The reaction of lignin model compounds during enzymatic bleaching with a Curvularia verruculosa haloperoxidase: impact on chlorination

Holzforschung ◽  
2020 ◽  
Vol 74 (2) ◽  
pp. 156-165
Author(s):  
Owik M. Herold-Majumdar ◽  
Pedro E.G. Loureiro ◽  
René Ullrich ◽  
Claus Felby
Keyword(s):  
Ammonium Chloride ◽  
High Performance ◽  
Bond Cleavage ◽  
Veratryl Alcohol ◽  
Reaction Products ◽  
Adsorbable Organic Halides ◽  
Organic Halides ◽  
Recent Developments ◽  
Lignin Model ◽  
Curvularia Verruculosa

AbstractRecent developments in enzymatic bleaching processes have led to replacement strategies of harsh chemicals by haloperoxidases. For this purpose, it is important to control the haloperoxidase-mediated formation of adsorbable organic halides (AOX). In this study, we studied the chlorination of monomeric and dimeric lignin model substrates. Guaiacol, acetovanillone, veratryl alcohol, pinoresinol and adlerol were treated with Curvularia verruculosa haloperoxidase and compared to a sodium hypochlorite treatment. High-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) analysis was employed for the characterization of the reaction products. Our results show that while treatment with haloperoxidases in the presence of sodium chloride and hydrogen peroxide leads to no improvement in AOX formation compared to chemical treatment with NaOCl, addition of ammonium chloride substantially lessens chlorination and promotes β-O-4 ether bond cleavage. The use of ammonium chloride in conjunction with enzymatic haloperoxidase-based bleaching could be a route to minimize lignin chlorination.

Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 1. Identification of the Reaction Products

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 617-624 ◽  
Author(s):  
L. Lin ◽  
Y. Yao ◽  
N. Shiraishi
Keyword(s):  
High Performance ◽  
Model Compound ◽  
Structural Characteristics ◽  
Main Reaction ◽  
Reaction Products ◽  
Lignin Model Compound ◽  
H Nmr ◽  
Lignin Model ◽  
Oxalic Acids ◽  
C Nmr

Summary Guaiacylglycerol-β-guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1H-NMR, 13C-NMR, 1H-1H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-α and further cleavages in both the β-O-4 linkage and Cβ–Cγ bonding could be the dominant reaction pathways.

The role of peroxidases, radical cations and oxygen in the degradation of lignin

1987 ◽  
Vol 321 (1561) ◽  
pp. 495-505 ◽  
Keyword(s):  
Radical Cation ◽  
Active Oxygen Species ◽  
Bond Cleavage ◽  
White Rot Fungi ◽  
Radical Cations ◽  
Veratryl Alcohol ◽  
White Rot ◽  
Oxygen Species ◽  
Lignin Model

Ligninase is an extracellular peroxidase produced by several species of white-rot fungi. It is able to oxidize methoxylated substrates to radical cation intermediates that can undergo C—H or C—C bond cleavage, thereby providing the basis for the oxidation of veratryl alcohol or degradation of lignin model compounds respectively. In some cases, the radical cation intermediate can act as an oxidant, accepting an electron from a suitable donor. It can thus function as a mediator, causing oxidation in a polymer not immediately accessible to the enzyme. This could be important in the degradation of natural lignocellulose substrates. However, the removal of a single electron by a mediator would leave a radical in the polymer. We propose that oxygen will bind to this radical to generate active oxygen species. This provides a potential mechanism for the auto-oxidation of lignin at a distance from the enzyme. A scheme is presented to account for the observation that ligninase can open the ring of veratryl alcohol.

Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 2. Reaction Behaviour and Pathways

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 625-630 ◽  
Author(s):  
L. Lin ◽  
S. Nakagame ◽  
Y. Yao ◽  
M. Yoshioka and N. Shiraishi ◽  
N. Shiraishi
Keyword(s):  
High Performance ◽  
Model Compound ◽  
Structural Characteristics ◽  
Gel Permeation Chromatography ◽  
Main Reaction ◽  
Reaction Products ◽  
Reaction Behavior ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Acid Catalyzed

Summary By means of high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC), the yields of the main reaction products and the polymeric portion formed in the reaction of guaiacylglycerol-β-guaiacyl ether (GG) under various acid-catalyzed conditions were quantified as a function of reaction time. Based on their forming sequence and reaction behavior, as well as their structural characteristics, an acid-catalyzed reaction mechanism of GG with phenol was proposed.

