Explore the vast range of titles available.

Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.

Literature is strongly contradictory about the molecular reasons for yellowing and brightness reversion of pure (lignin- and hemicellulose-free) celluloses, such as in highly bleached pulps, bacterial cellulose, or cotton linters. While oxidized groups—carbonyls (CO) and carboxyls (COOH)—have been recognized as the initiators of yellowing, they are generally always found together; thus, their effects are permanently superimposed in real-world cellulose. For this reason, their individual contributions could not be reliably determined. To tackle this conundrum, we have used a two-stage study: the employment of glucopyranose-derived model compounds and the use of special cellulosic pulps. Both substrates had either only carbonyl functions, only carboxyl functions, or defined ratios of both functionalities present at the same time. The model compounds alone already provided strong indications of the CO-related and COOH-related effects, and further confirmation was obtained by the pulp study. Here, in regard to the polymer case, the carbonyl groups are the minimum functional unit in cellulose responsible for chromophore generation (termed as the “CO effect”). The carbonyl groups are the precursors for the chromophores that are formed later upon yellowing/aging. Chromophore formation increases strictly linearly with the carbonyl content at a constant given carboxyl content. Carboxyl groups alone (i.e., in the absence of carbonyl groups) are fully innocent regarding the color generation. However, they have a strong promotive action when carbonyl groups are present (termed as the “COOH effect”), which includes acidic catalysis and an additional activation by electronic effects. The general roles of CO and COOH are the same for all aging types (e.g., thermal, acidic, or alkaline), while the respective rates of chromophore generation evidently depend on various parameters such as the temperature, medium, and pH value. Graphical abstract

The effective and straight-forward modification of nanostructured celluloses under aqueous conditions or as “never-dried” materials is challenging. We report a silanization protocol in water using catalytic amounts of hydrogen chloride and then sodium hydroxide in a two-step protocol. The acidic step hydrolyzes the alkoxysilane to obtain water-soluble silanols and the subsequent addition of catalytic amounts of NaOH induces a covalent reaction between cellulose surficial hydroxyl groups and the respective silanols. The developed protocol enables the incorporation of vinyl, thiol, and azido groups onto cellulose fibers and cellulose nanofibrils. In contrast to conventional methods, no curing or solvent-exchange is necessary, thereby the functionalized celluloses remain never-dried, and no agglomeration or hornification occurs in the process. The successful modification was proven by solid state NMR, ATR-IR, and EDX spectroscopy. In addition, the covalent nature of this bonding was shown by gel permeation chromatography of polyethylene glycol grafted nanofibrils. By varying the amount of silane agents or the reaction time, the silane loading could be tuned up to an amount of 1.2 mmol/g. Multifunctional materials were obtained either by prior carboxymethylation and subsequent silanization; or by simultaneously incorporating both vinyl and azido groups. The protocol reported here is an easy, general, and straight-forward avenue for introduction of anchor groups onto the surface of never-dried celluloses, ready for click chemistry post-modification, to obtain multifunctional cellulose substrates for high-value applications.

Since periodate oxidation selectively creates (masked) aldehyde groups that can serve as anchors for further modification steps, this method is suitable for modifying and functionalizing cellulose. Although numerous studies deal with that topic, there are still knowledge gaps regarding periodate oxidation. In our study, we focused on examining how the type of cellulose allomorph influences the reaction. We compared the oxidation of two allomorphs, namely cellulose I, cellulose II and mixtures of cellulose I and II, and examined changes in crystallinity and thermal decomposition behavior. Generally, periodate oxidation proceeded faster in the case of cellulose II samples, followed by the mixed cellulose I/II samples; cellulose I was the slowest. Based on our results, the major influencing factor is the overall crystallinity of the sample. The influence of the allomorph was minor. Crystallinity decreased upon oxidation, but no significant differences were found between the different cellulose polymorphs. Following the crystallinity during the oxidation reaction proved to be very difficult. Determining crystallinity with solid-state nuclear magnetic resonance (NMR) was largely hampered by superposition with new resonances that interfere with crystallinity determination. Structural changes during oxidation as evident from solid-state NMR are discussed in detail. Alternative methods for crystallinity analysis, such as near infrared spectroscopy, attenuated total reflection infrared spectroscopy, and Raman spectroscopy, had similar problems but to a lesser extent, with Raman being the method of choice. Thermogravimetric analysis showed thermal decomposition of oxidized cellulose I and II to be similar. An anomaly was found in the case of oxidized viscose fibers. Slightly oxidized samples showed increased mass loss in the temperature range up to 360 °C whereas higher oxidized samples and all pulp samples showed decreased mass loss.

