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Two different organosolv lignins (OSLs), that is, wheat straw and corn stover OSLs, were chemically and enzymatically functionalized. Functional groups were attached via the formation of stable ether bonds exploiting the reactivity of free phenolic OH groups along the lignin backbone. The functional groups introduced a range from compact charged and chargeable building blocks for the generation of surface-active lignins to oligomeric and polymeric species used in lignin block-copolymer productions. Combination of selected functions led to novel charged or chargeable polymeric lignin-based materials. Products could be realized with different degrees of technical loadings in terms of introduced functional groups., Industrially produced wheat straw and corn stover organosolv lignins were chemically and enzymatically functionalized via formation of ether bonds using various surface-active functionals.

Novel valorization routes for tannins were opened by the development of a simple, straightforward, robust, and flexible approach to the selective functionalization of condensed and hydrolyzable tannins. Irrespective of the different degrees of polymerization, different commercial tannins were efficiently functionalized by the generation of an ether linkage bound to a short linker carrying the desired functional group. Functionalizations could be realized at varying degrees of technical loadings, i.e., amounts of introduced tannin-alien functionalities per number of phenolic hydroxyl groups. The same strategy was found suitable for the synthesis of polyethylene glycol-functionalized tannin copolymers. Condensed tannins functionalized with carboxylic acid moieties could be converted into a tannin–oligopeptide hybrid., Commercially available condensed and hydrolyzable tannins were functionalized with different functional groups at different concentrations.

Microcapsules of sulfited Acacia mearnsii tannin (AmST-MCs) were generated for the first time via the sonochemical method. Their stability profile was assessed and set in the general context of tannin microcapsules (TMCs) generated under the same experimental conditions. The analytical data gathered in this work indicate an excellent stability of TMCs over time as well as under high temperature and pressure, which is a major milestone toward the meaningful applications of TMCs in industrial, pharmaceutical, and biomedical applications in which sterilization of TMCs might be a prerequisite. Active release is shown to be efficiently triggered by varying pH and/or salinity, with different profiles for TMCs from sulfited and nonsulfited species. Surfactants also affect the stability of TMCs significantly, with effects eventually amplifiable by pH and the inherent kosmotropic and chaotropic characteristics of salt components in solutions.

Organosolv pretreatment represents one of the most promising biomass valorization strategies for renewable carbon-based products; meanwhile, there is an overall lack of holistic approach to how extraction conditions affect the suitable end-usages. In this context, lignin extracted from silver birch (Betula pendula L.) by a novel hybrid organosolv/steam-explosion treatment at varying process conditions (EtOH %; time; catalyst %) was analyzed by quantitative NMR (1H-13C HSQC; 13C NMR; 31P NMR), gel permeation chromatography, Fourier transform infrared (FT-IR), Pyr-gas chromatography-mass spectroscopy (GC/MS), and thermogravimetric analysis, and the physicochemical characteristics of the lignins were discussed regarding their potential usages. Characteristic lignin interunit bonding motifs, such as β-O-4', β-β', and β-5', were found to dominate in the extracted lignins, with their abundance varying with treatment conditions. Low-molecular-weight lignins with fairly unaltered characteristics were generated via extraction with the highest ethanol content potentially suitable for subsequent production of free phenolics. Furthermore, β-β' and β-5' structures were predominant at higher acid catalyst contents and prolonged treatment times. Higher acid catalyst content led to oxidation and ethoxylation of side-chains, with the concomitant gradual disappearance of p-hydroxycinnamyl alcohol and cinnamaldehyde. This said, the increasing application of acid generated a broad set of lignin characteristics with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation purposes.

Softwood kraft lignin SKL was fractionated using aprotic acetone and protic methanol to yield both previously reported “traditional” fractions and novel refined fractions thereof. Based on differences in mutual H-bonding affinities exerted by the solvents on one side and the OH group characteristics of the lignin oligo- and polymers on the other side, the 85% acetone-insoluble kraft lignin fraction AIKL, for example, could be further fractionated in 16% methanol-soluble and 67% methanol-insoluble parts. Sequential use of the two solvents practically resembled a refinement protocol that shed light on eventual “structural impurities” contained in the traditional fractions, which is not delineable easily in front of the background of a dominating spectroscopic image. Exploiting H-bonding characteristics offers a valid option for the facile generation of truly “structurally purified” lignin fractions. Acetone-insoluble, methanol-soluble MSAIKL, for example, exhibits 25% less aliphatic interunit bonding while being enriched in phenolic groups up to 25%, thus representing condensed, lower-molecular-weight structures with overall H-bond accepting character that was still contained in the overall larger-molecular-weight acetone-insoluble AIKL. More “polyphenylpropanoidic” parts practically free of condensed units, determining the overall structural picture of the unrefined lignins due to their overall abundance, are represented by the globally insoluble fractions like acetone-insoluble, methanol-insoluble MIAIKL. The original fractions and refined fractions generated based on targeting specific H-bonding affinities give a more homogeneous picture with respect to trends in glass transition temperatures, clearly indicating that Tg is dominated by actually both MW and nature of OH groups.

