The isolation of lignin with native-like structure

Searching for renewable alternatives for fossil carbon resources to produce chemicals, fuels and materials is essential for the development of a sustainable society. Lignin, a major component of lignocellulosic biomass, is an abundant renewable source of aromatics and is currently underutilized as it is often burned as an undesired side stream in the production of paper and bioethanol. This lignin harbors great potential as source of high value aromatic chemicals and materials. Biorefinery schemes focused on lignin are currently under development with aim of acquiring added value from lignin. However, the performance of these novel lignin-focused biorefineries is closely linked with the quality of extracted lignin in terms of the level of degradation and modification. Thus, the reactivity including the degradation pathways of the native lignin contained in the plant material needs to be understood in detail to potentially achieve higher value from lignin. Undegraded native-like lignin with an as close as possible structure to native lignin contained in the lignocellulosic plant material serves as a promising model lignin to support detailed studies on the structure and reactivity of native lignin, yielding key understanding for the development of lignin-focused biorefineries. The aim of this review is to highlight the different methods to attain “native-like” lignins that can be valuable for such studies. This is done by giving a basic introduction on what is known about the native lignin structure and the techniques and methods used to analyze it followed by an overview of the fractionation and isolation methods to isolate native-like lignin. Finally, a perspective on the isolation and use of native-like lignin is provided, showing the great potential that this type of lignin brings for understanding the effect of different biomass treatments on the native lignin structure.</p

“Lignin-first” catalytic valorization for generating higher value from lignin

In this Activity article, Peter J. Deuss (tenure-track assistant professor of green and smart biomass processing at the University of Groningen) and Christian Kugge (R&D specialist at Svenska Cellulosa Aktiebolaget) discuss the catalytic routes to transforming lignin into higher-value products and the opportunities for industry and academia to develop new technologies

New opportunities and future directions for higher-value lignin applications

In this Activity article, Christian Kugge (R&D specialist at Svenska Cellulosa Aktiebolaget) and Peter J. Deuss (tenure-track assistant professor of green and smart biomass processing at the University of Groningen) exchange views from industrial and academic perspectives, respectively, on the future research directions for lignin valorization and the challenges associated with the production of fuels from lignin

Artificial metalloenzymes : modified proteins as tuneable transition metal catalysts

Electronic version excludes material for which permission has not been granted by the rights holderThis thesis describes the design, synthesis and application of artificial metalloenzymes for transition metal catalysed reactions not performed by natural enzymes. Unique cysteine containing protein templates were covalently modified with transition metal ligand complexes that generate catalytic activity, which allows for the use of virtually any protein template. SCP-2L was selected as template for the linear hydrophobic tunnel that traverses the protein, which has high affinity for linear aliphatic molecules. The use of catalysts based on this protein to induce increased activity in the biphasic hydroformylation of linear α-olefins is investigated in this work. For this purpose, unique cysteine containing mutants of SCP-2L were modified with phosphine ligands by application of a novel bioconjugation procedure. Application of rhodium adducts of the phosphine modified protein constructs led to up to a 100 fold increase of the turn over numbers was measured compared to a Rh/TPPTS model system which is used in industry. Furthermore, good selectivity towards the linear product was observed. If it can be confirmed that the found catalytic results truly are the result of substrate encapsulation by the protein scaffold, this system represents the first rationally designed artificial metalloenzyme which exploits the shape selectivity of the protein scaffold to direct the outcome of a catalytic reaction. In addition, a study was performed for the development of enantioselective artificial metalloenzymes. Nitrogen ligands were covalently introduced in SCP-2L and the obtained conjugates were applied in the copper catalysed Diels-Alder and Michael addition reaction. A promising 25% ee was found for the Diels-Alder reaction between azachalcone and cyclopentadiene using one of the created constructs. Further development of these catalyst systems with the use of both synthetic (e.g. optimisation of ligand structure) and biomolecular tools (e.g. optimisation of protein environment) for optimisation can lead to very efficient and enantioselective conversions in the future

