Lignocellulosic nanofibril aerogel via gas phase coagulation and diisocyanate modification for solvent absorption.

Cellulose-based aerogels are considered to be carriers that can absorb oils and organic solvents owing to the merits of low density and high surface area. However, the natural hydrophility and poor mechanical strength often obstruct their widespread applications. In this work, Miscanthus-based dual cross-linked lignocellulosic nanofibril (LCNF) aerogels were prepared by gas phase coagulation and methylene diphenyl dissocyanate (MDI) modification. Due to physical and chemical cross-linking strategies, the optimally 4 M-LCNF aerogels had high surface area of 157.9 m2/g, water contact angle of 138.1°, and enhanced compression properties. Moreover, the modified aerogels exhibited absorption performance for various organic solvents, and the maximal absorption capacity of chloroform was 42 g/g aerogel. Because LCNF was directly produced from Miscanthus without using bleaching reagents, this research provided a more sustainable methodology to utilize lignocelluloses to design robust aerogels to deal with the leakage of oil and organic solvents in industrial applications.

Development of a light activatable lignin nanosphere based spray coating for bioimaging and antimicrobial photodynamic therapy.

Many coating materials are commercially available to combat microbial infections. However, these coatings are difficult to synthesize, and are mostly composed of toxic chemicals. Lignin is an under-explored natural biopolymer with multifaceted potential. Lignin, with adhesive, UV resistant, and antimicrobial properties, is a suitable candidate to develop coating materials. Here we report a smart method to fabricate a sustainable nanospray coating from lignin which does not require any toxic chemicals or additives during synthesis. Initially, we have developed stable lignin nanospheres in a single step in aqueous medium, which were later utilized as a lignin nanospray (LNSR). The LNSR was characterized by dynamic light scattering, scanning electron microscopy, FTIR and other analytical techniques. This LNSR showed remarkable UV blocking, antioxidant and light-activated antimicrobial properties. Interestingly, for the first time, the LNSR demonstrated photoluminescence, making it useful for bioimaging. Moreover, singlet oxygen generation potential was observed in the LNSR, which could render it useful in phototheranostic applications (i.e. light assisted imaging and photodynamic therapy). Further, the LNSR was directly utilized to fabricate a sustainable coating. The nanospray coating exhibited maximum light-induced cell killing when applied to common microbes as detected by live-dead cell imaging. Taken together, the lignin nanospray coating developed via a direct pathway holds great promise to disinfect microbes in the presence of light.

Green synthesis of lignin nano- and micro-particles: Physicochemical characterization, bioactive properties and cytotoxicity assessment.

Lignin particles (LPs) have gained prominence due to their biodegradability and bioactive properties. LP production at nano and micro scale produced from organosolv lignin and the understanding of size's effect on their properties is unexplored. This work aimed to produce and characterize lignin nanoparticles and microparticles using a green synthesis process, based on ethanol-solubilized lignin and water. Spherical shape LPs, with a mean size of 75 nm and 215 nm and with a low polydispersity were produced, as confirmed by transmission electron microscopy and dynamic light scattering. LPs thermal stability improved over raw lignin, and the chemical structure of lignin was not affected by the production method. The antimicrobial tests proved that LPs presented a bacteriostatic effect on Escherichiacoli and Salmonella enterica. Regarding the antioxidant potential, LPs had a good antioxidant activity that increased with the reaction time and LPs concentration. LPs also presented an antioxidant effect against intracellular ROS, reducing the intracellular ROS levels significantly. Furthermore, the LPs showed a low cytotoxic effect in Caco-2 cell line. These results showed that LPs at different scales (nano and micro) present biological properties and are safe to be used in different high value industrial sectors, such as biomedical, pharmaceutical and food.

Study and optimization of parameters affecting the acetylation process of lignin sulfonate biopolymer.

Here, firstly lignin sulfonate was produced from sulfite liquor provided by Mazandaran wood & paper industries (Chookam). Then, the role of effective parameters including reaction temperature, duration time, and amounts of pyridine and acetic anhydride respectively as the catalyst and the esterification agent on the acetylation rate of lignin sulfonate were studied and the process parameters were optimized through multiple experiments. In this investigation, using 1 g lignin sulfonate, the effect of various levels of temperature (ranged from room temperature to 140 °C), reaction time (12-72 h), pyridine volume (0-30 mL), and acetic anhydride volume (5-30 mL) were evaluated. Based on the results of several esterification processes, the optimal values of temperature and reaction time were obtained to be 100 °C and 48 h, respectively, and the optimal volumes of acetic anhydride and pyridine were 20 mL (with equal amounts). Besides, the characterization tests of lignin sulfonate and acetylated lignin sulfonate were performed using FT-IR and NMR techniques. Also in this paper, the morphology and crystallinity/amorphicity of lignin sulfonate and acetylated lignin sulfonate were examined using SEM images and XRD patterns.

