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As a prominent member of the vitamin E group, α‐tocopherol is an important lipophilic antioxidant. It has a special oxidation chemistry that involves phenoxyl radicals, quinones and quinone methides. During the oxidation to the ortho‐quinone methide, an intermediary zwitterion is formed. This aromatic intermediate turns into the quinone methide by simply rotating the initially oxidized, exocyclic methyl group into the molecule's plane. This initial zwitterionic intermediate and the quinone methide are not resonance structures but individual species, whose distinct electronic structures are separated by a mere 90° bond rotation. In this work, we hindered this crucial rotation, by substituting the affected methyl group with alkyl or phenyl groups. The alkyl groups slowed down the conversion to the quinone methide by 18‐times, while the phenyl substituents, which additionally stabilize the zwitterion electronically, completely halted the conversion to the quinone methide at −78 °C, allowing for the first time the direct observation of a tocopherol‐derived zwitterion. Employing a 13C‐labeled model, the individual steps of the oxidation sequence could be observed directly by NMR, and the activation energy for the rotation could be estimated to be approximately 2.8 kcal/mol. Reaction rates were solvent dependent, with polar solvents exerting a stabilizing effect on the zwitterion. The observed effects confirmed the central relevance of the rotation step in the change from the aromatic to the quinoid state and allowed a more detailed examination of the oxidation behavior of tocopherol. The concept that a simple bond rotation can be used to switch between an aromatic and an anti‐aromatic structure could find its use in molecular switches or molecular engines, driven by the specific absorption of external energy. [ABSTRACT FROM AUTHOR]

The article discusses a teaching and learning sequence for secondary education chemistry classes focusing on green and sustainable chemistry using the example of wood biorefinery. It emphasizes the importance of informed decision-making regarding environmental pollution, greenhouse gas emissions, and resource usage. The teaching sequence aims to promote scientific literacy, informed decision-making, and active participation in socio-political decisions among students by integrating traditional chemistry content with principles of green and sustainable chemistry. The article also highlights the role of individual citizens in contributing to sustainability goals and emphasizes the need for scientific education to enable informed choices and responsible actions. [Extracted from the article]

Screening for new bioactive microbial metabolites, we found a novel okaramine derivative, for which we propose the trivial name lemmokaramine, as well as two already known okaramine congeners – okaramine H and okaramine J - responsible for antimicrobial activity of the recently described microscopic filamentous fungus, Keratinophyton lemmensii BiMM-F76 (= CCF 6359). In addition, two novel substances, a new cyclohexyl denominated lemmensihexol and a new tetrahydroxypyrane denominated lemmensipyrane, were purified and characterized. The compounds were isolated from the culture extract of the fungus grown on modified yeast extract sucrose medium by means of flash chromatography followed by preparative HPLC. The chemical structures were elucidated by NMR and LC-MS. The new okaramine (lemmokaramine) exerted antimicrobial activity against Gram-positive and Gram-negative bacteria, yeasts and fungi and anticancer activity against different mammalian cell lines (Caco-2, HCT116, HT29, SW480, MCM G1, and MCM DLN). Furthermore, we found a significant antioxidant effect of lemmokaramine following H2O2 treatment indicated by activation of the Nrf2 pathway. This is the first report describing analysis and structural elucidation of bioactive metabolites for the onygenalean genus Keratinophyton. [ABSTRACT FROM AUTHOR]

The purpose of this article is to provide the reader with an overview of the methods used to determine the molecular weights of cellulose. Methods that employ direct dissolution of the cellulose polymer are described; hence methods for investigating the molecular weight of cellulose in derivatized states, such as ethers or esters, only form a minor part of this review. Many of the methods described are primarily of historical interest since they have no use in modern cellulose chemistry. However, older methods, such as osmometry or ultracentrifuge experiments, were the first analytical methods used in polymer chemistry and continue to serve as sources of fundamental information (such as the cellulose structure in solution). The first part of the paper reviews methods, either absolute or relative, for the estimation of average molecular weights. Regardless of an absolute or relative approach, the outcome is a molecular weight average (MWA). In the final section, coupling methods are described. The primary benefit of performing a pre-separation step on the molecules is the discovery of the molecular weight distribution (MWD). Here, size exclusion chromatography (SEC) is unquestionably the most powerful and most commonly-applied method in modern laboratories and industrial settings. [ABSTRACT FROM AUTHOR]

2,5-Dihydroxy- 1,4-benzoquinone (DHBQ) is one of the key chromo-phores occurring in all types of aged cellulosics. This study investigates the mechanism of H2O2 degradation of DHBQ under conditions relevant to pulp bleaching (3.0% H2O2, NaOH, pH 10), to obtain insights useful for improved pulp processing. DHBQ is degraded quantitatively into malonic add with an activation energy (Ea) of 16.1 kcal/mol and activation entropy (Δ‡S°) of ~28 cal/mol-K. Higher concentrations of sodium cations increase the reaction rate. Theoretical computations indicate the formation or an intermediate Io having an O--U bridge between C-2 and C-S of the 1,4-cydohexadione structure. Io undergoes O--O homolysis to form a biradical Bt, which is fragmented into malonate anions. The calculated Ea (17.8 kcal/mol) agrees well with the experimental one. Coordination of Na+ to Io and Bt decreases their energies and enhances the O--O homolysis rate, which is consistent with the acceleration by sodium cation and the negative Δ‡S°. The homolysis of Io is much favored over that of the neutral counterpart, with the unpaired electrons of Bt being stabilized by the geminal anionic oxygen. This difference in the stability of the intermediates translates into significant variations in the reaction rate and the product distribution between pH 10 and neutral/addie conditions. [ABSTRACT FROM AUTHOR]

