Tapping the Full Potential of Infrared Spectroscopy for the Analysis of Technical Lignins.

We present an approach to overcome the challenges associated with the increasing demand of high-throughput characterization of technical lignins, a key resource in emerging bioeconomies. Our approach offers a resort from the lack of direct, simple, and low-cost analytical techniques for lignin characterization by employing multivariate calibration models based on infrared (IR) spectroscopy to predict structural properties of lignins (i. e., functionality, molar mass). By leveraging a comprehensive database of over 500 well-characterized technical lignin samples - a factor of 10 larger than previously used sets - our chemometric models achieved high levels of quality and statistical confidence for the determination of different functional group contents (RMSEPs of 4-16 %). However, the statistical moments of the molar mass distribution are still best determined by size-exclusion chromatography. Analyses of over 500 technical lignins offered also a great opportunity to provide information on the general variability in kraft lignins and lignosulfonates (from different origins). Overall, the effected savings in analysis time (>7 h), resources, and required sample mass combined with non-destructiveness of the measurement satisfy key demands for efficient high-throughput lignin analyses. Finally, we discuss the advantages, disadvantages, and limitations of our approach, along with critical insights into the associated chemical-analytical and spectroscopic challenges.

A novel approach to analyze the impact of lytic polysaccharide monooxygenases (LPMOs) on cellulosic fibres.

Enzymatic treatment of cellulosic fibres is a green alternative to classical chemical modification. For many applications, mild procedures for cellulose alteration are sufficient, in which the fibre structure and, therefore, the mechanical performance of cellulosic fibres are preserved. Lytic polysaccharide monooxygenases (LPMOs) bear a great potential to become a green reagent for such targeted cellulose modifications. An obstacle for wide implementation of LPMOs in tailored cellulose chemistry is the lack of suitable techniques to precisely monitor the LPMO impact on the polymer. Soluble oxidized cello-oligomers can be quantified using chromatographic and mass-spectrometric techniques. A considerable portion of the oxidized sites, however, remain on the insoluble cellulose fibres, and their quantification is difficult. Here, we describe a method for the simultaneous quantification of oxidized sites on cellulose fibres and changes in their molar mass distribution after treatment with LPMOs. The method is based on quantitative, heterogeneous, carbonyl-selective labelling with a fluorescent label (CCOA) followed by cellulose dissolution and size-exclusion chromatography (SEC). Application of the method to reactions of seven different LPMOs with pure cellulose fibres revealed pronounced functional differences between the enzymes, showing that this CCOA/SEC/MALS method is a promising tool to better understand the catalytic action of LPMOs.

Towards Tailored Dialdehyde Cellulose Derivatives: A Strategy for Tuning the Glass Transition Temperature.

The derivatization of dialdehyde cellulose (DAC) has received increasing attention in the development of sustainable thermoplastics. In this study, a series of dialcohol celluloses were generated by borohydride reduction, which exhibited glass transition temperature (Tg ) values ranging from 23 to 109 °C, depending on the initial degree of oxidation (DO) of the DAC intermediate. However, the DAC derivatives did not exhibit thermoplastic behavior when the DO of the modified DAC was below 26 %. The influence of introduced side chains was highlighted by comparing DAC-based thermoplastic materials obtained by either oximation or borohydride reduction. Our results provide insights into the generation of DAC-based thermoplastics and highlight a strategy for tailoring the Tg by adjusting the DO during the periodate oxidation step and selecting appropriate substituents in subsequent modifications.

Profiling of historical rag papers by their non-cellulosic polysaccharide composition.