Influence of lignin content on the intrinsic modulus of natural fibers and on the stiffness of composite materials.

Agricultural wastes are an alternative to the use of wood in plastic composites, thanks to their abundance, easy availability and other environmental and economic advantages. Agricultural wastes can be processed to obtain lignocellulosic fibers of different compositions that will allow better performance of their composites and the final desired residues' valorization. In this context, the current investigation aims at the management of corn stover wastes to be applied as reinforcement of polypropylene (PP). Four types of lignocellulosic fibers were obtained by submitting the wastes to mechanical, thermomechanical, semi-chemical or chemical processes. Corn fibers were characterized in terms of chemical composition, morphology and mechanical properties. In addition, PP was reinforced with corn fibers and the composites' stiffness evaluated. An assessment of the influence of the fiber composition on the mechanical performance of the composites is conducted. It is observed the key role of lignin content on the intrinsic modulus of the reinforcing fibers, which directly affected the final stiffness of composites. The best performance was achieved for an optimal kappa number between 40 and 50, corresponding to the semi-chemical fibers. The intrinsic modulus of the fibers, as well as the efficiency factor, length and orientation factors in composites were determined via micromechanical models.

One-pot preparation of zwitterion-type lignin polymers.

In this work, a simple approach was examined to prepare zwitterion-type lignin (ZL) in a one-pot reaction system. Kraft lignin (KL) was modified with 3-chloro-2-hydroxypropansulfonic acid sodium salt (CHPSS) and glycidyltrimethylammonium chloride (GTMAC) in an aqueous solution simultaneously. The maximum amounts of sulfonate (1.57 mmol/g) and quaternary-N (2.16 mmol/g) groups on ZL were achieved under the reaction conditions of 7/1 molar ratio of CHPSS/KL, 9/1 molar ratio of GTMAC/KL, 40 g/L concentration of KL, 3/5 molar ratio of NaOH/KL, 4 h reaction time and 80 °C. The chemical structure, thermal stability, and surface activity of the ZL were compared with those of cationic lignin (CL) and sulfonated lignin (SL) produced under optimized conditions. The signals for hydrogen, carbon, and hydrogen­carbon in the spectra of 1H-, 13C-, and HSQC-NMR indicated that the sulfonation and quaternization occurred on both aliphatic and phenolic hydroxy groups of lignin. The flocculation performance of ZL for simulated dye wastewater was further analyzed. The main novelties of this work were the introduction of a one-pot process to simultaneously impart anionic and cationic functional groups onto kraft lignin, and the development of a new biodegradable zwitterion-type flocculant for removing dye pigments from a simulated solution.

Total syntheses of schizandriside, saracoside and (±)-isolariciresinol with antioxidant activities.

Lignans are widely distributed in plants and exhibit significant pharmacological effects, including anti-tumor and antioxidative activities. Here, we describe the total synthesis of schizandriside (1), a compound we previously isolated from Saraca asoca by monitoring antioxidative activity using the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay. Starting from a tandem Michael-aldol reaction, the lignan skeleton was synthesized in 6 steps, including a cyclization step. To determine the stereochemistry of 1, we synthesized the natural product (±)-isolariciresinol (18) from alcohol 17. Comparison of the spectral data showed good agreement. Glycosylation was investigated using four different glycosyl donors. Only the Koenigs-Knorr condition using silver trifluoromethanesulfonate with 1,1,3,3-tetramethylurea provided the glycosylated product. Deprotection and purification using reverse-phase high-performance liquid chromatography gave schizandriside (1) and its diastereomer saracoside (2). Synthesized 1, 2 and 18 showed antioxidant activity with IC50 = 34.4, 28.8, 53.0 µM, respectively.

Lignocellulose nanofibers prepared by ionic liquid pretreatment and subsequent mechanical nanofibrillation of bagasse powder: Application to esterified bagasse/polypropylene composites.

In the present study, we examined the efficacy of choline acetate (ChOAc, a cholinium ionic liquid))-assisted pretreatment of bagasse powder for subsequent mechanical nanofibrillation to produce lignocellulose nanofibers. Bagasse sample with ChOAc pretreatment and subsequent nanofibrillation (ChOAc/NF-bagasse) was prepared and compared to untreated control bagasse sample (control bagasse), bagasse sample with nanofibrillation only (NF-bagasse) and with ChOAc pretreatment only (ChOAc-bagasse). The specific surface area was 0.83m2/g, 3.1m2/g, 6.3m2/g, and 32m2/g for the control bagasse, ChOAc-bagasse, NF-bagasse, and the ChOAc/NF-bagasse, respectively. Esterified bagasse/polypropylene composites were prepared using the bagasse samples. ChOAc/NF-bagasse exhibited the best dispersion in the composites. The tensile toughness of the composites was 0.52J/cm3, 0.73J/cm3, 0.92J/cm3, and 1.29J/cm3 for the composites prepared using control bagasse, ChOAc-bagasse, NF-bagasse, and ChOAc/NF-bagasse, respectively. Therefore, ChOAc pretreatment and subsequent nanofibrillation of bagasse powder resulted in enhanced tensile toughness of esterified bagasse/polypropylene composites.