2,5-Dihydroxy-1,4-benzoquinone (DHBQ) is one of the key chromophores formed upon aging in cellulosic materials. This study addresses the degradation mechanism of DHBQ by hydrogen peroxide to provide a solid knowledge base for optimization of bleaching sequences aiming at DHBQ removal. Kinetic analysis provided an activation energy (Ea) of 20.4 kcal/mol. Product analyses indicated the product mixture to contain malonic acid, acetic acid, and carbon dioxide. DFT(B3LYP) computation presented a plausible mechanism for the formation of these products from DHBQ. DHBQ forms intermediate I2k, having an intramolecular O-O bridge between C-2 and C-5 of the 1,4-cyclohexadione structure. This O-O bond is homolytically cleaved, and the subsequent β-fragmentation of the resulting radical forms ketene and oxaloacetic acid. While ketene yields acetic acid, oxaloacetic acid then gives malonic acid and carbon dioxide through further attack of hydrogen peroxide via an intermediate that is oxidatively decarboxylated. The calculated Ea value (23.3 kcal/mol) in the rate-determining step, i.e., the homolysis of I2k, agreed well with the experimental value. There is also a minor pathway in which the spin state changes to triplet during the homolysis of I2k; in this way two malonyl radicals are formed that are converted to two molecules of malonic acid. [ABSTRACT FROM AUTHOR]

Abstract: The sonochemical degradation of cellulose by a 24-kHz ultrasound probe system and the oxidative modification of cellulose upon sonication were studied. Both aqueous cellulose suspension (heterogeneous system) as well as cellulose solutions in N,N-dimethylacetamide/LiCl (homogeneous system) were used. In both cases, a significant reduction in the degree of polymerization was observed. The rate of the degradation process was dependent on the degree of polymerization of the starting material, temperature, cellulose amount in suspension, cellulose concentration in solution, and the pH value of the aqueous suspension. In solution, the degradation process was accompanied by cellulose oxidation as seen in the introduction of carbonyl groups. The introduction of carbonyl groups could be shown to occur close to chain ends. Sonochemical degradation of cellulose is a very efficient non-classical method in accordance with “green chemistry” concepts. [Copyright &y& Elsevier]

Composites of cellulose and conjugated polymers based on oligo- and polythiophene are reported, inspired by the assembly of cellulose and lignin in wood as a composite that survives harsh environmental conditions and meets most complex demands. The regioselectively oligothiophene-substituted cellulose derivatives were synthesized according to a protecting group strategy and used to prepare the polythiophene-cellulose composites through a FeCl3-initiated oxidative co-polymerization with thiophene co-monomers. The optical property of the cellulose derivatives with mono-, bi- and terthiophene moieties at the C-6 position was investigated with ultraviolet-visible (UV-Vis) and circular dichroism (CD) spectroscopy. The UV-Vis absorption spectra exhibited a broad band reflecting the intense π-π* transition within the conjugated oligothiophene side chains, which were greater than those of the corresponding reference monomers owing to their intermolecular π-electron interactions, even in solution. This was also supported by the negative CD band, indicative of cellulosic supramolecular stacking structures in solution. The soluble polythiophene-cellulose composites were prepared by the oxidative co-polymerization of the oligothiophene substituted celluloses with excess 3-hexylthiophene in the presence of FeCl3 as the oxidative initiator. The supplied amount of thiophene co-monomer was crucial for producing large π-conjugated structures and a cross-linked network structure. The soluble composites, with properties, such as electric conductivity, semiconductivity, or photoelectroactivity, were applied for the preparation of thin films which will have to be optimized for the respective application. [ABSTRACT FROM AUTHOR]

Contrary to concepts handed down in the literature from the early days of vitamin E research, one-electron oxidation of vitamin E does not involve 5a-C-centered radicals. A combined approach of analytical techniques, in particular electron paramagnetic resonance spectroscopy (EPR), organic synthesis of special derivatives, isotopic labeling, kinetic studies, and computational chemistry was used to re-evaluate the one-electron and two-electron oxidation chemistry of α-tocopherol (α-toc). EPR in combination with 5a-13C-labeled compounds provided no indication of the involvement of 5a-C-centered radicals. Oxidation of special tocopherol derivatives were used to disprove the occurrence of 5a-C-centered one-electron intermediates. Additionally it was shown that those vitamin E reactions that were commonly evoked to plead for the involvement of C-centered tocopheryl radicals actually proceeded via heterolytic, i.e., non-radical, intermediates. The results will help to clear widely spread misunderstandings about the chemistry of vitamin E and will have mechanistic implications for the synthesis of tocopherol-based supramolecular structures and 5a-substituted α-tocopherol derivatives. [ABSTRACT FROM AUTHOR]

