El doctor en química D. Jorge Rencoret Pazos galardonado con el premio de investigación 'Real Maestranza de Caballeria de Sevilla' a investigadores jóvenes en su convocatoria de 2012

2 páginas.-- Artículo sobre la entrega del premio de investigación convocado en 2012 para investigadores jóvenes por la "Real Maestranza de Caballería" de Sevilla. Escrito por el Dr. Pedro J. Sánchez Sot

Maize tricin-oligolignol metabolites and their implications for monocot lignification

Lignin is an abundant aromatic plant cell wall polymer consisting of phenylpropanoid units in which the aromatic rings display various degrees of methoxylation. Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as a true monomer in grass lignins. To elucidate the incorporation pathways of tricin into grass lignin, the metabolites of maize (Zea mays) were extracted from lignifying tissues and profiled using the recently developed 'candidate substrate product pair' algorithm applied to ultra-high-performance liquid chromatography and Fourier transform-ion cyclotron resonance-mass spectrometry. Twelve tricin-containing products (each with up to eight isomers), including those derived from the various monolignol acetate and p-coumarate conjugates, were observed and authenticated by comparisons with a set of synthetic tricin-oligolignol dimeric and trimeric compounds. The identification of such compounds helps establish that tricin is an important monomer in the lignification of monocots, acting as a nucleation site for starting lignin chains. The array of tricin-containing products provides further evidence for the combinatorial coupling model of general lignification and supports evolving paradigms for the unique nature of lignification in monocots

Lignin from tree barks: chemical structure and valorization

Lignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E. globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p-hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in bether linkages (83%), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of &5:50:45), with a predominance of b-ethers (73–75%) and lower amounts of condensed carbon–carbon linkages; the lignin from A. dealbata bark also includes some resorcinol-related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P. abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in b-O-4’ alkyl–aryl ether linkages (44%) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorizationinfo:eu-repo/semantics/publishedVersio

Racismo y matrices de “inclusión” de la migración haitiana en Chile: elementos conceptuales y contextuales para la discusión

La presente reflexión se enfoca en el análisis de las representaciones y experiencias de racismo y exclusión en relación a matrices socioculturales que los migrantes haitianos identifican como posibilidades de inserción en la sociedad chilena. Contextualiza el proceso en un determinado momento histórico, social y político tanto en el país de origen como de destino; desarrollando junto con ello los conceptos de neorracismo y racismo sutil para describir experiencias, prácticas y cogniciones presentes en los discursos de los y las migrantes haitianos/as en Chile.This analysis focuses on the representations and experiences of racism and exclusion in relation to socio-cultural matrices identified by Haitian migrants as aspects that could improve the chances of integration in the Chilean society. It contextualizes the process in a particular historical, social and political moment both in the country of origin as that of destination; developing along the concepts of neo-racism and subtle racism to describe experiences, practices and cognitions present in the speeches of haitian migrants in Chile.Esta reflexão centra-se na análise das representações e experiências de racismo e exclusão em relação a matrizes socioculturais que os imigrantes haitianos identificam como possibilidades de integração na sociedade chilena. Contextualiza o processo num determinado momento histórico, social e político, tanto no país de origem como de destino; desenvolvendo junto com isso os conceitos de neo-racismo e racismo sutil para descrever experiências, práticas e cognições presentes nos discursos de os/asmigrantes haitianos/asno Chile

A structural characterization of the lignins from sugarcane (Saccharum spp. L) bagasse and straw

The structure of the lignins of sugarcane bagasse and straw was investigated. The lignins were characterized both in situ and in isolated preparations (Milled-Wood Lignin, MWL, and Cellulolytic Lignin, CEL) by Py-GC/MS and 2D-NMR. It was concluded that they are p-hydroxyphenyl-guaiacyl-syringyl lignins with associated p-coumarates and ferulates. 2D-NMR indicated that the main substructures present are β–O–4´-ethers, followed by β–5´ phenylcoumarans and with lower amounts of β–β´ resinols and β–1´ spirodienones.This study has been funded by the EU project LIGNODECO (KBBE-244362) and the Spanish project AGL2011-25379 (co-financed by FEDER funds). Jorge Rencoret thanks the CSIC for a JAE-DOC contract of the program “Junta para la Ampliación de Estudios” co-financed by Fondo Social Europeo (FSE). Funding provided by the Minas Gerais State Research Foundation (FAMEPIG) from the Brazilian National Council for Science and Technology Development (CNPq), and from the Coordination for the Improvement of Higher Education Personnel (CAPES) is greatly appreciated.N

