Lignin Degradation in Oxygen Delignification Catalysed by [PMo7V5O40]8- Polyanion. Part I. Study on Wood Lignin

Holzforschung ◽  
2000 ◽  
Vol 54 (4) ◽  
pp. 381-389 ◽  
Author(s):  
D.V. Evtuguin ◽  
C. Pascoal Neto ◽  
J. Rocha
Keyword(s):  
13C Nmr Spectroscopy ◽  
Low Molecular Weight ◽  
Reaction Products ◽  
Oxygen Delignification ◽  
Wood Residue ◽  
Wet Chemistry ◽  
Acid Catalysed Reactions ◽  
A Minor ◽  
Oxidative Delignification ◽  
Competing Reactions

Summary The behaviour of lignin in wood delignification by oxygen in acidic media in the presence of the molybdovanadophosphate heteropolyanion [PMO7V5O40]8−as studied using wet chemistry methods, solid and liquid state 13C NMR spectroscopy. Lignin is oxidised by [PMO7V5O40]8− almost completely to carbon dioxide, with a minor yield of intermediate low-molecular weight aromatic products. The analysis of the reaction products shows that the lignin acidolysis and homolysis involving the oxygen participation in oxidation take place. The residual lignin in the wood residue is more “condensed” and richer in guaiacyl structural units than that in the initial wood. The analysis of “condensed” structures issued from permanganate oxidation of residual lignins suggests that these are formed predominantly by acid-catalysed reactions. The use of an organic solvent, such as ethanol, in the pulping solution favours the oxidative delignification, protecting the lignin against competing reactions (condensation).

Lignin reactions in oxygen delignification catalysed by Mn(II)-substituted molybdovanadophosphate polyanion

Holzforschung ◽  
2004 ◽  
Vol 58 (6) ◽  
pp. 640-649 ◽  
Author(s):  
Armindo Gaspar ◽  
Dmitry V. Evtuguin ◽  
Carlos Pascoal Neto
Keyword(s):  
Eucalyptus Globulus ◽  
Oxidative Degradation ◽  
Reaction System ◽  
Reaction Products ◽  
Oxygen Delignification ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Qualitative And Quantitative ◽  
Lignin Model ◽  
Oxidative Delignification

Abstract The lignin oxidation in the oxygen delignification/bleaching process catalysed by Mn(II) substituted heptamolybdopentavanadophosphate polyanion (HPA-5-MnII) was studied using monomeric lignin model compounds and Eucalyptus globulus dioxane lignin adsorbed on the bleached sulphite pulp. The analysis of reaction products after lignin models oxidation in the presence HPA-5-MnII and the parent heptamolybdopentavanadophosphate polyanion (HPA-5) showed similar qualitative and quantitative patterns, indicating the identical lignin oxidative delignification mechanisms with both catalysts. The higher delignification selectivity of the pulp in the reaction system HPA-5-MnII/O2 than with HPA-5/O2 was explained by the protective effect of MnII in the heteropolyanion towards oxidative degradation of polysaccharides. The study of lignin adsorbed on bleached sulphite pulp, in the HPA-5-MnII/O2 delignification system, showed the cleavage of β-O-4 linkages as the major contribution to the lignin depolymerisation. The formation of Cα-O-polysaccharide linkages in β-O-4 structures of lignin during the delignification was observed.

scholarly journals Utilization of low molecular weight organic compounds by the filterable fraction of a lotic microbiome

2020 ◽  
Author(s):  
Lydia-Ann J Ghuneim ◽  
Marco A Distaso ◽  
Tatyana N Chernikova ◽  
Rafael Bargiela ◽  
Evgenii A Lunev ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Community Dynamics ◽  
Lag Phase ◽  
Minor Role ◽  
Low Molecular Weight ◽  
Freshwater Systems ◽  
North Wales ◽  
Clusters Of Orthologous Groups ◽  
A Minor ◽  
Substrate Addition

