Uncatalysed and potassium-catalysed pyrolysis of the cell-wall constituents of biomass and their model compounds

Cell-wall components (cellulose, hemicellulose (oat spelt xylan), lignin (Organosolv)), and model compounds (levoglucosan (an intermediate product of cellulose decomposition) and chlorogenic acid (structurally similar to lignin polymer units)) have been investigated to probe in detail the influence of potassium on their pyrolysis behaviours as well as their uncatalysed decomposition reaction. Cellulose and lignin were pretreated to remove salts and metals by hydrochloric acid, and this dematerialized sample was impregnated with 1% of potassium as potassium acetate. Levoglucosan, xylan and chlorogenic acid were mixed with CHCOOK to introduce 1% K. Characterisation was performed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). In addition to the TGA pyrolysis, pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) analysis was introduced to examine reaction products. Potassium-catalysed pyrolysis has a huge influence on the char formation stage and increases the char yields considerably (from 7.7% for raw cellulose to 27.7% for potassium impregnated cellulose; from 5.7% for raw levoglucosan to 20.8% for levoglucosan with CHCOOK added). Major changes in the pyrolytic decomposition pathways were observed for cellulose, levoglucosan and chlorogenic acid. The results for cellulose and levoglucosan are consistent with a base catalysed route in the presence of the potassium salt which promotes complete decomposition of glucosidic units by a heterolytic mechanism and favours its direct depolymerization and fragmentation to low molecular weight components (e.g. acetic acid, formic acid, glyoxal, hydroxyacetaldehyde and acetol). Base catalysed polymerization reactions increase the char yield. Potassium-catalysed lignin pyrolysis is very significant: the temperature of maximum conversion in pyrolysis shifts to lower temperature by 70 K and catalysed polymerization reactions increase the char yield from 37% to 51%. A similar trend is observed for the model compound, chlorogenic acid. The addition of potassium does not produce a dramatic change in the tar product distribution, although its addition to chlorogenic acid promoted the generation of cyclohexane and phenol derivatives. Postulated thermal decomposition schemes for chlorogenic acid are presented. © 2008 Elsevier B.V. All rights reserved.

The metabolism of n-methyl compounds

The metabolism of compounds containing the N-methyl group is discussed with particular consideration being made to the possible role of the product of oxidative metabolism, the N-hydroxymethyl moiety, in the generation of potentially toxic, reactive electrophiles. Particular pathways which are considered are: (i), the production of formaldehyde; (ii), the generation of iminium ions or imines; and (iii), the formation of N-formyl compounds which might act as formylating agents. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1-hydroxy-methyl-1-methylurea (the product of oxidative metabolism of 3-(4-chlorophenyl)-1,1-dimethylurea) are model carbinolamides which do not readily release formaldehyde. The electrophilic properties of these model carbinolamides were investigated: neither reacted with nucleophiles such as cyanide or glutathione under physiological conditions. In contrast, N-(acetoxymethyl)-4-chlorobenzamide yielded the cyanomethylamide with potassium cyanide and S-(4-chlorobenzamidomethyl)glutathione with glutathione. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1,1-dimethylurea were not biotransformed to electrophilic moieties when incubated with mouse hepatic 9000 x g supernatant and Acetyl-CoA or PAPS-generating system. N-(Acetoxymethyl)-4-chlorobenzamide was non-mutagenic to Salmonella typhimurium in the short term bacterial assay; but toxicity to the bacteria was observed. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1,1-dimethylurea showed no mutagenicity or toxicity in the mutagenicity assay including an Aroclor-induced rat hepatic 9000 x g supernatant. Addition of Acetyl-CoA or a PAPS-generating system did not produce a mutagenic response. 4-Chloro-N-formlbenzamide did not act as a formylating agent towards the weak nucleophile aniline. However, 4-chloro-N-formylbenzamide, N-formylbenzamide, 3-(4-chlorophenyl)-1-formyl-1-methylurea and 3-(4-chlorophenyl)-1-formylurea are all metabolised by mouse hepatic mirosomes and post-microsomal supernatant. The results demonstrate the potential for N-hydroxymethyl compounds to generate highly reactive species if these are substrates for conjugation with sulphate (or acetate). The model compounds employed here, apparently do not show any ability to be conjugated themselves, however, other N-hydroxymethyl compounds might be readily conjugated. The formation of N-formyl compounds does not appear to be toxicologically significant, as adjudged on limited experiments performed, but rather represent a detoxification pathway.

Organic synthesis and fungicidal activity of oxylipin-based compounds

Previous research has shown that the naturally occurring reactive electrophilic species (RES), 12-oxophytodienoic acid (OPDA), not only serves as a precursor for jasmonic acid but is also a potent antifungal compound. However, both the low amount present in plants and the multistep synthesis required to produce this compound on a scale viable for agrochemical use currently limits its practical value. The aim of this research was to generate a range of molecular mimics of OPDA with a minimum number of synthetic steps and screen for antifungal activity. Synthetic 4-octyl-cyclopentenone containing the cyclopentenone ring and an eight carbon alkyl chain was found to show the highest in vitro antifungal activity against C. herbarum and B. cinerea with minimum inhibition concentration (MIC) of 100-200µM. This indicates that structurally simplified 4-octyl-cyclopentenone can be successfully synthesised to mimic the antifungal activity of OPDA against specific fungal strains. Application of 4-octyl-cyclopentenone could act as surfactant by disrupting and disorganising the lipid membrane non-specifically, resulting in the leakage of potassium ions, which was the proposed mode of action of this compound. However, the sensitivity of fungi to this compound is not correlated to the lipid composition of fungal spores. (E)-2-alkenals were also studied for their antimicrobial activity and (E)-2-undecenal was found to have the highest antimicrobial activity against a range of pathogens. The hydrophilic moiety (the a,ß-unsaturated carbonyl group), common to both (E)-2-undecenal and 4-octyl-cyclentenone is essential to their bioactivity, and the hydrophobic moiety plays an important role in their antimicrobial activities. 4-Octyl-cyclopentenone showed no visible toxicity to the test plant, Arabidopsis thaliana, suggesting that its high antifungal activity against Botrytis and Cladosporium could be exploited for commercialisation as a new generation of agrochemical.