Integrated Conversion of Lignocellulosic Biomass to Bio-Based Amphiphiles using a Functionalization-Defunctionalization Approach.

Concerns over the sustainability and end-of-life properties of fossil-derived surfactants have driven interest in bio-based alternatives. Lignocellulosic biomass with its polar functional groups is an obvious feedstock for surfactant production but its use is limited by process complexity and low yield. Here, we present a simple two-step approach to prepare bio-based amphiphiles directly from hemicellulose and lignin at high yields (29 % w/w based on the total raw biomass and >80 % w/w of these two fractions). Acetal functionalization of xylan and lignin with fatty aldehydes during fractionation introduced hydrophobic segments and subsequent defunctionalization by hydrogenolysis of the xylose derivatives or acidic hydrolysis of the lignin derivatives produced amphiphiles. The resulting biodegradable xylose acetals and/or ethers, and lignin-based amphiphilic polymers both largely retained their original natural structures, but exhibited competitive or superior surface activity in water/oil systems compared to common bio-based surfactants.

Quantification of Native Lignin Structural Features with Gel-Phase 2D-HSQC0 Reveals Lignin Structural Changes During Extraction.

Our ability to study and valorize the lignin fraction of biomass is hampered by the fundamental and still unmet challenge of precisely quantifying native lignin's structural features. Here, we developed a rapid elevated-temperature 1H-13C Heteronuclear Single-Quantum Coherence Zero (HSQC0) NMR method that enables this precise quantification of native lignin structural characteristics even with whole plant cell wall (WPCW) NMR spectroscopy, overcoming fast spin relaxation in the gel phase. We also formulated a Gaussian fitting algorithm to perform automatic and reliable spectral integration. By combining HSQC0 measurements with yield measurements following depolymerisation, we can confirm the combinatorial nature of radical coupling reactions during biosynthesis leading to a random sequential organization of linkages within a largely linear lignin chain. Such analyses illustrate how this analytical method can greatly facilitate the study of native lignin structure, which can then be used for fundamental studies or to understand lignin depolymerization methods like reductive catalytic fractionation or aldehyde-assisted fractionation.

Extraction and Surfactant Properties of Glyoxylic Acid-Functionalized Lignin.

The amphiphilic chemical structure of native lignin, composed by a hydrophobic aromatic core and hydrophilic hydroxy groups, makes it a promising alternative for the development of bio-based surface-active compounds. However, the severe conditions traditionally needed during biomass fractionation make lignin prone to condensation and cause it to lose hydrophilic hydroxy groups in favour of the formation of C-C bonds, ultimately decreasing lignin's abilities to lower surface tension of water/oil mixtures. Therefore, it is often necessary to further functionalize lignin in additional synthetic steps in order to obtain a surfactant with suitable properties. In this work, multifunctional aldehyde-assisted fractionation with glyoxylic acid (GA) was used to prevent lignin condensation and simultaneously introduce a controlled amount of carboxylic acid on the lignin backbone for its further use as surfactant. After fully characterizing the extracted GA-lignin, its surface activity was measured in several water/oil systems at different pH values. Then, the stability of water/mineral oil emulsions was evaluated at different pH and over a course of 30 days by traditional photography and microscopy imaging. Further, the use of GA-lignin as a surfactant was investigated in the formulation of a cosmetic hand cream composed of industrially relevant ingredients. Contrary to industrial lignins such as Kraft lignin, GA-lignin did not alter the color or smell of the formulation. Finally, the surface activity of GA-lignin was compared with other lignin-based and fossil-based surfactants, showing that GA-lignin presented similar or better surface-active properties compared to some of the most commonly used surfactants. The overall results showed that GA-lignin, a biopolymer that can be made exclusively from renewable carbon, can successfully be extracted in one step from lignocellulosic biomass. This lignin can be used as an effective surfactant without further modification, and as such is a promising candidate for the development of new bio-based surface-active products.

Lignin: A Sustainable Antiviral Coating Material.