Abstract Filterable microorganisms participate in dissolved organic carbon (DOC) cycling in freshwater systems, however their exact functional role remains unknown. We determined taxonomic identity and community dynamics of prokaryotic microbiomes in the 0.22 µm-filtered fraction and unfiltered freshwater from the Conwy River (North Wales, UK) in microcosms and, using targeted metabolomics and 14C-labelling, examined their role in utilization of amino acids, organic acids, and sugars spiked at environmentally-relevant (nanomolar) concentrations. To identify changes in community structure, we used 16S rRNA amplicon and shotgun sequencing. Unlike the unfiltered water samples where the consumption of DOC was rapid, the filtered fraction showed a 3-days lag phase before the consumption started. Analysis of functional categories of clusters of orthologous groups of proteins (COGs) showed COGs associated with energy production increased in numbers in both fractions with substrate addition. The filtered fraction utilized low-molecular-weight (LMW) DOC at much slower rates than the whole community. Addition of nanomolar concentrations of LMW DOC did not measurably influence the composition of the microbial community nor the rate of consumption across all substrate types in either fraction. We conclude that due to their low activity, filterable microorganisms play a minor role in LMW DOC processing within short residence time of lotic freshwater systems.

scholarly journals Proteolytic and peroxidatic reactions of commercial horseradish peroxidase with myelin basic protein

1978 ◽  
Vol 169 (3) ◽  
pp. 567-575 ◽  
Author(s):  
Wendy Cammer ◽  
Lesley Z. Bieler ◽  
William T. Norton
Keyword(s):  
Horseradish Peroxidase ◽  
Myelin Basic Protein ◽  
Basic Protein ◽  
Protein A ◽  
Low Molecular Weight ◽  
Basic Proteins ◽  
Molecular Weights ◽  
Low Concentrations ◽  
High Concentrations ◽  
A Minor

Degradation of myelin basic protein during incubations with high concentrations of horseradish peroxidase has been demonstrated [Johnson & Cammer (1977) J. Histochem. Cytochem.25, 329–336]. Possible mechanisms for the interaction of the basic protein with peroxidase were investigated in the present study. Because the peroxidase samples previously observed to degrade basic protein were mixtures of isoenzymes, commercial preparations of the separated isoenzymes were tested, and all three degraded basic protein, but to various extents. Three other basic proteins, P2 protein from peripheral nerve myelin, lysozyme and cytochrome c, were not degraded by horseradish peroxidase under the same conditions. Inhibitor studies suggested a minor peroxidatic component in the reaction. Therefore the peroxidatic reaction with basic protein was studied by using low concentrations of peroxidase along with H2O2. Horseradish peroxidase plus H2O2 caused the destruction of basic protein, a reaction inhibited by cyanide, azide, ferrocyanide, tyrosine, di-iodotyrosine and catalase. Lactoperoxidase plus H2O2 and myoglobin plus H2O2 were also effective in destroying the myelin basic protein. Low concentrations of horseradish peroxidase plus H2O2 were not active against other basic proteins, but did destroy casein and fibrinogen. Although high concentrations of peroxidase alone degraded basic protein to low-molecular-weight products, suggesting the operation of a proteolytic enzyme contaminant in the absence of H2O2, incubations with catalytic concentrations of peroxidase in the presence of H2O2 converted basic protein into products with high molecular weights. Our data suggest a mechanism for the latter, peroxidatic, reaction where polymers would form by linking the tyrosine side chains in basic-protein molecules. These data show that the myelin basic protein is unusually susceptible to peroxidatic reactions.

The Chemistry of Phenol-Formaldehyde Resin Vulcanization of EPDM: Part I. Evidence for Methylene Crosslinks

1995 ◽  
Vol 68 (5) ◽  
pp. 717-727 ◽  
Author(s):  
Martin van Duin ◽  
Aniko Souphanthong
Keyword(s):  
Molecular Weight ◽  
Phenol Formaldehyde ◽  
Polymer System ◽  
Phenol Formaldehyde Resin ◽  
Formaldehyde Resin ◽  
Low Molecular Weight ◽  
Hydroxyl Groups ◽  
Reaction Products ◽  
Cure Reaction ◽  
Weight Model

