Investigation of structure of milled wood and dioxane lignins of Populus nigra and Cupressus sempervirens using the DFRC method

In this study, derivatisation followed by reductive cleavage (DFRC) were used to investigate milled wood lignin (MWL) and dioxane lignin (DL) structures of Populus nigra and Cupressus sempervirens. After the DFRC reactions, the constituents obtained from these two kinds of lignin were recognised structurally using several chromatographic and spectral methods such as ¹³C NMR, GC-MS, and GPC. Comparative results showed that the dominant structural components of the two kinds of lignin are obtained from the cleavage of ??-O-4 bonds. The main component of DL and MWL of P. nigra is 4-hydroxy-3,5-dimethoxy-1-phenyl-??-hydroxypropene (syringyl structures). Also, some guaiacyl structures were observed. The dominant component identified in both lignins of C. sempervirens is 4-hydroxy-3-methoxy-1-phenyl-??-hydroxypropene (guaiacyl structures). The cleavage method has a good performance for both P. nigra and C. sempervirens and the results obtained are in good agreement with previously published data.     

Structure elucidation and NMR spectral assignments of four neolignan glycosides with enantiometric aglycones from Osmanthus ilicifolius

Four new 8-O-4' type neolignan glycosides with enantiometric aglycones, (7S,8R)-erythro-guaiacylglycerol-beta-O-4'-sinapyl ether 9-O-beta-D-glucopyranoside (1), (7R,8S)-erythro-guaiacylglycerol-beta-O-4'-sinapyl ether 9-O-beta-D-glucopyranoside (2), (7S,8R)-erythro- syringylglycerol-beta-O-4'-sinapyl ether 9-O-beta-D-glucopyranoside (3) and (7R,8S)-erythro- syringylglycerol-beta-O-4'-sinapyl ether 9-O-beta-D-glucopyranoside (4), were isolated from the leaves of Osmanthus ilicifolius. Their structures were established on the basis of NMR, circular dichroism (CD), MS and chemical data. The NMR assignments for the compounds were carried out using (1)H, (13)C, COSY, HMQC, HMBC and NOESY NMR experiments.     

A Comparison of Phenolic Monomers Produced from Different Types of Lignin by Phosphotungstic Acid Catalysts

Herein we studied the chemical structure of different types of lignin samples and the potential to prepare phenolic monomers was illustrated by phosphotungstic acid catalysts. Different types of H/G/S lignin components had different structures. The lignin extracted from poplar had the highest molecular weight and β-O-4 aryl ether contents, followed by pine and straw lignin samples. After depolymerization by PTA catalyst, the yields of phenolic monomers detected was 8.06 wt % (poplar), 5.44 wt % (pine) and 4.52 wt % (straw), respectively. Further, the ratios of H/G/S in the phenol monomers were also different, indicating that the S, G and H types structural units were continuously transformed with each other during the reaction. In our study, the change in the types of lignin samples resulted into an improvement of the distribution of phenolic products, and also the selectivity of phenolic monomers significantly.     

On the interaction of UV screens with the lignocellulosic matrix

In this report, we describe our attempt to understand the photochemical interactions that occur between dihydroxybenzophenone (DHB)-based UV screens and lignin when high-yield pulps are treated with such materials. Milled wood lignin (MWL) and filter paper were used as models, and various irradiation protocols were carried out in the presence and absence of UV screens. After irradiation, the lignin and the UV screen were extracted and the products analyzed. These experiments showed that upon irradiation, fragments of MWL-containing chromophores were linked to cellulose via an acid-labile linkage. In the presence of UV screens, these reactions were minimized. Molecular weight measurements of the extracted lignin showed that the MWL is degraded upon solid-state irradiation. The samples that contained UV screens showed a reduced tendency to degrade. Using quantitative 31P NMR, it was possible to probe further the detailed structural changes that occurred in MWL during irradiation. In general, DHB-based UV screens and derivatives were found to interact actively with MWL when irradiated.     

