排序方式: 共有13条查询结果,搜索用时 15 毫秒
1.
HO. radical is an aggressive reagent to abstract hydrogen from diverse substitutes and lead them to degradation, however, in
reaction of active oxygen species with lignins, complex phenolic polymers, in dispersed lignocellulose such as pulp for environment-benign
delignification, HO. radicals should be eliminated as more as possible to prevent cellulose from unfavorably concomitant degradation. A reaction
system of O3 is constructed under UV laser flash irradiation, and HO. radicals are controlled efficiently by it. A new mechanism is proposed, for the first time, that O. radicals generated from reaction of O3 with UV laser flash irradiation might be the contributor to scavenge HO. radicals. 相似文献
2.
A critique on the structural analysis of lignins and application of novel tandem mass spectrometric strategies to determine lignin sequencing
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Joseph Banoub Guo‐Hua Delmas Jr. Nicolas Joly Grahame Mackenzie Nadja Cachet Bouchra Benjelloun‐Mlayah Michel Delmas 《Journal of mass spectrometry : JMS》2015,50(1):5-48
This review is devoted to the application of MS using soft ionization methods with a special emphasis on electrospray ionization, atmospheric pressure photoionization and matrix‐assisted laser desorption/ionization MS and tandem MS (MS/MS) for the elucidation of the chemical structure of native and modified lignins. We describe and critically evaluate how these soft ionization methods have contributed to the present‐day knowledge of the structure of lignins. Herein, we will introduce new nomenclature concerning the chemical state of lignins, namely, virgin released lignins (VRLs) and processed modified lignins (PML). VRLs are obtained by liberation of lignins through degradation of vegetable matter by either chemical hydrolysis and/or enzymatic hydrolysis. PMLs are produced by subjecting the VRL to a series of further chemical transformations and purifications that are likely to alter their original chemical structures. We are proposing that native lignin polymers, present in the lignocellulosic biomass, are not made of macromolecules linked to cellulose fibres as has been frequently reported. Instead, we propose that the lignins are composed of vast series of linear related oligomers, having different lengths that are covalently linked in a criss‐cross pattern to cellulose and hemicellulose fibres forming the network of vegetal matter. Consequently, structural elucidation of VRLs, which presumably have not been purified and processed by any other type of additional chemical treatment and purification, may reflect the structure of the native lignin. In this review, we present an introduction to a MS/MS top–down concept of lignin sequencing and how this technique may be used to address the challenge of characterizing the structure of VRLs. Finally, we offer the case that although lignins have been reported to have very high or high molecular weights, they might not exist on the basis that such polymers have never been identified by the mild ionizing techniques used in modern MS. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Renewability is not Enough: Recent Advances in the Sustainable Synthesis of Biomass‐Derived Monomers and Polymers
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Audrey Llevot Patrick‐Kurt Dannecker Marc von Czapiewski Lena C. Over Zafer Söyler Prof. Dr. Michael A. R. Meier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11510-11521
Taking advantage of the structural diversity of different biomass resources, recent efforts were directed towards the synthesis of renewable monomers and polymers, either for the substitution of petroleum‐based resources or for the design of novel polymers. Not only the use of biomass, but also the development of sustainable chemical approaches is a crucial aspect for the production of sustainable materials. This review discusses the recent examples of chemical modifications and polymerizations of abundant biomass resources with a clear focus on the sustainability of the described processes. Topics such as synthetic methodology, catalysis, and development of new solvent systems or greener alternative reagents are addressed. The chemistry of vegetable oil derivatives, terpenes, lignin, carbohydrates, and sugar‐based platform chemicals was selected to highlight the trends in the active field of a sustainable use of renewable resources. 相似文献
4.
Bardet M Lundquist K Parkås J Robert D von Unge S 《Magnetic resonance in chemistry : MRC》2006,44(10):976-979
The 13C NMR signals from the aromatic ring carbons in a series of lignin model compounds of the arylglycerol beta-aryl ether type in DMSO solution have been assigned. The model compounds investigated are representative of the erythro and threo forms of differently substituted arylglycerol beta-aryl ethers. 相似文献
5.
Summary: Applying special computer mathematical treatments to increase resolution of experimental spectra there were established a set of stable characteristic bands for isolated softwood lignins. In the 740–1620 cm−1 spectral range the band maximum positions did not change but values of bandwidths and peak intensities were varied in limits 15% and 32%. After analysis of the infrared spectra of 30 investigated samples a softwood lignin spectral model was constituted. This model allowed to clear discrepancies in the bands parameters of different mild isolated (lignins of Bjorkman, Pepper and Freudenberg), dioxane and technical lignin spectra. It was helpful for studying lignin structure changes during degradation procedures. 相似文献
6.
Oliveira Samuel C. Pereira Félix M. Ferraz André Silva Flávio T. Goncalves Adilson R. 《Applied biochemistry and biotechnology》2000,84(1-9):595-615
The herbicides applied in soils can be easily lost, owing to leaching, volatilization, and bio-and photodegradation. Controlled-release
systemsusing polymeric matrices claim to solve these problems. The movement of the herbicides in the soilisalso an important
phenomenon to be studied in order to evaluate the loss processes. The development of mathematical models is a relevantrequirement
for simulation and optimization of such systems. This study reviews mathematical models as an initial step for modeling data
obtained for controlled-release systems of herbicides (diuron, 2,4-dichlorophenoxyacetic acid, and ametryn) using sugarcane
bagasse lignin as a polymeric matrix. The release kinetic studies were carried out using several acceptorsystems includinga
water bath, soil, and soil-packed columns. Generally, these models take into account phenomena such as unsteady-state mass
transfer by diffusion (Fick'slaw) and convection, consumption by several processes, and partitioning processes, resulting
in partial differential equations with respect to time and space variables. 相似文献
7.