Abstract The application of phenol-formaldehyde resins as crosslinking agents is increasing in importance due to the good high temperature properties of the corresponding vulcanizate and the use in thermoplastic vulcanizates. With respect to the chemistry of phenol-formaldehyde cure (reaction mechanism and structure of crosslink) there are still problems that have to be resolved. The reaction products of the phenol-formaldehyde resin curing of EPDM, contain 2-ethylidene norbornene (ENB) as the third monomer, have been studied. Since such an investigation is rather difficult to perform for the polymer system, a low molecular weight model for EPDM was used: 2-ethylidene norbornane (ENBH). Reaction of ENBH and a resole results in scission of the dimethylene ether bridges, i.e. in degradation of the resole into mono-, bis- and terisooctylphenol units. These are consequently converted into products, consisting of two ENBH molecules linked by mono-, bis- and terisooctylphenol units. The solid resole seems to be a technological solution for storing phenol in combination with formaldehyde. These results support the use of 2-hydroxymethylphenol (HMP) as a low molecular weight model for the resole. At low temperatures and/or short reaction times HMP oligomers (= resoles) and HMP oligomers linked to one ENBH molecule are formed, which are converted into ENBH/HMP (1:1) condensation products. The reaction products of ENBH with both the resole and HMP are shown to contain methylene linked structures, as demonstrated by the formation of monisooctylphenol crosslinks and the presence of residual unsaturation and hydroxyl groups, besides chroman linked structures. This is the first experimental evidence that during phenol-formaldehyde resin cure of rubber, formation of methylene bridges occurs.

Decomposition of Ethoxyethynyl(trimethyl)tin - Studied by 119Sn and 13C NMR Spectroscopy

1999 ◽  
Vol 54 (6) ◽  
pp. 705-708 ◽  
Author(s):  
Bemd Wrackmeyer ◽  
Sergei V. Ponomarev
Keyword(s):  
Chemical Shifts ◽  
Acid Ethyl Ester ◽  
13C Nmr Spectroscopy ◽  
Major Product ◽  
Coupling Constants ◽  
Data Sets ◽  
Thermally Induced ◽  
Nmr Data ◽  
Induced Decomposition ◽  
A Minor

The thermally induced decomposition of ethoxyethynyl(trimethyl)tin (1) was studied by 119Sn NMR which revealed the formation o f bis(trimethylstannyl) ketene (2) as the major product, bis(trimethylstannyl) acetic acid ethyl ester (3) as a minor product, and a small amount o f tetramethyltin (4). Full NMR data sets, including coupling constants and isotope induced chemical shifts 1Δ12/ 13C(119Sn) are provided for 1-3 . The first example o f ultra-high resolution 119Sn NMR is shown

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

2016 ◽  
Vol 14 (3) ◽  
pp. 809-820 ◽  
Author(s):  
Alfonso Pinedo ◽  
Mariana López ◽  
Elisa Leyva ◽  
Brenda Zermeño ◽  
Benito Serrano ◽  
...  
Keyword(s):  
Uv Light ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Initial Reaction Rate ◽  
Degradation Pathway ◽  
Photocatalytic Decomposition ◽  
Initial Reaction ◽  
Low Molecular Weight ◽  
Reaction Products ◽  
Constant Flow Rate

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

The Reactions of Alkoxide-Alkanol Negative Ions with Ketene. An ab initio and Ion Cyclotron Resonance Study

1985 ◽  
Vol 38 (3) ◽  
pp. 355 ◽  
Author(s):  
RN Hayes ◽  
JC Sheldon ◽  
JH Bowie
Keyword(s):  
Ab Initio ◽  
Cyclotron Resonance ◽  
Negative Ions ◽  
Ion Cyclotron Resonance ◽  
Reaction Sequence ◽  
Major Pathway ◽  
Stable Species ◽  
Product Ions ◽  
A Minor ◽  
Competing Reactions

Alkanol-alkoxide negative ions [RO----HOR] react with ketene to form stable species H-C≡C-O----HOR. The initial intermediate in the reaction sequence is produced by the formation of a hydrogen bond between the negatively charged oxygen of [RO----HOR] and a hydrogen of ketene. This intermediate decomposes by competing reactions, viz. ( i ) a minor pathway involving direct elimination of ROH, and (ii) a major pathway involving a rearrangement sequence. Intermediates and product ions have been defined by using ab initio calculations at the 4-31G level. The differences between the reactions of [RO----HOR]/ketene and [RO---- HOR]/acetaldehyde systems are discussed.