The effect of ball milling on birch, pine, reed, walnut shell enzymatic hydrolysis recalcitrance and the structure of the isolated residual enzyme lignin

Methodologies for the high-yield recovery of lignin with retention of its native C[sbnd]O bonded structure is an essential prerequisite for many novel high-end lignin applications. Enzymatic residual lignin isolation is such a methodology that leaves the lignin untouched by using enzymatic desaccharification. Thus, a series of representative lignocellulose substrates (birch, pine, walnut shell and reed) were evaluated for effective native lignin isolation, with emphasis on the effect on the lignin structure and purity. The effect of enzyme loading and ball milling severity were studied by tracking residual saccharides and the structural integrity of the isolated lignin. Prolongation of ball milling time could achieve a higher carbohydrate removal and avoid the loading of extra enzyme. However, the application of two or more steps of enzymatic hydrolysis with higher enzyme loading and short ball milling time was shown as an alternative to long ball milling time to achieve similar carbohydrate removal and avoid extensive decrease of the lignin molecular weight (MW). This MW decrease was caused by breaking of some linkages, but not too a large enough extent to cause significant differences in the 2D HSQC NMR spectra. The recalcitrance towards increased enzyme hydrolysis activity by ball milling was different for the four representative biomasses and followed an order of walnut shell > reed ≈ pine > birch by comprehensive analysis the obtained data. Overall, the results showed a clear two-way synergy between enzymatic treatment and ball milling efficiency to isolate lignin with high yield, high native linkage content, purity and minimal MW reduction

The Effect of Acidic Ternary Deep Eutectic Solvent Treatment on Native Lignin

Ternary deep eutectic solvents (DESs) are gaining increased attention to serve as a cheap green alternative medium for the processing of lignocellulosic biomass. For example, mixtures of choline chloride (ChCl), ethylene glycol (EG), and oxalic acid (OA) were recently explored for the fractionation of lignocellulosic biomass into its main components. Interestingly, during this processing, the recovered lignin was structurally modified by incorporation of EG, which altered its solubility properties and led to the need for different lignin recovery strategies. This offers an excellent starting point for a deeper investigation of the effect of acidic DES systems on the structure of lignin. In particular, native-like residual enzyme lignins (RELs) that are hard to completely dissolve in organic solvents are specifically suitable for this task. Here, a ternary DES is used consisting of ChCl/EG with OA or trifluoromethanesulfonic acid (HOTf) as a third component. The results showed that both solvent systems led to high EG incorporation into REL. The HOTf system showed a lesser extent of lignin depolymerization at similar modification levels as it already induced modification at lower temperature (25–30 °C). Low recovery yields from typical acidic precipitation were observed for treatment with both acidic DES systems. Analysis of THF and DCM extracts showed that the products in the water phase included small EG modified lignin fragments and aromatic monomers released from lignin aryl ether linkage cleavage. This analysis details the types of other products that can be expected and where these will end up during fractionation. These results show that the treatment of lignin with acidic DES in the presence of alcohols leads to low- and high-molecular-weight products that are not effectively recovered by typical precipitation procedures

Towards Thermally Reversible Networks Based on Furan-Functionalization of Jatropha Oil

A novel biobased monomer for the preparation of thermally reversible networks based on the Diels-Alder reaction was synthesized from jatropha oil. The oil was epoxidized and subsequently reacted with furfurylamine to attach furan groups via an epoxide ring opening reaction. However, furfurylamine also reacted with the ester groups of the triglycerides via aminolysis, thus resulting in short-chain molecules that ultimately yielded brittle thermally reversible polymers upon cross-linking via a Diels-Alder reaction. A full-factorial experimental design was used in finding the optimum conditions to minimize ester aminolysis and to maximize the epoxide ring opening reaction as well as the number of furans attached to the modified oil. The optimum conditions were determined experimentally and were found to be 80 °C, 24 h, 1:1 molar ratio, with 50 mol % of LiBr with respect to the modified oil, resulting in 35% of ester conversion, 99% of epoxide conversion, and an average of 1.32 furans/triglyceride. Ultimately, further optimization by a statistical approach led to an average of 2.19 furans per triglyceride, which eventually yielded a flexible network upon cross-linking via a Diels-Alder reaction instead of the brittle one obtained when the furan-functionalization reaction was not optimized

