Sphingobacterium sp. T2 manganese superoxide dismutase catalyses the oxidative demethylation of polymeric lignin via generation of hydroxyl radical

Sphingobacterium sp. T2 contains two extracellular manganese superoxide dismutase enzymes which exhibit unprecedented activity for lignin oxidation but via an unknown mechanism. Enzymatic treatment of lignin model compounds gave products whose structures were indicative of aryl–Cα oxidative cleavage and demethylation, as well as alkene dihydroxylation and alcohol oxidation. 18O labeling studies on the SpMnSOD-catalyzed oxidation of lignin model compound guiaiacylglycerol-β-guaiacyl ether indicated that the an oxygen atom inserted by the enzyme is derived from superoxide or peroxide. Analysis of an alkali lignin treated by SpMnSOD1 by quantitative 31P NMR spectroscopy demonstrated 20–40% increases in phenolic and aliphatic OH content, consistent with lignin demethylation and some internal oxidative cleavage reactions. Assay for hydroxyl radical generation using a fluorometric hydroxyphenylfluorescein assay revealed the release of 4.1 molar equivalents of hydroxyl radical by SpMnSOD1. Four amino acid replacements in SpMnSOD1 were investigated, and A31H or Y27H site-directed mutant enzymes were found to show no lignin demethylation activity according to 31P NMR analysis. Structure determination of the A31H and Y27H mutant enzymes reveals the repositioning of an N-terminal protein loop, leading to widening of a solvent channel at the dimer interface, which would provide increased solvent access to the Mn center for hydroxyl radical generation

Ether bond cleavage of a phenylcoumaran beta-5 lignin model compound and polymeric lignin catalysed by a LigE-type etherase from Agrobacterium sp

A LigE-type beta-etherase enzyme from lignin-degrading Agrobacterium sp. has been identified, which assists degradation of polymeric lignins. Testing against lignin dimer model compounds revealed that it does not catalyse the previously reported reaction of Sphingobium SYK-6 LigE, but instead shows activity for a β-5 phenylcoumaran lignin dimer. The reaction products did not contain glutathione, indicating a catalytic role for reduced glutathione in this enzyme. Three reaction products were identified: the major product was a cis-stilbene arising from C−C fragmentation involving loss of formaldehyde; two minor products were an alkene arising from elimination of glutathione, and an oxidised ketone, proposed to arise from reaction of an intermediate with molecular oxygen. Testing of the recombinant enzyme against a soda lignin revealed the formation of new signals by two-dimensional NMR analysis, whose chemical shifts are consistent with the formation of a stilbene unit in polymeric lignin

Technical and "green potential" of ionic liquids

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Efficient Synthesis of 7-Substituted or 3,7-Disubstituted 1H-Indazoles

E f f i c i e n t S y n t h e s i s o f 7-S u b s t i t u t e d o r 3 , 7-D i s u b s t i t u t e d 1 H-I n d a z o l e s Abstract: This work reports on the synthesis of the novel indazole scaffolds 7-OTf-1H-indazole (trifluoromethanesulfonic acid 1H-indazol-7-yl ester), 7-iodo-1H-indazole and 3-bromo-7-iodo-1H-indazole. These new compounds are potent building blocks in divergent syntheses of indazoles via palladium cross-coupling reactions

Influence of Ethanol Organosolv Pulping Conditions on Physicochemical Lignin Properties of European Larch

Over the years, the organosolv pulping process has proven to be a valuable pretreatment method for various lignocellulosic feedstocks. The objective of this study was to characterize and assess the potential applicability of the organosolv lignin fraction from European larch sawdust, as no research has been conducted in this field so far. Eight different samples were prepared from the European larch sawdust under varied reaction conditions and one milled wood lignin sample as reference. The reaction temperature and sulfuric acid loading were varied between 420 and 460 K and 0.00 and 1.10% (w/w on dry wood basis) H2SO4, respectively. The antiradical potential (via DPPH• method), chemical structure (via ATR-FTIR, 1H NMR, 31P NMR, and thioacidolysis), as well as the molecular weight distribution of the isolated lignins were analyzed and compared. Results from thioacidolysis show a direct correlation between the amount of β-ether bonds broken and pulping process severity. Similarly, both antiradical potential and phenolic hydroxyl group content exhibit a direct relationship to reaction temperature and catalyst loading. On the contrary, the content of aliphatic hydroxyl groups and the average molecular weights both decreased with increasing process severity. The high content of phenolic hydroxyl groups and antioxidative potential of the larch organosolv fractions, especially for the sample isolated at 460 K and 1.10% H2SO4 loading, indicate good applicability as antioxidants as well as feedstocks for further downstream valorization and require additional research in this area