Hemicellulose and pectin are noteworthy components of historical European rag papers, and have not been studied in detail so far. Rag papers were made from used textiles, and fiber-based utilities, such as ropes and bags. These had been prepared until the mid-19th century from plant-based fibers. Their polysaccharide composition could relate to their condition and history. This information can be expected to hold importance for the preservation and conservation of historical objects. We investigated a collection of rag papers of different age for their composition of non-cellulosic polysaccharides, and compared the findings with modern rag papers and wood pulps. Furthermore, a non-destructive determination of the hemicellulose and pectin content by near-infrared spectroscopy was developed. Historical rag papers had a lower hemicellulose/pectin content than pulps; the fractions of rhamnose, galactose, and arabinose were higher, while xylose was lower. In modern rag papers, xylose tended to be at the higher end of the range, which suggests a degradation of hemicelluloses/pectin over time or a change in raw materials and manufacturing. Rag papers also showed higher crystallinity than wood pulp papers. These findings provide insights into rag paper characteristics and offer potential classification methods.

Cellulose fibers and ellagitannin-rich extractives from rambutan (Nephelium Lappaceum L.) peel by an eco-friendly approach.

This study assesses the viability of an accelerated solvent extraction technique employing environmentally friendly solvents to extract ellagitannins while producing cellulose-rich fibers from rambutan peel. Two sequential extraction protocols were investigated: 1) water followed by acetone/water (4:1, v:v), and 2) acetone followed by acetone/water (4:1, v:v), both performed at 50 °C. The first protocol had a higher extraction yield of 51 %, and the obtained extractives featured a higher total phenolic (531.4 ± 22.0 mg-GAE/g) and flavonoid (487.3 ± 16.9 mg-QE/g) than the second protocol (495.4 ± 32.8 mg-GAE/g and 310.6 ± 31.4 mg-QE/g, respectively). The remaining extractive-free fibers were processed by bleaching using either 2 wt% sodium hydroxide with 3 wt% hydrogen peroxide or 4-5 wt% peracetic acid. Considering bleaching efficiency, yield, and process sustainability, the single bleaching treatment with 5 wt% of peracetic acid was selected as the most promising approach to yield cellulose-rich fibers. The samples were analyzed by methanolysis to determine the amount and type of poly- and oligosaccharides and studied by 13C solid-state nuclear magnetic resonance spectroscopy and thermal gravimetric analysis. The products obtained from the peels demonstrate significant potential for use in various sectors, including food, nutraceuticals, cosmetics, and paper production.

Lignin-Based Polyurethanes from the Blocked Isocyanate Approach: Synthesis and Characterization.

Lignin, the world's second most abundant biopolymer, has been investigated as a precursor of polyurethanes due to its high availability and large amount of hydroxyls present in its structure. Lignin-based polyurethanes (LPUs) are usually synthesized from the reaction between lignin, previously modified or not, and diisocyanates. In the present work, LPUs were prepared, for the first time, using the blocked isocyanate approach. For that, unmodified and hydroxypropylated Kraft lignins were reacted with 4,4'-methylene diphenyl diisocyanate in the presence of diisopropylamine (blocking agent). Castor oil was employed as a second polyol. The chemical modification was confirmed by 31P nuclear magnetic resonance (31P NMR) analysis, and the structure of both lignins was elucidated by a bidimensional NMR technique. The LPUs' prepolymerization kinetics was investigated by temperature-modulated optical refractometry and Fourier-transform infrared spectroscopy. The positive effect of hydroxypropylation on the reactivity of the Kraft lignin was verified. The structure of LPU prepolymers was accessed by bidimensional NMR. The formation of hindered urea-terminated LPU prepolymers was confirmed. From the results, the feasibility of the blocked isocyanate approach to obtain LPUs was proven. Lastly, single-lap shear tests were performed and revealed the potential of LPU prepolymers as monocomponent adhesives.

Antimicrobial, antioxidant, and sun protection potential of the isolated compounds from Spermacoce princeae (K. Schum).