Parallel synthesis and splicing redirection activity of cell-penetrating peptide conjugate libraries of a PNA cargo

A novel method for the parallel synthesis of peptide-biocargo conjugates was developed that utilizes affinity purification for fast isolation of the conjugates in order to avoid time consuming HPLC purification. The methodology was applied to create two libraries of cell-penetrating peptide (CPP)-PNA705 conjugates from parallel-synthesized peptide libraries. The conjugates were tested for their ability to induce splicing redirection in HeLa pLuc705 cells. The results demonstrate how the novel methodology can be applied for screening purposes in order to find suitable CPP-biocargo combinations and further optimization of CPPs.</p

Selective Demethoxylation of Guaiacols to Phenols using Supported MoO 3 Catalysts

Lignin-derived monomers with methoxy substituents are abundantly present in bioliquids derived from lignocellulosic biomass. Examples are the products obtained from the reductive catalytic fractionation of lignin (RCF) and pyrolysis of lignocellulosic biomass and hydrotreated products thereof. An attractive valorization step for these liquids involves demethoxylation to obtain alkylated phenols through selective catalytic hydrodeoxygenation (HDO). Within the context of sustainable chemistry, there is a strong drive to use cheap, non-precious metal catalysts for this purpose. In this study, the HDO of guaiacol (5 wt% in toluene) was investigated in a continuous fixed-bed reactor at 380 °C, 20 bar over supported MoO3 catalysts. MoO3 (5 %) supported on TiO2 (P25) was shown to give superior performance compared with MoO3 supported on anatase TiO2, Al2O3, SiO2, Nb2O5, CeO2, and ZrO2. Additional studies involving variation of the Mo loading and process conditions were performed, and the highest selectivity to demethoxylated phenolics like phenol and methylated phenols was 82 % at 97 % conversion of guaiacol. Both 4-n-propylguaiacol and a realistic guaiacols-rich feed isolated from a representative pyrolysis oil were also successfully demethoxylated with the 5 % MoO3/TiO2 catalyst

Combined lignin defunctionalisation and synthesis gas formation by acceptorless dehydrogenative decarbonylation

The valorization of lignin, consisting of various phenylpropanoids building blocks, is hampered by its highly functionalized nature. The absence of the γ-carbinol group in an unnatural C2 β-O-4 motif compared to the native lignin C3 β-O-4 motif provides great opportunities for developing new valorization routes. Thus efficient defunctionalisation approaches that transform the C3 β-O-4 motif into a simplified C2 β-O-4 motif are of interest. Based on a study with a series of model compounds, we established a feasible application of an iridium-catalysed acceptorless dehydrogenative decarbonylation method to efficiently remove the γ-carbinol group in a single step. This defunctionalisation generates valuable synthesis gas, which can be collected as a reaction product. By this direct catalytic transformation, a yield of ∼70% could be achieved for a C3 β-O-4 model compound that was protected from undergoing retro-aldol cleavage by alkoxylation of the benzylic secondary alcohol in the α position. A phenylcoumaran model compound containing a γ-carbinol group as well as a benzylic primary alcohol also proved to be reactive under dehydrogenative decarbonylation conditions, which can further contribute to the reduction of the structural complexity of lignin. Notably, the liberation of synthesis gas was confirmed and the signals for the defunctionalized C2 β-O-4 motif were observed when this dehydrogenative decarbonylation approach was applied on organosolv lignins. This selective defunctionalized lignin in conjunction with the formation of synthesis gas has the potential to enhance the development of profitable and sustainable biorefineries.</p