Designing functional polyoxometalate-based ionic liquid crystals and ionic liquids

International audiencePolyoxometalate (POM) compounds constitute a wide family rich of more than several thousand inorganic compounds which can be finely tuned at the molecular level. Considering their high diversities in structures and properties, the incorporation of such inorganic components into liquid crystalline phases or ionic liquid phases is particularly relevant for the elaboration of functional materials. By adjusting the molecular structures of the anions and the nature of the counter cations, many authors designed different types of mesophases sometimes with application in optoelectronics, or true POM-based Ionic liquids (POM-ILs with melting temperature below 100 °C). The latter turn out to be highly interesting for various applications in catalysis, depollution, or protection of the historical heritage. This review focuses on the recent developments in these organic/inorganic hybrid materials, POMbased Ionic liquid crystal and POM-ILs and their applications

The versatile electrophilic reactivity of 4,6-dinitrobenzo[d]isoxazole-3-carbonitrile

International audienceThe interaction of 4,6-dinitrobenzo[d]isoxazole-3-carbonitrile (5a) with methoxide ion has been kinetically investigated in methanol and a 20:80(v/v)MeOH-Me 2 SO mixture. In methanol, stopped-flow experiments have revealed that a monomethoxyl σ-adduct (5a-Me) is first formed, resulting from a fast MeO-addition at the unsubstituted 7-carbon. Rate and equilibrium constants for this σ-complexation process could be determined, allowing a ranking of 5a within the pK a scale established for Meisenheimer electrophiles in methanol. With a pK a value of 13.50, the electrophilicity of 5a falls in the range of 1,3,6,8-tetranitronaphthalene, 2,4-dinitrothiophene or 4-nitrobenzofuroxan. This corresponds to a two-pK a units increase in electrophilicity from that of TNB, the common reference in σ-complex chemistry but it is notably below that of so-called superelectrophilic molecules like 4,6-dinitrobenzofuroxan. In addition to its ease of σ-complexation, 5a is found to undergo a slow but thermodynamically favourable addition of MeO-to the cyano group bonded to the isoxazole ring, leading to a complete conversion of the adduct 5a-Me into a dinitroimidate 6. The reactivity of 6 could be kinetically assessed. Going to 80% Me 2 SO still afforded initially the adduct 5a-Me but this anionic species undergoes addition of a second molecule of MeO-to the CN group, giving a dianion whose structure is unprecedented in the literature. Combining the above results with synthetic observations showing that 5a can readily contribute to S N Ar reactions under appropriate experimental conditions emphasizes the multifaceted electrophilic reactivity of this electron-deficient heterocycle

Influence of base-catalyzed organosolv fractionation of larch wood sawdust on fraction yields and lignin properties

Lignocellulose-based biorefineries are considered to play a crucial role in reducing fossil-fuel dependency. As of now, the fractionation is still the most difficult step of the whole process. The objective of this study is to investigate the potential of a base-catalyzed organosolv process as a fractionation technique for European larch sawdust. A solvent system comprising methanol, water, sodium hydroxide as catalyst, and anthraquinone as co-catalyst is tested. The influence of three independent process variables, temperature (443-446 K), catalyst loading (20-30% w/w), and alcohol-to-water ratio (30-70% v/v), is studied. The process conditions were determined using a fractional factorial experiment. One star point (443 K, 30% v/v MeOH, 30% w/w NaOH) resulted in the most promising results, with a cellulose recovery of 89%, delignification efficiency of 91%, pure lignin yield of 82%, residual carbohydrate content of 2.98% w/w, and an ash content of 1.24% w/w. The isolated lignin fractions show promising glass transition temperatures (>= 424 K) with high thermal stabilities and preferential O/C and H/C ratios. This, together with high contents of phenolic hydroxyl (>= 1.83 mmol/g) and carboxyl groups (>= 0.52 mmol/g), indicates a high valorization potential. Additionally, Bjorkman lignin was isolated, and two reference Kraft cooks and a comparison to three acid-catalyzed organosolv fractionations were conducted