Laccase-Mediator Pretreatment of Wheat Straw Degrades Lignin and Improves Saccharification

14 páginas.-- 4 figuras.-- 4 tablas.-- 49 referenciasThe authors thank Dr. Angulo for performing the NMR analyses that were acquired on a Bruker AVANCE III 500-MHz instrument from the NMR facilities of the General Research Services of the University of Seville (SGI CITIUS)gricultural by-products such as wheat straw are attractive feedstocks for the production of second-generation bioethanol due to their high abundance. However, the presence of lignin in these lignocellulosic materials hinders the enzymatic hydrolysis of cellulose. The purposes of this work are to study the ability of a laccase-mediator system to remove lignin improving saccharification, as a pretreatment of wheat straw, and to analyze the chemical modifications produced in the remaining lignin moiety. Up to 48 % lignin removal from ground wheat straw was attained by pretreatment with Pycnoporus cinnabarinus laccase and 1-hydroxybenzotriazole (HBT) as mediator, followed by alkaline peroxide extraction. The lignin removal directly correlated with increases (∼60 %) in glucose yields after enzymatic saccharification. The pretreatment using laccase alone (without mediator) removed up to 18 % of lignin from wheat straw. Substantial lignin removal (37 %) was also produced when the enzyme-mediator pretreatment was not combined with the alkaline peroxide extraction. Two-dimensional nuclear magnetic resonance (2D NMR) analysis of the whole pretreated wheat straw material swollen in dimethylsulfoxide-d6 revealed modifications of the lignin polymer, including the lower number of aliphatic side chains involved in main β-O-4′ and β-5′ inter-unit linkages per aromatic lignin unit. Simultaneously, the removal of p-hydroxyphenyl, guaiacyl, and syringyl lignin units and of p-coumaric and ferulic acids, as well as a moderate decrease of tricin units, was observed without a substantial change in the wood polysaccharide signals. Especially noteworthy was the formation of Cα-oxidized lignin units during the enzymatic treatment.This study was funded by the INDOX EU-project (KBBE-2013-7-613549); the LIGNOCELL, LIGNIN, NOESIS, and BIORENZYMERY Spanish MICINN (co-financed by FEDER funds) projects (AGL2011-25379, CTQ2014-60764-JIN, BIO2014-56388 R and AGL2014-53730-R); and the CSIC (201440E097) Project. A.P. thanks the Spanish MINECO for a FPI fellowship. A. Lomascolo and E. Record from INRA (Marseille, France) are acknowledged for the P. cinnabarinus laccase, and H. Lund and M. Tovborg from Novozymes (Bagsvaerd, Denmark) for Celluclast 1.5L and Novozyme 188.Peer reviewe

Hydroxystilbene glucosides are incorporated into Norway spruce bark lignin

Recent investigations have revealed that, in addition to monolignols, some phenolic compounds derived from the flavonoid and hydroxystilbene biosynthetic pathways can also function as true lignin monomers in some plants. In this study, we found that the hydroxystilbene glucosides isorhapontin (isorhapontigenin-O-glucoside) and, at lower levels, astringin (piceatannol- O-glucoside) and piceid (resveratrol-O-glucoside) are incorporated into the lignin polymer in Norway spruce (Picea abies) bark. The corresponding aglycones isorhapontigenin, piceatannol, and resveratrol, along with glucose, were released by derivatization followed by reductive cleavage, a chemical degradative method that cleaves b-ether bonds in lignin, indicating that the hydroxystilbene glucosides are (partially) incorporated into the lignin structure through b-ether bonds. Twodimensional NMR analysis confirmed the occurrence of hydroxystilbene glucosides in this lignin, and provided additional information regarding their modes of incorporation into the polymer. The hydroxystilbene glucosides, particularly isorhapontin and astringin, can therefore be considered genuine lignin monomers that participate in coupling and crosscoupling reactions during lignification in Norway spruce barkinfo:eu-repo/semantics/publishedVersio

Deciphering the unique structure and acylation pattern of Posidonia oceanica lignin