Nanoencapsulation of active substances with controlled release in harmless matrices has been the subject of numerous scientific efforts mainly due to the significant biomedical potential of such endeavors. Lignin, the environmentally sustainable byproduct of the pulp and paper industry, contains a multitude of phenolic hydroxyl groups, some of which, are known to readily and strongly chelate with iron ions. In this effort we demonstrated that the concerted use of chelation chemistry, oil in water emulsion principles, and low energy sonication, offers a facile, one-pot strategy to assemble lignin nanocapsules (LNCs) of a controlled architecture. Under these conditions capsules are shown to rapidly assemble utilizing two driving forces, the p-stacking propensity of lignin and its metal chelating ability at alkaline pH. Detailed size exclusion chromatographic evidence validates that the formation of capsules is driven mainly by the enumerated physical interactions with no significant chemical modification of the lignin. The developed process was systematically optimized so as to create the foundations for the morphology and the yield of the capsules being modulated as a function of sonication time, power, and surface contact area. Both pure LNCs and Fe-LNCs were synthesized in high yields with size distributions varying from 0.3 to 6 mm and their release efficiencies were evaluated in detail. As anticipated, the complexation effects of the phenolic OH groups offered to the Fe-LNCs, increased stability, reduced shell thickness (allowing for greater loading efficiencies), and lower release kinetics, compared to LNCs.

Stimuli-responsive behavior of lignin microcapsules (LMCs) has been investigated along with the detailed characterization of their stability profiles. The disassembly of LMCs was found to be salt species-dependent, indicating the specific relevance of inherent kosmotropic and chaotropic characteristics. For the first time, a connection between the Hofmeister series and the stability profile of lignin microscale materials is established. LMCs showed excellent stability in water and under high temperature and pressure (autoclaving conditions). Active release is efficiently triggered by pH changes and balancing chaotropic and kosmotropic effects via salinity tuning.

The mechanism of lignin nanoprecipitation and subsequent self-assembly was elucidated by studying generation of lignin nanoparticles (LNPs) from aqueous ethanol. LNP formation was found to follow a kinetically controlled nucleation–growth mechanism in which large lignin molecules formed the initial critical nuclei. Using this information, we demonstrate entrapment of budesonide in LNPs and subsequent pH-triggered and surfactant-responsive release of this synthetic anti-inflammatory corticosteroid. Overall, our results not only provide a promising intestinal delivery system for budesonide but also deliver fundamental mechanistic understanding for the entrapment of actives in LNPs with controlled size and release properties.

The biotechnological conversion of lignocellulosic biomass is a pivotal aspect in the development of sustainable and environmentally friendly biorefinery and valorization processes for nonfossil biomass. Lipoxygenase, a noncellulolytic oxidizing enzyme normally operating on linoleic acid metabolism, is demonstrated to catalyze the oxidative functionalization of lignin. Lipoxygenase was used for structurally altering the most important types of technical lignins. Noteworthy oxidation is achieved by activation via a radical mechanism leading to both oxygen- and carbon-centered radicals. Since this activation also occurs on the lignin backbone, the ketyl and benzyl radicals generated can be used to functionalize lignins via formation of carbon-carbon bonds.

A new fractionation protocol for wheat straw organosolv lignin was developed on the basis of the dominating H-bonding orientations of its components. Acetone as H-bond accepting aprotic polar solvent and methanol as H-bond donating and accepting protic polar solvent were used in sequence. Obtained fractions were structurally and thermally analysed. The protocol allowed for the generation of purified lignin fractions and the isolation of a novel, yet unobserved lignin carbohydrate complex (LCC) fraction. This LCC fraction was found to contain exclusively phenyl glycosides and &gamma, esters as LCC motifs.

Driven by the need of a simple method to arrive at rather accurate molecular mass key data for different lignin samples across different laboratories, we revisited thoroughly the different aspects that comprise the determination of molecular weight key data of lignins by means of gel permeation chromatography. We considered setup issues and their effect on calibration, implications emerging from sample preparation, issues connected to data acquisition, and effects of raw data evaluation. Considering identified key issues, we propose a standardized setup in connection with a standardized data treatment that ensures the generation of precise GPC results. The introduction of an additional lignin-type depending correction factor, which is delineated using averaged bidimensional NMR-based advanced structural information obtained for a given lignin type, allows us to account for system-inherent bias, rendering the precise measurements de facto accurate.