Novel nanocomposites with selective antibacterial action and low cytotoxic effect on eukaryotic cells.

In the present study we synthesized lignin-tetra ethoxysilane (TEOS) nanocomposite and characterized it using UV-spectroscopy, Fourier Transform Infra-red spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Field Emission-Scanning Electron Microscopy (FE-SEM) and Scanning Electron Microscopy (SEM). XRD spectra and SEM micrographs confirmed a relatively high degree of crystallinity (peaks located at lower angle, 2θ=12° and 2θ=22.0°) and porous nature of nanocomposite. The lignin-TEOS nanocomposites depicted antibacterial activity against the test microorganisms (Pseudomonas aerugenosa MTCC 741, Escherichia coli MTCC 739, Bacillus subtilis MTCC 441 and Staphylococcus aureus MTCC 96) whereas at the same concentration did not show any significant cytotoxicity against various tissue-specific cancer cell lines such as breast cancer: MCF-7, MDA-MB-231, MDA-MB-468, BT-549; lung cancer: A-549; prostate cancer: PC-3, Du-145; as well as primary control cells-Human hepatic stellate cells (HHSteCs). The present study suggests the plausible translational role of these nanocomposites as an antimicrobial agent for wound dressings due to its potent antimicrobial activity with low toxicity to non-target eukaryotic cells. Nevertheless, these nanocomposites may also be used as packaging materials due to their antimicrobial activity.

NMR Assignment for Diaryl Ether Structures (4-O-5 Structures) in Pine Wood Lignin.

A 4-O-5-tetramer lignin model compound carrying ß-O-4 linkages on each of the side-chain moieties was synthesized, as well as 4-O-5-coupled dehydrodiconiferyl alcohol. By comparison with their NMR data, two cross-signals in the HSQC spectrum of pine milled wood lignin recorded in DMSO-d6 were assigned to H2/C2 and H6/C6 correlations on the aromatic rings of 4-O-5-linked units. Although the H2/C2 correlation peak appeared in the same region as syringyl units, nitrobenzene oxidation of the pine lignin did not yield any syringyl-type product, but did release a 4-O-5-type product.

Antiproliferative effect of synthetic lignin against human breast cancer and normal fetal lung cell lines. Potency of low molecular weight fractions.

PURPOSE: Due to a lack of chemotherapeutics to efficiently control neoplastic processes, there is a need for discovering new, more efficient anticancer drugs that would distinguish malignant from normal cells. MATERIALS AND METHODS: We studied the effect of short (4 h) and long (72 h) treatment with different concentrations of the enzymatically synthesized lignin model compound (DHP) on the proliferation of two human cell lines grown in tissue culture: breast adenocarcinoma (MCF7) and normal fetal lung fibroblast (MRC5) cell lines. RESULTS: The growth of both MRC5 and MCF7 cell lines was inhibited by DHP after 4 h-treatment, while the carcinoma cell line was also sensitive to the long-term treatment with lower dose of DHP in comparison with the fetal cells. The low molecular weight DHP fractions inhibited growth of the MRC5 cells at lower concentrations compared to the treatment with all DHP fractions. CONCLUSION: The higher sensitivity to DHP of the human malignant cells compared to the normal transformed ones gives the possibility to further study DHP as a therapeutic agent.

Short and stereoselective total synthesis of furano lignans (+/-)-dihydrosesamin, (+/-)-lariciresinol dimethyl ether, (+/-)-acuminatin methyl ether, (+/-)-sanshodiol methyl ether, (+/-)-lariciresinol, (+/-)-acuminatin, and (+/-)-lariciresinol monomethyl ether and furofuran lignans (+/-)-sesamin, (+/-)-eudesmin, (+/-)-piperitol methyl ether, (+/-)-pinoresinol, (+/-)-piperitol, and (+/-)-pinoresinol monomethyl ether by radical cyclization of epoxides using a transition-metal radical source.