scholarly journals PROPELLANS – PERSPECTIVE FRAME COMPOUNDS FOR THE CREATION OF HIGH-ENERGY SUBSTANCES

2021 ◽  
pp. 144-148
Author(s):  
А.А. Минакова ◽  
С.Г. Ильясов
Keyword(s):  
Gradual Increase ◽  
Theoretical Calculations ◽  
High Energy ◽  
Biologically Active ◽  
Reaction Products ◽  
Energy Characteristics ◽  
Alkyl Derivatives ◽  
Nitro Derivatives ◽  
Selective Formation ◽  
Competing Reactions

Важной задачей современной органической химии является открытие новых, ранее не известных науке веществ, которые могли бы расширить область наших знаний и пополнить номенклатуру высокоэнергетических или биологически активных продуктов. 3,7,10-Триоксо-2,4,6,8,9,11-гексааза[3.3.3|пропеллан и его нитропроизводные являются новейшими продуктами класса гетероциклов, их азотсодержащая полициклическая структура предполагает наличие интересных и полезных свойств, что обусловливает проявленный интерес к данной работе. Химия 3,7,10-триоксо-2,4,6,8,9,11-гексааза[3.3.3|пропеллана малоизучена и представлена лишь двумя алкилпроизводными и теоретическими расчетами энергетических характеристик нитропроизводных. В статье преставлены результаты исследования нитрования 3,7,10-триоксо-2,4,6,8,9,11-гексааза[3.3.3]пропеллана (THAP) концентрированнойазотной кислотой. Установлено, что в процессе нитрования наблюдается протекание двух конкурирующих реакций – лактам-лактимной перегруппировки и нитрования. Было показано, что продукты реакции сильно зависят от температуры реакционной массы. Установлено, что температуре -40 ºС протекает образование лактимной формы ТНАР, тогда как при постепенном увеличении температуры сначала образуется мононитропроизводное пропеллана, а при температуре 40 ºС идёт селективное образование 3,7,10-триоксо-2,6-динитро-2,4,6,8,9,11-гексааза[3.3.3]пропеллана с выходом 30%. An important task of modern organic chemistry is the discovery of new substances previously unknown to science, which could expand the area of our knowledge and replenish the range of high-energy or biologically active products. 3,7,10-Trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane and its nitro derivatives are the newest products of the class of heterocycles; interest in this work. The chemistry of 3,7,10-trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane is poorly understood and is represented by only two alkyl derivatives and theoretical calculations of the energy characteristics of nitro derivatives. The article presents the results of a study of the nitration of 3,7,10-trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane (THAP) with concentrated nitric acid. It was found that in the process of nitration, there are two competing reactions - lactam-lactam rearrangement and nitration. It was shown that the reaction products strongly depend on the temperature of the reaction mixture. It was found that at a temperature of -40 ºС the formation of the lactimic form of THAP proceeds, whereas with a gradual increase in temperature, a mononitro derivative of propellane is first formed, and at a temperature of 40 ºС, the selective formation of 3,7,10-trioxo-2,6-dinitro-2,4,6,8,9,11-hexaaza[3.3.3]propellane in 30% yield.

Factor XII-Dependent Fibrinolysis: A Double Function of Plasma Kallikrein and the Occurrence of a Previously Undescribed Factor XII- and Kallikrein-Dependent Plasminogen Proactivator

1979 ◽  
Vol 41 (04) ◽  
pp. 756-773 ◽  
Author(s):  
C Kluft ◽  
M M Trumpi-Kalshoven ◽  
A F H Jie ◽  
E C Veldhuyzen-Stolk
Keyword(s):  
Plasminogen Activator ◽  
Low Molecular Weight ◽  
Plasma Kallikrein ◽  
Factor Xii ◽  
Normal Plasma ◽  
Double Function ◽  
Plasma Fractions ◽  
A Minor ◽  
Molecular Weight Form ◽  
Minor Activity