Reaction with specific scavenger agents, so-called trapping, is a direct way to prove the occurrence of reactive intermediates in a reaction system, and thus to elucidate the underlying reaction mechanisms. After an introduction on chemical intermediates, chemical trapping and the peculiarities of trapping methodology in the presence of cellulose, four chapters from cellulose chemistry were selected to illustrate how trapping can be used to determine reactive intermediates, to prove the occurrence of reactive intermediates in the respective reaction system, and to finally help establish the reaction mechanism. The four topics are: radical and ionic intermediates in Lyocell dopes that cause cellulose degradation, the chemistry of cellulose in DMAc/LiCl solutions, aging of alkali cellulose under steeping conditions, and cellulose degradation during carbanilation in dimethyl sulfoxide (DMSO) mixtures. [ABSTRACT FROM AUTHOR]

Abstract: Bromination of the ethano-dimer of α-tocopherol ( 6 ) afforded pyrano-spirodimer of α-tocopherol ( 7 ) quantitatively, while the methano-dimer of α-tocopherol ( 10 ) produced a mixture of products, including the furano-spirodimer 11 , pyrano-spirodimer 7 , and 5-bromo-γ-tocopherol ( 12 ), the latter two formed in an unusual dealkylative fragmentation step. The mechanisms were studied by a combination of trapping reactions as well as kinetic and computational studies. [Copyright &y& Elsevier]

The presence of hydroxyl radicals during aging ("ripening") of alkali cellulose has been confirmed by selective trapping. As none of the spin traps available to date was working under such strongly alkaline conditions, a novel, alkali-stable trapping agent was developed, γ-tocopheryl-iso propyl ether. This spin trap reacts selectively with hydroxyl radicals, but not with other reactive oxygen species or radicals present. The presence of hydroxyl radicals was confirmed additionally by the inhibition of the chain degradation in the presence of the OH trap, which allowed estimating the contribution of OH radicals to the overall degradation of alkali cellulose during aging. [ABSTRACT FROM AUTHOR]

Abstract: Two model compounds ( 3 and 4 ) having the typical α-tocopherol-type substitution pattern of the aromatic ring, but lacking the annulated pyran ring, have been synthesized. Upon oxidation, the two possible ortho-quinone methides (oQMs) of each are formed in equal ratio. DFT calculations suggest that there is no angular strain in 3 and 4 , and each of the oQM pairs is of similar energy. These results prove that the commonly observed regioselectivity in oxidations of vitamin E-type model compounds is not an electronic substitution effect, but a consequence of annulation. [Copyright &y& Elsevier]

Abstract: α-Tocopherol is the most important lipophilic antioxidant of the chromanol type protecting biomembranes from lipid peroxidation (LPO). Therefore, α-tocopherol and its derivatives are frequently used in the therapy or prevention of oxygen radical-derived diseases. In the present study, novel chromanol-type antioxidants (twin-chromanol, cis- and trans-oxachromanol) as well as the well-known short-chain analogue of α-tocopherol, pentamethyl-chromanol, were tested for their antioxidative potency in rat heart mitochondria (RHM). Our experiments revealed that the bioenergetic parameters of mitochondria were not deteriorated in the presence of chromanols (up to 50nmol/mg protein). Exposure of RHM to cumene hydroperoxide and Fe2+ (final concentrations 50μM each), inducing LPO, significantly affected their bioenergetic parameters which were determined in the presence of glutamate and malate (substrates of mitochondrial complex I). Alterations of the bioenergetic parameters were partially prevented in a concentration-dependent manner by preincubating RHM with antioxidants before adding the radical-generating system. In the lower concentration range, twin-chromanol turned out to be more efficient than pentamethyl-chromanol, both being far more protective than cis- and trans-oxachromanol. Measurement of protein-bound SH groups and thiobarbituric acid-reactive substances revealed that this protective effect was due to their antioxidative action. Furthermore, HPLC measurements of α-tocopherol and α-tocopheryl quinone in rat liver mitochondria demonstrated an α-tocopherol-sparing effect of twin-chromanol. In conclusion, new chromanol-type antioxidants, especially twin-chromanol, were able to improve bioenergetic and biochemical parameters of mitochondria exposed to oxidative stress. [Copyright &y& Elsevier]

Abstract: Condensation of γ-tocopherol with aldehydes provides 2,4-disubstituted 1,3,8-trioxaphenanthrenes in a simple one-pot reaction. The reaction proceeded under acid catalysis according to a two-step alkylation–acetalisation mechanism in yields between 58 and 81%. The title compounds are precursors for the thermal generation of ortho-quinone methides, which can be in situ reduced to give antioxidants of the 5a-substituted α-tocopherol-type. The products were analytically characterized by NMR and HRMS. [Copyright &y& Elsevier]

Abstract: The Polonowski reaction of NBnMO (4) afforded tropone (10) and the novel isoindole 11 besides the expected products benzaldehyde and acetmorpholide, in a temperature-dependent ratio. The reaction proceeded via two primary carbenium–iminium ion intermediates, an exo-centered species 5 which underwent a benzylium–tropylium type rearrangement, and a ring-centered species 6, which reacted further to isoindole 11 by intramolecular electrophilic substitution. The experimental findings were in good agreement with DFT computational data. [Copyright &y& Elsevier]

Abstract: A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride–acetic acid complex (BF3·2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR/MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken. Four cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers, cellulose triacetate, pulp after thermal treatment in N,N-dimethylacetamide, and pulp containing carbonyl-selective labels, and up to 11 chromophores per sample have been identified. [Copyright &y& Elsevier]