Studies on photostability of butyrylated, milled wood lignin using spectroscopic analyses

Photo-stabilisation of butyrylated milled wood lignin (MWL) was investigated in this study. Chemical changes were confirmed by NMR and FT-IR spectra after butyrylation. Improvements in the photostability of MWL by butyrylation were evaluated by spectral analyses including ESR, FT-IR and UV-VIS spectra. From ESR analyses, butyrylation reduces the amount of phenoxyl free radicals of MWL after UV irradiation, which results in inhibiting the photo-oxidation of lignin followed by a significant decrease in the formation of colored chromophores. The carbonyl, carboxyl and quinonoid structures were less detected in the butyrylated MWL after UV irradiation than those of untreated MWL, and the content of degraded water-soluble materials from the photo-degradation of MWL was also reduced upon butyrylation.     

Photochemically Induced Solid-State Degradation, Condensation, and Rearrangement Reactions in Lignin Model Compounds and Milled Wood Lignin

Abstract— Milled wood lignin produced from alkaline hydrogen peroxide-bleached softwood thermomechanical pulp (TMP) fibers was adsorbed on pure cellulose and irradiated for variable periods of time under oxygen and/or nitrogen. The absolute amounts of β-O-4 ethers, phenolic hydroxyl groups, carboxylic acids and various condensed phenolic units were quantified, nondestructively, using ³¹P NMR spectroscopy. Photoirradiation was found to severely cleave the β-O-4 ethers present in lignin with the concomitant formation of new phenolic units. The rate of this cleavage was found to be faster under oxygen than under nitrogen. The catalytic role of oxygen can be rationalized by invoking the formation of peroxy free radicals that may initiate new sites of radical generation ( e.g. ketyl radicals) within the lignin causing the subsequent breakdown of the β-O-4 linkage. The photoirradiation was found to cause a net increase of the C₅-related condensed phenolic units in lignin. Among these, C_α-C₅ and/ or C_β-C₅ phenolic moieties were found to predominate. Similar irradiation of a binary mixture of model compounds resembling structures present in softwood lignin resulted in 18 products that were identified and quantified using gas chromatography coupled to mass spectrometry. The photochemical products obtained supported the phenacyl and ketyl mechanistic pathways to pho-toyellowing, whereas the detection of β-5 coupling products (common in both the model compound and milled wood lignin studies) may point a new avenue toward the formation of light-induced products that has not been previously considered in the solid state.     

structural elucidation of novel phosphocholine-containing glycosylinositol-phosphoceramides in filamentus fungi: (2). Spectral analysis of the sugar-inositol portion by 2D-NMR

The sugar-inositol portion of the novel glycosylinositol-phosphoceramides, ZGL1 and ZGL2, from the filamentus fungi, Acremonium sp., were elucidated by a combination of NMR techniques including (1)H-(1)H (COSY and HOHAHA) and (1)H-(13)C (HMQC and HMBC) spectroscopy. Further, examination of the (1)H-(31)P HMQC spectrum showed connectivity of inositol and ceramide through phosphate.     