Lignin Degradation in Oxygen Delignification Catalysed by [PMo7V5O40]8- Polyanion. Part II. Study on Lignin Monomeric Model Compounds

Holzforschung ◽  
2000 ◽  
Vol 54 (5) ◽  
pp. 511-518 ◽  
Author(s):  
D.V. Evtuguin ◽  
C. Pascoal Neto ◽  
H. Carapuça ◽  
J. Soares
Keyword(s):  
Reaction System ◽  
Veratryl Alcohol ◽  
Vanillyl Alcohol ◽  
Coupling Reactions ◽  
Reaction Products ◽  
Oxygen Delignification ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Oxidation ◽  
Lignin Model

Summary Vanillyl and veratryl alcohols were used as monomeric lignin model compounds in experiments aiming to enhance the understanding of the lignin oxidation mechanisms involved in the oxygen delignification in acidic media catalysed by [PMo7V5O40]8− (HPA-5) heteropolyanion. Based on the model compound experiments, the first step of lignin oxidation is suggested to be a one-electron oxidation by the catalyst. This step is followed by coupling reactions and/or by further oxidation by the catalyst. The ratio of coupling/oxidation reaction products depends on the oxidation conditions and decreases with temperature raise. The higher oxidation rate of vanillyl alcohol as compared to the veratryl alcohol in the reaction system O2/HPA-5 was explained by the redox properties of the catalyst. The insufficiently high redox potential of HPA-5 did not allow the efficient oxidation of veratryl alcohol. The former was oxidised by VO2 + ions dissociated from the HPA-5 under the acidic conditions. The reactivity of different lignin structural units in the reaction system O2/HPA-5 was estimated by electrochemical methods using various lignin model compounds.

Microstructure of sputter deposited Ni-Sb ohmic contacts on GaAs

1989 ◽  
Vol 47 ◽  
pp. 450-451
Author(s):  
S. Yegnasubramanian ◽  
V.C. Kannan ◽  
R. Dutto ◽  
P.J. Sakach
Keyword(s):  
High Performance ◽  
Ohmic Contacts ◽  
Surface Defects ◽  
Pure Metal ◽  
Device Fabrication ◽  
Native Oxide ◽  
Metal Thin Films ◽  
Recent Developments ◽  
Different Temperatures ◽  
Sputter Deposited

Recent developments in the fabrication of high performance GaAs devices impose crucial requirements of low resistance ohmic contacts with excellent contact properties such as, thermal stability, contact resistivity, contact depth, Schottky barrier height etc. The nature of the interface plays an important role in the stability of the contacts due to problems associated with interdiffusion and compound formation at the interface during device fabrication. Contacts of pure metal thin films on GaAs are not desirable due to the presence of the native oxide and surface defects at the interface. Nickel has been used as a contact metal on GaAs and has been found to be reactive at low temperatures. Formation Of Ni2 GaAs at 200 - 350C is reported and is found to grow epitaxially on (001) and on (111) GaAs, but is shown to be unstable at 450C. This paper reports the investigations carried out to understand the microstructure, nature of the interface and composition of sputter deposited and annealed (at different temperatures) Ni-Sb ohmic contacts on GaAs by TEM. Attempts were made to correlate the electrical properties of the films such as the sheet resistance and contact resistance, with the microstructure. The observations are corroborated by Scanning Auger Microprobe (SAM) investigations.

What Can Digitization Do For Formulated Product Innovation and Development

2020 ◽  
Author(s):  
James McDonagh ◽  
William Swope ◽  
Richard L. Anderson ◽  
Michael Johnston ◽  
David J. Bray
Keyword(s):  
High Performance ◽  
Quality Data ◽  
High Quality Data ◽  
Base Level ◽  
Hybrid Approaches ◽  
Digital Ecosystem ◽  
Recent Developments ◽  
Chemical Simulation ◽  
High Level ◽  
Physical And Chemical

Digitization offers significant opportunities for the formulated product industry to transform the way it works and develop new methods of business. R&D is one area of operation that is challenging to take advantage of these technologies due to its high level of domain specialisation and creativity but the benefits could be significant. Recent developments of base level technologies such as artificial intelligence (AI)/machine learning (ML), robotics and high performance computing (HPC), to name a few, present disruptive and transformative technologies which could offer new insights, discovery methods and enhanced chemical control when combined in a digital ecosystem of connectivity, distributive services and decentralisation. At the fundamental level, research in these technologies has shown that new physical and chemical insights can be gained, which in turn can augment experimental R&D approaches through physics-based chemical simulation, data driven models and hybrid approaches. In all of these cases, high quality data is required to build and validate models in addition to the skills and expertise to exploit such methods. In this article we give an overview of some of the digital technology demonstrators we have developed for formulated product R&D. We discuss the challenges in building and deploying these demonstrators.<br>

Recent Developments in the Asymmetric Detrifluoroacetylative Reactions of in situ Generated Mono-Fluorinated Enolates

2020 ◽  
Vol 24 (18) ◽  
pp. 2181-2191
Author(s):  
Li Wang ◽  
Ziyi Li ◽  
Jiang Liu ◽  
Jianlin Han ◽  
Hiroki Moriwaki ◽  
...  
Keyword(s):  
Organic Chemistry ◽  
Bond Cleavage ◽  
Synthetic Methodology ◽  
Research Topics ◽  
Synthetic Organic Chemistry ◽  
Nucleophilic Reactions ◽  
F Center ◽  
Recent Developments