Reaction of 2-hydroxy-para-benzoquinones with DMSO/Ac2O produced dimethylsulfonium ylides, of which crystal structures as well as solid and liquid state NMR spectra were recorded. The ylides react with tertiary methylamine N-oxides in a one-pot, multi-step process to 3-methylamino-substituted benzoquinones. The mechanism starts with a deoxygenative deprotonation of the amine N-oxides, followed by a formal electrophilic displacement of DMSO by the resulting carbonium–iminium ion. [Copyright &y& Elsevier]

Methyl 4-O-methyl-β-d-ribo-hex-3-ulopyranoside (2), a model compound for partially oxidized anhydroglucose units in cellulose, was crystallized from CHCl3/n-hexane by vapor diffusion to give colorless plates. Crystal structure determination revealed the monoclinic space group P21 with Z=2C8H14O6 and unit cell parameters of a=8.404(2), b=4.5716(10), c=13.916(3) A˚, and β=107.467(4)°. The structure was solved by direct methods and refined to R=0.0476 for 1655 reflections and 135 parameters. The hexulopyranoside occurs in a distorted chair conformation. Both hydroxyls are involved in hydrogen bonding and form zigzag bond chains along the b-axis. One of the two hydrogen bonds is bifurcated. The solid-state 13C NMR spectrum of 2 exhibits eight carbon resonances, with well-separated signals for the two methoxyls (1-OMe: 55.72 ppm, 4-OMe: 61.25 ppm) and a keto resonance with relatively large downfield shift (206.90 ppm). Differences in the C-4 and the methoxyls’ chemical shifts in the solid and liquid states were found. [Copyright &y& Elsevier]

Two carbenium-iminium ions, an exo-centered species and a ring-centered form , are derived from the widely used oxidant and cellulose solvent N-methylmorpholine-N-oxide () by heterolytic degradation. rearranges into in the presence of water, in an endothermic, bimolecular reaction involving a highly organized transition state, which is the first example of a carbenium-iminium ion interconversion. The reaction mechanism was investigated by a combined approach consisting of trapping reactions, isotopic labeling, kinetic studies, and computations on the DFT level. [Copyright &y& Elsevier]

The reaction of α-tocopheryl acetate (vitamin E acetate, 3) with concentrated nitric acid proceeds according to a non-radical, two-step mechanism, producing 5-nitromethyl-γ-tocopheryl acetate (4) in good yields. In the first step, oxidation of 3 affords a benzylic cation intermediate (8), which in the second step adds nitrite to give 4. The acetyl group, which stabilizes intermediate 8 intramolecularly, remains bound to the tocopheryl moiety throughout the reaction. [Copyright &y& Elsevier]

Reaction of tocopheryl bromide 2a or chromanyl bromide 2b with triphenyl phosphine produced phosphomium salt intermediates (3a–b), which further reacted with acyl chlorides to novel furotocopherol compounds 4–11 in good yields. The cyclization proceeded according to a two step esterification–Wittig mechanism. Similarly, furotocopheryl dimer 12 was prepared starting from oxalyl chloride. The coupling of tocopheryl phosphonium salt 3a onto modified polystyrene provided a new, vitamin E-loaded resin. [Copyright &y& Elsevier]

Condensation of trimethylhydroquinone with aldehydes provides 2,4-disubstituted 5,7,8-trimethyl-4H-benzo[1,3]dioxin-6-ols in a straightforward one-pot reaction. These compounds are 3-oxa-derivatives of α-tocopherol (vitamin E) and represent an interesting novel class of phenolic antioxidants. The formation reaction proceeds according to a two-step mechanism consisting of electrophilic substitution and acetalization, and provides the product as a cis/trans-mixture of diastereomers. [Copyright &y& Elsevier]

Certain cellulose samples, especially those of higher molecular weight, are initially insoluble in N,N-dimethylacetamide (DMAc, 1)/lithium chloride, which is a very common solvent system for cellulosic materials. According to a common protocol, heating or refluxing these samples in DMAc, or in DMAc containing dissolved LiCl, represents one of several so-called ‘activation’ procedures, which are aimed at facilitating subsequent dissolution. In the present work, it is shown that the improved solubility achieved by this method is not only caused by a better activation or improved accessibility of the pulp, but also by a progressing degradation of the cellulosic material (DP loss).The degradation of cellulose in DMAc or DMAc/LiCl is due to two separate chemical processes. The first one, involving N,N-dimethylacetoacetamide (2) which is the primary condensation product of DMAc, causes a slow degradation by thermal endwise peeling. The glucose units peeled off the reducing end are released as furan structures (3). The mechanism appears to be a thermal cleavage of the glycosidic bond, which becomes quite selective towards the proximal anhydroglucose unit by a neighbor group-assisted effect according to quantum-chemical calculations. Due to its stepwise and thus slow mechanism, this pathway contributes only insignificantly to the overall cellulose degradation.The second degradation mechanism causes random chain cleavage and thus pronounced and rather fast changes in the molecular weight distribution. It involves N,N-dimethylketeniminium ions (5), whose presence in DMAc/LiCl at temperatures above 80 °C—the coalescence temperature of DMAc as determined by dynamic NMR—was unambiguously demonstrated by specific trapping in a thermal [2+2]-cycloaddition with lipophilic olefins. The keteniminium ion is an extremely reactive electrophile, which is able to directly cleave glycosidic bonds. The detrimental effect of this intermediate on the integrity of cellulosic pulps was confirmed by addition of an external degrading agent of the keteniminium type. Also the precursor compound, a ketene aminal, was confirmed to be present in heated DMAc or DMAc/LiCl by trapping with allyl alcohol in a spontaneous Claisen-type rearrangement. [Copyright &y& Elsevier]

