play important roles in the colloidal properties and the water-repellency observed in the heated humic substances and in the post-fire soil area.

Chemical composition of lipophilic extractives from Eucalyptus globulus Labill. wood

Summary The composition of lipophilic extractives in the chloroform soluble fraction of the acetone extract from Eucalyptus globulus wood has been examined. The lipid extract was fractionated by solid-phase extraction on aminopropyl-phase cartridges into four different fractions of increasing polarity. The total lipid extract and the resulting fractions were analyzed by gas chromatography and gas chromatography-mass spectrometry, using high temperature capillary columns. The main compounds identified included sterols, sterol esters, fatty acids, steroid ketones, hydrocarbons and triglycerides. Minor compounds such as fatty alcohols, mono- and diglycerides, waxes and tocopherols were also identified among the lipids from E. globulus wood.

Thermally assisted hydrolysis and alkylation as a novel pyrolytic approach for the structural characterization of natural biopolymers and geomacromolecules

Abstract The high-temperature reaction of macromolecules with tetra-alkylammonium hydroxides has significantly improved the use of the conventional pyrolytic procedures which are widely used for the structural characterization of natural biopolymers and geomacromolecules. This new pyrolytic approach has overcome some of the analytical limitations of conventional pyrolysis allowing the detection of polar compounds as their alkyl derivatives. We report recent developments of the high-temperature hydrolysis and alkylation procedure, carried out in the presence of tetra-alkylammonium hydroxides, for the structural characterization of natural biopolymers and geomacromolecules such as lignins, humic substances, coals, asphaltenes and kerogens.

Characterization of humic acids from low-rank coals by 13C-NMR and pyrolysis-methylation. Formation of benzenecarboxylic acid moieties during the coalification process

Abstraet--Humic acid (HA) fractions isolated from a peat and lignite deposit were studied by CP/MAS ~3C-NMR and pyrolysis-methylation. Loss of carbohydrates, removal of methoxyls and formation of catechols during the coalification process was evident. Pyrolysis-methylation released a great variety of components, the lignin-derived monomers being the most prominent. A very striking feature was the release of benzenecarboxylic moieties after pyrolysis-methylation which have not been observed previously by pyrolytic techniques. These moieties were released in higher amounts from the lignite HA, suggesting that the content in carboxylic groups increase with coalification, at least up to the lignite stage. Oxidation of the C-3 side chain of the lignin structure would produce these benzenecarboxylic acids and benzylic ketones.

Ease of delignification assessment of wood from different Eucalyptus species by pyrolysis (TMAH)-GC/MS and CP/MAS 13C-NMR spectrometry

Abstract Flash-pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) of woods from different species of Eucalyptus yields series of guaiacyl-type (G) and syringyl-type (S) units in slightly but characteristically different relative proportions. Such differences have been used to suggest a fine and appropriate index of the ease of delignification of the different Eucalyptus species when pulped by the Kraft process. The pyrolytic data were in agreement with those obtained from CP/MAS 13C-NMR spectra of the woods. On the other hand, the various eucalypt woods showed additional differences in their pyrolytic patterns regarding the relative amounts and structure of the high molecular weight aromatic compounds arising from the pyrolysis of polyphenolic wood constituents, which might be used as a basis for chemotaxonomic differentiation of the origin of the woods

Evidence for a polyalkyl nature of soil humin

cell water in MC than in BSC. Our results confirmed this. Grana are greatly reduced in chloroplasts of BSC in NAPD-ME plants. Reduction of oxaloacetate to malate in the MC effectively transfers reducing power from the MC to the BSC - most likely enriched in the heavy isotope. In any case, water from the MC was considerably enriched in deuterium relative to the BSC. A considerable fractionation of both hydrogen and carbon isotopes is associated with photosynthesis [7]. Mobilization of the photosynthate and biosynthesis of cellular components result in smaller fractionations. This is seen in the hydrogen and carbon isotopic data for organic matter (Table 1). Hydrogen and carbon isotopic values were taken from water and tissues collected from root, veins (BSC), and intercostal tissue (MC) of Zea mays seedlings. Water from the MC was greatly depleted in the light isotope presumably due to evapotranspiration. These results could help explain the observation that [6, 7] hydrogen isotopic ratios of organic matter in NADP:ME plants are heavy compared with other C 4 plants.

Pyrolytic alkylation-gas chromatography-mass spectrometry of model polymers Further insights into the mechanism and scope of the technique

The mechanism of the high-temperature hydrolysis and alkylation with tetraalkylammonium hydroxides of bio- and geopolymers has been approached mainly by studying the behaviour of single standard compounds. In the present work, we have applied this technique to three polymers of known structure, i.e. suberin, polycitraconic acid (PCA) and a lignin dehydrogenase polymer (DHP), related respectively to natural polyesters, fulvic acids and lignins, in order to get new insight into the reaction mechanism. As further application of the technique, the case study of the lignin signature during the coalification process has been analyzed by pyrolysis-butylation of humic acids extracted from two peat and lignite samples.