An overview of the different inhibitors formed by pre-treatment of lignocellulosic materials and their inhibition of ethanol production in yeast and bacteria is given. Different high temperature physical pre-treatment methods are available to render the carbohydrates in lignocellulose accessible for ethanol fermentation. The resulting hydrolyzsates contain substances inhibitory to fermentation—depending on both the raw material (biomass) and the pre-treatment applied. An overview of the inhibitory effect on ethanol production by yeast and bacteria is presented. Apart from furans formed by sugar degradation, phenol monomers from lignin degradation are important co-factors in hydrolysate inhibition, and inhibitory effects of these aromatic compounds on different ethanol producing microorganisms is reviewed. The furans and phenols generally inhibited growth and ethanol production rate (QEtOH) but not the ethanol yields (YEtOH) in Saccharomyces cerevisiae. Within the same phenol functional group (aldehyde, ketone, and acid) the inhibition of volumetric ethanol productivity was found to depend on the amount of methoxyl substituents and hence hydrophobicity (log P). Many pentose-utilizing strains Escherichia coli, Pichia stipititis, and Zymomonas mobilis produce ethanol in concentrated hemicellulose liquors but detoxification by overliming is needed. Thermoanaerobacter mathranii A3M3 can grow on pentoses and produce ethanol in hydrolysate without any need for detoxification.

Inhibition of ethanol-producing yeast and bacteria by degradation products produced during pre-treatment of biomass.

In this review, primary attention is given to the antioxidant (and prooxidant) activity of polyphenols arising from their interactions with iron both in vitro and in vivo. In addition, an overview of oxidative stress and the Fenton reaction is provided, as well as a discussion of the chemistry of iron binding by catecholate, gallate, and semiquinone ligands along with their stability constants, UV–vis spectra, stoichiometries in solution as a function of pH, rates of iron oxidation by O2 upon polyphenol binding, and the published crystal structures for iron–polyphenol complexes. Radical scavenging mechanisms of polyphenols unrelated to iron binding, their interactions with copper, and the prooxidant activity of iron–polyphenol complexes are briefly discussed.

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A Review of the Antioxidant Mechanisms of Polyphenol Compounds Related to Iron Binding

Minerals and organic matter (OM) may form intricate associations via myriad interactions. In soils, the associations of OM with mineral surfaces are mainly investigated because of their role in determining the long-term retention of OM. OM “must decay in order to release the energy and nutrients that drive live processes all over the planet” ( Janzen, 2006 ). Thus, the processes and mechanisms that retain OM in soil are a central concern to very different branches of environmental research. An agronomist may want to synchronize periods of high nutrient and energy release with the growth stages of a crop. An environmental chemist may wish to either immobilize an organic soil contaminant or enhance its decomposition into less harmful metabolites, while climate scientists need to understand the processes that mediate the production of potent greenhouse gases from decomposing OM. Associations of OM with pedogenic minerals (henceforth termed mineral–organic associations (MOAs)) are known to be key controls in these and many other processes. Here we strive to present an overview of the current knowledge on MOAs and identify key questions and future research needs.

Chapter One – Mineral–Organic Associations: Formation, Properties, and Relevance in Soil Environments

Ten phenols were selected as natural laccase mediators after screening 44 different compounds with a recalcitrant dye (Reactive Black 5) as a substrate. Their performances were evaluated at different mediator/dye ratios and incubation times (up to 6 h) by the use of Pycnoporus cinnabarinus and Trametes villosa laccases and were compared with those of eight known synthetic mediators (including -NOH- compounds). Among the six types of dyes assayed, only Reactive Blue 38 (phthalocyanine) was resistant to laccase-mediator treatment under the conditions used. Acid Blue 74 (indigoid dye), Reactive Blue 19 (anthraquinoid dye), and Aniline Blue (triarylmethane-type dye) were partially decolorized by the laccases alone, although decolorization was much more efficient and rapid with mediators, whereas Reactive Black 5 (diazo dye) and Azure B (heterocyclic dye) could be decolorized only in the presence of mediators. The efficiency of each natural mediator depended on the type of dye to be treated but, with the only exception being Azure B (<50% decolorization), nearly complete decolorization (80 to 100%) was attained in all cases. Similar rates were attained with the best synthetic mediators, but the reactions were significantly slower. Phenolic aldehydes, ketones, acids, and esters related to the three lignin units were among the best mediators, including p-coumaric acid, vanillin, acetovanillone, methyl vanillate, and above all, syringaldehyde and acetosyringone. The last two compounds are especially promising as ecofriendly (and potentially cheap) mediators for industrial applications since they provided the highest decolorization rates in only 5 to 30 min, depending on the type of dye to be treated.