The course of the reaction between N-methylmorpholine-N-oxide (NMMO, 1a) and cyanuric chloride (2) is strictly dependent on the hydrate water content of the amine oxide. In solid phase, both substances undergo an explosion-like, extremely exothermic reaction. In solution, this process becomes controllable and leads to a quantitative degradation of NMMO into morpholine and formaldehyde, with 2 only acting as an inducing agent. The reaction can be conducted in a way that a clean deoxygenative demethylation is achieved. The monohydrate of NMMO (1b) is quantitatively converted into N-methylmorpholine and hypochlorous acid by the action of 2. This conversion can be used in synthesis either to deoxygenate tertiary amine N-oxide monohydrates, or to produce chlorohydrins in non-aqueous, organic media in superior yields. The semisesquihydrate of NMMO (1c) reacts with 2 under consumption of water until non-hydrated NMMO is present, which is then further converted into morpholine and HCHO, as in the case of 1a being directly employed as the starting material. [Copyright &y& Elsevier]

Examines the synthesis and oxidation behavior of pentamethyl, a multifunctional oxatocopherol-type antioxidant. Formation of exocyclic methylene; Release of acetaldehyde upon oxidation; Reaction of quinone to acetophenone.

Primary and secondary amines are N-methylated by a mixture of paraformaldehyde and oxalic acid dihydrate in good to excellent yields. The reaction proceeds without involvement of organic solvents and toxic formalin. Reaction temperatures of 100°C are required for the decomposition of oxalic acid into the intermediate formic acid which acts as the actual reductant. The reaction conditions have been optimized, and the mechanism has been elucidated by means of deuteration experiments. [ABSTRACT FROM AUTHOR]

Polyanionic cellulose carbamates were synthesized by rapid and efficient homogeneous aminolysis of cellulose carbonate half-esters in an ionic liquid/DMF medium. Cellulose bis-2,3-O-(3,5-dimethylphenyl carbamate), as a model compound, reacted with different chloroformates to cellulose carbonates. These intermediates were subjected to aminolysis, for which both the reactivity of different chloroformates towards C6-OH and the reactivity/suitability of the respective carbonate half-ester in the aminolysis were comprehensively studied. Phenyl chloroformate and 4-chlorophenyl chloroformate readily reacted with C6-OH of the model cellulose derivative, while 4-nitrophenyl chloroformate did not. The intermediate 4-chlorophenyl carbonate derivative with the highest DS (1.05) was then used to evaluate different aminolysis pathways, applying three different amines (propargyl amine, β-alanine, and taurine) as reactants. The latter two zwitterionic compounds are only sparingly soluble in pure DMF as the typical reaction medium for aminolysis; therefore, several alternative procedures were suggested, carefully evaluated, and critically compared. Solubility problems with β-alanine and taurine were overcome by the binary solvent system DMF/[EMIM]OAc (1:1, v/v), which was shown to be a promising medium for rapid and efficient homogeneous aminolysis and for the preparation of the corresponding cellulose carbamate derivatives or other compounds that are not accessible by conventional isocyanate chemistry. The zwitterionic cellulose carbamate derivatives presented in this work could be promising chiral cation exchangers for HPLC enantiomer separations. [ABSTRACT FROM AUTHOR]

Polysaccharides, oligosaccharides, and their derivatives, particularly of amylose, cellulose, chitosan, and β-cyclodextrin, are well-known chiral selectors (CSs) of chiral stationary phases (CSPs) in chromatography, because they can separate a wide range of enantiomers. Typically, such CSPs are prepared by physically coating, or chemically immobilizing the polysaccharide and β-cyclodextrin derivatives onto inert silica gel carriers as chromatographic support. Over the past few years, new chiral selectors have been introduced, and progressive methods to prepare CSPs have been exploited. Also, chiral recognition mechanisms, which play a crucial role in the investigation of chiral separations, have been better elucidated. Further insights into the broad functional performance of commercially available chiral column materials and/or the respective newly developed chiral phase materials on enantiomeric separation (ES) have been gained. This review summarizes the recent developments in CSs, CSP preparation, chiral recognition mechanisms, and enantiomeric separation methods, based on polysaccharides and β-cyclodextrins as CSs, with a focus on the years 2019–2020 of this rapidly developing field. [ABSTRACT FROM AUTHOR]

N,N-Dimethylacetamide (DMAc, 1)/lithium chloride is a frequently used solvent system for cellulosic materials. Heating or refluxing insoluble samples in DMAc/LiCl represents a common protocol for facilitating the subsequent dissolution. It is shown by kinetics using gel permeation chromatography (GPC) that the improved solubility is not caused by an alleged ‘activation’ of the pulp, but by progressing degradation of the cellulosic material. Ketene aminal 2 and N,N-dimethylketeniminium ions (3), the latter being known as reagent for cleavage of ethers and acetals, have been demonstrated to be present in DMAc and DMAc/LiCl at elevated temperatures by specific trapping of these intermediates in a Claisen rearrangement and in a thermal [2+2]-cycloaddition, respectively. [Copyright &y& Elsevier]