Copyright © 2020 American Chemical Society. Lignins from different parts of the seagrass Posidonia oceanica-namely sheaths, rhizome, and roots-as well as from fibrous balls from P. oceanica detritus were isolated and thoroughly characterized by pyrolysis coupled with gas chromatography/mass spectrometry, derivatization followed by reductive cleavage, two-dimensional nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The lignins of P. oceanica were enriched in guaiacyl (G) over syringyl (S) units, with S/G ratios ranging from 0.1 (fibrous balls) to 0.5 (rhizome). β-O-4′ ethers and phenylcoumarans were the most abundant lignin substructures, followed by resinols, and minor amounts of dibenzodioxocins and spirodienones. Moreover, all lignins were found to be highly I-Acylated (up to 44% of total units), mainly with p-hydroxybenzoates but also, to a lesser extent, with acetates. The data indicated that this acylation extensively occurred in both G-and S-lignin units, contrary to what happens in palms, poplar, and willow, where p-hydroxybenzoates overwhelmingly appear at the I-position of S-units

Role of surface tryptophan for peroxidase oxidation of nonphenolic lignin

Background: Despite claims as key enzymes in enzymatic delignification, very scarce information on the reaction rates between the ligninolytic versatile peroxidase (VP) and lignin peroxidase (LiP) and the lignin polymer is available, due to methodological difficulties related to lignin heterogeneity and low solubility.Results: Two water-soluble sulfonated lignins (from Picea abies and Eucalyptus grandis) were chemically characterized and used to estimate single electron-transfer rates to the H2O2-activated Pleurotus eryngii VP (native enzyme and mutated variant) transient states (compounds I and II bearing two- and one-electron deficiencies, respectively). When the rate-limiting reduction of compound II was quantified by stopped-flow rapid spectrophotometry, from fourfold (softwood lignin) to over 100-fold (hardwood lignin) lower electron-transfer efficiencies (k 3app values) were observed for the W164S variant at surface Trp164, compared with the native VP. These lignosulfonates have ~20–30 % phenolic units, which could be responsible for the observed residual activity. Therefore, methylated (and acetylated) samples were used in new stopped-flow experiments, where negligible electron transfer to the W164S compound II was found. This revealed that the residual reduction of W164S compound II by native lignin was due to its phenolic moiety. Since both native lignins have a relatively similar phenolic moiety, the higher W164S activity on the softwood lignin could be due to easier access of its mono-methoxylated units for direct oxidation at the heme channel in the absence of the catalytic tryptophan. Moreover, the lower electron transfer rates from the derivatized lignosulfonates to native VP suggest that peroxidase attack starts at the phenolic lignin moiety. In agreement with the transient-state kinetic data, very low structural modification of lignin, as revealed by size-exclusion chromatography and two-dimensional nuclear magnetic resonance, was obtained during steady-state treatment (up to 24 h) of native lignosulfonates with the W164S variant compared with native VP and, more importantly, this activity disappeared when nonphenolic lignosulfonates were used.Conclusions: We demonstrate for the first time that the surface tryptophan conserved in most LiPs and VPs (Trp164 of P. eryngii VPL) is strictly required for oxidation of the nonphenolic moiety, which represents the major and more recalcitrant part of the lignin polymer

Oxidation of model lipids representative for main paper pulp lipophilic extractives by the laccase-mediator system.

Several model lipids representative for main paper pulp lipophilic extractives - including alkanes, fatty alcohols, fatty acids, resin acids, free and esterified sterols, and triglycerides – were treated with Pycnoporus cinnabarinus laccase in the presence of 1-hydroxybenzotriazole as mediator. The reaction products were analyzed by GC and GC-MS. The laccase alone decreased the amount of some unsaturated lipids, however, the most rapid and extensive lipid modification was obtained with the laccase-mediator system. Most unsaturated lipids were largely oxidized and the dominant oxidation products detected were epoxy and hydroxy-fatty acids from fatty acids, and free and esterified 7-ketosterols and steroid ketones from sterols and sterol esters. In contrast, saturated lipids were not modified, although some of them were oxidized when the enzymatic reactions were carried out in the presence of unsaturated lipids. The results obtained are discussed in the context of enzymatic control of pitch deposits, to explain the removal of lipid mixtures during laccase-mediator treatment of different pulp types.This study was funded by the BIORENEW EU-project (NMP2-CT-2006-026456) and the Spanish MEC (BIO2007-28719-E). Beldem (Andenne, Belgium) is acknowledged for laccase supply. S.M. thanks the Spanish CSIC and CELESA for an I3P contract and J.R thanks the CSIC for an I3P fellowship.Peer reviewe