BACKGROUND: Spermacoce princeae (K. Schum) has been used in the treatment of bacterial skin infections in Uganda. Pharmacological studies revealed that extracts of S. princeae exhibited antibacterial, antioxidant, and sun protection potential. This study aimed at isolating and identifying pure compounds from the extracts based on comprehensive analytical characterization by multiple analytical techniques. METHODS: The plant samples were extracted by sequential maceration using n-hexane, ethyl acetate, methanol, and distilled water. The compounds were isolated using a combination of chromatographic techniques and their structures were elucidated by multiple spectroscopic techniques. The antibacterial and antifungal activity determination of the isolated compounds was carried out using an agar well diffusion and potato dextrose assay against Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Candida albicans, and Aspergillus flavus while the antioxidant activity was screened with the 2,2-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay. The sun protection factor was determined using a Shimadzu Ultra Violet-visible (UV-VIS) double beam spectrophotometer between 290 to 320 nm. RESULTS: Eleven compounds; quercetin (1), kaempferol-3-O-rutinoside (2), rutin (3, 12), myo-inositol (4), asperulosidic acid (5), hexadecanoic acid (6), ß-sitosterol (7), stigmasterol (8), campesterol (9), ursolic acid (10), and ß-sitosterol glucoside (11) were identified in the S. princeae extracts. Compound 2 had good antifungal activity against C. albicans (zone of inhibition, 23.0 ± 0.1 mm). Compound 10 showed antibacterial and antifungal activity against S. aureus, P. aeruginosa, C. albicans, and A. flavus. Compound 2 had a good percentage radical scavenging effect (IC50 = 64.81 µg/ml) and a good sun protection factor (SPF = 26.83). CONCLUSION: This study reports the first-time isolation and identification of compounds 1 to 11 from S. princeae, which contribute to its antimicrobial, antioxidant, and sun protection potential.

Hemocompatibility of cellulose phosphate aerogel membranes with potential use in bone tissue engineering.

Cellulose is an appealing material for tissue engineering. In an attempt to overcome some obstacles with cellulose II cell scaffolding materials related to insufficient biomineralization, lack of micron-size porosity, and deficiency in surface charge, respective solutions have been proposed. These included covalent phosphorylation of different cellulose materials targeting relatively low degrees of substitution (DS 0.18-0.23) and processing these cellulose derivatives into scaffolding materials by a dissolution/coagulation approach employing the hitherto rarely used TBAF/DMSO/H2O system for cellulose dissolution. Here, we report bioactivity and preliminary hemocompatibility testing of dual-porous cellulose phosphate aerogels (contrasted with the phosphate-free reference) obtained via coagulation (water/ethanol), solvent exchange and scCO2 drying. Deposition of hydroxyapatite from simulated body fluid (7 days of immersion) revealed good bioactivity (1.5-2.2 mg Ca2+ per mg scaffold). Incubation of the scCO2-dried and rehydrated scaffolding materials in heparin anticoagulated human whole blood was conducted to study selected parameters of hemostasis (prothrombin F1+2 fragment, PF4, count of thrombocyte-leukocyte conjugates) and inflammatory response (C5a fragment, leukocyte activation marker CD11b). Adhesion of leukocytes on the surface of the incubated substrates was assessed by scanning electron and fluorescence microscopy (DAPI staining). The results suggest that phosphorylation at low DS does not increase platelet activation. However, a significant increase in platelet activation and thrombin formation was observed after a certain fraction of the negative surface charges had been compensated by Ca2+ ions. The combination of both phosphorylation and calcification turned out to be a potent means for controlling the inflammatory response, which was close to baseline level for some of the studied samples.

From liquid to solid-state, solvent-free oxidative ammonolysis of lignins - an easy, alternative approach to generate "N-lignins".