Methylation followed by depolymerization and gas chromatography (GC) is an effective methodology for the linkage analysis of polysaccharides, including fucoidan, a sulphated algal polysaccharide. However, this sample material demands attention to experimental details to prevent aberrations in the analytical result. The use of deficient bases for methylation, the presence of water, analyte degradation during hydrolysis, and coelution of the target analytes during gas chromatography create doubts about published results. We therefore investigated critical parameters of the method and carefully optimized the steps of the protocol to ensure the integrity of the results for the fucose monomers. Fucoidan from Cladosiphon okamuranus was used as reference sample to determine the glycosidic bonds, and sulphate positions in the monomer. Fucoidan in protonated form was methylated in a strictly water-free environment using lithium dimsyl as base and methyl iodide for methylation. The methylated polymer was isolated by solid phase extraction, which was crucial to recover also the highly sulfated fraction. Hydrolysis was conducted with trifluoroacetic acid. To separate all target analytes in GC-FID/MS, a stationary phase with high cyanopropyl content (HP-88) was required, as the commonly employed phenyl siloxane phases result in co-elution, which distorts the result severely. [Display omitted] • Lithium dimsyl and a strictly water-free environment are required for good methylation results. • SPE-C18 is suited to isolate permethylated, sulphated fucoidan. • For GC, stationary phases with cyanopropyl substituents (e. g. HP-88) must be used to achieve adequate separation. • Fucoidan from C. okamuranus is composed of 1,3-linked fucose, sulphated at C-4. [ABSTRACT FROM AUTHOR]

The traditional binder used in mineral wool is phenolic resin that makes mineral wool insulations reliable and efficient. The toxicity and health hazards of phenol and formaldehyde are becoming more and more pressing, and the industrial production needs to focus on safer precursors. Several formulations of bio-based binders for mineral wool have been developed, meeting the challenge of performing equally well as conventional binders. Technical lignins, due to their intrinsic structure and their abundance, are good candidates for future industrial adhesives. Carbohydrates are other class of biomaterials widely used in both research and patent formulations toward mineral wool binders. Proteins and cardanol are still largely unknown precursors, although they have hidden potentials for reliable binder systems. Even if conventional binders are not replaced completely with bio-based alternatives today, a partial use is already a step forward in the right direction – toward future biorefinery-based industries and knowledge-based bioeconomies in general. [ABSTRACT FROM AUTHOR]

Demonstrates the autocatalytic decomposition of N-methylmorpholine N-oxide (NMMO), one of the most important amine oxides in organic synthesis, induced by Mannich-type intermediates. Rates of the degradation of NMMO; Effects of acids and bases on the reaction rate; Role of the carbenium-iminium ion in the decomposition of NMMO.

The effect of ball milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of crude milled wood lignin (MWLc) preparation is studied to better understand the process' fundamentals and find optimal conditions for MWL isolation (i.e., to obtain the most representative sample with minimal degradation). Softwood (loblolly pine) MWLc preparations with yields of 20-75% have been isolated and characterized based on their molar mass distribution (by Size Exclusion Chromatography (SEC)), hydroxyl groups of different types (31P NMR), methoxyl groups (HS-ID GC-MS), and sugar composition (based on methanolysis). Classical MWL purification is not used to access the whole extracted lignin. The results indicate that lignin degradation during ball milling occurs predominantly in the high molar mass fraction and is less pronounced in the low molar mass fraction. This results in a significant decrease in the Mz and Mw of the extracted MWLc with an increase in the yield of MWLc, but has only a very subtle effect on the lignin structure if the yield of MWLc is kept below about 55%. Therefore, no tedious optimization of process variables is necessary to achieve the required MWLc yield in this range for structural studies of softwood MWL. The sugar composition shows higher amounts of pectin components in MWLs of low yields and higher amounts of glucan and mannan in high-yield MWLs, confirming that lignin extraction starts from the middle lamella in the earlier stages of MWL isolation, followed by lignin extraction from the secondary wall region. [ABSTRACT FROM AUTHOR]

A new and robust high performance thin-layer chromatography (HPTLC) method has been developed for carbohydrate analysis in biorefinery streams. The samples can be applied directly from industrial streams without any purification or pretreatment, saving time and resources and avoiding potential alterations to the samples’ composition. The main neutral monosaccharides found in wood-based lignocellulosic biomass – glucose, xylose, mannose, arabinose and galactose – can be separated and quantified using acetonitrile:1-pentanol:water (4:1:1, v/v/v) on silica impregnated with a phosphate buffer. Common minor compounds – glucuronic acid, galacturonic acid, rhamnose, cellobiose and hydroxymethylfurfural (HMF) – can also be detected qualitatively. Matrix compounds, which are a major part of biomass, do not interfere with the analysis. Validation showed that the method is selective, has good repeatability and has limits of detection and quantification in the nanogram range. The visual fingerprint offers information on the samples’ constituents in the case of unknown samples. Also, incomplete hydrolysis is indicated by the visibility of oligosaccharides. [ABSTRACT FROM AUTHOR]

Reports on the production of 5a-bromo-alpha-tocopherol after the bromination of alpha-tocopherol (Vitamin E) with elemental bromine. Illustration of examples employing amino protection; Superiority of the approach over reductive alkylation.

Describes the selective enzymatic oxidation of aromatic methyl groups to aldehydes. Representative examples of benzyl alcohols oxidized to the corresponding benzaldehydes; Mechanism for the oxidation of methyl groups on aromatic rings.