31P NMR in wood chemistry: A review of recent progress

Over the past few years substantial efforts in our laboratory have been devoted toward the development of novel NMR techniques for the analysis of soluble and solid lignocellulosic substances. These efforts were undertaken in order to expand the frontiers of application of NMR for the detection of functional groups present in such materials. Our methodology involves the selective phosphorus-tagging of a variety of functional groups present in lignin and carbohydrates, followed by solution and solid state³¹P NMR spectroscopies. This paper attempts to review the status of this technique by discussing its development for the analysis of soluble and solid lignocellulosic samples. Solution³¹P NMR can be used to examine soluble lignin and carbohydrate samples after phosphitylation with 1,3,2 dioxaphospholanyl chloride. This is a novel and powerful means to determine the three principal forms of phenolic hydroxyls present in ligninsi.e. p-hydroxyphenyl, guaiacyl, and syringyl structures. In addition, primary hydroxyls, carboxylic acids, and the two diastereomeric forms of arylglycerol-beta-aryl ether units (β-O-4 structures) present in lignins can also be determined from a single³¹P NMR experiment. When applied to carbohydrates, the technique gave characteristic signals for thealpha andbeta anomers and the epimeric forms of monosaccharides. Completely resolved³¹P NMR spectra were also obtained when lignin-carbohydrate model compounds were examined. Solid state³¹P NMR can be used to determine quinone chromophore groups present in solid lignocellulosic samples. The method is based on literature accounts that describe adduct formation between trimethyl phosphite and quinones followed by solid state³¹P NMR. This reaction when reexamined in our laboratory showed that the presence of carboxylic acids in high yield pulps significantly affected the solid state³¹P NMR signal intensity. This realization permitted the development of an experimental protocol that allowed solid state³¹P NMR signals to be received from high yield pulps that contain information only onortho-quinones and coniferaldehyde chromophores. It was thus found that about 0.7ortho-quinone groups are present in every 100 C₉ units within the lignin of a black spruce refiner mechanical pulp sample, in agreement with previously applied independent techniques.     

Investigation of the chemical modifications of beech wood lignin during heat treatment

Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS ¹³C NMR, ¹³C NMR, ³¹P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin.     

狗枣猕猴桃叶化学成分研究(Ⅱ)

从狗枣猕猴桃叶中分离出4个新的黄酮类化合物, 经1D NMR, 2D NMR及ESI-MS等波谱分析鉴定了其结构, 分别是4'-甲氧基-槲皮素-7-O-(4"-O-乙酰基-鼠李糖基)-3-O-β-D-吡喃葡萄糖苷(1), 山柰甲黄素-7-O-(3"-O-乙酰基-鼠李糖基)-3-O-芸香糖苷(2), 山柰酚-7-O-(4"-O-乙酰基-鼠李糖基)-3-O-芸香糖苷(3)和4'-甲氧基-槲皮素-7-O-(4"-O-乙酰基-鼠李糖基)-3-O-芸香糖苷(4).     

Fractionation and physico-chemical analysis of degraded lignins from the black liquor of Eucalyptus pellita KP-AQ pulping

The degraded Eucalyptus pellita kraft lignin from the black liquor of KP-AQ pulping was precipitated directly at pH ∼2.0 without further purifying, since the lignin obtained is more representative with a whole distribution of molecular weight. The precipitated lignin was fractionated into six fractions by successive extraction with organic solvents. A comparison study of the lignin heterogeneity between the fractions was made in terms of fractional yield, content of associated polysaccharides, alkaline nitrobenzene oxidation, molecular weight distribution, ¹H NMR and ¹³C NMR spectroscopy and thermal stability. It was found that the lignin fractions contained higher associated hemicelluloses and ratios of non-condensed syringyl/guaiacyl units which were extracted by organic solvents with higher Hildebrand solubility parameters. The results from GPC and TGA showed that the polydispersity and the thermal stability of the lignin fractions increased with increasing molecular weight. In the low molecular weight fraction, small amounts of β-aryl ether bond (β-O-4) surviving the KP-AQ pulping were detected by both ¹H and ¹³C NMR spectra.     

Antioxidant secondary metabolites from Geranium lasiopus Boiss. & Heldr

Chromatographic studies on the EtOAc soluble portion of the MeOH extract of Geranium lasiopus led to the isolation of eight flavonoids (kaempferol (1), quercetin (2), quercetin 3-O-β-glucopyranoside (3), quercetin 3-O-β-galactopyranoside (4), kaempferol 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (5), quercetin 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (6), kaempferol 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (7) and quercetin 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (8)), two simple phenolic compounds (gallic acid (9) and its methyl ester (10)) and a hydrolysable tannin (pusilagin (11)). The structures of the compounds were elucidated by 1- and 2-dimensional NMR techniques ((1)H, (13)C, COSY, HMBC, HMQC) and ESI-TOF-MS spectrometry. Inhibitory effects on H(2)O(2)-induced lipid peroxidation in human red blood cells of the different extracts of G. lasiopus, as well as isolated compounds, were investigated. All tested compounds showed comparable or higher activity than that of ascorbic acid and trolox.     