SummaryFibrinolytic studies in euglobulin fractions of Fletcher trait plasma (deficient in prekallikrein) revealed reduced activities as compared to normal plasma. A quantitative assay for total plasminogen activator plus proactivator in plasma showed that the amount in Fletcher trait patients is about half of normal (normal = ± 100 blood activator units [BAU]/ ml). Plasma kallikrein partially purified in a high and low molecular weight form exerted plasminogen activator activity amounting to 10–15 BAU/ml plasma. So, the absence of kallikrein in the deficient plasma can not fully account for the reduction in activator activity. Additions of kallikrein preparations or normal plasma fractions resulted in additional activator activity in Fletcher trait plasma which was assessed at 30–40 BAU/ml. This activity was assumed to originate from a previously undescribed plasminogen proactivator whose activation is kallikrein- and factor XH-dependent.Fractionation experiments demonstrated the presence of two major activities and a minor activity caused by kallikrein in normal plasma.It is concluded that plasma kallikrein has two functions in the generation of factor XII- dependent fibrinolytic activity: one as a direct plasminogen activator and another as a factor in the activation of a major factor XH-dependent plasminogen proactivator.

Dose Escalation of Low Molecular Weight Heparin to Manage VTE Treatment Failure in Cancer Patients

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 4050-4050
Author(s):  
Marc Carrier ◽  
Gregoire Le Gal ◽  
Sarah Tierney ◽  
Kimberley Do ◽  
Philip Wells ◽  
...  
Keyword(s):  
Treatment Failure ◽  
Cancer Patients ◽  
Bleeding Episode ◽  
Low Molecular Weight ◽  
Minor Bleeding ◽  
Failure Event ◽  
Recurrent Vte ◽  
A Minor ◽  
Therapeutic Doses

Abstract Introduction: Cancer patients with venous thromboembolism (VTE) are at high risk of treatment failures (i.e. recurrent VTE while on therapeutic anticoagulants). Management of these treatment failures is controversial/poorly studied. Whereas some clinicians recommend inferior vena cava (IVC) filter insertion, others do not. We sought to assess the efficacy and safety of escalating the dose of low-molecular weight heparin (LMWH) in the management of treatment failure recurrent VTE in cancer patients. Methods: Retrospective cohort study of outpatients with cancer and treatment failure recurrent VTE seen at the Ottawa Hospital Thrombosis Unit from January 2007 to June 2008. Patients were followed for three months following the treatment failure event. Results: Thirty cancer patients had recurrent VTE despite ongoing anticoagulation. The mean age was 60.7 years. Twenty two patients (73.3%) were on LMWH treatment at the time of the recurrent event. Of these 22 patients, 4 (18.2%) were on full (100%) therapeutic doses, 15 (68.2%) on 75% of therapeutic doses and 3 (13.6%) on prophylactic doses of LMWH. All 4 patients on full therapeutic dose were treated by increasing the weight-adjusted dose of LMWH by 20% for 6 weeks. Patients on 75% of therapeutic doses were treated by increasing the weight-adjusted LMWH by 25% for 6 weeks (4/15 patients) or 3 months (11/15 patients). All three patients on prophylactic doses were treated with one month of full therapeutic doses of LMWH followed by 75% thereafter. No patients had an IVC filter inserted or a major bleeding episode. One patient had a minor bleeding episode (4.5%; 95% CI: 1.1–21.9%), 2 patients died (9.1%; 95% CI: 2.8–28.0) (no VTE-related death) and one patient (4.5%; 95% CI: 1.1–21.9%) had a second treatment failure event during the three-month follow-up period while on full therapeutic doses of LMWH. Eight patients (26.7%) were on vitamin-K antagonist at the time of the recurrent VTE due to treatment failure. Five (62.5) patients had a therapeutic INR on the day of the recurrent VTE. All patients were treated with LMWH at full doses for a month followed by 75% thereafter. One patient (12.5%; 95%CI 2.8–48.3) had a minor bleeding episode during follow-up. Conclusion: Escalading the dose of LMWH following a recurrent VTE due to treatment failure seems to be a safe and effective method to prevent further recurrence in cancer patients. Our data challenges the concept of using IVC filters in this setting.

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