A new chemical modification protocol to generate N-lignins is presented, based on Indulin AT and Mg2+-lignosulfonate. The already known ammonoxidation reaction in liquid phase was used as a starting point and stepwise optimised towards a full solid-state approach. The "classical" liquid ammonoxidation products, the transition products from the optimization trials, as well as the "solid-state" products were comprehensively analysed and compared to the literature. The N-lignins obtained with the conventional ammonoxidation protocol showed the same properties as reported. Their molar mass distributions and the hydroxy group contents, hitherto not accessible due to solubility problems, were measured according to a recently reported protocol. N-Indulin showed an N-content up to 11 wt% and N-lignosulfonate up to 16 wt%. The transition experiments from liquid to solid-state gave insights into the influence of chemical components and reaction conditions. The use of a single chemical, the urea-hydrogen peroxide complex (UHP, "carbamide peroxide"), was sufficient to generate N-lignins with satisfying N-content. This chemical acts both as an N-source and as the oxidant. Following the optimization, a series of solid-state ammonoxidation tests were carried out. High N-contents of 10% in the case of Indulin and 11% in the case of lignosulfonate were obtained. By varying the ratio of UHP to lignin, the N-content can be controlled. Structural analysis showed that the N is organically bound to the lignin, similar to the "classical" ammonoxidation products obtained under homogeneous conditions. Overall, a new ammonoxidation protocol was developed which does not require an external gas supply nor liquids or dissolved reactants. This opens the possibility for carrying out the lignin modification in closed continuous reactor systems, such as extruders. The new, facile solid-state protocol will hopefully help N-lignins to find more consideration as a fertilizing material and in soil-improving materials.

Debugging periodate oxidation of cellulose: Why following the common protocol of quenching excess periodate with glycol is a bad idea.

Periodate oxidation of cellulose to produce "dialdehyde cellulose" (DAC) has lately received increasing attention in sustainable materials development. Despite the longstanding research interest and numerous reported studies, there is still an enormous variation in the proposed preparation and work-up protocols. This apparently reduces comparability and causes reproducibility problems in DAC research. Two simple but prevalent work-up protocols, namely glycol quenching and filtration/washing, were critically examined and compared, resulting in this cautionary note. Various analytical techniques were applied to quantify residual iodine species and organic contaminations from quenching side reactions. The commonly practiced glycol addition cannot remove all oxidising iodine compounds. Both glycol and the formed formaldehyde are incorporated into DAC's polymeric structure. Quenching of excess periodate with glycol can thus clearly be discouraged. Instead, simple washing protocols are recommended which do not bear the risk of side reactions with organic contaminants. While simple washing was sufficient for mildly oxidised celluloses, higher oxidised samples were more likely to trap residual (per)iodate, as determined by thiosulfate titration. For work-up, simple washing with water is proposed while determining potential iodine contaminations after washing with a simple colorimetric test and, if needed, removal of residual periodate by washing with an aqueous sodium thiosulfate solution.

Template-Directed Polymerization of Binary Acrylate Monomers on Surface-Activated Lignin Nanoparticles in Toughening of Bio-Latex Films.

Fabricating bio-latex colloids with core-shell nanostructure is an effective method for obtaining films with enhanced mechanical characteristics. Nano-sized lignin is rising as a class of sustainable nanomaterials that can be incorporated into latex colloids. Fundamental knowledge of the correlation between surface chemistry of lignin nanoparticles (LNPs) and integration efficiency in latex colloids and from it thermally processed latex films are scarce. Here, an approach to integrate self-assembled nanospheres of allylated lignin as the surface-activated cores in a seeded free-radical emulsion copolymerization of butyl acrylate and methyl methacrylate is proposed. The interfacial-modulating function on allylated LNPs regulates the emulsion polymerization and it successfully produces a multi-energy dissipative latex film structure containing a lignin-dominated core (16% dry weight basis). At an optimized allyl-terminated surface functionality of 1.04 mmol g-1 , the LNPs-integrated latex film exhibits extremely high toughness value above 57.7 MJ m-3 . With multiple morphological and microstructural characterizations, the well-ordered packing of latex colloids under the nanoconfinement of LNPs in the latex films is revealed. It is concluded that the surface chemistry metrics of colloidal cores in terms of the abundance of polymerization-modulating anchors and their accessibility have a delicate control over the structural evolution of core-shell latex colloids.

Exploring Alkyl-O-Alkyl Ether Structures in Softwood Milled Wood Lignins.