一维SEMDY和旋转坐标NOE差谱NMR新技术用于天然化合物中寡糖的结构研究

报告从日本续断根部的乙醇提取物中分得二个新的五糖三萜皂甙,应用一维SEMDY和旋转坐标NOE差谱等NMR新技术互相配合的方法对它们的结构进行了研究,确定为：3-O-α-L-吡喃鼠李糖（1→3）-β-D-吡喃葡萄糖（1→3）-α-L-吡喃鼠李糖（1→2）-α-L-吡喃阿拉伯糖-常春藤甙元-28-O-β-吡喃葡萄糖酯甙（1）,和3-O-[β-D-吡喃葡萄糖（1→4）] [α-L-吡喃鼠李糖（1→3）]-β-D-吡喃葡萄糖（1→3）-α-L-吡喃鼠李糖（1→2）-α-L-吡喃阿拉伯糖-齐墩果酸（2）·结果表明,一维SEMDY和旋转坐标NOE差谱技术互相配合的方法测定寡糖链结构十分有效,高度重叠的糖基1H-NMR信号可按一定规律分离,容易鉴别,糖基之间的连接顺序和连接位置可以准确测定,不需要对化合物进行化学降解或衍生化。     

Structural Changes in Milled Wood Lignin (MWL) of Chinese Quince (Chaenomeles sinensis) Fruit Subjected to Subcritical Water Treatment

Subcritical water treatment has received considerable attention due to its cost effectiveness and environmentally friendly properties. In this investigation, Chinese quince fruits were submitted to subcritical water treatment (130, 150, and 170 °C), and the influence of treatments on the structure of milled wood lignin (MWL) was evaluated. Structural properties of these lignin samples (UL, L130, L150, and L170) were investigated by high-performance anion exchange chromatography (HPAEC), FT-IR, gel permeation chromatography (GPC), TGA, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 2D-Heteronculear Single Quantum Coherence (HSQC) -NMR, and ³¹P-NMR. The carbohydrate analysis showed that xylose in the samples increased significantly with higher temperature, and according to molecular weight and thermal analysis, the MWLs of the pretreated residues have higher thermal stability with increased molecular weight. The spectra of 2D-NMR and ³¹P-NMR demonstrated that the chemical linkages in the MWLs were mainly β-O-4′ ether bonds, β-5′ and β-β′, and the units were principally G- S- H- type with small amounts of ferulic acids; these results are consistent with the results of Py-GC/MS analysis. It is believed that understanding the structural changes in MWL caused by subcritical water treatment will contribute to understanding the mechanism of subcritical water extraction, which in turn will provide a theoretical basis for developing the technology of subcritical water extraction.     

A new steroidal saponin from Agave shrevei

A new steroidal saponin was isolated from the leaves of Agave shrevei. Its structure was established as 3-[O-beta-D-glucopyranosyl-(1-->2)-O-[O-beta-D-glucopyranosyl-(1-->4)-O-[O-beta-D-glucopyranosyl-(1-->6)]-O-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranosyl)-oxy]-(3beta,5alpha,25R)-spirostane. The structural identification was performed using detailed analyses of 1H- and 13C-NMR spectra including 2D NMR spectroscopic techniques (COSY, HETCOR, HMBC, and HMQC) and chemical conversions. The haemolytic activity of the steroidal saponin was evaluated using an in vitro assay.     