The development of an efficient and mild synthetic methodology for the construction of bioactive fluorine-containing molecules represents one of the hot research topics in general synthetic organic chemistry. In this review, some recent progresses achieved in the development of detrifluoroacetylatively generated mono-fluorinated enolates via CC bond cleavage and their asymmetric nucleophilic reactions for assembly of chiral quaternary C-F center containing compounds.

scholarly journals Comparing Ligninolytic Capabilities of Bacterial and Fungal Dye-Decolorizing Peroxidases and Class-II Peroxidase-Catalases

2021 ◽  
Vol 22 (5) ◽  
pp. 2629
Author(s):  
Dolores Linde ◽  
Iván Ayuso-Fernández ◽  
Marcos Laloux ◽  
José E. Aguiar-Cervera ◽  
Antonio L. de Lacey ◽  
...  
Keyword(s):  
Veratryl Alcohol ◽  
Flow Measurements ◽  
Reduction Potentials ◽  
Rate Limiting Step ◽  
Lower Extent ◽  
Lignin Model ◽  
Bacteria And Fungi ◽  
Compound Ii ◽  
Rate Limiting ◽  
Lignin Macromolecule

We aim to clarify the ligninolytic capabilities of dye-decolorizing peroxidases (DyPs) from bacteria and fungi, compared to fungal lignin peroxidase (LiP) and versatile peroxidase (VP). With this purpose, DyPs from Amycolatopsis sp., Thermomonospora curvata, and Auricularia auricula-judae, VP from Pleurotus eryngii, and LiP from Phanerochaete chrysosporium were produced, and their kinetic constants and reduction potentials determined. Sharp differences were found in the oxidation of nonphenolic simple (veratryl alcohol, VA) and dimeric (veratrylglycerol-β- guaiacyl ether, VGE) lignin model compounds, with LiP showing the highest catalytic efficiencies (around 15 and 200 s−1·mM−1 for VGE and VA, respectively), while the efficiency of the A. auricula-judae DyP was 1–3 orders of magnitude lower, and no activity was detected with the bacterial DyPs. VP and LiP also showed the highest reduction potential (1.28–1.33 V) in the rate-limiting step of the catalytic cycle (i.e., compound-II reduction to resting enzyme), estimated by stopped-flow measurements at the equilibrium, while the T. curvata DyP showed the lowest value (1.23 V). We conclude that, when using realistic enzyme doses, only fungal LiP and VP, and in much lower extent fungal DyP, oxidize nonphenolic aromatics and, therefore, have the capability to act on the main moiety of the native lignin macromolecule.

scholarly journals Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin VII: acidolyses of non-phenolic C6-C2-type model compounds using HBr, HCl and H2SO4, and a proposal on the characteristic action of Br− and Cl−

2020 ◽  
Vol 66 (1) ◽  
Author(s):  
Qiaoqiao Ye ◽  
Tomoya Yokoyama
Keyword(s):  
Model Compound ◽  
Bond Cleavage ◽  
Type Model ◽  
Enol Ether ◽  
Lignin Model Compound ◽  
Benzyl Cation ◽  
Acid Type ◽  
Unstable Compound ◽  
Lignin Model ◽  
Acidolysis Reaction

AbstractA non-phenolic C6-C2-type lignin model compound with the β-O-4 bond, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (I), was acidolyzed in aqueous 82% 1,4-dioxane containing HBr, HCl, or H2SO4 with a concentration of 0.2 mol/L at 85 ℃ to examine the differences between these acidolyses. Compound I primarily converted to an enol ether compound, 1-(2-methoxyphenoxy)-2-(3,4-dimethoxyphenyl)ethene (II), via the benzyl cation followed by acidolytic β-O-4 bond cleavage regardless of the acid-type, although the disappearance rates of compound I were remarkably different (HBr > HCl >> H2SO4). Acidolyses of compound II using these acids under the same conditions showed a similar tendency, but the rate differences were much smaller than in the acidolyses of compound I. Acidolyses of the α-methyl-etherified derivative of compound I (I-α-OMe) using these acids under the same conditions suggested that the formation rates of the benzyl cation from compound I-α-OMe (also from compound I) are not largely different between the acidolyses using these acids, but those of compound II from the benzyl cation are remarkably different. Acidolysis of the α-bromo-substituting derivative of compound I (I-α-Br) using HBr under the same conditions showed a characteristic action of Br¯ in the acidolysis. Br¯ adds to the benzyl cation generated from compound I or I-α-OMe to afford unstable compound I-α-Br, resulting in acceleration of the formation of compound II and of the whole acidolysis reaction.

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