Knowledge about the carbohydrate composition of pulp and paper samples is essential for their characterization, further processing, and understanding the properties. In this study, we compare sulfuric acid hydrolysis and acidic methanolysis, followed by GC–MS analysis of the corresponding products, by means of 42 cellulose and polysaccharide samples. Results are discussed and compared to solid-state NMR (crystallinity) and gel permeation chromatography (weight-averaged molecular mass) data. The use of the hydrolysis methods in the context of cellulose conservation science is evaluated, using e-beam treated and artificially aged cellulose samples.

Cellulose derivatives have many potential applications in the field of biomaterials and composites, in addition to several ways of modification leading to them. Silanization in aqueous media is one of the most promising routes to create multipurpose and organic–inorganic hybrid materials. Silanization has been widely used for cellulosic and nano-structured celluloses, but was a problem so far if to be applied to the common cellulose derivative “dialdehyde cellulose” (DAC), i.e., highly periodate-oxidized celluloses. In this work, a straightforward silanization protocol for dialdehyde cellulose is proposed, which can be readily modified with (3-aminopropyl)triethoxysilane. After thermal treatment and freeze-drying, the resulting product showed condensation and cross-linking, which was studied with infrared spectroscopy and 13C and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. The cross-linking involves both links of the hydroxyl group of the oxidized cellulose with the silanol groups (Si-O-C) and imine-type bonds between the amino group and keto functions of the DAC (-HC=N-). The modification was achieved in aqueous medium under mild reaction conditions. Different treatments cause different levels of hydrolysis of the organosilane compound, which resulted in diverse condensed silica networks in the modified dialdehyde cellulose structure.

Fusarium is a genus that mostly consists of plant pathogenic fungi which are able to produce a broad range of toxic secondary metabolites. In this study, we focus on a type A trichothecene-producing isolate (15-39) of Fusarium sporotrichioides from Lower Austria. We assessed the secondary metabolite profile and optimized the toxin production conditions on autoclaved rice and found that in addition to large amounts of T-2 and HT-2 toxins, this strain was able to produce HT-2-glucoside. The optimal conditions for the production of T-2 toxin, HT-2 toxin, and HT-2-glucoside on autoclaved rice were incubation at 12 °C under constant light for four weeks, darkness at 30 °C for two weeks, and constant light for three weeks at 20 °C, respectively. The HT-2-glucoside was purified, and the structure elucidation by NMR revealed a mixture of two alpha-glucosides, presumably HT-2-3-O-alpha-glucoside and HT-2-4-O-alpha-glucoside. The efforts to separate the two compounds by HPLC were unsuccessful. No hydrolysis was observed with two the alpha-glucosidases or with human salivary amylase and Saccharomyces cerevisiae maltase. We propose that the two HT-2-alpha-glucosides are not formed by a glucosyltransferase as they are in plants, but by a trans-glycosylating alpha-glucosidase expressed by the fungus on the starch-containing rice medium.

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 H 2 O 2 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 .

Chromophores, colored substances of rather high stability that reduce brightness, are present in all kinds of cellulosic products, such as pulp, fibers, aged cellulosic material, and even in very low concentrations in highly bleached pulps. Thus, they are the prime targets of industrial pulp bleaching. In this study, the three cellulosic key chromophores 2,5-dihydroxy-1,4-benzoquinone (DHBQ, 1), 5,8-dihydroxy-1,4-naphthoquinone (DHNQ, 2), and 2,5-dihydroxyacetophenone (DHAP, 3) were bleached with ozone at pH 2 resembling industrial conditions (Z-stage). Bleaching kinetics were followed by UV/Vis spectrophotometry. The chemical structures of the degradation products were analyzed using NMR spectroscopy as well as GC/MS and confirmed by comparison with authentic reference compounds. The main, stable intermediates in the ozonation reactions have been elucidated by employing ozone not in excess but roughly stoichiometric amounts: mesoxalic acid (4) from DHBQ (1), rhodizonic acid (5) from DHNQ (2), and hydroxy-[1,4]-benzoquinone (8) from DHAP (3). As the final products at a large excess of ozone, a complex mixture of carboxylic acids (C1 to C4) was obtained, with the C4 acids being formed by subsequent condensation of smaller fragments (malonic acid and mesoxalic acid) rather than directly as ozonation products. At shorter reaction times and lower ozone excess, some aldehydes and ketones (C2 and C3) were contained in addition. The mixture of the degradation products was not completely stable but tended to undergo further changes, such as decarboxylation and condensation reactions. The reaction mechanisms of degradation by ozone, intermediate formation and re-condensation are described and discussed.Graphic abstract

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.