Intramolecular radical cyclization of suitably substituted epoxy ethers 4a-g using bis(cyclopentadienyl)titanium(III) chloride as the radical source resulted in trisubstituted tetrahydrofurano lignans and 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane lignans depending on the reaction conditions. The titanium(III) species was prepared in situ from commercially available titanocene dichloride and activated zinc dust in THF. Upon radical cyclization followed by acidic workup, epoxy olefinic ethers 4a-g afforded furano lignans dihydrosesamin 1a, lariciresinol dimethyl ether 1b, acuminatin methyl ether 1e, and sanshodiol methyl ether 1g directly and lariciresinol 1h, acuminatin 1i, and lariciresinol monomethyl ether 1j after removal of the benzyl protecting group by controlled hydrogenolysis of the corresponding cyclized products. The furofuran lignans sesamin 2a, eudesmin 2b, and piperitol methyl ether 2e were also prepared directly by using the same precursors 4a-f on radical cyclization followed by treatment with iodine and pinoresinol 2h, piperitol 2i, and pinoresinol monomethyl ether 2j after controlled hydrogenolysis of the benzyl protecting group of the corresponding cyclized products. Two naturally occurring acyclic lignans, secoisolariciresinol 5h and secoisolariciresinol dimethyl ether 5b, have also been prepared by exhaustive hydrogenolysis of 2h and 2b, respectively.

C-H insertion approach to the synthesis of endo,exo-furofuranones: synthesis of (+/-)-asarinin, (+/-)-epimagnolin A, and (+/-)-fargesin.

A series of novel 5-aryl-4-aryloxymethyl-3-diazotetrahydrofuran-2-ones (12, 24, and 35a/b) have been prepared and found to undergo regio- and stereoselective C-H insertion reactions to afford 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane-8-ones (18, 26, and 36a/b) with endo,exo stereochemistry. Subsequent reduction of the lactone ring and cyclization of the resulting diols 27 and 37a/b permitted the synthesis of three endo,exo-furofuran lignans: asarinin (2), fargesin (3), and epimagnolin A (4). En route to the key diazo compounds 24 and 35a/b, a modified procedure for the Ghosez keteniminium-olefin cyclization was developed, which was required to minimize the decomposition of acid-sensitive functional groups such as electron-rich benzylic ethers that were present in the target compounds 2-4.

Synthesis and biological activity of bromolignans and cyclolignans.

Nine lignan derivatives (4-12) have been obtained from (-)-yatein by treatment with DDQ and NBS. They showed moderate antineoplastic activity (P-388, A-549, HT-29) compared with podophyllotoxin, but some of them have a better therapeutic index. None of the tested compounds shows anti-viral (HSV-1, VSV) or enzyme inhibitor (ADA, DHFR, GST) activities.

The role of dianion coupling in the synthesis of dibenzylbutane lignans.

Dianion coupling reactions have been used to prepare structurally related lignan natural products in racemic form. A readily available alpha-idocarboxylic acid 10 has been employed in separate sequences to afford the tetrahydrofuran lignan burseran [6] and the butyrolactone lignan deoxypodorhizon [7]. The key strategy for both burseran and deoxypodorhizon involved reaction of the appropriate dianion with an alpha-iodo carboxylate salt 13. Equilibration under acid or base was employed to create the trans stereochemistry of the substituted benzyl side chains of both burseran and deoxypodorhizon. To achieve proper dianion reactivity and to avoid side reactions in the synthetic sequence to deoxypodorhizon, it was necessary to develop the chemistry of acylsulfonamide dianions. As a further structure proof, our synthetic deoxypodorhizon was also utilized as a substrate in a successful sequence to isostegane [8], a known relay intermediate to the antineoplastic prototype steganacin [9].

Synthesis of lignan aryldihydronaphthalene lactones by cyclization of cinnamyl arylpropiolate esters: revised structure of beta-apopolygamatin.

Unlike arylpropargyl arylpropiolates (e.g., 3) which yield, on heating in xylene, arylnaphthalene type I and type II lactones (4 and 5, respectively) in 1:1 ratio, cinnamyl arylpropiolates (e.g., 7) on heating in DMF gave the aryldihydronaphthalene-2-carboxylic acid lactones (e.g., 8) in excellent yield and regioselectivity. It is suggested that the aryldihydronaphthalene lactone product isolated from the tumor-inhibiting extract of Polygala polygama and previously named beta-apopolygamatin [17] has in fact the structure 1-(3',4'-methylene-dioxyphenyl)-3-hydroxymethyl-7,8-dimethoxy-3,4- dihydro-2- naphthoic acid lactone [18].

Preparation and microbial decomposition of synthetic [14C]ligins.

A definitive assay for microbiological and biochemical research on the biodegradation of lignin was developed using radioactive synthetic lignins specifically labeled in the side chains, aromatic rings or in the methoxyl groups. The [14C]lignins were prepared by oxidative polymerization with peroxidase and H2O2 Of specifically labeled coniferyl alcohol (4-hydroxy-3-methyoxycinnamyl alcohol). The synthetic polymers were shown by spectroscopic and chemical methods to contain the same intermonomer linkages found in natural lignins. Incubation of the [14C]lignins with known lignin-degrading fungi and with a forest soil resulted in 14CO2 evolution.