Recent studies have suggested that there are significant amounts of various alkyl ether (Alk-O-Alk; Alk = alkyl) moieties in a spruce native lignin preparation, milled wood lignin (SMWL). However, the comprehensive NMR assignment to these moieties has not been addressed yet. This study focused on investigating different types of Alk-O-Alk structures at the α- and γ-positions of the lignin side chain in an heteronuclear single-quantum coherence (HSQC) spectrum of SMWL using experimental NMR data of lignin and synthesized model compounds. Ambiguous structural features were predicted by computer simulation of 1H and 13C NMR spectra to complement the experimental NMR data. As a result, specific regions in the HSQC spectrum were attributed to different Alk-O-Alk moieties of Alk-O-Alk/ß-O-4 and Alk-O-Alk/ß-ß' structures. However, the differences between the specific regions were rather subtle; they were not well separated from each other and some major lignin moieties. Furthermore, SMWL contained a large variety of Alk-O-Alk moieties but in minute individual amounts, resulting in rather broad, superimposing resonances. Thus, evaluation did not allow assigning individual types of Alk-O-Alk moieties from the HSQC spectra; instead, they were quantified as total (α- and γ-linked) Alk-O-Alk based on the balance of structural units in the 13C NMR spectra. At last, potential formation mechanisms of various Alk-O-Alk ether structures in lignin biosynthesis, lignin aging, and during ball milling of wood were hypothesized and discussed.

Reductive Amination of Dialdehyde Cellulose: Access to Renewable Thermoplastics.

The reductive amination of dialdehyde cellulose (DAC) with 2-picoline borane was investigated for its applicability in the generation of bioderived thermoplastics. Five primary amines, both aliphatic and aromatic, were introduced to the cellulose backbone. The influences of the side chains on the course of the reaction were examined by various analytical techniques with microcrystalline cellulose as a model compound. The obtained insights were transferred to a 39%-oxidized softwood kraft pulp to study the thermal properties of thereby generated high-molecular-weight thermoplastics. The number-average molecular weights (Mn) of the diamine celluloses, ranging from 60 to 82 kD, were investigated by gel permeation chromatography. The diamine celluloses exhibited glass transition temperatures (Tg) from 71 to 112 °C and were stable at high temperatures. Diamine cellulose generated from aniline and DAC showed the highest conversion, the highest Tg (112 °C), and a narrow molecular weight distribution (D̵ of 1.30).

Silviridoside: A New Triterpene Glycoside from Silene viridiflora with Promising Antioxidant and Enzyme Inhibitory Potential.

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-ß-D-galacturonopyranosyl-quillaic acid 28-O-ß-D-glucopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→3)]-ß-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.

Assessment of Electrothermal Pretreatment of Rambutan (Nephelium lappaceum L.) Peels for Producing Cellulose Fibers.

Agroindustrial wastes are renewable sources and the most promising sustainable alternative to lignocellulosic biomass for cellulose production. This study assessed the electrothermal pretreatment of rambutan peel (RP) for producing cellulose fibers. The pretreatment was carried out by Ohmic heating at a solid-to-liquid ratio of 1:10 (w/v) in a water/ethanol (1:1, v/v) mixture as the electrical transmission medium at 60 ± 1 °C for different holding times (15, 30, and 60 min). Ohmic heating did not significantly influence the total fiber yield for the various holding times. However, the compositions of the samples in terms of extractives, lignin, hemicellulose, and α-cellulose content were significantly influenced. In addition, the electrothermal pretreatment method reduced the bleaching time of RP by 25%. The pretreated fibers were thermally stable up to 240 °C. Ohmic heating pretreatment times of 15 and 30 min were found most promising, reducing the required bleaching chemicals and increasing the α-cellulose yield. The pretreated bleached cellulose fibers had similar properties to nontreated bleached fibers and could be efficiently processed into stable gels of strong shear-thinning behavior with potential application as rheology modifiers in food products. Our results demonstrate that rambutan peel could serve as a promising sustainable alternative to woody biomass for cellulose production. Ohmic heating meets the requirements for industrial applications as it is eco-friendly, improves the efficiency and energy consumption in fiber processing, and could as well be included in the processing of similar food wastes.