The oxidation of four lignins obtained by organosolv pulping of eucalyptus wood (Acetosolv-eucalyptus Acetosolv lignin [EAL]),
sugarcanebagasse (Acetosolv-bagasse Acetosolv lignin [BAL] and in acetone/water/FeCl3-bagasse acetone/water lignin [BAWL]), and a softwood mixture (Organocell, Munich, Germany) was performed to obtain vanillin,
vanillic acid, and oxidized lignin. Experiments were carried out in a cetic acid under oxygen flow using HBr, cobalt(II),
and manganese(II) acetates as catalysts. After 10 h the total vanillin and vanillic acid yields were BAL 0.05 mmol, EAL 0.38
mmol, BAWL 0.45 mmol, and Organ ocell 0.84 mmol. Acetosolv lignins are crosslinked, which explains the lower yields in mononuclear
products. The reaction volume (Δ V) of this reaction is −817 cm3/mol, obtained in experiments performed under oxygen pressure, showing the high influence of pressure on the oxidation. The
major part of the, lignin stays in solution (oxidized lignin), which was analyzed by infrared spectroscopy, showing an increased
in carbonyl and hydroxyl groups in comparison with the original lignin. The oxidized lignin can be used as chelating agent
in the treatment of effluents containing heavy metals. 相似文献
8.
HO radical is an aggressive reagent to abstract hydrogen from diverse substitutes and lead them to degradation, however, in reaction of active oxygen species with lignins, complex phenolic polymers, in dispersed lignocellulose such as pulp for environment-benign delignification, HO radicals should be eliminated as more as possible to prevent cellulose from unfavorably concomitant degradation. A reaction system of O3 is constructed under UV laser flash irradiation, and HO radicals are controlled efficiently by it. A new mechanism is proposed, for the first time, that O radicals generated from reaction of O3 with UV laser flash irradiation might be the contributor to scavenge HO radicals. 相似文献
9.
T. Liiti S. L. Maunu J. Sipil B. Hortling 《Solid state nuclear magnetic resonance》2002,21(3-4):171-186
Solid-state 13C NMR spectroscopy and dipolar dephasing technique was used to determine the extent of condensation in various technical lignins. The accuracy of dipolar dephasing method was first investigated with the aid of some lignin model compounds and two various methods to determine the degree of condensation were compared. On the basis of the model compound experiments both methods based on dipolar dephasing technique can be applied to investigate the extent of condensation in lignin. The lignin results indicate that technical softwood lignins, as well as enzymatically isolated wood lignin, are more condensed than milled wood lignin, which is generally assumed to represent native lignin. Residual lignins isolated after oxygen delignification and peroxide bleaching stages were found more condensed than residual lignin in unbleached pulps. In studies of the spent liquor lignins of flow-through kraft pulping the extent of condensation was found to increase as the cooking proceeded. 相似文献
10.
Dr. Fengxia Yue Dr. Fachuang Lu Prof. Dr. Runcang Sun Prof. Dr. John Ralph 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16402-16410
Pinoresinol structures, featuring a β‐β′‐linkage between lignin monomer units, are important in softwood lignins and in dicots and monocots, particularly those that are downregulated in syringyl‐specific genes. Although readily detected by NMR spectroscopy, pinoresinol structures largely escaped detection by β‐ether‐cleaving degradation analyses presumably due to the presence of the linkages at the 5 positions, in 5‐5′‐ or 5‐O‐4′‐structures. In this study, which is aimed at helping better understand 5‐linked pinoresinol structures by providing the required data for NMR characterization, new lignin model compounds were synthesized through biomimetic peroxidase‐mediated oxidative coupling reactions between pre‐formed (free‐phenolic) coniferyl alcohol 5‐5′‐ or 5‐O‐4′‐linked dimers and a coniferyl alcohol monomer. It was found that such dimers containing free‐phenolic coniferyl alcohol moieties can cross‐couple with the coniferyl alcohol producing pinoresinol‐containing trimers (and higher oligomers) in addition to other homo‐ and cross‐coupled products. Eight new lignin model compounds were obtained and characterized by NMR spectroscopy, and one tentatively identified cross‐coupled β‐O‐4′‐product was formed from a coniferyl alcohol 5‐O‐4′‐linked dimer. It was demonstrated that the 5‐5′‐ and 5‐O‐4′‐linked pinoresinol structures could be readily differentiated by using heteronuclear multiple‐bond correlation (HMBC) NMR spectroscopy. With appropriate modification (etherification or acetylation) to the newly obtained model compounds, it would be possible to identify the 5‐5′‐ or 5‐O‐4′‐linked pinoresinol structures in softwood lignins by 2D HMBC NMR spectroscopic methods. Identification of the cross‐coupled dibenzodioxocin from a coniferyl alcohol 5‐5′‐linked moiety suggested that thioacidolysis or derivatization followed by reductive cleavage (DFRC) could be used to detect and identify whether the coniferyl alcohol itself undergoes 5‐5′‐cross‐linking during lignification. 相似文献