Knowledge gaps in the biosafety data of the nanocellulose (NC) for biomedical use through various routes of administration call for closer look at health and exposure evaluation. This work evaluated the potentially immunogenic contaminants levels, for example, endotoxin and (1,3)-β-d-glucan, in four representative NCs, that is, wood-based NCs and bacterial cellulose (BC). The hot-water extracts were analyzed with ELISA assays, HPSEC-MALLS, GC, and NMR analysis. Varying levels of endotoxin and (1,3)-β-d-glucan contaminats were found in these widely used NCs. Although the β-(1,3)-d-glucan was not detected from the NMR spectra due to the small extract samples amount (2-7 mg), the anomerics and highly diastereotopic 6-CH2 signals may suggest the presence of β-(1,4)-linkages with β-(1,6) branching in the polysaccharides of NCs' hot-water extracts, which were otherwise not detectable in the enzymatic assay. In all, the article highlights the importance of monitoring various water-soluble potentially immunogenic contaminants in NC for biomedical use. [ABSTRACT FROM AUTHOR]

A novel method for the precise and accurate quantification of wood monosaccharides by gas-chromatography mass-spectrometry in complex lignocellulosic biomass matrices is presented. Instead of using the syn- or the anti-peak obtained by blocking the anomeric center using e.g. oximation, the sum of each syn- and anti-peak pair is used for quantification rendering the approach of the apparently constant syn- and anti-peak area ratio. Each wood monosaccharide syn- and anti-peak could essentially be distinguished upon O -ethoximation followed by trifluoroacetylation and separation on a 14% cyanopropyl/phenyl- 86% dimethylpoly-siloxane column. Additionally, internal standardization was carried out applying isotopically labeled compounds. Hence, the analytical figures of merit, such as precision and accuracy, could be substantially improved compared to standard gas-chromatography mass spectrometry as well as high-performance anion exchange chromatography (HPAEC) coupled to pulsed-amperometric detection (PAD). The applicability of the novel gas-chromatography mass-spectrometry approach is demonstrated by analysis of five selected lignocellulosic biomass sample matrices typically occurring in a biorefinery scenario. Even in exceedingly complex sample matrices precise and accurate data are obtained according to the methodology presented. [ABSTRACT FROM AUTHOR]

No abstract available [ABSTRACT FROM AUTHOR]

Advected cyanobacteria, algal blooms and cyanotoxins have been increasingly detected in freshwater ecosystems. This review gives an insight into the present state of knowledge on the taxonomy, dynamics, toxic effects, human and ecological health implications of cyanobacteria, algal blooms and cyanotoxins in the East African Community lakes. The major toxigenic microalgae in East African lakes include Microcystis, Arthrospira, Dolichospermum, Planktolyngbya and Anabaenopsis species. Anatoxin-a, homoanatoxin-a, microcystins (MCs), cylindrospermopsin and nodularin have been quantified in water from below method detection limits to 81 µg L−1, with peak concentrations characteristically reported for the wet season. In whole fish, gut, liver and muscles, MCs have been found at concentrations of 2.4 to 1479.24 μg kg−1, which can pose human health risks to a daily consumer. While there have been no reported cases of cyanotoxin-related poisoning in humans, MCs and anatoxin-a (up to 0.0514 μg kg−1) have been identified as the proximal cause of indiscriminate fish kills and epornitic mortality of algivorous Phoeniconaias minor (lesser flamingos). With the unequivocal increase in climate change and variability, algal blooms and cyanotoxins will increase in frequency and severity, and this will necessitate swift action towards the mitigation of nutrient-rich pollutants loading into lakes in the region. [ABSTRACT FROM AUTHOR]