N-Alkylated Chitin Nanocrystals as a Collector in Malachite Flotation.

The majority of reagents currently used in mineral flotation processes are fossil-based and potentially harmful to the environment. Therefore, it is necessary to find environmentally-friendly alternatives to reduce the impact of mineral processing activities. Chitin nanocrystals are a renewable resource that, due to the natural presence of amino groups on its surface, represents a promising collector for various minerals of economic relevance. This study examines the one-pot functionalization of chitin nanocrystals with aldehyde structures to obtain hydrophobized colloids suitable for mineral flotation. The chemical properties of these nano-colloids were investigated by nuclear magnetic resonance spectroscopy, their colloidal behavior and structure by electrophoretic light scattering and atomic force microscopy, and their wettability through water contact angle measurements. The functionalized N-alkylated chitin nanocrystals possessed a hydrophobic character, were able to dress mineral particles and featured a performance in the flotation of malachite similar to commercial collectors, which proves the high potential of chitin nanocrystals in this field of application.

Acetylation of cellulose - Another pathway of natural cellulose aging during library storage of books and papers.

Gaseous acetic acid is formed under conditions of storage of historic paper objects. Its presence not only promotes hydrolytic cleavage of cellulose, but also causes acetylation of the cellulosic material to very small degree. The acetylation reaction proceeds under ambient conditions and without catalyst. Different analytical methods were used to prove the presence of organic acetates on cellulosic paper matrices. DESI-MS in combination with 2H-isotopic labeling showed the presence of sugar fragments with different acetylation patterns. A method based on Zemplen saponification was applied and worked also in the presence of a large excess of acetic acid and/or inorganic acetates. The acetylation effect was quantified for model papers and original, naturally aged paper samples. While cellulose acetylation was clearly proven to be another general pathway of paper aging, further studies of this acetylation phenomenon are needed with regard to conservational aspects and suitable paper storage conditions.

The in vitro synthesis of cellulose - A mini-review.

The implementation of cellulose as a green alternative to classical polymers sparks research on the synthesis of defined derivatives of this biopolymer for various high-tech applications. Apart from the scientific challenge, the in vitro synthesis of cellulose using a bottom-up approach provides specimens with absolutely accurate substituent patterns and degrees of polymerization, not accessible from native cellulose. Synthetic cellulose exhibiting a comparably high degree of polymerization (DP) was obtained starting from cellobiose by biocatalytic synthesis implementing cellulase. Cationic ring-opening polymerization has been established in the last two decades, representing an excellent means of precise modification with regards to regio- and stereoselective substitution. This method rendered isotopically enriched cellulose as well as enantiomers of native cellulose ("l-cellulose", "d,l-cellulose") accessible. In this review, techniques for in vitro cellulose synthesis are summarized and critically compared - with a special focus on more recent developments. This is complemented by a brief overview of alternative enzymatic approaches.

Facile Preparation of Mechanically Robust and Functional Silica/Cellulose Nanofiber Gels Reinforced with Soluble Polysaccharides.

Nanoporous silica gels feature extremely large specific surface areas and high porosities and are ideal candidates for adsorption-related processes, although they are commonly rather fragile. To overcome this obstacle, we developed a novel, completely solvent-free process to prepare mechanically robust CNF-reinforced silica nanocomposites via the incorporation of methylcellulose and starch. Significantly, the addition of starch was very promising and substantially increased the compressive strength while preserving the specific surface area of the gels. Moreover, different silanes were added to the sol/gel process to introduce in situ functionality to the CNF/silica hydrogels. Thereby, CNF/silica hydrogels bearing carboxyl groups and thiol groups were produced and tested as adsorber materials for heavy metals and dyes. The developed solvent-free sol/gel process yielded shapable 3D CNF/silica hydrogels with high mechanical strength; moreover, the introduction of chemical functionalities further widens the application scope of such materials.