Chemical synthesis of beta-O-4 type artificial lignin

An artificial lignin polymer containing only the beta-O-4 substructure was synthesized. The procedure consists of two key steps: 1) polycondensation of a brominated monomer by aromatic Williamson reaction; and 2) subsequent reduction of the carbonyl polymer. 13C-NMR and HMQC spectra of the polymer were consistent with beta-O-4 substructures in milled wood lignin isolated from Japanese fir wood. The weight average degree of polymerization (DP(w)) ranged from 19.5 to 30.6, which is comparable to enzymatically synthesized artificial lignin from p-hydroxycinnamyl alcohols (dehydrogenation polymer, DHP) and some isolated lignins. Using this new lignin model polymer, it will now be possible to reinvestigate the properties and reactivity of the main lignin structure in terms of its polymeric character.     

New insights into the molecular architecture of hardwood lignins by chemical degradative methods

Lignins are composed of phenylpropane units interconnected by labile and resistant bonds. A two-step degradation, thioacidolysis, provides detailed information on these network polymers. The first step involves lignin depolymerization with ethanethiol and BF₃ etherate. The determination of the recovered thioethylated monomers provides an estimation of lignin units only involved in labile ether bonds. The ligninderived dimers, representative of resistant interunit bonds, are determined after a further desulfurization step. Results obtained for native and industrial hardwood lignins underline their structural differences. Native hardwood lignins are typified by a high proportion of linear fragments linked bifunctionally by β-O-4 bonds.     

Catalytic Decomposition of Lignin Model Compounds to Aromatics over Acidic Catalysts

Recent progress on the catalytic decomposition of lignin model compounds to aromatics was reported in this review. Cesium-exchanged heteropolyacid catalysts (Cs_xH_3.0?xPW₁₂O₄₀), palladium catalysts supported on cesium-exchanged heteropolyacid (Pd/Cs_xH_3.0?xPW₁₂O₄₀), and palladium catalysts supported on various activated carbon aerogels (ACAs) (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/Cs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were prepared, and they were employed for the decomposition of C–O bond in lignin to aromatics. Phenethyl phenyl ether, benzyl phenyl ether, and 4-phenoxyphenol were used as dimeric lignin model compounds representing for β-O-4, α-O-4, and 4-O-5 bonds in lignin, respectively. It was observed that Cs_xH_3.0?xPW₁₂O₄₀ and Pd/Cs_xH_3.0?xPW₁₂O₄₀ were highly active for the decomposition of phenethyl phenyl ether and benzyl phenyl ether to aromatics. However, these catalysts showed very low catalytic performance in the decomposition of 4-phenoxyphenol. Palladium catalysts supported on various ACAs (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were efficient for the decomposition of 4-phenoxyphenol to aromatics. Acidity of the catalysts played a key role in determining the catalytic performance in the decomposition of 4-phenoxyphenol to aromatics.     

Computational study of bond dissociation enthalpies for substituted β-O-4 lignin model compounds

The biopolymer lignin is a potential source of valuable chemicals. Phenethyl phenyl ether (PPE) is representative of the dominant β-O-4 ether linkage. DFT is used to calculate the Boltzmann-weighted carbon-oxygen and carbon-carbon bond dissociation enthalpies (BDEs) of substituted PPE. These values are important for understanding lignin decomposition. Exclusion of all conformers that have distributions of less than 5% at 298 K impacts the BDE by less than 1 kcal mol(-1). We find that aliphatic hydroxyl/methylhydroxyl substituents introduce only small changes to the BDEs (0-3 kcal mol(-1)). Substitution on the phenyl ring at the ortho position substantially lowers the C-O BDE, except in combination with the hydroxyl/methylhydroxyl substituents, for which the effect of methoxy substitution is reduced by hydrogen bonding. Hydrogen bonding between the aliphatic substituents and the ether oxygen in the PPE derivatives has a significant influence on the BDE. CCSD(T)-calculated BDEs and hydrogen-bond strengths of ortho-substituted anisoles, when compared with M06-2X values, confirm that the latter method is sufficient to describe the molecules studied and provide an important benchmark for lignin model compounds.