Transmission of viruses through contact with contaminated surfaces is an important pathway for the spread of infections. Antiviral surface coatings are useful to minimize such risks. Current state-of-the-art approaches toward antiviral surface coatings either involve metal-based materials or complex synthetic polymers. These approaches, however, even if successful, will have to face great challenges when it comes to large-scale applications and their environmental sustainability. Here, an antiviral surface coating was prepared by spin-coating lignin, a natural biomass residue of the paper production industry. We show effective inactivation of herpes simplex virus type 2 (>99% after 30 min) on a surface coating that is low-cost and environmentally sustainable. The antiviral mechanism of the lignin surface was investigated and is attributed to reactive oxygen species generated upon oxidation of lignin phenols. This mechanism does not consume the surface coating (as opposed to the release of a specific antiviral agent) and does not require regeneration. The coating is stable in ambient conditions, as demonstrated in a 6 month aging study that did not reveal any decrease in antiviral activity. This research suggests that natural compounds may be used for the development of affordable and sustainable antiviral coatings.

Dual Valorization of Lignin as a Versatile and Renewable Matrix for Enzyme Immobilization and (Flow) Bioprocess Engineering.

Lignin has emerged as an attractive alternative in the search for more eco-friendly and less costly materials for enzyme immobilization. In this work, the terephthalic aldehyde-stabilization of lignin is carried out during its extraction to develop a series of functionalized lignins with a range of reactive groups (epoxy, amine, aldehyde, metal chelates). This expands the immobilization to a pool of enzymes (carboxylase, dehydrogenase, transaminase) by different binding chemistries, affording immobilization yields of 64-100 %. As a proof of concept, a ω-transaminase reversibly immobilized on polyethyleneimine-lignin is integrated in a packed-bed reactor. The stability of the immobilized biocatalyst is tested in continuous-flow deamination reactions and maintains the same conversion for 100 cycles. These results outperform previous stability tests carried out with the enzyme covalently immobilized on methacrylic resins, with the advantage that the reversibility of the immobilized enzyme allows recycling and reuse of lignin beyond the enzyme inactivation. Additionally, an in-line system also based on lignin is added into the downstream process to separate the reaction products by catch-and-release. These results demonstrate a fully closed-loop sustainable flow-biocatalytic system based exclusively on lignin.

Establishing lignin structure-upgradeability relationships using quantitative 1H-13C heteronuclear single quantum coherence nuclear magnetic resonance (HSQC-NMR) spectroscopy.

Lignin depolymerization could provide an attractive renewable aromatic feedstock for the chemical industry. Past studies have suggested that lignin structural features such as ether content are correlated to lignin's upgradeability. An obstacle to the development of a conclusive causal relationship between lignin structure and upgradeability has been the difficulty to quantitatively measure lignin structural features. Here, we demonstrated that a modified HSQC-NMR method known as HSQC0 can accurately quantify lignin functionalities in extracted lignin using several synthetic polymer models. We then prepared a range of isolated lignin samples with a wide range of ether contents (6-46%). By using a simple ether cleavage model, we were able to predict final depolymerization yields very accurately (<4% error), conclusively demonstrating the direct causal relationship between ether content and lignin activity. The accuracy of this model suggests that, unlike in native lignin, ether linkages no longer appear to be randomly distributed in isolated lignin.

Anion-Exchange Properties of Trifluoroacetate and Triflate Salts of N-Alkylammonium Resorcinarenes.

The synthesis of N-benzyl- and N-cyclohexylammonium resorcinarene trifluoroacetate (TFA) and triflate (OTf) salt receptors was investigated. Solid-state analysis by single-crystal X-ray diffraction revealed that the N-alkylammonium resorcinarene salts (NARSs) with different upper substituents had different cavity sizes and different affinities for anions. Anion-exchange experiments by mixing equimolar amounts of N-benzylammonium resorcinarene trifluoroacetate and N-cyclohexylammonium resorcinarene triflate, as well as N-benzylammonium resorcinarene triflate and N-cyclohexylammonium resorcinarene trifluoroacetate showed that the NARS with flexible benzyl groups preferred the larger OTf anion, whereas the rigid cyclohexyl groups preferred the smaller TFA anions. The anion-exchange processes were confirmed in the solid state by single-crystal and powder X-ray diffraction experiments and in the gas phase by electrospray ionization mass spectrometry.