• Styrene-butadiene-styrene (SBS) had no impact on the oxidation kinetics of bitumen. • Mainly olefinic and allylic SBS sites are attacked during field ageing. • SBS degradation occurs in the field while the average bitumen size remains constant. • Multiple ageing cycles replicate unique field ageing phenomena in the laboratory. • Prolonged laboratory ageing induces severe changes in aromatic bitumen structures. Polymers play a crucial role in modifying the mechanical and rheological properties of bituminous construction materials. One of the most employed polymers, particularly in road engineering, is styrene–butadiene–styrene (SBS). However, long-term interactions of the SBS composite mixture with solar radiation and atmospheric gases result in material deterioration. Despite its prevalent use, the specific contribution of the polymer in these processes remains insufficiently understood. To address this gap in knowledge, we developed an analytical framework to precisely determine the chemistry of SBS-modified bitumen. Unmodified and SBS-modified samples were aged according to different ageing procedures to analyse thermal and thermochemical influences. These samples were then compared to genuine samples obtained from construction sites/test fields. Infrared spectroscopy revealed the formation of carbonyls and sulfoxides during all ageing procedures. The highest increase was observed in the field-aged sample. High temperatures during laboratory ageing affected the sulfoxide formation, as decomposition became a limiting factor. Comparing unmodified and SBS-modified samples showed that the oxygen uptake was similar during all ageing procedures, indicating that the presence of SBS did not impact the oxidation susceptibility. Two-dimensional nuclear magnetic resonance (NMR) spectroscopy facilitated the quantification of SBS substructures, showing a loss of 21% olefinic and 25% allylic SBS groups during field ageing. Aromatic SBS structures remained unaffected. The addition of ozone and nitrogen dioxide led to a degradation of 5% olefinic and 10% allylic structures during thermochemical ageing, while the variations during thermal ageing were less than 3%. Field ageing did not alter the aromatic structures in the bitumen phase in the SBS-modified binder but revealed significant decreases in the unmodified sample. Diffusion-ordered NMR spectroscopy showed that the average molecular size of the polymer halved during field ageing. Multiple ageing cycles were required to replicate this trend in the laboratory. However, extending the ageing time and adding reactive oxygen species reduced the number of aromatic structures in the bitumen phase, while no alteration occurred in the field. This study introduces the most precise framework to evaluate the chemical state of SBS-modified binders. The developed framework can be applied to monitor degradation, determine the lifetime and validate ageing technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • The papyrus writing-ground was analysed by near-infrared (NIR) spectroscopy. • Spectra were evaluated using PCA, HCA, PLS-DA, and SOM. • Cluster analysis and PLS-DA proved to be useful tools for distinguishing modern papyri from ancient papyri. • Natural and accelerated ageing did not affect the classification. • A PLS-DA classification model identifired recent Papyri samples by NIR even after accelerated ageing. Papyrus has been used for millennia to record information, for sophisticated works of art as well as mundane notes. The collection, identification, and translation of papyrus fragments therefore opens a gateway into the past. To aid the efforts to access the history recorded in papyri, we investigated the suitability of NIR spectroscopy to perform two tasks: One is to support the authentication of ancient papyri, by differentiation of papyri that were manufactured more recently and subjected to accelerated ageing to resemble the originals. The other is the extensive task to piece together papyrus fragments into readable texts again. In museums around the world, more than 100,000 ancient papyrus fragments still wait for their proper assembly, deciphering and publication. The papyrus writing-ground was analysed by near-infrared (NIR) spectroscopy, and the spectra were evaluated using principal component analysis (PCA), hierarchical cluster analysis (HCA), partial least squares discriminant analysis (PLS-DA), and self-organizing maps (SOM). Cluster analysis and PLS-DA proved to be useful tools for distinguishing modern papyri from ancient papyri which were provided by collections in Vienna and Leipzig. Neither natural nor accelerated ageing affected the classification. A PLS-DA classification model, constructed from NIR spectra of 89 model scores, detected recent Papyri samples with 100 % sensitivity and specificity, even after accelerated ageing. The identification of groups of fragments of ancient papyri based on NIR spectra and chemometry is not straightforward. HCA, which focuses on the differences between samples, only grouped the fragments of 4 out of 20 papyri correctly. SOM, which rather focuses on the similarities, grouped 6 sets of fragments correctly. An automated grouping of fragments remains difficult, since the fragments themselves are heterogeneous while similarities between unrelated ancient papyri can be large. [ABSTRACT FROM AUTHOR]

A combination of maleic acid and sodium hypophosphite as a durable press finishing agent has been reported as a safer but equally effective alternative to conventional formaldehyde-based cross-linking agents for applications in cellulose-based fiber and textile finishing. However, the mechanistic details of this system have not yet been fully elucidated to allow optimization of the conditions. Effective cross-linking treatment requires high curing temperatures of ≥160 °C, which enhances oxidative and thermal degradation of cellulose. In this work, the sequential steps of the cross-linking mechanism were investigated both with model compounds and cellulosic substrates. Extensive NMR studies on model compounds revealed several side reactions alongside the synthesis of the targeted cross-linkable moiety. As an alternative, to circumvent side reactions, a two-step procedure was used by synthesizing the cross-linker sodium 2-[(1,2-dicarboxyethyl)phosphinate]succinic acid in a well-defined pre-condensation reaction before application onto the cellulosic substrate. Further, the effect of the cross-linking treatment on the molecular weight distribution of cellulose was studied by gel permeation chromatography, which showed degradation due to maleic acid/sodium hypophosphite treatment. By using sodium 2-[(1,2-dicarboxyethyl)phosphinate]succinic acid and sodium hypophosphite, this degradation could be significantly limited. [Display omitted] [ABSTRACT FROM AUTHOR]

A new triterpene glycoside, silviridoside, was isolated from the aerial parts of Silene viridiflora (Caryophyllaceae) using different chromatographic techniques. The structure of silviridoside was comprehensively elucidated as 3-O-β-D-galacturonopyranosyl-quillaic acid 28-O-β-D-glucopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→3)]-β-D-fucopyranosyl ester by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HR-MS). Silviridoside showed promising antioxidant activity in different antioxidant assays such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) (2.32 mg TE/g), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) (1.24 mg TE/g), cupric-reducing antioxidant capacity (CUPRAC) (9.59 mg TE/g), ferric-reducing antioxidant power (FRAP) (5.13 mg TE/g), phosphomolybdenum (PHD) (0.28 mmol TE/g), and metal-chelating (MCA) (6.62 mg EDTA/g) assays. It exhibited a good inhibitory potential on acetylcholinesterase (AChE) (2.52 mg GALAE/g), butyrylcholinesterase (BChE) (7.16 mg GALAE/g), α-amylase (0.19 mmol ACAE/g), α-glucosidase (1.21 mmol ACAE/g), and tyrosinase (38.83 mg KAE/g). An in silico evaluation of the pharmacodynamic, pharmacokinetic, and toxicity properties of silviridoside showed that the new compound exhibited reasonable pharmacodynamic and pharmacokinetic properties without any mutagenic effect, but slight toxicity. Thus, it could be concluded that silviridoside could act as a promising lead drug for pharmaceutical and nutraceutical developments to combat oxidative stress and various disorders, but a future optimization is necessary. [ABSTRACT FROM AUTHOR]