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Lignin-derived compounds as efficient laccase mediators for decolorization of different types of recalcitrant dyes.

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

/pdf/in-posidonia-oceanica-cadmium-induces-changes-in-dna-3cu7uj83mr.pdf

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

The literature relating to the pKa -values of guaiacyl- and syringyl-derived phenols has been thoroughly surveyed and summarized. In addition, the pKa -values of a number of guaiacyl, syringyl and other phenols related to lignin have been determined using a spectrophotometric method combined with multivariate evaluation. Differences and similarities between the acidities of a number of substances are extensively discussed. The pKa -value strongly affects the delignification during pulping, bleaching and leaching of lignin during pulp washing.

pKa-Values of Guaiacyl and Syringyl Phenols Related to Lignin

The degradation of native and residual (kraft) lignins by oxygen in acidic media has been studied using appropriate model compounds. A mechanism is proposed involving acid-promoted conversion of lignin units into ring-conjugated structures, followed by electron transfer from these structures to oxygen to yield hydroperoxyl radical and the cation radical. The latter, after addition of water, reacts with oxygen affording the corresponding peroxyl radical intermediate. Electron transfer from additional Substrate to this peroxyl radical (in a chain reaction) and protonation give an oc-hydroxy hydroperoxide intermediate which undergoes heterolytic fragmentation to yield the corresponding carbonyl-containing products. Experimental Support for the validity of this mechanism is provided. Acidic oxygenation of lignin is compared with acidic degradation in the absence of oxygen (\"acidolysis\"), with degradation during chlorine dioxide bleaching, with acidic sulfonation, and with alkaline oxidative degradation under conventional oxygen bleaching conditions. The possibility of using oxygen in acidic media (\"acidic oxygenation\") äs an alternative delignification metnod is briefly discussed.

https://www.degruyter.com/view/j/hfsg.1994.48.issue-s1/hfsg.1994.48.s1.51/hfsg.1994.48.s1.51.pdf

Studies on the degradation of lignins by oxygen in acidic media

This report presents a method to characterize underivatized lignin by Capillary Zone Electrophoresis (CZE), in which separation is achieved by differences in mobility due to differences in the charge-to-size ratios of the solutes. A comparison has been made between the separation of lignin by CZE and earlier studies1 regarding the size and phenolic content of dissolved lignin. The samples were isolated at different times from a flow-through kraft cook and characterized by CZE in an alkaline solution. The resulting electropherograms show a molecular mobility distribution. The molecular mobility distribution of each fraction is in good agreement with its molecular size distribution and phenolic content. As the cook proceeds, the mobility of the lignin fragments increases with increasing phenolic content. Although the molecular size distribution shows a slight increase in molecular weight at the end of the cook according to Size Exclusion Chromatography (SEC), this does not seem to affect the mobili...

Characterization of Dissolved Kraft Lignin by Capillary Zone Electrophoresis

Stilbenes, representing stilbenoid structures present in residual lignins, have been synthesized by condensation of monochloroacetaldehyde diethylacetal with appropriate phenols and phenol ethers, followed by alkali- or acid-promoted rearrangement of the resulting 1,1-diaryl-2-chloroethanes. It is proposed that the mechanism of these rearrangement steps involves aryl migration with formation of intermediates of the spiro-cyclohexadienone type. The yields of individual stilbenes vary within wide ranges and are in certain cases moderate. However, the method is competitive due to its simplicity and the availability of the starting materials required.

Lignin Chromophores. III. Syntheses of Hydroxy- and Alkoxystilbenes via Aryl Migration

Hydroxy- and methoxy-substituted 1,4-diarylbuta-1,3-dienes, models for potential chromophores assumed to be present in residual lignins, have been prepared using Wittig, Knoevenagel and Perkin syntheses. ∗ Part III, see ref.1 ∗∗ A preliminary report on the results of this work was presented (by N.-O.N.) at the 1981 International Symposium on Wood and Pulping Chemistry, Stockholm, June 9–12, 1981, Preprints Vol. 5, pp. 96-99. ∗∗∗ Parts of the present work were carried out (J.G. and A.E.O.) at the Swedish Pulp and Paper Research Institute, Box 5604, S-114 86 Stockholm, Sweden, which is the present address of N.-O. N.

Nils-Olof Nilvebrant

Papers

pKa-Values of Guaiacyl and Syringyl Phenols Related to Lignin

Studies on the degradation of lignins by oxygen in acidic media

Characterization of Dissolved Kraft Lignin by Capillary Zone Electrophoresis

Lignin Chromophores. III. Syntheses of Hydroxy- and Alkoxystilbenes via Aryl Migration

Lignin Chromophores, Part IV∗ Syntheses of 1,4-Diarylbuta-1,3-dienes∗∗