Isolation of lignins from hardwood and softwood biomass samples, containing 26.1% and 28.1% lignin, respectively, has been performed with the use of alkaline and organosolv pretreatment methods. The effect of catalyst loading, ethanol content, particle size, and pretreatment time on the yields and properties of the isolated lignins were investigated. Alkaline lignins had higher carbohydrate content - up to 30% - and exhibited higher molecular weights in the range of 3000 Da, with a maximum phenolic hydroxyl content of 1 mmol g−1 for birch and 2 mmol g−1 for spruce. Organosolv lignins, on the other hand, showed high purity - 93% or higher - despite the more extensive biomass dissolution into the pretreatment medium; they also exhibited a lower range of molecular weights between 600 and 1600 Da depending on the source and pretreatment conditions. Due to the lower molecular weight, phenolic hydroxyl content was also increased, reaching as high as 4 mmol g−1 with a simultaneous decrease in aliphatic hydroxyl content as low as 0.6 mmol g−1. Efficient lignin dissolution of 62% for spruce and 69% for birch, achieved at optimal pretreatment conditions, was combined with extensive hemicellulose removal.

In this study, the application of different chemical and enzymatic treatment methods for the fractionation of the birch outer bark components was evaluated. More specifically, untreated and steam exploded, hydrothermally and organosolv treated bark samples were incubated with enzyme mixtures that consisted of cellulases, hemicellulases and esterases, and the effect of enzymes was analyzed with 31P NMR and {13C-1H} HSQC. The biocatalysts performed the cleavage of ester bonds resulting in reduction of methoxy and aliphatic groups in the remaining solid fraction, whereas the aromatic fraction remained intact. Moreover, the suberin and lignin fraction were isolated chemically and their properties were characterized by gas chromatography (GC-MS), 31P NMR, {13C-1H} HSQC and gel permeation chromatography (GPC). It was demonstrated that the lignin fraction was enriched in guaiacyl phenolics but still contained some associated aliphatic acids and carbohydrates, whereas the suberin fraction presented a polymodal pattern of structures with different molecular weight distributions. This work will help in getting a deeper fundamental knowledge of the bark structure, the intermolecular connection between lignin and suberin fractions, as well as the potential use of enzymes in order to degrade the recalcitrant bark structure toward its valorization. Validerad; 2016; Nivå 2; 2016-11-02 (andbra)

This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo-mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur-containing compounds in the low-molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass-transition temperatures (Tg) between 70 and 170C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox-Flory equation adequately described the relationship between the number average molecular masses (Mn) and T g's-irrespective of the method applied. DMA showed that low-molecular-weight lignin exhibits a good flow behavior as well as high-temperature crosslinking capability. Unfractionated and high molecular weight lignin (Mw >5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt-flow is required as the first step.

Tannins and flavonoids are secondary metabolites of plants that display a wide array of biological activities. This peculiarity is related to the inhibition of extracellular enzymes that occurs through the complexation of peptides by tannins. Not only the nature of these interactions, but more fundamentally also the structure of these heterogeneous polyphenolic molecules are not completely clear. This first paper describes the development of a new analytical method for the structural characterization of tannins on the basis of tannin model compounds employing an in situ labeling of all labile H groups (aliphatic OH, phenolic OH, and carboxylic acids) with a phosphorus reagent. The 31P NMR analysis of 31P-labeled samples allowed the unprecedented quantitative and qualitative structural characterization of hydrolyzable tannins, proanthocyanidins, and catechin tannin model compounds, forming the foundations for the quantitative structural elucidation of a variety of actual tannin samples described in part 2 of this series.

An unprecedented analytical method that allows simultaneous structural and quantitative characterization of all functional groups present in tannins is reported. In situ labeling of all labile H groups (aliphatic and phenolic hydroxyls and carboxylic acids) with a phosphorus-containing reagent (Cl-TMDP) followed by quantitative 31P NMR acquisition constitutes a novel fast and reliable analytical tool for the analysis of tannins and proanthocyanidins with significant implications for the fields of food and feed analyses, tannery, and the development of natural polyphenolics containing products.

Novel processing methods and product concepts are required to extend the role of lignin for future biomass and biofuel applications in emerging platforms such as the biorefinery. The possible strategies of lignin valorisation are focused into two main directions, namely the selective functionalisation of the lignin polymer or in its oxidative depolymerization to get polyfunctional monomeric compounds. Here we report a panel of biocatalysis, organometallic catalysis, biomimetic catalysis and plasma oxidation processes developed by our research group for the activation of the environmental friendly oxidants oxygen and hydrogen peroxide in the oxidative functionalisation of lignin and lignin model compounds. L'articolo è disponibile sul sito dell'editore: http://www.sciencedirect.com